土木工程毕业设计外文翻译

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土木工程毕业设计外文翻译原文+翻译

The bridge crack produced the reason to simply analyseIn recent years, the traffic capital construction of our province gets swift and violent development, all parts have built a large number of concrete bridges. In the course of building and using in the bridge, relevant to influence project quality lead of common occurrence report that bridge collapse even because the crack appears The concrete can be said to " often have illness coming on " while fracturing and " frequently-occurring disease ", often perplex bridge engineers and technicians. In fact , if take certain design and construction measure, a lot of cracks can be overcome and controlled. For strengthen understanding of concrete bridge crack further, is it prevent project from endanger larger crack to try one's best, this text make an more overall analysis , summary to concrete kind and reason of production , bridge of crack as much as possible, in order to design , construct and find out the feasible method which control the crack , get the result of taking precautions against Yu WeiRan.Concrete bridge crack kind, origin cause of formation In fact, the origin cause of formation of the concrete structure crack is complicated and various, even many kinds of factors influence each other , but every crack has its one or several kinds of main reasons produced . The kind of the concrete bridge crack, on its reason to produce, can roughly divide several kinds as follows :(1) load the crack caused Concrete in routine quiet .Is it load to move and crack that produce claim to load the crack under the times of stress bridge, summing up has direct stress cracks , two kinds stress crack onces mainly. Direct stress crack refer to outside load direct crack that stress produce that cause. The reason why the crack produces is as follows, 1, Design the stage of calculating , does not calculate or leaks and calculates partly while calculating in structure; Calculate the model is unreasonable; The structure is supposed and accorded with by strength actually by strength ; Load and calculate or leak and calculate few; Internal force and matching the mistake in computation of muscle; Safety coefficient of structure is not enough. Do not consider the possibility that construct at the time of the structural design; It is insufficientto design the section; It is simply little and assigning the mistake for reinforcing bar to set up; Structure rigidity is insufficient; Construct and deal with improperly; The design drawing can not be explained clearly etc.. 2, Construction stage, does not pile up and construct the machines , material limiting ; Is it prefabricate structure structure receive strength characteristic , stand up , is it hang , transport , install to get up at will to understand; Construct not according to the design drawing, alter the construction order of the structure without authorization , change the structure and receive the strength mode; Do not do the tired intensity checking computations under machine vibration and wait to the structure . 3, Using stage, the heavy-duty vehicle which goes beyond the design load passes the bridge; Receive the contact , striking of the vehicle , shipping; Strong wind , heavy snow , earthquake happen , explode etc.. Stress crack once means the stress of secondary caused by loading outside produces the crack. The reason why the crack produces is as follows, 1, In design outside load function , because actual working state and routine , structure of thing calculate have discrepancy or is it consider to calculate, thus cause stress once to cause the structure to fracture in some position. Two is it join bridge arch foot is it is it assign " X " shape reinforcing bar , cut down this place way , section of size design and cut with scissors at the same time to adopt often to design to cut with scissors, theory calculate place this can store curved square in , but reality should is it can resist curved still to cut with scissors, so that present the crack and cause the reinforcing bar corrosion. 2, Bridge structure is it dig trough , turn on hole , set up ox leg ,etc. to need often, difficult to use a accurate one diagrammatic to is it is it calculate to imitate to go on in calculating in routine, set up and receive the strength reinforcing bar in general foundation experience. Studies have shown , after being dug the hole by the strength component , it will produce the diffraction phenomenon that strength flows, intensive near the hole in a utensil, produced the enormous stress to concentrate. In long to step prestressing force of the continuous roof beam , often block the steel bunch according to the needs of section internal force in stepping, set up the anchor head, but can often see the crack in the anchor firm section adjacent place. So if deal with improper, in corner or component form sudden change office , block place to be easy to appear crack strengthreinforcing bar of structure the. In the actual project, stress crack once produced the most common reason which loads the crack. Stress crack once belong to one more piece of nature of drawing , splitting off , shearing. Stress crack once is loaded and caused, only seldom calculate according to the routine too, but with modern to calculate constant perfection of means, times of stress crack to can accomplish reasonable checking computations too. For example to such stresses 2 times of producing as prestressing force , creeping ,etc., department's finite element procedure calculates levels pole correctly now, but more difficult 40 years ago. In the design, should pay attention to avoiding structure sudden change (or section sudden change), when it is unable to avoid , should do part deal with , corner for instance, make round horn , sudden change office make into the gradation zone transition, is it is it mix muscle to construct to strengthen at the same time, corner mix again oblique to reinforcing bar , as to large hole in a utensil can set up protecting in the perimeter at the terms of having angle steel. Load the crack characteristic in accordance with loading differently and presenting different characteristics differently. The crack appear person who draw more, the cutting area or the serious position of vibration. Must point out , is it get up cover or have along keep into short crack of direction to appear person who press, often the structure reaches the sign of bearing the weight of strength limit, it is an omen that the structure is destroyed, its reason is often that sectional size is partial and small. Receive the strength way differently according to the structure, the crack characteristic produced is as follows: 1, The centre is drawn. The crack runs through the component cross section , the interval is equal on the whole , and is perpendicular to receiving the strength direction. While adopting the whorl reinforcing bar , lie in the second-class crack near the reinforcing bar between the cracks. 2, The centre is pressed. It is parallel on the short and dense parallel crack which receive the strength direction to appear along the component. 3, Receive curved. Most near the large section from border is it appear and draw into direction vertical crack to begin person who draw curved square, and develop toward neutralization axle gradually. While adopting the whorl reinforcing bar , can see shorter second-class crack among the cracks. When the structure matches muscles less, there are few but wide cracks, fragility destruction may take place in thestructure 4, Pressed big and partial. Heavy to press and mix person who draw muscle a less one light to pigeonhole into the component while being partial while being partial, similar to receiving the curved component. 5, Pressed small and partial. Small to press and mix person who draw muscle a more one heavy to pigeonhole into the component while being partial while being partial, similar to the centre and pressed the component. 6, Cut. Press obliquly when the hoop muscle is too dense and destroy, the oblique crack which is greater than 45?? direction appears along the belly of roof beam end; Is it is it is it destroy to press to cut to happen when the hoop muscle is proper, underpart is it invite 45?? direction parallel oblique crack each other to appear along roof beam end. 7, Sprained. Component one side belly appear many direction oblique crack, 45?? of treaty, first, and to launch with spiral direction being adjoint. 8, Washed and cut. 4 side is it invite 45?? direction inclined plane draw and split to take place along column cap board, form the tangent plane of washing. 9, Some and is pressed. Some to appear person who press direction roughly parallel large short cracks with pressure.(2) crack caused in temperature changeThe concrete has nature of expanding with heat and contract with cold, look on as the external environment condition or the structure temperature changes, concrete take place out of shape, if out of shape to restrain from, produce the stress in the structure, produce the temperature crack promptly when exceeding concrete tensile strength in stress. In some being heavy to step foot-path among the bridge , temperature stress can is it go beyond living year stress even to reach. The temperature crack distinguishes the main characteristic of other cracks will be varied with temperature and expanded or closed up. The main factor is as follows, to cause temperature and change 1, Annual difference in temperature. Temperature is changing constantly in four seasons in one year, but change relatively slowly, the impact on structure of the bridge is mainly the vertical displacement which causes the bridge, can prop up seat move or set up flexible mound ,etc. not to construct measure coordinate , through bridge floor expansion joint generally, can cause temperature crack only when the displacement of the structure is limited, for example arched bridge , just bridge etc. The annual difference in temperature of our country generally changes therange with the conduct of the average temperature in the moon of January and July. Considering the creep characteristic of the concrete, the elastic mould amount of concrete should be considered rolling over and reducing when the internal force of the annual difference in temperature is calculated. 2, Rizhao. After being tanned by the sun by the sun to the side of bridge panel , the girder or the pier, temperature is obviously higher than other position, the temperature gradient is presented and distributed by the line shape . Because of restrain oneself function, cause part draw stress to be relatively heavy, the crack appears. Rizhao and following to is it cause structure common reason most , temperature of crack to lower the temperature suddenly 3, Lower the temperature suddenly. Fall heavy rain , cold air attack , sunset ,etc. can cause structure surface temperature suddenly dropped suddenly, but because inside temperature change relatively slow producing temperature gradient. Rizhao and lower the temperature internal force can adopt design specification or consult real bridge materials go on when calculating suddenly, concrete elastic mould amount does not consider converting into and reducing 4, Heat of hydration. Appear in the course of constructing, the large volume concrete (thickness exceeds 2. 0), after building because cement water send out heat, cause inside very much high temperature, the internal and external difference in temperature is too large, cause the surface to appear in the crack. Should according to actual conditions in constructing, is it choose heat of hydration low cement variety to try one's best, limit cement unit's consumption, reduce the aggregate and enter the temperature of the mould , reduce the internal and external difference in temperature, and lower the temperature slowly , can adopt the circulation cooling system to carry on the inside to dispel the heat in case of necessity, or adopt the thin layer and build it in succession in order to accelerate dispelling the heat. 5, The construction measure is improper at the time of steam maintenance or the winter construction , the concrete is sudden and cold and sudden and hot, internal and external temperature is uneven , apt to appear in the crack. 6, Prefabricate T roof beam horizontal baffle when the installation , prop up seat bury stencil plate with transfer flat stencil plate when welding in advance, if weld measure to be improper, iron pieces of nearby concrete easy to is it fracture to burn. Adopt electric heat piece draw law piece draw prestressing force at the component ,prestressing force steel temperature can rise to 350 degrees Centigrade , the concrete component is apt to fracture. Experimental study indicates , are caused the intensity of concrete that the high temperature burns to obviously reduce with rising of temperature by such reasons as the fire ,etc., glueing forming the decline thereupon of strength of reinforcing bar and concrete, tensile strength drop by 50% after concrete temperature reaches 300 degrees Centigrade, compression strength drops by 60%, glueing the strength of forming to drop by 80% of only round reinforcing bar and concrete; Because heat, concrete body dissociate ink evaporate and can produce and shrink sharply in a large amount(3) shrink the crack causedIn the actual project, it is the most common because concrete shrinks the crack caused. Shrink kind in concrete, plasticity shrink is it it shrinks (is it contract to do ) to be the main reason that the volume of concrete out of shape happens to shrink, shrink spontaneously in addition and the char shrink. Plasticity shrink. About 4 hours after it is built that in the course of constructing , concrete happens, the cement water response is fierce at this moment, the strand takes shape gradually, secrete water and moisture to evaporate sharply, the concrete desiccates and shrinks, it is at the same time conduct oneself with dignity not sinking because aggregate,so when harden concrete yet,it call plasticity shrink. The plasticity shrink producing amount grade is very big, can be up to about 1%. If stopped by the reinforcing bar while the aggregate sinks, form the crack along the reinforcing bar direction. If web , roof beam of T and roof beam of case and carry baseplate hand over office in component vertical to become sectional place, because sink too really to superficial obeying the web direction crack will happen evenly before hardenning. For reducing concrete plasticity shrink,it should control by water dust when being construct than,last long-time mixing, unloading should not too quick, is it is it take closely knit to smash to shake, vertical to become sectional place should divide layer build. Shrink and shrink (do and contract). After the concrete is formed hard , as the top layer moisture is evaporated progressively , the humidity is reduced progressively , the volume of concrete is reduced, is called and shrunk to shrink (do and contract). Because concrete top layermoisture loss soon, it is slow for inside to lose, produce surface shrink heavy , inside shrink a light one even to shrink, it is out of shape to restrain from by the inside concrete for surface to shrink, cause the surface concrete to bear pulling force, when the surface concrete bears pulling force to exceed its tensile strength, produce and shrink the crack. The concrete hardens after-contraction to just shrink and shrink mainly .Such as mix muscle rate heavy component (exceed 3% ), between reinforcing bar and more obvious restraints relatively that concrete shrink, the concrete surface is apt to appear in the full of cracks crackle. Shrink spontaneously. Spontaneous to it shrinks to be concrete in the course of hardenning , cement and water take place ink react, the shrink with have nothing to do by external humidity, and can positive (whether shrink, such as ordinary portland cement concrete), can negative too (whether expand, such as concrete, concrete of slag cement and cement of fly ash). The char shrinks. Between carbon dioxide and hyrate of cement of atmosphere take place out of shape shrink that chemical reaction cause. The char shrinks and could happen only about 50% of humidity, and accelerate with increase of the density of the carbon dioxide. The char shrinks and seldom calculates . The characteristic that the concrete shrinks the crack is that the majority belongs to the surface crack, the crack is relatively detailed in width , and criss-cross, become the full of cracks form , the form does not have any law . Studies have shown , influence concrete shrink main factor of crack as follows, 1, Variety of cement , grade and consumption. Slag cement , quick-hardening cement , low-heat cement concrete contractivity are relatively high, ordinary cement , volcanic ash cement , alumina cement concrete contractivity are relatively low. Cement grade low in addition, unit volume consumption heavy rubing detailed degree heavy, then the concrete shrinks the more greatly, and shrink time is the longer. For example, in order to improve the intensity of the concrete , often adopt and increase the cement consumption method by force while constructing, the result shrinks the stress to obviously strengthen . 2, Variety of aggregate. Such absorbing water rates as the quartz , limestone , cloud rock , granite , feldspar ,etc. are smaller, contractivity is relatively low in the aggregate; And such absorbing water rates as the sandstone , slate , angle amphibolite ,etc. are greater, contractivity is relatively high. Aggregate grains of foot-path heavy to shrink light inaddition, water content big to shrink the larger. 3, Water gray than. The heavier water consumption is, the higher water and dust are, the concrete shrinks the more greatly. 4, Mix the pharmaceutical outside. It is the better to mix pharmaceutical water-retaining property outside, then the concrete shrinks the smaller. 5, Maintain the method . Water that good maintenance can accelerate the concrete reacts, obtain the intensity of higher concrete. Keep humidity high , low maintaining time to be the longer temperature when maintaining, then the concrete shrinks the smaller. Steam maintain way than maintain way concrete is it take light to shrink naturall. 6, External environment. The humidity is little, the air drying , temperature are high, the wind speed is large in the atmosphere, then the concrete moisture is evaporated fast, the concrete shrinks the faster. 7, Shake and smash the way and time. Machinery shake way of smashing than make firm by ramming or tamping way concrete contractivity take little by hand. Shaking should determine according to mechanical performance to smash time , are generally suitable for 55s / time. It is too short, shake and can not smash closely knit , it is insufficient or not even in intensity to form the concrete; It is too long, cause and divide storey, thick aggregate sinks to the ground floor, the upper strata that the detailed aggregate stays, the intensity is not even , the upper strata incident shrink the crack. And shrink the crack caused to temperature, worthy of constructing the reinforcing bar againing can obviously improve the resisting the splitting of concrete , structure of especially thin wall (thick 200cm of wall ). Mix muscle should is it adopt light diameter reinforcing bar (8 |? construct 14 |? ) to have priority , little interval assign (whether @ 10 construct @ 15cm ) on constructing, the whole section is it mix muscle to be rate unsuitable to be lower than 0 to construct. 3%, can generally adopt 0 . 3%~0. 5%.(4), crack that causes out of shape of plinth of the groundBecause foundation vertical to even to subside or horizontal direction displacement, make the structure produce the additional stress, go beyond resisting the ability of drawing of concrete structure, cause the structure to fracture. The even main reason that subside of the foundation is as follows, 1, Reconnoitres the precision and is not enough for , test the materials inaccuratly in geology. Designing, constructing without fully grasping the geological situation, this is the main reason that cause the ground not to subside evenly .Such as hills area or bridge, district of mountain ridge,, hole interval to be too far when reconnoitring, and ground rise and fall big the rock, reconnoitring the report can't fully reflect the real geological situation . 2, The geological difference of the ground is too large. Building it in the bridge of the valley of the ditch of mountain area, geology of the stream place and place on the hillside change larger, even there are weak grounds in the stream, because the soil of the ground does not causes and does not subside evenly with the compressing. 3, The structure loads the difference too big. Under the unanimous terms, when every foundation too heavy to load difference in geological situation, may cause evenly to subside, for example high to fill out soil case shape in the middle part of the culvert than to is it take heavy to load both sides, to subside soon heavy than both sides middle part, case is it might fracture to contain 4, The difference of basic type of structure is great. Unite it in the bridge the samly , mix and use and does not expand the foundation and a foundation with the foundation, or adopt a foundation when a foot-path or a long difference is great at the same time , or adopt the foundation of expanding when basis elevation is widely different at the same time , may cause the ground not to subside evenly too 5, Foundation built by stages. In the newly-built bridge near the foundation of original bridge, if the half a bridge about expressway built by stages, the newly-built bridge loads or the foundation causes the soil of the ground to consolidate again while dealing with, may cause and subside the foundation of original bridge greatly 6, The ground is frozen bloatedly. The ground soil of higher moisture content on terms that lower than zero degree expands because of being icy; Once temperature goes up , the frozen soil is melted, the setting of ground. So the ground is icy or melts causes and does not subside evenly . 7, Bridge foundation put on body, cave with stalactites and stalagmites, activity fault,etc. of coming down at the bad geology, may cause and does not subside evenly . 8, After the bridge is built up , the condition change of original ground . After most natural grounds and artificial grounds are soaked with water, especially usually fill out such soil of special ground as the soil , loess , expanding in the land ,etc., soil body intensity meet water drop, compress out of shape to strengthen. In the soft soil ground , season causes the water table to drop to draw water or arid artificially, the ground soil layer consolidates and sinks again,reduce the buoyancy on the foundation at the same time , shouldering the obstruction of rubing to increase, the foundation is carried on one's shoulder or back and strengthened .Some bridge foundation is it put too shallow to bury, erode , is it dig to wash flood, the foundation might be moved. Ground load change of terms, bridge nearby is it is it abolish square , grit ,etc. in a large amount to put to pile with cave in , landslide ,etc. reason for instance, it is out of shape that the bridge location range soil layer may be compressed again. So, the condition of original ground change while using may cause and does not subside evenly Produce the structure thing of horizontal thrust to arched bridge ,etc., it is the main reason that horizontal displacement crack emerges to destroy the original geological condition when to that it is unreasonable to grasp incompletely , design and construct in the geological situation.桥梁裂缝产生原因浅析近年来，我省交通基础建设得到迅猛发展，各地建立了大量的混凝土桥梁。

土木工程专业毕业设计- 外文翻译

Structure in Design of ArchitectureAnd Structural Material专业：土木工程学生：指导老师：We have and the architects must deal with the spatial aspect of activity, physical, and symbolic needs in such a way that overall performance integrity is assured. Hence, he or she well wants to think of evolving a building environment as a total system of interacting and space forming subsystems. Is represents a complex challenge, and to meet it the architect will need a hierarchic design process that provides at least three levels of feedback thinking: schematic, preliminary, and final.Such a hierarchy is necessary if he or she is to avoid being confused , at conceptual stages of design thinking ,by the myriad detail issues that can distract attention from more basic considerations .In fact , we can say that an architect’s ability to distinguish the more basic form the more detailed issues is essential to his success as a designer .The object of the schematic feed back level is to generate and evaluate overall site-plan, activity-interaction, and building-configuration options .To do so the architect must be able to focus on the interaction of the basic attributes of the site context, the spatial organization, and the symbolism as determinants of physical form. This means that ,in schematic terms ,the architect may first conceive and model a building design as an organizational abstraction of essential performance-space in teractions.Then he or she may explore the overall space-form implications of the abstraction. As an actual building configuration option begins to emerge, it will be modified to include consideration for basic site conditions.At the schematic stage, it would also be helpful if the designer could visualize his or her options for achieving overall structural integrity and consider the constructive feasibility and economic of his or her scheme .But this will require that the architect and/or a consultant be able to conceptualize total-system structural options in terms of elemental detail .Such overall thinking can be easily fed back to improve the space-form scheme.At the preliminary level, the architect’s emphasis will shift to the elaboration of his or her more promising schematic design options .Here the architect’s structural needs will shift to approximate design of specific subsystem options. At this stage the total structural scheme is developed to a middle level of specificity by focusing on identification and design of major subsystems to the extent that their key geometric, component, and interactive properties are established .Basic subsystem interaction and design conflicts can thus be identified and resolved in the context of total-system objectives. Consultants can play a significant part in this effort; these preliminary-level decisions may also result in feedback that calls for refinement or even major change in schematic concepts.When the designer and the client are satisfied with the feasibility of a design proposal at the preliminary level, it means that the basic problems of overall design are solved and details arenot likely to produce major change .The focus shifts again ,and the design process moves into the final level .At this stage the emphasis will be on the detailed development of all subsystem specifics . Here the role of specialists from various fields, including structural engineering, is much larger, since all detail of the preliminary design must be worked out. Decisions made at this level may produce feedback into Level II that will result in changes. However, if Levels I and II are handled with insight, the relationship between the overall decisions, made at the schematic and preliminary levels, and the specifics of the final level should be such that gross redesign is not in question, Rather, the entire process should be one of moving in an evolutionary fashion from creation and refinement (or modification) of the more general properties of a total-system design concept, to the fleshing out of requisite elements and details.To summarize: At Level I, the architect must first establish, in conceptual terms, the overall space-form feasibility of basic schematic options. At this stage, collaboration with specialists can be helpful, but only if in the form of overall thinking. At Level II, the architect must be able to identify the major subsystem requirements implied by the scheme and substantial their interactive feasibility by approximating key component properties .That is, the properties of major subsystems need be worked out only in sufficient depth to very the inherent compatibility of their basic form-related and behavioral interaction . This will mean a somewhat more specific form of collaboration with specialists then that in level I .At level III ,the architect and the specific form of collaboration with specialists then that providing for all of the elemental design specifics required to produce biddable construction documents .Of course this success comes from the development of the Structural Material.The principal construction materials of earlier times were wood and masonry brick, stone, or tile, and similar materials. The courses or layers were bound together with mortar or bitumen, a tar like substance, or some other binding agent. The Greeks and Romans sometimes used iron rods or claps to strengthen their building. The columns of the Parthenon in Athens, for example, have holes drilled in them for iron bars that have now rusted away. The Romans also used a natural cement called puzzling, made from volcanic ash, that became as hard as stone under water.Both steel and cement, the two most important construction materials of modern times, were introduced in the nineteenth century. Steel, basically an alloy of iron and a small amount of carbon had been made up to that time by a laborious process that restricted it to such special uses as sword blades. After the invention of the Bessemer process in 1856, steel was available in large quantities at low prices. The enormous advantage of steel is its tensile force which, as we have seen, tends to pull apart many materials. New alloys have further, which is a tendency for it to weaken as a result of continual changes in stress.Modern cement, called Portland cement, was invented in 1824. It is a mixture of limestone and clay, which is heated and then ground into a power. It is mixed at or near the construction site with sand, aggregate small stones, crushed rock, or gravel, and water to make concrete. Different proportions of the ingredients produce concrete with different strength and weight. Concrete is very versatile; it can be poured, pumped, or even sprayed into all kinds of shapes. And whereas steel has great tensile strength, concrete has great strength under compression. Thus, the two substances complement each other.They also complement each other in another way: they have almost the same rate ofcontraction and expansion. They therefore can work together in situations where both compression and tension are factors. Steel rods are embedded in concrete to make reinforced concrete in concrete beams or structures where tensions will develop. Concrete and steel also form such a strong bond─ the force that unites them─ that the steel cannot slip within the concrete. Still another advantage is that steel does not rust in concrete. Acid corrodes steel, whereas concrete has an alkaline chemical reaction, the opposite of acid.The adoption of structural steel and reinforced concrete caused major changes in traditional construction practices. It was no longer necessary to use thick walls of stone or brick for multistory buildings, and it became much simpler to build fire-resistant floors. Both these changes served to reduce the cost of construction. It also became possible to erect buildings with greater heights and longer spans.Since the weight of modern structures is carried by the steel or concrete frame, the walls do not support the building. They have become curtain walls, which keep out the weather and let in light. In the earlier steel or concrete frame building, the curtain walls were generally made of masonry; they had the solid look of bearing walls. Today, however, curtain walls are often made of lightweight materials such as glass, aluminum, or plastic, in various combinations.Another advance in steel construction is the method of fastening together the beams. For many years the standard method was riveting. A rivet is a bolt with a head that looks like a blunt screw without threads. It is heated, placed in holes through the pieces of steel, and a second head is formed at the other end by hammering it to hold it in place. Riveting has now largely been replaced by welding, the joining together of pieces of steel by melting a steel material between them under high heat.Priestess’s concrete is an improved form of reinforcement. Steel r ods are bent into the shapes to give them the necessary degree of tensile strengths. They are then used to priestess concrete, usually by one of two different methods. The first is to leave channels in a concrete beam that correspond to the shapes of the steel rods. When the rods are run through the channels, they are then bonded to the concrete by filling the channels with grout, a thin mortar or binding agent. In the other (and more common) method, the priestesses steel rods are placed in the lower part of a form that corresponds to the shape of the finished structure, and the concrete is poured around them. Priestess’s concrete uses less steel and less concrete. Because it is a highly desirable material.Progressed concrete has made it possible to develop buildings with unusual shapes, like some of the modern, sports arenas, with large spaces unbroken by any obstructing supports. The uses for this relatively new structural method are constantly being developed.建筑中的结构设计及建筑材料专业：土木工程学生：指导老师：建筑师必须从一种全局的角度出发去处理建筑设计中应该考虑到的实用活动，物质及象征性的需求。

土木工程毕业设计中英文翻译

土木工程毕业设计中英文翻译附录:中英文翻译英文部分:LOADSLoads that act on structures are usually classified as dead loads or live loads.Dead loads are fixed in location and constant in magnitude throughout the life of the ually the self-weight of a structure is the most important part of the structure and the unit weight of the material.Concrete density2varies from about 90 to 120 pcf (14 to 19 )for lightweight concrete,and is about 145 pcf (23 KN/m2)for normal concrete.In calculating the dead load of structural concrete,usually a 5 pcf (1 KN/m2)increment is included with the weight of the concrete to account for the presence of the KN/mreinforcement.Live loads are loads such as occupancy,snow,wind,or traffic loads,or seismic forces.They may be either fully or partially in place,or not present at all.They may also change in location.Althought it is the responsibility of the engineer to calculate dead loads,live loads are usually specified by local,regional,or national codes and specifications.Typical sources are the publications of the American National Standards Institute,the American Association of StateHighway and Transportation Officials and,for wind loads,the recommendations of the ASCE Task Committee on Wind Forces.Specified live the loads usually include some allowance for overload,and may include measures such as posting of maximum loads will not be exceeded.It is oftern important to distinguish between the specified load,and what is termed the characteristic load,that is,the load that actually is in effect under normal conditions of service,which may be significantly less.In estimating the long-term deflection of a structure,for example,it is the characteristic load that isimportant,not the specified load.The sum of the calculated dead load and the specified live load is called the service load,because this is the maximum load which may reasonably be expected to act during the service resisting is a multiple of the service load.StrengthThe strength of a structure depends on the strength of the materials from which it is made.Minimum material strengths are specified incertain standardized ways.The properties of concrete and its components,the methods of mixing,placing,and curing to obtain the required quality,and the methods for testing,are specified by the American Concrete Insititue(ACI).Included by refrence in the same documentare standards of the American Society for TestingMaterials(ASTM)pertaining to reinforcing and prestressing steels and concrete.Strength also depends on the care with which the structure isbuilt.Member sizes may differ from specified dimensions,reinforcement may be out of position,or poor placement of concrete may result in voids.An important part of the job of the ergineer is to provide proper supervision of construction.Slighting of this responsibility has had disastrous consequences in more than one instance.Structural SafetySafety requires that the strength of a structure be adequate for all loads that may conceivably act on it.If strength could be predicted accurately and if loads were known with equal certainty,then safely could be assured by providing strength just barely in excess of the requirements of the loads.But there are many sources of uncertainty in the estimation of loads as well as in analysis,design,andconstruction.These uncertainties require a safety margin.In recent years engineers have come to realize that the matter of structural safety is probabilistic in nature,and the safety provisions of many current specifications reflect this view.Separate consideration is given to loads and strength.Loadfactors,larger than unity,are applied to the calculated dead loads and estimated or specified service live loads,to obtain factorde loads that the member must just be capable of sustaining at incipient failure.Loadfactors pertaining to different types of loads vary,depending on the degree of uncertainty associated with loads of various types,and with the likelihood of simultaneous occurrence of different loads.Early in the development of prestressed concrete,the goal of prestressing was the complete elimination of concrete ternsile stress at service loads.The concept was that of an entirely new,homogeneous material that woukd remain uncracked and respond elastically up to the maximum anticipated loading.This kind of design,where the limiting tensile stressing,while an alternative approach,in which a certain amount of tensile amount of tensile stress is permitted in the concrete at full service load,is called partial prestressing.There are cases in which it is necessary to avoid all risk of cracking and in which full prestressing is required.Such cases include tanks or reservious where leaks must be avoided,submerged structures or those subject to a highly corrosive envionment where maximum protection of reinforcement must be insured,and structures subject to high frequency repetition of load where faatigue of the reinforcement may be a consideration.However,there are many cses where substantially improved performance,reduced cost,or both may be obtained through the use of a lesser amount of prestress.Full predtressed beams may exhibit an undesirable amount of upward camber because of the eccentric prestressing force,a displacement that is only partially counteracted by the gravity loads producing downward deflection.This tendency isaggrabated by creep in the concrete,which magnigies the upward displacement due to the prestress force,but has little influence on the should heavily prestressed members be overloaded and fail,they may do so in a brittle way,rather than gradually as do beams with a smaller amount of prestress.This is important from the point of view of safety,because suddenfailure without warning is dangeroud,and gives no opportunity for corrective measures to be taken.Furthermore,experience indicates that in many cases improved economy results from the use of a combination of unstressed bar steel and high strength prestressed steel tendons.While tensile stress and possible cracking may be allowed at full service load,it is also recognized that such full service load may be infrequently applied.The typical,or characteristic,load acting is likely to be the dead load plus a small fraction of the specified liveload.Thus a partially predtressed beam may not be subject to tensile stress under the usual conditions of loading.Cracks may from occasionally,when the maximum load is applied,but these will close completely when that load is removed.They may be no more objectionablein prestressed structures than in ordinary reinforced.They may be no more objectionable in prestressed structures than in ordinary reinforced concrete,in which flexural cracks always form.They may be considered a small price for the improvements in performance and economy that are obtained.It has been observed that reinforced concrete is but a special case of prestressed concrete in which the prestressing force is zero.Thebehavior of reinforced and prestressed concrete beams,as the failure load is approached,is essentially the same.The Joint European Committee on Concrete establishes threee classes of prestressed beams.Class 1:Fully prestressed,in which no tensile stress is allowed in the concrete at service load.Class 2:Partially prestressed, in which occasional temporary cracking is permitted under infrequent high loads.Class 3:Partially prestressed,in which there may be permanent cracks provided that their width is suitably limited.The choise of a suitable amount of prestress is governed by avariety of factors.These include thenature of the loading (for exmaple,highway or railroadbridged,storage,ect.),the ratio of live to dead load,the frequency of occurrence of loading may be reversed,such as in transmission poles,a high uniform prestress would result ultimate strength and in brittle failure.In such a case,partial prestressing provides the only satifactory solution.The advantages of partial prestressing are important.A smaller prestress force will be required,permitting reduction in the number of tendons and anchorages.The necessary flexural strength may be provided in such cases either by a combination of prestressed tendons and non-prestressed reinforcing bars,or by an adequate number of high-tensile tendons prestredded to level lower than the prestressing force isless,the size of the bottom flange,which is requied mainly to resist the compression when a beam is in the unloaded stage,can be reduced or eliminated altogether.This leads in turn to significant simplification and cost reduction in the construction of forms,as well as resulting in structures that are mor pleasing esthetically.Furthermore,by relaxing the requirement for low service load tension in the concrete,a significant improvement can be made in the deflection characteristics of a beam.Troublesome upward camber of the member in the unloaded stage fan be avoeded,and the prestress force selected primarily to produce the desired deflection for a particular loading condition.The behavior of partially prestressed beamsm,should they be overloaded to failure,is apt to be superior to that of fully prestressed beams,because the improved ductility provides ample warning of distress.英译汉:荷载作用在结构上的荷载通常分为恒载或活载。

土木工程毕业设计中英文翻译.doc

附录：中英文翻译英文部分：LOADSLoads that act on structures are usually classified as dead loads or live loads.Dead loads are fixed in location and constant in magnitude throughout the life of the ually the self-weight of a structure is the most important part of the structure and the unit weight of the material.Concrete density varies from about 90 to 120 pcf (14 to 19 2KN/m)for lightweight concrete,and is about 145 pcf (23 2KN/m)for normal concrete.In calculating the dead load of structural concrete,usually a 5 pcf (1 2KN/m)increment is included with the weight of the concrete to account for the presence of the reinforcement.Live loads are loads such as occupancy,snow,wind,or traffic loads,or seismic forces.They may be either fully or partially in place,or not present at all.They may also change in location.Althought it is the responsibility of the engineer to calculate dead loads,live loads are usually specified by local,regional,or national codes and specifications.Typical sources are the publications of the American National Standards Institute,the American Association of State Highway and Transportation Officials and,for wind loads,the recommendations of the ASCE Task Committee on Wind Forces.Specified live the loads usually include some allowance for overload,and may include measures such as posting of maximum loads will not be exceeded.It is oftern important to distinguish between the specified load,and what is termed the characteristic load,that is,the load that actually is in effect under normal conditions of service,which may be significantly less.In estimating the long-term deflection of a structure,for example,it is the characteristic load that is important,not the specified load.The sum of the calculated dead load and the specified live load is called the service load,because this is the maximum load which may reasonably be expected to act during the service resisting is a multiple of the service load.StrengthThe strength of a structure depends on the strength of the materials from which it is made.Minimum material strengths are specified in certain standardized ways.The properties of concrete and its components,the methods of mixing,placing,and curing to obtain the required quality,and the methods for testing,are specified by the American Concrete Insititue(ACI).Included by refrence in the same documentare standards of the American Society for Testing Materials(ASTM)pertaining to reinforcing and prestressing steels and concrete.Strength also depends on the care with which the structure is built.Member sizes may differ from specified dimensions,reinforcement may be out of position,or poor placement of concrete may result in voids.An important part of the job of the ergineer is to provide proper supervision of construction.Slighting of this responsibility has had disastrous consequences in more than one instance.Structural SafetySafety requires that the strength of a structure be adequate for all loads that may conceivably act on it.If strength could be predicted accurately and if loads were known with equal certainty,then safely could be assured by providing strength just barely in excess of the requirements of the loads.But there are many sources of uncertainty in the estimation of loads as well as in analysis,design,and construction.These uncertainties require a safety margin.In recent years engineers have come to realize that the matter of structural safety is probabilistic in nature,and the safety provisions of many current specifications reflect this view.Separate consideration is given to loads and strength.Load factors,larger than unity,are applied to the calculated dead loads and estimated or specified service live loads,to obtain factorde loads that the member must just be capable of sustaining at incipient failure.Load factors pertaining to different types of loads vary,depending on the degree of uncertainty associated with loads of various types,and with the likelihood of simultaneous occurrence of different loads.Early in the development of prestressed concrete,the goal of prestressing was the complete elimination of concrete ternsile stress at service loads.The concept was that of an entirely new,homogeneous material that woukd remain uncracked and respond elastically up to the maximum anticipated loading.This kind of design,where the limiting tensile stressing,while an alternative approach,in which a certain amount of tensile amount of tensile stress is permitted in the concrete at full service load,is called partial prestressing.There are cases in which it is necessary to avoid all risk of cracking and in which full prestressing is required.Such cases include tanks or reservious where leaks must be avoided,submerged structures or those subject to a highly corrosive envionment where maximum protection of reinforcement must be insured,and structures subject to high frequency repetition of load where faatigue of the reinforcement may be a consideration.However,there are many cses where substantially improved performance,reduced cost,or both may be obtained through the use of a lesser amount of prestress.Full predtressed beams may exhibit an undesirable amount of upward camber because of the eccentric prestressing force,a displacement that is only partially counteracted by the gravity loads producing downward deflection.This tendency is aggrabated by creep in the concrete,which magnigies the upward displacement due to the prestress force,but has little influence on the should heavily prestressed members be overloaded and fail,they may do so in a brittle way,rather than gradually as do beams with a smaller amount of prestress.This is important from the point of view of safety,because suddenfailure without warning is dangeroud,and gives no opportunity for corrective measures to be taken.Furthermore,experience indicates that in many cases improved economy results from the use of a combination of unstressed bar steel and high strength prestressed steel tendons.While tensile stress and possible cracking may be allowed at full service load,it is also recognized that such full service load may be infrequently applied.The typical,or characteristic,load acting is likely to be the dead load plus a small fraction of the specified live load.Thus a partially predtressed beam may not be subject to tensile stress under the usual conditions of loading.Cracks may from occasionally,when the maximum load is applied,but these will close completely when that load is removed.They may be no more objectionable in prestressed structures than in ordinary reinforced.They may be no more objectionable in prestressed structures than in ordinary reinforced concrete,in which flexural cracks always form.They may be considered a small price for the improvements in performance and economy that are obtained.It has been observed that reinforced concrete is but a special case of prestressed concrete in which the prestressing force is zero.The behavior of reinforced and prestressed concrete beams,as the failure load is approached,is essentially the same.The Joint European Committee on Concrete establishes threee classes of prestressed beams.Class 1:Fully prestressed,in which no tensile stress is allowed in the concrete at service load.Class 2:Partially prestressed, in which occasional temporary cracking is permitted under infrequent high loads.Class 3:Partially prestressed,in which there may be permanent cracks provided that their width is suitably limited.The choise of a suitable amount of prestress is governed by a variety of factors.These include thenature of the loading (for exmaple,highway or railroad bridged,storage,ect.),the ratio of live to dead load,the frequency of occurrence of loading may be reversed,such as in transmission poles,a high uniform prestress would result ultimate strength and in brittle failure.In such a case,partial prestressing provides the only satifactory solution.The advantages of partial prestressing are important.A smaller prestress force will be required,permitting reduction in the number of tendons and anchorages.The necessary flexural strength may be provided in such cases either by a combination of prestressed tendons and non-prestressed reinforcing bars,or by an adequate number of high-tensile tendons prestredded to level lower than the prestressing force is less,the size of the bottom flange,which is requied mainly to resist the compression when a beam is in the unloaded stage,can be reduced or eliminated altogether.This leads in turn to significant simplification and cost reduction in the construction of forms,as well as resulting in structures that are mor pleasing esthetically.Furthermore,by relaxing the requirement for low service load tension in the concrete,a significant improvement can be made in the deflection characteristics of a beam.Troublesome upward camber of the member in the unloaded stage fan be avoeded,and the prestress force selected primarily to produce the desired deflection for a particular loading condition.The behavior of partially prestressed beamsm,should they be overloaded to failure,is apt to be superior to that of fully prestressed beams,because the improved ductility provides ample warning of distress.英译汉：荷载作用在结构上的荷载通常分为恒载或活载。

土木工程毕业外文翻译

1.Central iron & Steel Research institute, Beijing 100081, China2.Chinese Society for Metals, Beijing 100711, China高层建筑与钢结构HUi Wei-jun,DONG HanWENG Yu-ging,CHEN Si-lian,WANG Mao-giu摘要耐火钢其实就是对火灾有一定抵抗能力的钢材，日本认为耐火钢是焊接结构用轧制钢材的一类，在我国它是建筑用低合金钢的一种。

耐火钢于普通的建筑用钢不同，它要求具有良好的耐高温性能，作为常温下的承载材料，只要求在遇到火灾的较短时间内（1到3小时）高温条件下能够保持高的屈服强度，常温下钢材强度的2/3相当于该材料的长期允许应力值，当发生火灾时，如果耐火钢的屈服点仍然在此值以上，建筑物就不会倒塌。

因此，就要求耐火钢在一定高温下的屈服不低于室温下屈服强度的2/3。

本文研究的目的在于研究提高耐火港的强韧性、抗震性和耐火性能。

关键字高层建筑；钢结构；发展应用1.前言近年来，虽然一般的建筑结构设计取得了很大的进步，但是取得显著成绩的还要数超高层建筑结构设计。

最初的高层建筑设计是从钢结构的设计开始的。

钢筋混凝土和受力外包钢筒系统运用起来是比较经济的系统，被有效地运用于大批的民用建筑和商业建筑中。

50层到100层的建筑被成为超高层建筑。

而这种建筑在美国被广泛的应用是由于新的结构系统的发展和创新。

这样的高度需要大柱和梁的尺寸，这样以来可以使建筑物更加坚固以至于在允许的限度范围内承受风荷载而不产生弯曲和倾斜。

过分的倾斜会导致建筑物的隔离构件、顶棚以及其它建筑细部产生循环破坏。

除此之外，过大的摇动也会使建筑物的使用者感觉到这样的晃动而产生不舒服的感觉。

无论是钢筋混凝土结构系统还是钢结构系统都充分利用了整个建筑的刚度潜力，因此，不能指望利用多余的刚度来限制侧向位移。

土木工程毕业设计--外文翻译

1 Introduction and scope1.1 Aims of the ManualThis Manual provides guidance on the design of reinforced and prestressed concrete building structures. Structures designed in accordance with this Manual will normally comply with DD ENV 1992-1-1: 19921 (hereinafter referred to as EC2).1.2 Eurocode systemThe structural Eurocodes were initiated by the European Commission but are now produced by the Comité Européen de Normalisation (CEN) which is the European standards organization, its members being the national standards bodies of the EU and EFTA countries,e.g. BSI.CEN will eventually publish these design standards as full European Standards EN (Euronorms), but initially they are being issued as Prestandards ENV. Normally an ENV has a life of about 3 years to permit familiarization and trial use of the standard by member states. After formal voting by the member bodies, ENVs are converted into ENs taking into account the national comments on the ENV document. At present the following Eurocode parts have been published as ENVs but as yet none has been converted to an EN:DD ENV 1991-1-1: Basis of design and actions on structures (EC1)DD ENV 1992-1-1: Design of concrete structures (EC2)DD ENV 1993-1-1: Design of steel structures (EC3)DD ENV 1994-1-1: Design of composite steel and concrete structures (EC4)DD ENV 1995-1-1: Design of timber structures (EC5)DD ENV 1996-1-1: Design of masonry structures (EC6)DD ENV 1997-1-1: Geotechnical design (EC7)DD ENV 1998-1-1: Earthquake resistant design of structures (EC8)DD ENV 1999-1-1: Design of aluminium alloy structures (EC9)Each Eurocode is published in a number of parts, usually with ‘General rules’ and ‘Rules for buildings’ in Part 1. The various parts of EC2 are:Part 1.1 General rules and rules for buildings;Part 1.2 Supplementary rules for structural fire design;Part 1.3 Supplementary rules for precast concrete elements and structures;Part 1.4 Supplementary rules for the use of lightweight aggregate concrete;Part 1.5 Supplementary rules for the use of unbonded and external prestressing tendons;Part 1.6 Supplementary rules for plain or lightly reinforced concrete structures;Part 2.0 Reinforced and prestressed concrete bridges;Part 3.0 Concrete foundations;Part 4.0 Liquid retaining and containment structures.All Eurocodes follow a common editorial style. The codes contain ‘Principles’ and‘Application rules’. Principles are general statements, definitions, requirements and sometimes analytical models. All designs must comply with the Principles, and no alternative is permitted. Application rules are rules commonly adopted in design. They follow the Principles and satisfy their requirements. Alternative rules may be used provided that compliance with the Principles can be demonstrated.Some parameters in Eurocodes are designated by | _ | , commonly referred to as boxed values. The boxed values in the Codes are indicative guidance values. Each member state is required to fix the boxed value applicable within its jurisdiction. Such information would be found in the National Application Document (NAD) which is published as part of each ENV.There are also other purposes for NADs. NAD is meant to provide operational information to enable the ENV to be used. For certain aspects of the design, the ENV may refer to national standards or to CEN standard in preparation or ISO standards. The NAD is meant to provide appropriate guidance including modifications required to maintain compatibility between the documents. Very occasionally the NAD might rewrite particular clauses of the code in the interest of safety or economy. This is however rare.1.3 Scope of the ManualThe range of structures and structural elements covered by the Manual is limited to building structures that do not rely on bending in columns for their resistance to horizontal forces and are also non-sway. This will be found to cover the vast majority of all reinforced and prestressed concrete building structures. In using the Manual the following should be noted:• The Manual has been drafted to comply with ENV 1992-1-1 together with the UK NAD• Although British Standards have been referenced as loading codes in Sections 3 and 6,to comply with the UK NAD, the Manual can be used in conjunction with other loading codes • The structures are braced and non-sway• The concrete is of normal weight• The structure is predominantly in situ• Prestressed concrete members have bonded or unbonded internal tendons• The Manual can be used in conjunction with all commonly used materials in construction; however the data given are limited to the following:– concrete up to characteristic cylinder strength of 50N/mm2 (cube strength 602N/mm)– high-tensile reinforcement with characteristic strength of 4602N/mm– mild-steel reinforcement with characteristic strength of 2502N/mm– prestressing tendons with 7-wire low-relaxation (Class 2) strands• High ductility (Class H) has been assumed for:– all ribbed bars and grade 250 bars, and– ribbed wire welded fabric in wire sizes of 6mm or over• Normal ductility (Class N) has been assumed for plain or indented wire welded fabric.For structures or elements outside this scope EC2 should be used.1.4 Contents of the ManualThe Manual covers the following design stages:• gene ral principles that govern the design of the layout of the structure• initial sizing of members• estimating of quantities of reinforcement and prestressing tendons• final design of members.2 General principlesThis section outlines the general principles that apply to both initial and final design of both reinforced and prestressed concrete building structures, and states the design parameters that govern all design stages.2.1 GeneralOne engineer should be responsible for the overall design, including stability, and should ensure the compatibility of the design and details of parts and components even where some or all of the design and details of those parts and components are not made by the same engineer.The structure should be so arranged that it can transmit dead, wind and imposed loads in a direct manner to the foundations. The general arrangement should ensure a robust and stable structure that will not collapse progressively under the effects of misuse or accidental damage to any one element.The engineer should consider engineer site constraints, buildability2, maintainability and decommissioning.The engineer should take account of his responsibilities as a ‘Designer’ under the Construction (Design & Management) Regulations.32.2 StabilityLateral stability in two orthogonal directions should be provided by a system of strongpoints within the structure so as to produce a braced non-sway structure, in which the columns will not be subject to significant sway moments. Strongpoints can generally be provided by the core walls enclosing the stairs, lifts and service ducts. Additional stiffness can be provided by shear walls formed from a gable end or from some other external or internal subdividing wall. The core and shear walls should preferably be distributed throughout the structure and so arranged that their combined shear centre is located approximately on the line of the resultant in plan of the applied overturning forces. Where this is not possible, the resulting twisting moments must be considered when calculating the load carried by each strongpoint. These walls should generally be of reinforced concrete not less than 180mm thick to facilitate concreting, but they may be of 215mm brickwork or 190mm solid blockwork properly tied and pinned up to the framing for low- to medium-rise buildings.Strongpoints should be effective throughout the full height of the building. If it is essential for strongpoints to be discontinuous at one level, provision must be made to transfer the forces toother vertical components.It is essential that floors be designed to act as horizontal diaphragms, particularly if precast units are used.Where a structure is divided by expansion joints each part should be structurally independent and designed to be stable and robust without relying on the stability of adjacent sections.2.3 RobustnessAll members of the structure should be effectively tied together in the longitudinal, transverse and vertical directions.A well-designed and well-detailed cast-in situ structure will normally satisfy the detailed tying requirements set out in subsection 5.11.Elements whose failure would cause collapse of more than a limited part of the structure adjacent to them should be avoided. Where this is not possible, alternative load paths should be identified or the element in question strengthened.2.4 Movement jointsMovement joints may need to be provided to minimize the effects of movements caused by, for example, shrinkage, temperature variations, creep and settlement.The effectiveness of movement joints depends on their location. Movement joints should divide the structure into a number of individual sections, and should pass through the whole structure above ground level in one plane. The structure should be framed on both sides of the joint. Some examples of positioning movement joints in plan are given in Fig. 2.1.Movement joints may also be required where there is a significant change in the type of foundation or the height of the structure. For reinforced concrete frame structures in UK conditions, movement joints at least 25mm wide should normally be provided at approximately 50m centres both longitudinally and transversely. In the top storey and for open buildings and exposed slabs additional joints should normally be provided to give approximately 25m spacing. Joint spacing in exposed parapets should be approximately 12m.Joints should be incorporated in the finishes and in the cladding at the movement joint locations.2.5 Fire resistance and durabilityFor the required period of fire resistance (prescribed in the Building Regulations), the structure should:• have adequate loadbearing capacity• limit the temperature rise on the far face by sufficient insulation, and• have sufficient integrity to prevent the formation of crack s that will allow the passage of fire and gases.Fig. 2.1 Location of movement jointsThe design should take into account the likely deterioration of the structure and its components in their environment having due regard to the anticipated level of maintenance. The following inter-related factors should be considered:• the required performance criteria• the expected environmental conditions• the composition, properties and performance of materials• the shape of members and detailing• the quality of workmanship• any protective measure• the likely maintenance during the intended life.Concrete of appropriate quality with adequate cover to the reinforcement should be specified. The above requirements for durability and fire resistance may dictate sizes for members greater than those required for structural strength alone.3 Design principles – reinforced concrete3.1 LoadingThe loads to be used in calculations are:(a) Characteristic dead load,k G : the weight of the structure complete with finishes, fixtures and fixed partitions (BS 4648)(b) Characteristic imposed load,k Q (BS6399，Parts1and 53)(c) Characteristic wind load, W k (90% of the load derived from CP3, Chapter V, Part 62)* (d) Nominal earth load,n E (BS 78004)(e) At the ultimate limit state the horizontal forces to be resisted at any level should be the greater of:(i) 1.5% of the characteristic dead load above that level, or(ii) 90% of the wind load derived from CP3, Chapter V, Part 62, multiplied by the appropriate partial safety factor.The horizontal forces should be distributed between the strongpoints according to their stiffness.In using the above documents the following modifications should be noted:(f) The imposed floor loads of a building should be treated as one load to which the reduction factors given in BS 6399: Part 1:51996are applicable.(g) Snow drift loads obtained from BS 6399: Part 3:51998 should be multiplied by 0.7 and treated in a similar way to an imposed load and not as an accidental load.3.2 Limit statesThis Manual adopts the limit-state principle and the partial factor format of EC2.3.2.1 Ultimate limit stateThe design loads are obtained by multiplying the characteristic loads by the appropriate partial factor f from Table 3.1.The ‘adverse’ and ‘beneficial’ factors should be used so as to produce the most onerous condition.3.2.2 Serviceability limit statesProvided that span/effective depth ratios and bar diameter and spacing rules are observedit will not be necessary to check for serviceability limit states.fThe Table uses the simplified combination permitted in EC2.†For pressures arising from an accidental head of water at ground level a partial factor of 1.15 may be used.3.3 Material and design stressesDesign stresses are given in the appropriate sections of the Manual. It should be noted that EC2 specifies concrete strength class by both the cylinder strength and cube strength (for exampleN/mm at 28 days). C25/30 is a concrete with cylinder strength of 25 and cube strength of 302Standard strength classes are C20/25, C25/30, C30/37, C35/45, C40/50, C45/55 and C50/60. All design equations which include concrete compressive strength use the characteristic 28 day cylinder strength,f.ckPartial factors for concrete are 1.5 for ultimate limit state and 1.0 for serviceability limit state. The strength properties of reinforcement are expressed in terms of the characteristic yield strength,f.ykPartial factors for reinforcement steel are 1.15 for ultimate limit state and 1.0 for serviceability limit state.4 Initial design – reinforced concrete4.1 IntroductionIn the initial stages of the design of building structures it is necessary, often at short notice,to produce alternative schemes that can be assessed for architectural and functional suitability and which can be compared for cost. They will usually be based on vague and limited information on matters affecting the structure such as imposed loads and nature of finishes, let alone firm dimensions, but it is nevertheless expected that viable schemes be produced on which reliable cost estimates can be based.It follows that initial design methods should be simple, quick, conservative and reliable. Lengthy analytical methods should be avoided.This section offers some advice on the general principles to be applied when preparing a scheme for a structure, followed by methods for sizing members of superstructures. Foundation design is best deferred to later stages when site investigation results can be evaluated.The aim should be to establish a structural scheme that is suitable for its purpose, sensibly economical, and not unduly sensitive to the various changes that are likely to be imposed as the overall design develops.Sizing of structural members should be based on the longest spans (slabs and beams) and largest areas of roof and/or floors carried (beams, columns, walls and foundations). The same sizes should be assumed for similar but less onerous cases – this saves design and costing time at this stage and is of actual benefit in producing visual and constructional repetition and hence, ultimately, cost benefits.Simple structural schemes are quick to design and easy to build. They may be complicated later by other members of the design team trying to achieve their optimum conditions, but a simple scheme provides a good ‘benchmark’ at the initial stage.Loads should be carried to the foundation by the shortest and most direct routes. In constructional terms, simplicity implies (among other matters) repetition; avoidance of congested, awkward or structurally sensitive details and straightforward temporary works with minimal requirements for unorthodox sequencing to achieve the intended behaviour of the completed structure.Standardized construction items will usually be cheaper and more readily available than purpose-made items.4.2 LoadsLoads should be based on BS 4648，BS6399：Parts1 and 53 andCP3：ChapterV ：Part 62Imposed loading should initially be taken as the highest statutory figures where options exist. The imposed load reduction allowed in the loading code should not be taken advantage of in the initial design stage except when assessing the load on the foundations.Loading should be generous and not less than the following in the initial stages:floor finish (screed) 1.82kN/mmceiling and service load 0.52kN/mmAllowance for:demountable lightweight partitions* 1.02kN/mmblockwork partitions† 2.52kN/mmWeight of reinforced concrete should be taken as 243kN/mDesign loads should be obtained using Table 3.1.4.3 Material propertiesFor normal construction in the UK, a characteristic cylinder concrete strength ck f of 252N/mm should be assumed for the initial design. In areas with poor aggregates this may have to be reduced.For UK steels a characteristic strength yk f of 4602N/mm should be used for high-tensile reinforcement and 2502N/mm for mild steel.4.4 Structural form and framingThe following measures should be adopted:(a) provide stability against lateral forces and ensure braced construction by arranging suitable shear walls deployed symmetrically wherever possible(b) adopt a simple arrangement of slabs, beams and columns so that loads are carried to the foundations by the shortest and most direct routes(c) allow for movement joints (see subsection 2.4)(d) choose an arrangement that will limit the span of slabs to 5m to 6m and beam spans to 8m to l0m on a regular grid; for flat slabs restrict column spacings to 8m(e) adopt a minimum column size of 300mm × 300mm or equivalent area(f) provide a robust structure.The arrangement should take account of possible large openings for services and problems with foundations, e.g. columns immediately adjacent to site boundaries may require balanced or other special foundations.4.5 Fire resistance and durabilityThe size of structural members may be governed by the requirement of fire resistance and may also be affected by the cover necessary to ensure durability. Table 4.1 shows the minimum practical member sizes for different periods of fire resistance and the cover to the main reinforcement required for continuous members in dry and humid environments without frost. For other exposure classes, cover should be increased. For simply supported members, sizes and cover should be increased (see Section 5 and Appendix C).4.6 StiffnessTo provide adequate stiffness, the effective depths of beams, slabs and the waist of stairs should not be less than those derived from Table 4.2.Beams should be of sufficient depth to avoid the necessity for excessive compression reinforcement and to ensure that economical amounts of tension and shear reinforcement are provided. This will also facilitate the placing of concrete.*To be treated as imposed loads.†To be treated as dead load s when the layout is fixed.Table 4.1 Minimum member sizes and cover† for initial design of continuous members†C over is to main reinforcement.Table 4.2 Basic ratios of span/effective depth for initial design (yk f = 4602N/mm )1. For two-way spanning slabs (supported on beams), the check on the ratio of span/effective depth should be carried out on the shorter span. For flat slabs, the longer span should be taken.2. For flanged sections with the ratio of the flange to the rib width greater than 3, the Table value should be multiplied by 0.8.3. For members, other than flat slab panels, which support partitions liable to be damaged by excessive deflection of the member, and where the span exceeds 7m, the Table value should be multiplied by 7/span.4. For flat slabs where the greater span exceeds 8.5m, the Table value should be multiplied by 8.5/span.第一章引言和适用范围1.1手册的作用这本手册为设计钢筋和预应力混凝土建筑结构提供了指导。

土木工程专业毕业设计外文翻译

High-Rise BuildingsIn troducti onIt is difficult to defi ne a high-rise buildi ng . One may say that a low-rise build ing ranges from 1 to 2 stories . A medium-rise buildi ng p robably ran ges betwee n 3 or 4 stories up to 10or 20 stories or more .Although the basic principles of vertical and horiz on tal subsystem desig n rema in the samefor low- , medium- , or high-rise build ings , whe n a build ing gets high the verticalsubsystemsbecome a con trolli ng p roblem for two reas ons . Higher vertical loads will requirelarger colu mns , walls , and shafts . But , more sig nifica ntly , the overtur ning mome nt and theshear deflect ions p roduced by lateral forces are much larger and must be carefully pro vided for .The vertical subsystems in a high-rise buildi ng tran smit accumulated gravity load from storyto story , thus requiri ng larger colu mn or wall secti ons to support such loadi ng .In additi onthese same vertical subsystems must tran smit lateral loads , such as wi nd or seismic loads , tothe foun datio ns. However , in con trast to vertical load , lateral load effects on build ings arenot lin ear and in crease rap idly with in crease in height . For example under wind load , theoverturning moment at the base of buildings varies approximately as the square of a buildings mayvary as the fourth power of buildings height , other things being equal. Earthquake produces an evenmore pronoun ced effect.When the structure for a low-or medium-rise building is designed for dead and live load , it isalmost an in here nt property that the colu mns , walls , and stair or elevator shafts can carrymost of the horiz on tal forces . The p roblem is p rimarily one of shear resista nee . Moderateadditi on braci ng for rigid frames in easily be pro vided by filli ng certa in pan els ( or eve n“short ” buildi all pan els ) without in creas ing the sizes of the colu mns and girders otherwise required forvertical loads.Unfortunately , this is not is for high-rise buildings because the problem is p rimarily resistanee to mome nt and deflect ion rather tha n shear alone . Sp ecial structural arra ngeme nts will often have to be made and additi onal structural material is always required for the columns , girders ,walls , and slabs in order to made a high-rise buildi ngs sufficie ntly resista nt to much higherlateral deformati ons .As p reviously men ti oned , the qua ntity of structural material required per square foot offloor of a high-rise buildings is in excess of that required for low-rise buildings . The verticalcomponents carrying the gravity load , such as walls , columns , and shafts , will need to bestrengthened over the full height of the build ings . But qua ntity of material required for resisting lateral forces is eve n more sig nifica nt .With rei nforced con crete , the qua ntity of material also in creases as the nu mber ofstories in creases . But here it should be no ted that the in crease in the weight of material addedfor gravity load is much more sizable tha n steel , whereas for windIn crease the effective width of the mome nt-resisti ng subsystems . This is very usefulbecause in creas ing the width will cut dow n the overtur n force directly and willreduce deflecti on by the third po wer of the width in crease , other things rema iningcin sta nt . However , this does require that vertical components of the widenedsubsystem be suitably connected to actually gain this ben efit.Desig n subsystemssuch that the components are made to in teract in the most efficientmanner . For example , use truss systems with chords and diagonals efficiently stressed ,place reinforcing for walls at critical locati ons , and op timize stiff ness ratios for rigid frames .In crease the material in the most effective resist ing components . For exa mple ,materials added in the lower floors to the flan ges of colu mns and conn ect ing girderswill directly decrease the overall deflect ion and in crease the mome nt resista neewithout con tribut ing mass in the upper floors where the earthquake p roblem isaggravated .Arrange to have the greater part of vertical loads be carried directly on the primarymoment-resisting components . This will help stabilize the build ings aga inst ten sileovertu rning forces by p reco mp ress in gthe major overturn-resisti ng components .The local shear in each story can be best resisted by strategic pl aceme nt if solid wallsor the use of diagonal members in a vertical subsystem . Resist ing these shears solelyby vertical members in bending is usually less econo mical , since achiev ing sufficient bending resista nee in the colu mns and conn ect ing girders will require morematerial and con struct ion en ergy tha n using walls or diago nal members .Sufficie nt horiz on tal dia phragm acti on should be pro vided floor . This will help tobring the various resist ing eleme nts to work together in stead of sep arately .Create mega-frames by joining large vertical and horizontal components such as two or moreelevator shafts at multistory intervals with a heavy floor subsystems , or by use of verydee p girder trusses .Remember that all high-rise build ings are esse ntially vertical can tilevers which aresupported at the ground . When the above principles are judiciously applied , structurally desirable schemes can be obta ined by walls , cores , rigid frames, tubular con struct ion , and othervertical subsystems to achieve horiz on tal stre ngth and rigidity . Some of these app licati ons will now be described in subseque nt secti ons in the followi ng .Shear-Wall SystemsWhen shear walls are comp atible with other fun cti onal requireme nts , they can beeconomically utilized to resist lateral forces in high-rise buildings . For example , ap artme nt build ings n aturally require many sep arati on walls . Whe n some of these are desig ned to be load the in crease for lateral force resista nee is not that much more since the weight of a concrete buildings helps to resist overturn . On the other hand , the problem of desig n for earthquake forces . Additi onal mass in the upper floors will give rise to a greater overall lateral force un der the of seismic effects .In the case of either concrete or steel design , there are certain basic principles for pro vid ing additi onal resista nee to lateral to lateral forces and deflecti ons in high-rise build ings without too much sacrifire in economy .1.2. 3. 4. 5. 6. 7.solid , they can act as shear walls to resist lateral forces and to carry the vertical load aswell . For buildi ngs up to some 20storise , the use of shear walls is com mon .If give n sufficie nt len gth ,such walls can econo mically resist lateral forces up to 30 to 40 stories or more .However , shear walls can resist lateral load only the plane of the walls ( i.e .not in adireti on perpen dicular to them ) . There fore ,it is always n ecessary to pro vide shear walls in two perpen dicular directi ons can be at least in sufficie nt orie ntati on so that lateral force in any direct ion can be resisted .In additi on , that wall layout should reflect con siderati on of any torsi onal effect .In desig n p rogress , two or more shear walls can be conn ected to from L-sha ped or cha nnel-sha ped subsystems .In deed ‘internal shear walls can be conn ected to from a rectangular shaft that will resist lateral forces very efficiently . If all external shear walls are continuously connected , then the whole buildings acts as tube , and conn ected , the n the whole buildi ngs acts as a tube , and is excelle nt Shear-Wall Seystems resist ing lateral loads and torsi on .Whereas con crete shear walls are gen erally of solid type with openings whe n necessary, steel shear walls are usually made of trusses . These trusses can have single diagonals , “X” diagona|sor “ K” arrang e nhs . A trussed wall will have its members act esse ntially in direct tension or comp ressi on un der the acti on of view , and they offer some opportunity anddeflection-limitation point of view , and they offer some opportunity for penetration between members . Of course , the inclined members of trusses must be suitable p laced so as not to in terfere with requireme nts for wion dows and for circulati on service pen etrati ons though these walls .As stated above , the walls of elevator , staircase ,and utility shafts form n atural tubes and are com monly empio yed to resist both vertical and lateral forces . Since these shafts are no rmally recta ngular or circular in cross-sect ion , they can offer an efficie nt means for resist ing mome nts and shear in all directi ons due to tube structural action . But a p roblem in the desig n of these shafts is pro vided sufficie nt stre ngth around door openings and other pen etrati ons through these eleme nts . For rein forced concrete construction , special steel reinforcements are placed around such opening .In steel con struct ion , heavier and more rigid conn ecti ons are required to resist rack ing at the openings .In many high-rise build ings , a comb in ati on of walls and shafts can offer excelle ntresista nee to lateral forces whe n they are suitably located ant conn ected to one ano ther . It is also desirable that the stiff ness offered these subsystems be more-or-less symmertrical in all direct ions .Rigid-Frame SystemsIn the desig n of architectural build ings , rigid-frame systems for resist ing vertical and lateral loads have long bee n acce pted as an imp orta nt and sta ndard means for designingbuilding . They are empioyed for low-and medium means for designing build ings . They are empio yed for low- and medium up to high-rise build ing p erha ps 70 or 100 stories high . Whe n comp ared to shear-wall systems , these rigid frames both with in and at the outside of a buildi ngs . They also make use of the stiff ness in beams and colu mns that are required for the build ings in any case , but the colu mns are made stron ger whe n rigidly conn ected to resist the lateral as well as vertical forces though frame bending .Freque ntly , rigid frames will not be as stiff as shear-wall con struct ion , and therefore may p roduce excessive deflecti ons for the more sle nder high-rise buildi ngs desig ns . But because of this flexibility , they are ofte n con sidered as being more ductile and thus less susceptible to catastr op hic earthquake failure whe n comp ared with ( some ) shear-wall desig ns . For exa mple , if over stress ing occurs at certa in p orti ons of a steel rigid frame ( i.e., near the joi nt ) , ductility will allow the structure as a whole to deflect a little more , but it will by no means colla pse eve n un der a much larger force tha n exp ected on the structure . For this reas on , rigid-frame con struct ion is considered by some to be a “ best ” seisresisting type for high-rise steel buildings . On the other hand ,it is also unlikely that a well-designed share-wall system would colla pse.In the case of con crete rigid frames ,there is a diverge nee of opinion .It true that if a con crete rigid frame is desig ned in the conven ti onal manner , without sp ecial care to produce higher ductility , it will not be able to withstand a catastrophic earthquake that can p roduce forces several times lerger tha n the code desig n earthquake forces . therefore , some believe that it may not have additi onal cap acity p ossessed by steel rigid frames . But moder n research and exp erie nee has in dicated that con crete frames can be desig ned to be ductile , whe n sufficie nt stirr ups and joinery rein forceme nt are designed in to the frame . Modern buildings codes have specifications for the so-called ductile con crete frames . However , at p rese nt , these codesofte n require excessive rein forceme nt at certa in points in the frame so as to cause con gesti on and result in construction difficulties 。

土木工程毕业设计外文翻译

Ecological Engineering 35(2009)1043–1050Contents lists available at ScienceDirectEcologicalEngineeringj o u r n a l h o m e p a g e :w w w.e l s e v i e r.c o m /l o c a t e /e c o l e ngEnhancement of nitrogen removal in towery hybrid constructed wetland to treat domestic wastewater for small rural communitiesa r t i c l e i n f o Article history:Received 11September 2008Received in revised form 6January 2009Accepted 23March 2009Keywords:Constructed wetlands Nitriﬁcation DenitriﬁcationDomestic wastewater Nitrogen removal Nitrifying bacteria Denitrifying bacteriaa b s t r a c tEfforts to protect watercourses,especially sources of drinking water,particularly in rural areas,are now underway in China.Nitrogen present in wastewater,due to its role in eutrophication and potential toxicity to aquatic species,is a focus of primary concern.Constructed wetlands (CWs),a simpler,less costly treat-ment alternative,have been used to treat domestic wastewater for small communities.Although showing great promise for removing carbonaceous materials from wastewater,wetland systems have not been suc-cessful in removing nitrogen mainly due to lack of dissolved oxygen (DO).To enhance nitrogen removal,a novel CW conﬁguration with three stages,towery hybrid constructed wetland (THCW),was designed.The ﬁrst and third stages were rectangle subsurface horizontal ﬂow CWs,and the second stage was a cir-cular three-layer free-water ﬂow CW.Increased DO by passive aeration of a tower type cascade overﬂow from the upper layer into the lower layer in the second stage of the wetland enhanced nitriﬁcation rates.Denitriﬁcation rates were also improved by additional organic matter supplied as a result of bypass inﬂu-ent directly into the second stage.Evergreen tree Pond Cypress (Taxodium ascendens ),industrial plants Mat Rush (Schoenoplectus trigueter )and Wild Rice shoots (Zizania aquatica ),ornamental ﬂoriferous plants Pygmy Waterlily (Nymphaea tetragona )and Narrow-leaved Cattail (Typha angustifolia )were planted in the wetland.The average percentage of removal was 89%,85%,83%,83%and 64%for total suspended solid,chemical oxygen demand,ammonia nitrogen,total nitrogen and total phosphorus,respectively.There was no signiﬁcant difference (p <0.05)at low and high hydraulic loads (16cm/d and 32cm/d)for perfor-mance of THCW.Nitrifying and denitrifying bacteria as well as potential nitriﬁcation activity and potential denitriﬁcation rates measured have shown that nitriﬁcation–denitriﬁcation is the main mechanism for nitrogen removal in the wetland.THCW also provided additional aesthetic beneﬁts.©2009Elsevier B.V.All rights reserved.1.IntroductionWidespread demands for improved receiving water quality,especially drinking water are currently driving the implementa-tion of advanced wastewater treatment techniques.In rural areas of China,the domestic sewage was discharged directly into water-courses,lakes,rivers,soil or sea.This discharge of poorly treated sewage is responsible for many watercourses,reservoirs and lakes not meeting their quality objectives.Many small communities located in rural areas of China lack adequate domestic wastewa-ter treatment facilities.Wastewater collection and treatment are problematic in these areas due to mountainous terrain,dispersed population,and a lower economic base.In order for resource-scarce,economically developing rural areas to adopt wastewater treatment,the treatment technologies must be cost-effectiveand easy to adopt,require less energy input and maintenance costs,and be capable of meeting efﬂuent discharge standards.The centralized wastewater treatment plants based on activated sludge or bacterial beds processes which are utilized in large and small cities are not economically adaptable for such rural areas,mainly due to the construction costs of sewage collec-tors.On the other hand,the nitrogen content of many watercourses,reservoirs and lakes in China does not meet the standards of national and local governments.It now seems clear that in many lakes,most estuaries,and almost all coastal waters,nitrogen also plays a major role in eutrophication.Therefore,national regula-tions have recently been issued;the project is called “new country construction”.The regulations stipulate that the domestic wastew-ater in rural areas must be treated before being discharged into a watercourse or soil.Constructed wetlands (CWs)have been scientiﬁcally tested and constructed for on-site treatment in rural areas for small units and small villages.Simple construction,large buffering capacity,little1044 F.Ye,Y.Li/Ecological Engineering35(2009)1043–1050excess sludge production,simple operation and maintenance,as well as low operational and maintenance costs are the advantages of CWs.The treatment efﬁciency is generally good in terms of sus-pended solid(SS),biochemical oxygen demand(BOD)and chemical oxygen demand(COD)removal;but nitrogen removal,particularly ammonia nitrogen(NH3-N),in most of the present generation of operating wetland systems(predominately horizontalﬂow beds)is deﬁcient mainly due to the insufﬁcient amount of oxygen available to the nitrifying microbial population in CWs.Generally nitrogen removal in subsurface horizontalﬂow(SSHF)systems is about 30–40%,and means of30%(NH3-N)and39.6%total nitrogen(TN) are given for268European constructed wetlands.However,sin-gle sets of data concerning removal efﬁciency differ extremely in most of the long-term evaluated SSHF systems(Vymazal,2005). This problem is caused by an unsatisfactory hydraulic conductivity and an oxygenation deﬁciency in the root zone.To achieve higher elimination rates,verticalﬂow systems have been developed.But, again,removal of nutrients often turned out to be insufﬁcient in all these designs of constructed wetlands.Nitriﬁcation does occur in conventional wetland systems,but typically requires long hydraulic retention time(HRT).Biological nitriﬁcation–denitriﬁcation is usually the most sig-niﬁcant nitrogen removal mechanism in CWs;other mechanisms such as plant uptake,substrate adsorption and ammonia volatiliza-tion are generally of less importance(Green,1997).Although plant uptake of nitrogen occurs,only a minor fraction can typically be removed by plants on a sustainable basis.The uptake capacity of emergent macrophytes,if harvested,is roughly200–2500kg N/ka per year,whereas the capacity of submerged macrophytes is lower(<700kg N/ka per year)(Brix,1994).Furthermore,if the wetlands are not harvested,the vast majority of the nutri-ents that have been incorporated into the plant tissue will be returned to the water by decomposition processes.The biologi-cal nitriﬁcation–denitriﬁcation process depends on various factors such as temperature,pH,alkalinity and,above all,electron and dissolved oxygen(DO)availability.The removal of NH3-N is largely dependent on the O2supply.The bed medium is con-tinuously water-saturated and therefore generally anaerobic.The plants transport O2to the rhizosphere,thereby creating aerobic microsites,adjacent to the roots and rhizomes where NH4+will be oxidizedﬁrst to nitrite by nitrifying bacteria such as Nitrosomonas and then to nitrate by bacteria with the same enzymatic equip-ment as Nitrobacter.After diffusion in an anaerobic zone of the wetland and in the presence of an electron source such as lac-tate or hydrogen gas,nitrates will serve as an electron sink for a very large family of bacteria called nitrate reducers.Nitrate is ﬁnally reduced to N2and emitted into the atmosphere(Drio et al., 1997).The rate of nitriﬁcation is signiﬁcantly lower than that of denitriﬁcation and,in fact,becomes the limiting factor for con-trolling nitrogen removal.When1g of NH3-N is oxidized to be NO3-N,4.3g of oxygen is required.For NH3-N with a concentra-tion of1mg/L,nitriﬁcation will not occur successfully until the DO reaches4.6mg/L.The mineralization of the excess inﬂuent BOD likely depleted the available oxygen and retarded nitriﬁca-tion.However,the oxygen conducted by aquaculture is limited.Root oxygen release rates from a number of submerged aquatic plants is reported to be in the range of0.5–5.2g/(m2d)(Caffreya and Kempb,1991),and from free-ﬂoating plants0.25–9.6g/(m2d)(Brix, 1997).The DO in subsurface water in vegetated subsurface bed (VSB)wetlands is normally low.For example,DO concentrations averaged less than1ppm for VSB microcosm planted systems (Steinberg and Coonrod,1994).Many studies have shown that the oxygen release from roots of different macrophytes is far less than the amount needed for aerobic degradation of organic mat-ter and nitriﬁcation.Due to low DO in VSB wetlands,nitriﬁcation is considered the rate limiting step for nitrogen removal.Nitriﬁ-cation can occur at low DO,but the reaction rate is considerably less than that at DO levels greater than2mg/L(Grady et al., 1980).In order to improve the nitriﬁcation rate,aeration was employed to increase the dissolved oxygen and nitriﬁcation rate.But while the removal rate of NH3-N was increased,the removal rate of NO3-N was decreased(Green,1997).Wetlands have two environ-mental characteristics that promote denitriﬁcation:one is anoxic sediments,a requisite condition for denitriﬁcation(redox poten-tial<300mV);another is a source of carbon fuel for denitriﬁcation (Vymazal,2005).About87%of the nitrogen removal by the planted wetlands was due to denitriﬁcation,with13%due to accumula-tion in sediment and plant biomass.The plants(including plant litter)and inﬂuent organic matter were each responsible for about 50%of nitrogen removal,mainly through supplying organic carbon and creating anaerobic conditions for denitriﬁcation(van Oostrom, 1995;Newman et al.,2000).Denitriﬁcation of1g NO3-N to be N2,the organic material equivalent to2.86g BOD is needed.It was found that a C:N ratio(measured as mg BOD5:mgNO x-N) of less than2.3would limit denitriﬁcation rates.However,the decomposition of organic matter takes place mainly in the forepart of CWs,which results in a lack of organic matter in the back part of CWs and low denitriﬁcation.So nitrogen removal via the nitriﬁcation–denitriﬁcation coupling may be improved if a part of CWs is sufﬁcient in oxygen to accomplish the nitriﬁcation of NH3-N;meanwhile another part of CWs is anoxic and BOD is enough to denitrify.Small-scale constructed wetlands for rural domestic wastewater treatment are a relatively new technology,and the physical,chem-ical and biological processes which facilitate treatment are still not well understood.In hybrid systems the advantage and disadvan-tage of SSHF and free-water surface(FWS)or subsurface vertical ﬂow(SSVF)systems can be combined to complement each other. It is possible to produce an efﬂuent in low COD(or BOD),which is fully nitriﬁed and partly denitriﬁed,and hence has a much lower TN concentration.The objectives of this study were:1.To evaluate the performance of the novel CW,towery hybrid con-structed wetland(THCW),especially nitrogen removal under a high hydraulic load.The THCW was designed to increase the nitriﬁcation rate by elevating the DO level in wastewater by pas-sive oxygenation due to a cascade-type current,and improve the denitriﬁcation rate by supplying a part of the wastewater directly into the middle part of the wetland,and then couple the nitriﬁcation–denitriﬁcation.2.To assess the effects of evergreen perennial woody plants andherbage plants together in THCW on removing nitrogen,espe-cially during winter season,and plant biomass contribution to nitrogen removal processes in this wetland.3.To investigate whether the hybrid system combined with SSHFand FWS exhibits better performance in removing or transform-ing wastewater pollutants,especially nitrogen.2.Materials and methods2.1.System descriptionA THCW system designed by our research group was constructed at a village in Northern Ningbo,China.It consists of three stages dimensioned for the equivalent of40people(PE)(Fig.1).The climate is characterized by an average rainfall of1300–1400mmF.Ye,Y.Li/Ecological Engineering35(2009)1043–10501045Fig.1.Flow diagram of towery hybrid constructed wetland:1,ﬁrst stage;2,second towery stage;3,third stage(discharge);4,wetland plants;5,bottom circular cell;6, middle circular cell;7,upper circular cell;8,cascade.and an air temperature annual average of16.2◦C.Extremes vary between−4.2◦C at the lowest and38.8◦C at the highest.The cold period represents about3months from December to February and during this period the efﬂuent mean temperature was close to8◦C with5.5◦C as the lowest.Theﬁrst and third stages were8m long and6m wide with a depth of1.0m.The beds were constituted of three layers,the lowest layer of washed gravel(2–6cm)with a depth of20cm,the middle layer ofﬁne gravel(0.5–2.0cm)with a depth of65cm,and the upper layer of soil(0.1–0.2cm)with a depth of15cm.The bottom slope was about1%.The second stage consisted of three circular cells with diameters of7m,5m and3m, respectively,from the bottom cell to the upper cell,each0.6m deep,providing approximately38.5m2of surface area.The over-ﬂow from the upper cell drops into the lower cell immediately creating a turbulent cascade,which increases DO and maintains oxic conditions.The bottom of the wetland was lined with a high-density polyethylene liner and the circumference of the wetland was con-structed with approximately5cm of brick to eliminate seepage and mixing of wastewater with underground water.Seedlings of Pond Cypress(Taxodium ascendens)purchased from a nurs-ery were planted0.8m apart around the circumference of the bottom of the whole wetland,and Mat Rush(Schoenoplectus trigueter)was planted in the center of the bottom of the whole wetland in a density of approximately56plants per m2in November and harvested in May of the next year.Wild Rice shoots(Zizania aquatica)were planted in a density of approx-imately9plants per m2after the Mat Rush was harvested to grow from June to October.In the second stage,the upper circular cell was planted with Pygmy Waterlily(Nymphaea tetrag-ona)in a density of approximately6plants per m2,and the middle circular cell was planted with Narrow-leaved Cattail (Typha angustifolia)in a density of approximately36plants per m2.80%of the raw wastewaterﬂowed continuously into theﬁrst stage of the wetland.20%of the raw wastewater was pumped directly into the uppermost circular cell in the second stage of the wetland,and overﬂowed into the middle circular cell,then over-ﬂowed to the bottom cell.This wastewater together with water from theﬁrst stageﬂowed into the third stage of the wetland,and discharged from the end of the third stage of the wetland.Water depth was controlled with a standpipe.In Phase1,the THCW was operated with a hydraulic loading of16cm/d(corresponding to HRT of5.4d)for4months(from May2006to August2006).In Phase2, the THCW was operated with a high hydraulic loading of32cm/d (corresponding to HRT of2.7d)for8months(from September2006 to April2007).The domestic wastewater was pretreated in a septic tank(Table1).2.2.Analytical procedure2.2.1.Chemical analysisWastewater samples were collected daily(regular working days) from the inlet of theﬁrst stage,outlet of the second stage(only during the Phase2test)and outlet of the third stage in the THCW wetland,and formed into weekly composite samples that were pre-served and analyzed for total suspended solid(TSS),COD,NH3-N, TN,and total phosphorous(TP).Weekly in situ temperature,pH and DO measurements of each stage and cell were made using an YSI probe.TSS,COD,TN,TP and NH3-N were determined according to the Standard Methods(APHA,1998).Wild Rice shoots(Z.aquatica)and Mat Rush(S.trigueter)were harvested(by cutting all visible portions above the water surface) in October2006and May2007,respectively.The harvested plants were washed in distilled water and dried in the sun for24h and later in an oven of105◦C for another24h.The plants were weighed before and after drying for water content analysis.The dried plants were powdered and prepared for total Kjeldahl nitrogen(TKN)anal-ysis according to the Standard Methods(APHA,1998).2.2.2.Measurement of nitriﬁcation and denitriﬁcationThe potential nitriﬁcation activity(PNA)was determined on samples in the upper5cm of sediment taken from the front part of the third stage of the wetland.The test media used con-tained per litre:0.14g K2HPO4;0.027g KH2PO4;0.59g(NH4)2SO4;1.20g NaHCO3;0.3g CaCl2·2H2O;0.2g MgSO4;0.00625g FeSO4;0.00625g EDTA;1.06g NaClO3;the pH was7.5.Sodium chlorate was used to inhibit the oxidation of nitrite to nitrate.50mL sediment slurry samples were added to100mL of test media and incubated at 25◦C on a horizontal shaker at150rpm.Subsamples were collected after2,6,20,and24h of incubation.Nitrite concentrations were measured colorimetrically.PNA was calculated by angular coefﬁ-cient assessment of linear regression calculated for hours and the amount of nitrite produced.Results were normalized for volume loss during sampling,referred to by dry weight(DW)and expressed as nmol of nitrite per gram dry matter per hour.Potential denitriﬁcation rate(PDR)was measured using the acetylene inhibition technique.Sediment core samples were col-lected at four locations in the back part of the third stage(two located in bulk,two located in rhizome,diameter=3.5cm),and immediately wrapped tightly in aluminium foil to prevent diffu-sion of oxygen into the sediment cores.Each of these four samples were put into a1500mL Erlenmeyerﬂask,and incubated in water enriched with nutrients(15mg/L NO3-N,72mg/L Ca,10mg/L Mg, 27mg/L Na,39mg/L K and2.5mg/L PO4-P).The headspace of the ﬂasks wasﬂushed with N2for30min.Theﬂasks were shaken on a rotary shaker at60rpm.The cores were incubated for8h in dark-1046 F.Ye,Y.Li /Ecological Engineering 35(2009)1043–1050Table 1Physical and chemical characteristics of inﬂuent and efﬂuents from THCW.a .ParameterInﬂuentEfﬂuent of the second stage in Phase 2Wetland efﬂuent Removal rate (%)Phase 1Phase 2pH7.11(0.04)7.02(0.04) 6.98(0.05) 6.86(0.04)–TSS (mg/L)124.2(20.6)28.2*(3.6)16.6*(5.2)14.2*(5.6)88.57(16.3)DO (mg/L) 1.28(0.52) 2.98*(0.38) 2.04*(0.12) 2.22*(0.13)–CODcr (mg/L)320.2(13.9)119.2*(8.8)46.7*(5.1)49.3(13.9)84.60(9.6)NH 3-N (mg/L)45.6(1.8)12.6*(0.9)8.5*(1.1)7.7*(1.3)83.11(10.2)TN (mg/L)69.38(6.66)49.06(5.12)12.4*(4.1)11.9*(3.9)82.85(8.5)TP (mg/L)6.22(0.96) 2.91*(0.85) 2.06*(0.96)2.23*(0.96)64.15(7.9)aArithmetic mean (standard error in parentheses)of 62samples (4replicates/sample)collected weekly over 1-year period.Values followed by an asterisk are signiﬁcantly different from the inﬂuent (p <0.05)within the same row.ness at 20◦C.Gas samples were taken with a syringe after each hour.Headspace samples were analyzed for N 2O concentration on a gas chromatograph (Shimadzu GC-14B)equipped with an elec-tron capture detector at an operating temperature of 340◦C.PDR was expressed as mg N 2O-N per m 2sediment per hour.2.2.3.Microbial number analysisThe nitrifying and denitrifying bacteria in the sediment of the wetland were enumerated using the most probable number (MPN)calculation (Carter and Gregorich,2006)using the follow-ing media.The medium for nitrifying bacteria:13.5g Na 2HPO 4;0.7g KH 2PO 4;0.1g MgSO 4·7H 2O;0.5g NaHCO 3;2.5g (NH 4)2SO 4;14.4mg FeCl 3·6H 2O;18.4mg CaCl 2·7H 2O;1L distilled water;pH 8.0.The medium for denitrifying bacteria: 1.0g KNO 3;0.1g Na 2HPO 4;2.0g Na 2S 2O 7;0.1g NaHCO 3;0.1g MgCl 2;1L distilled water;pH 7.0.The sediments for nitrifying and denitrifying bacteria measure-ments were removed from the sediment–water interface (0–2cm)and from a deeper level (5–8cm),respectively,with the aid of a 4.7cm (inner diameter)glass tube.Slime was scraped from rocks,rooted aquatic plant materials,and were then dispersed by blend-ing into the cold water with a mixer.Aliquots (1mL)of serial 10-fold sterile distilled water dilutions of the sediment sample were trans-ferred to 96-cell microtiter plates containing each type of mediumand incubated at 28◦C for 21d (nitrifying bacteria)and 5d (denitri-fying bacteria),respectively.In order to determine the dry weight of sediment samples,10g of sediment samples were oven-dried at 105◦C overnight to produce a constant weight.The amounts of nitrifying and denitrifying bacteria in the sediment were analyzed bimonthly during the wetland operation period.2.2.4.Statistical analysisSoftware SPSS was used for all statistical analyses with one-way ANOVA test.Differences were considered as signiﬁcant if p <0.05.Signiﬁcance of differences within means was evaluated with the Duncan’s test.Pearson’s correlations were used for signiﬁcant lin-ear relationships assessment between PDA and hydraulic load,and PDR and hydraulic load.3.ResultsThe changes in the physico-chemical parameters at inﬂuent,efﬂuent of the second stage during Phase 2and efﬂuent of the third stage are presented in Table 1.Water pH did not change greatly.DO was relatively higher in efﬂuent than inﬂuent as the result of passive oxygenation of the cascade overﬂow in the second stage of THCW.Mean DO increased from 1.28±0.52mg/L in inﬂuent to 2.98±0.38mg/L in efﬂuent of the second stage during Phase 2Fig.2.COD,NH 3-N,TN and TP contents on inﬂuent and discharge ports as well as removal rates from THCW during operation period.F.Ye,Y.Li/Ecological Engineering35(2009)1043–10501047Fig.3.PNA(nmol/g DW/h)and PDR(mg N2O-N/m2/h)of sediment in third stage of THCW at the end of experiment.testing.The highest removal rate that was observed was for the TSS of88.57±16.3%.Organic matter measured as COD has shown removal of84.60±9.6%.Nitrogen removal was high and averaged 83.11±10.2%and82.85±8.5%for NH3-N and TN,respectively. However,at the end of the second stage during Phase2testing, NH3-N and TN removal rates were72%and29%,respectively.It suggested that a major amount of nitrogen was transformed into NO3-N by nitriﬁcation in the second stage and54%of nitrogen was removed by denitriﬁcation and/or other mechanisms in the third stage of the wetland.Phosphorus removal of64.15±7.9%was also observed.In comparison to results of Phase2,the greater removal for all measured pollutants took place during Phase1due to the lower hydraulic loading rate employed.But there were no signiﬁ-cant differences in removal rates for all pollutants between the two hydraulic loads(p<0.02).Fig.2describes inﬂuent and efﬂuent concentrations,as well as removal rates of CODcr,NH3-N,TN and TP during a12-month investigation period.During both Phase1and2of the study, NH3-N and TN had been removed efﬁciently over the12-month experiment.The highest nitrogen removal rates were observed during theﬁrst10weeks and the last10weeks when the water temperature was high.However,the wetland also showed high nitrogen,organic matter and phosphorus removal efﬁciencies dur-ing the winter season.Additionally,mean nitrogen loss attributed to nitriﬁcation–denitriﬁcation was signiﬁcantly(p<0.003)higher during the summer than in winter.Ammonia volatilization may be ruled out since the maximum pH measured in the wetland was 7.7,and it should not have been sufﬁcient for signiﬁcant ammonia gas production.Also found were no statistically signiﬁcant differ-ences between all average removals at two different hydraulic loads (16cm/d and32cm/d).As shown in Fig.2,phosphorus removal did not change signif-icantly during the operation period,even at the higher hydraulic load and in the winter season.There was no signiﬁcant difference in TP efﬂuent concentrations during winter and summer operations.As seen in Fig.3,PNA and PDR increased with time over theﬁrst 4months.About1month later when hydraulic loading was ele-vated from16cm/d to32cm/d,PNA decreased during October to December2006and PDR decreased during October2006to Jan-uary2007.Then PNA did not change signiﬁcantly till the end of the test,and PDR increased a little.PNA and PDR tallied well with MPN counts of nitrifying bacteria and denitrifying bacteria,respectively, thus showing two good positive correlations(p<0.05).As seen in Table2,the numbers of nitrifying bacteria and denitri-fying bacteria in the sediment of the wetland were all in the range of104–105MPN/g sediment.A quantitative estimation of nitrify-ing and denitrifying bacteria and their corresponding PNA and PDR (Fig.3)in the sediment of the wetland indicated higher numbers of nitrifying bacteria than denitrifying bacteria,and higher activity of PNA.To show the effects of plant harvesting on nitrogen removal,TKN content in dried weight of harvested plants in October2006and May2007was measured.It showed a much larger nitrogen mass in Mat Rush(S.trigueter)than Wild Rice shoots(Z.aquatica).Average nitrogen contents in the dried plants were6.8±0.3/kg dry plant and 4.7±0.2/kg dry plant,and the TN uptake rates of these emergent plants were17.18kg/ha per day and12.63kg/ha per day for Mat Rush(S.trigueter)and Wild Rice shoots(Z.aquatica),respectively.4.DiscussionNitriﬁcation does not remove nitrogen from wastewaters.But nitriﬁcation coupled with denitriﬁcation seems to be the major removal process in many CWs.Nitriﬁcation occurs when oxygen is present in a high enough concentration to support the growth of strictly aerobic nitrifying bacteria.Nitriﬁcation takes place in all types of CWs;however,the extent of this process is determined by oxygen availability.As NH3-N is the dominant types of nitro-gen in many wastewaters,nitriﬁcation is a limiting process for nitrogen removal from most types of CWs.Denitriﬁcation is con-sidered as a major removal mechanism for nitrogen in most types of CWs.However,the concentrations of nitrates are usually very low in wastewater and,therefore,denitriﬁcation must be coupled with nitriﬁcation.Different requirements for the presence of oxy-gen for nitriﬁcation and denitriﬁcation are the major obstacle in many treatment wetlands for achieving higher nitrogen removal.It is generally accepted that DO concentrations above1.5mg/L are essential for nitriﬁcation to occur.In this wetland,average 2.22±0.13mg/L DO in outﬂow during the study,which most likely resulted from the tower type cascade in the middle of THCW, indicated that DO concentrations support nitriﬁcation;this result would be consistent with much more nitrifying bacteria in the sed-iment(Table2).High DO and available organic matter,due to the bypass of inﬂuent directly into the second stage,thereby reduced competition between heterotrophs and nitriﬁers.More slow grow-ing nitrifying bacteria therefore colonized the rhizome and surface of the sediment.In THCW,the nitrogen load removal rate was about1440g N/m2 per year.As compared to other single and combined CWs(Table3), THCW exhibited higher removal rates of nitrogen than single CWs,and NH3-N removal rates were comparable to the results in the hybrid system.However,the TN removal rate was higher than that observed both in single wetland and combined systems (Cooper,1999;Platzer,1999;Kyambadde et al.,2005),suggest-Table2The amount of nitrifying bacteria and denitrifying bacteria in THCW.Bacteria Times12345MeanNitrifying bacteria(MPN/g sediment)8.89×104 2.55×105 3.67×105 3.16×105 4.23×105 2.90×105 Denitrifying bacteria(MPN/g sediment)9.12×1049.02×104 2.77×105 5.11×1057.03×105 3.34×1051048 F.Ye,Y.Li/Ecological Engineering35(2009)1043–1050Table3Removal of nitrogen in THCW and other various types of CWs.CW type Efﬁciency(%)in concentration(mg/L)Efﬁciency of TN load(g/m2/year)Ref.NH3-N TNFFP a–54.8b407b Vymazal(2007) FWS55.1c41.2d247d Vymazal(2007) SSHF48.3e42.3f250g Vymazal(2007) SSVF84.2h44.6i630j Vymazal(2007) SSVF–SSHF84––O’Hogain(2003) SSVF–SSHF78––Cooper(1999) SSHF–SSVF9761–Brix et al.(2003) SSHF–SSVF99–Laber et al.(2003) SSHF–SSVF–SSHF–SSVF–SSHF8086–Brix et al.(2003) SSVF–SSHF–FWS–65–Mander et al.(2003) SSHF–FWS–82–Masi et al.(2002) SSHF–FWS8481b–Vymazal(2005) This study(SSHF–FWS)8383(TKN)1440a Free-ﬂoating plant.b Mean values of14wetlands.c Mean values of64wetlands.d Mean values of247wetlands.e Mean values of151wetlands.f Mean values of137wetlands.g Mean values of113wetlands.h Mean values of80wetlands.i Mean values of51wetlands.j Mean values of42wetlands.ing that nitriﬁcation–denitriﬁcation coupling may be improved in this wetland.Several possible mechanisms for nitrogen removal in treatment wetlands are included,but the principal mechanism most often cited in long-term nitrogen removal is denitriﬁcation (Reed et al.,1995).The wetland also showed high nitrogen,organic matter and phosphorus removal efﬁciencies during the winter sea-son due to the presence of growing plants,such as Mat Rush(S. trigueter)and Pond Cypress(T.ascendens).Comparatively,this wetland exceeded reduction efﬁciencies of 60%reported for a FWS pilot wetland using duckweed for treat-ment of domestic primary efﬂuent in Israel at a hydraulic load of 22cm/d with10–20%nitrogen removal and negligible phospho-rus removal(Ran et al.,2004).Although the hydraulic load was increased by about double in Phase2,TP removal efﬁciencies of this wetland remained high compared to Phase1and were in agreement with other studies(Kyambadde et al.,2005;Tuncsiper,2007).This supports the fact that the plants have limited ability for uptake of phosphorus nutrient and that adsorption or precipitation by bed media contributes to phosphorus removal.Phosphorus removal was also dependent on water temperature.Removal efﬁciencies for all measured pollutants were higher at lower hydraulic loading rates than those at higher hydraulic load-ing rates.Sun et al.(1998)had shown a decrease in organic removal with the increase in hydraulic load using an SSHF system at more than0.3kg/(m2d)hydraulic load which was similar to our wetland. However,thisﬁnding is in contrast to the FWS system with much lower loads.COD showed a decrease in hydraulic loads higher than 30cm/d when BOD5did not(Ran et al.,2004).This indicated that hydraulic efﬁciency is higher at lower hydraulic loads and varies between different conﬁgurations of CWs.COD removal rate was not as high as expected in THCW,which may be because of the bypass(about20%)of inﬂuent into the middle wetland,resulting in low HRT of this wastewater.NH3-N removal rate even at short HRT of2.7d in Phase2was comparable or greater than otherﬁndings in single wetlands(Kyambadde et al.,2005;Tuncsiper et al.,2006; Tuncsiper,2007).They also found that the highest removal efﬁcien-cies were achieved at2d HRT in the SSHF,and6d HRT in the FWS and subsurfaceﬂow(SF)systems,suggesting that the longer HRT may be inefﬁcient at nutrient removal.Reed and Brown(1995)sug-gested that to achieve low levels of ammonia(2mg/L)a6–8d HRT in the SF wetland must be maintained during the growing season.Commonly,the sediment is considered to be the site where the predominant denitriﬁcation occurs in wetlands.Denitriﬁcation in periphytic communities on submerged plants can make a sig-niﬁcant contribution to overall denitriﬁcation in a wetland.PNA and PDR values obtained in THCW were higher than other reports (Bastviken et al.,2005),which perhaps contributed to higher lev-els of oxygen available for nitrifying bacteria and to the available organic carbon for denitrifying bacteria,as well as to the growth of mixed varieties plants in this wetland.Bachand and Horne(2000) noted a higher nitrate removal rate in wetlands containing mixed stands of emergent macrophytes than in those containing mono-culture.Bastviken et al.(2005)found that submerged plants exhibit a considerably higher denitrifying capacity than emergent plants. Although the macrophytes in this THCW were all emergent plants and a part of plants were harvested,the below-ground portion of the plants still remained in the wetland;these may provide organic carbon and be a suitable surface for bacterial attach-ment.DNA–DNA hybridization data indicated that most bacteria of the total population lived in the upper(5cm)soil layer.Hybridizations with all denitriﬁcation probes also showed that denitrifying bac-teria are enriched in the vicinity of plant roots,as compared to bulk,root-free soil(Joergensen,1989).So the sediments for nitri-fying and denitrifying bacteria measurements were removed from the sediment–water interface(0–2cm),and from a deeper level (5–8cm),paring the performance of the wetland over time,it suggested that microbial activity along with loading change was a little lag,and was not an accurate parameter.Higher DO concentration due to passive oxygenation resulting from the cascade current in the second stage of THCW may be contribut-ing to the higher PDR,and approximately two orders of magnitude higher numbers of nitrifying bacteria,and comparable denitrifying bacteria in this study as compared to that found in other reports (Bastviken et al.,2003;He et al.,2004).In sediments of a Danish fjord estuary,denitriﬁcation activity determined by15N isotope measurements and by the acetylene inhibition technique showed that denitriﬁcation capacity was high-。

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土木工程毕业设计外文翻译外文原文I：A fundamental explanation of the behaviour ofreinforced concrete beams in flexure basedon the properties of concrete under multiaxial stressM. D. KotsovosDepartment of Civil Engineering, Imperial College of Science and Technology, London (U. K.)The paper questions the validity of the generally accepted view that for a reinforced concretestructure to exhibit "ductile" behaviour under increasing load it is necessary for the stressstrain relationships of concrete to have a gradually descending post-ultimate branch.Experimental data are presented for reinforced concrete beams in bending which indicate the presence of longitudinal compressive strains on the compressive face in excess of 0.0035. It is shown that these strains, which are essential for "ductile" behaviour, are caused by acomplex multiaxial compressive state of stress below ultimate strength rather than postultimate material characteristics. The presence of a complex stress system provides a fundamental explanation for beam behaviour which does not affect existing design procedures.1. INTRODUCTIONThe "plane sections" theory not, only is generally considered to describe realistically the deformation response of reinforced and prestressed concrete beams under flexure and axial load, but is also formulated so that it provides a design tool noted for both its effectiveness and simplicity [1]. The theory describes analytically the relationship between load-carrying capacity and geometric characteristics of a beam by considering the equilibrium conditions at critical cross-sections. Compatibility of deformation is satisfied by the "plane cross-sections remain plane" assumption and the longitudinal concrete and steel stresses are evaluated by the material stress-strain characteristics. Transverse stresses and strains are ignored for the purposes of simplicity.The stress-strain characteristics of concrete in compression are considered to be adequately described by the deformational response of concrete specimens such as prisms or cylinders under uniaxial compression and the stress distribution in the compression zone of a cross-section at the ultimate limit state, as proposed by current codes of practice such as CP 110 [1], exhibits a shape similar to that shown in figure 1. The figure indicates that the longitudinal stress increases with thedistance from the neutral axis up to a maximum value and then remains constant. Such a shape of stress distribution has been arrived at on the basis of both safety considerations and the widely held view that the stress-strain relationship ofconcrete in compression consists of both an ascending and a gradually descending portion (seefig. 2). The portion beyond ultimate defines the post-ultimate stress capacity of the material which, Typical stress-strain relationship for concrete in compression. as indicated in figure 1, is generally considered to make a major contribution to the maximum load-carrying capacity of the beam.However, a recent analytical investigation of the behaviour of concrete under concentrations of load has indicated that the post-ultimate strength deformational response of concrete under compressive states of stress has no apparent effect on the overall behaviour of the structural forms investigated ( [2], [3]). If such behaviour is typical for any structure, then the large compressive strains (in excess of 0.0035) measured on the top surface of a reinforced concrete beam at its ultimate limit state (see fig. 1), cannot be attributed to post-ultimate uniaxial stress-strain characteristics. Furthermore, since the compressive strain at the ultimate strength level of any concrete under uniaxial compression is of the order of 0.002 (see fig. 2), it would appear that a realistic prediction of the beam response under load cannot be based solely on the ascending portion of the uniaxial stress-strain relationship of concrete.In view of the above, the work described in the following appraises the widely held view that a uniaxial stress-strain relationship consisting of an ascending and a gradually descending portion is essential for the realistic description of the behaviour of a reinforced concrete beam in flexure. Results obtained from beams subjected to flexure under two-point loading indicate that the large strains exhibited by concrete in the compression zone of the beams are due to a triaxial state of stress rather than the uniaxial post-ultimate stress-strain characteristics of concrete. It is shown that the assumption that the material itself suffers a completeand immediate loss of load-carrying capacity when ultimate strength is exceeded is compatible with the observed "ductile" structural behaviour as indicated by load-deflexion or moment-rotation relationships.2. EXPERIMENTAL DETAILS2.1. SpecimensThree rectangular reinforced concrete beams of 915 mm span and 102 mm height x 51 mm width cross-section were subjected to two-point load with shear spans of 305 mm (see fig. 3). The tension reinforcement consisted of two 6 mmdiameter bars with a yield load of 11.8 kN. The bars were bent back at the ends of the beams so as to provide compression reinforcement along the whole length of the shear pression and tension reinforcement along each shear span were linked by seven 3.2 mm diameter stirrups. Neither compression reinforcement nor stirrups were provided in the central portion of the beams. Due to the above reinforcement arrangement all beams failed in flexure rather than shear, although the shear span to effective depthratio was 3.The beams, together with control specimens, were cured under damp hessian at 20~ for seven days and then stored in the laboratory atmosphere (20o C~and 40% R.H.) for about 2 months, until tested. Full details of the concrete mix used are given in table I.2.2. TestingLoad was applied through a hydraulic ram and spreader beam in increments of approximately 0.5 kN. At each increment the load was maintained constant for approximately 2 minutes in order to measure the load and the deformation response of the specimens. Load was measured by using a load cell and deformation response by using both 20 mm long electrical resistance strain gauges and displacement transducers. The strain gauges were placed on the top and side surfaces of thebeams in the longitud{nal and the transverse directions as shown in figure 4. The figure also indicates the position of the linear voltage displacement transducers (LVDT's) which were used to measure deflexion at mid-span and at the loaded cross-sections.The measurements were recorded by an automatic computer-based data-logger (Solatron) capable of measuring strains and displacements to a sensitivity of ±2 microstrain and ±0.002 ram, respectively.3. EXPERIMENTAL RESULTSThe main results obtained from the experiments together with information essential for a better understanding of beam behaviour are shown in figures 5 to 14. Figure 5 shows the uniaxial compression stressstrain relationships of the concrete used in the investigation, whereas figures 6 and 7 show the relationships between longitudinal and transverse strains, measured on the top surface of the beams (a) at the cross-sections where the flexure cracks which eventually cause failure are situated (critical sections) and (b)at cross-sections within the shear span, respectively.Figures 6 and 7 also include the longitudinal straintransverse strain relationship corresponding to the stress-strain relationships of figure 5.Figure 8 shows the typical change in shape of the transverse deformation profile of the top surface of the beams with load increasing to failure and figure 9 provides a schematic representation of the radial forces and stresses developing with increasing load due to the deflected shape of the beams. Typical load-deflexion relationships of the beams are shown in figure 10, whereas figure 11 depicts the variation on critical sections of the average vertical strains measured on the side surfaces of the beams with the transverse strains measured on the top surface. Figure 12 indicates the strength and deformation response of a typical concrete under various states of triaxial stress and figure 13 presents the typical crack pattern of the beams at the moment of collapse. Finally, figure 14 shows the shape of the longitudinal stress distribution on the compressive zone of a critical section at failure predicted on the basis of the concepts discussed in the following section.中文翻译I：在多向应力作用下从混凝土的特性看受弯钢筋混凝土梁变化的一个基本试验M. D. Kotsovos 伦敦皇家科学与技术学院土木工程系本文所探讨的问题是通常认为在荷载递增下钢筋混凝土结构呈现弹性状态，这必须是因为混凝土的应力-应变关系有一个逐渐递减的临界部分的真实性。