桥梁工程和桥梁美学

桥梁工程和桥梁美学

桥梁工程的发展概况

早在公元前1世纪，Marcus Vitrucios Pollio 的著作中就有关于建筑材料和结构类型的记载和评述。后来古希腊人创立了静力学的基本原

理，Leonardo da Vinci 、Cardeno和Galileo 等人在工作和应用中也证实了这些原理的正确性。而在15世纪至16世纪期间，工程师们似乎并没有注意到这些文字记载，只是单凭经验和传统来建造桥梁和渡槽。到了17世纪末，随着Leibnitz、Newton 和Bernoulli的数学理论的创立，桥梁建筑技术得到了快速发展。Lahire (1695)和belidor（1729）出版的关于结构理论分析的著作为材料力学领域奠定了基础。

Kuzmanovic （1977）指出，石材和木材是桥梁建筑最早采用的材料。在从木材到钢材的转变过程中，铁作为一种过渡材料被用于桥梁建筑中。根据近期的记载。早在1840年，法国就在Grisoles 建造了一座跨度为39英尺（12米）的横

跨Garoyne 运河的混凝土桥梁，但钢筋混凝土桥直到本世纪初才出现，而预应力混凝土到1927年才开始使用。

早在中世纪，罗马和欧洲的其他一些城市开始建造集上下部结构于一体的半圆弧石拱桥，而文艺复兴时期则是坦拱逐渐占主导地位。这种观念在18世纪末有了明显的改进，并发现其在结构上能适应后来的铁路荷载。在材料的分析和使用上，石拱桥至今没有发生大的变化，但是由于在17世纪70年代初期（Lahire,1965）引进了压力线的概念，使得拱桥的理论分析得到了改进。通过模型试验，有关拱结构的主要失效形式的理论得到了证实（Frezier ,1739）。对于无铰拱，Culmann (1851 ) 引进了弹性中心的方法，显示了可用三个协调方程求解三个多余参数。

当palladio建造了一座跨度为10英尺的三角形木制框架桥后，16世纪开始，木桁架在桥梁中得到应用。这些设计同样遵循桥梁设计的三个基本原则：方便（实用性）、美观和耐久性（强度）。18世纪50年代西欧建造了若干座支承于石制桥墩上的木桁架桥，其跨度达到200英尺（61米）。19世纪期间，美国和俄罗斯由于其跨越主要河流的需要，而且两国都具有丰富的适用于建桥的木材资源，因此木制桥梁在美、俄两国有可能取得更为显著的成绩。木制桥梁具有良好的经济性，因为其初期投资较低，施工速度较快。

尽管有文献记载，早在1734年，在普鲁士就修建了第一座横跨Oder河的铁链桥，但从木桥到钢桥的过渡大概开始于1840年。美国于1840年建成了第一座全铁桁架桥，其后，英格兰、德国和俄罗斯分别于1845年、1853年和1857年也建成了铁桁架桥。1840年，第一座铁桁架拱桥出现在Utica的Erie运河上。

理论分析的推动作用

主要从19世纪发展起来的机构分析理论着重于桁架的分析，首部关于桥梁工程的著作于1811年出版。1846年出现了一种Warren 三角形桁架和计算这种桁架精确内力的分析方法。用板件组合而成的工字形梁在英国逐渐普及并在小跨度桥梁中得到应用。

1866年Culmann阐述了悬臂桁架桥的原理，一年后在德国的Hassfurt的

Main 河上就建造了首座主跨跨度达425英尺（130米）的悬臂梁桥。美国的首座悬臂梁桥于1875年建于Kentucky河上。19世纪最引人注目的铁路悬臂梁桥

要数Firth of Forth桥，此桥建于1883年至1890年间，跨度达1，711英尺（521.5米）大约就在这一时期，结构钢在桥梁工程中作为一种主要材料被推广应用，尽管此时钢材的性能大都较差。几个早期的工程实例是：（1）St.Louis 的Eads 桥；（2）New York的Brooklyn 桥；（3）Missouri 的Glasgow 大桥，这些桥都建于1874年至1883年间。

谈起对结构分析河设计理论的改进特别应该提到：Maxwell 所作的贡献，尤其是他在超静定桁架方面的工作；Cremona 关于图解静力学的著作（1872）；由Mohr 重新定义的力法以及Clapeyron 提出的三弯矩方程

新材料的推动作用

自从20世纪初起，混凝土就是一直是最有效和最重要的建筑材料之一。由于混凝土可以较容易地浇注成各种形状的结构物，因此它在建筑上的使用价值几乎是无限的。只要有普通水泥和合适的骨料混凝土就可以替代其他材料建造某些类型的结构，诸如桥梁下部结构及基础等。

另外，在本世纪初，钢筋混凝土在多跨框架结构中的应用对结构分析提出了新的分析要求用19 世纪的古典分析方法不能用来分析高次静定结构。

Manderla (1880)和Bendixen (1914)论证了节点转角的重要性，提出了节点

弯矩和转角之间的关系，从而可求解未知的节点弯矩，这种方法被称为转角－挠度法。Calisev (1923)的工作使得框架结构的分析有可能进一步简化，他利用逐步近似的方法将方程组的求解简化为一个简单表达式的迭代计算。

Cross (1930)进一步改进和归纳了这种方法，从而形成了弯矩分配法。

在结构分析领域的近期发展中最重要的改进之一是将设计的范围延伸到弹塑性

范围，即所谓的荷载因子法或极限状态设计法。Tresca (1846) 根据一些世纪观察结果提出了塑性分析法，Saint-Venant (1870)系统地阐述了这种分析方法。第一次世界大战以后，塑性的概念吸引着研究人员和工程师们的注意力，开始主要是在德国。二次世界大战后，随着科研学术重心的转移，英国和美国的科研人员对此进行了广泛的研究。概率设计法是一种新的设计方法，这种方法有望替代传统的确定性方法。

一个主要的进步是1969版的美国联邦公路管理局（FHWA）的“钢筋混凝土桥梁勾践设计准则”中包括了强度和正常使用的极限状态设计法。这本设计准则是与“美国各州公路工作者协会（AASHO）”1969年的设计规范联合使用的，它的表达方式使其很容易适应极限状态设计规范的发展。根据这本设计准则，钢筋混凝土勾践（包括柱）的配料可以通过其各个阶段的工作性能来限定：弹性的、带裂缝工作的极限状态的。设计是荷载作用效应，所有根据作用荷载计算所得的量叫做设计值，如：设计弯矩、设计轴载或或设计剪力。结构的承载力被认为是结构抗力方面的参数，所有根据材料的理论强度计算得来并经过修正得强度计算值叫做结构抗力值，如：弯矩抗力值（抵抗弯矩），轴力抗力值或剪力抗力值。在正常使用极限状态下，需验算构件得挠度、最大裂缝宽度和疲劳强度。

桥型

一种值得注意得桥型是吊桥，首座吊桥1796年建于美国。随着Tacoma大桥得跨塌，动力稳定被作为问题来研究，并取得了显著得理论成果。

Steinman (1929) 总结了全世界建于1741年至1928年间得大约250座吊桥。随着州际体系得建立和结构等级分类的需要，某些桥型在桥梁界占有重要的地位。这些桥型包括混凝土上部结构（板桥、T梁桥、混凝土箱梁桥）、钢梁桥、钢箱

梁桥、组合界哦故、正交异性板结构、分段施工的结构、曲线梁桥和斜拉桥。预制构件受到了足够的重视，箱型截面梁也占有重要的地位。

桥梁的外观及桥梁美学

Grimm(1975)考证了历史上首例关于控制建筑环境美学的立法记录，这发生在1647年，当时的新阿姆斯特丹委员会派三名官员负责此事。1954年，美国联邦最高法院认为，立法机关有权决定公共场所不但要有利于公众健康，还要做到赏心悦目；不但要干净，还要宽敞；不但要通畅，还要布局均衡。1969年的环境政策法规要求联邦政府各机构对目前尚未量化的环境舒适性指标提出评价方法，在考虑技术经济指标的同时，对美观给予适当的考虑。

尽管在很多土木工程结构中，几乎是凭直观考虑美学问题，尤其在过去，但桥梁工程师们并没有忽略美学方面的训练。最近关于的研究似乎可以得到一种美学设计方法论（Grimm和Preiser,1976）。有关颜色、光线、质地、形状、比例以及其他感知形态的美学研究已经展开，这个方向无论在理论上还是经验上都是明确的。

美学控制机制一般都与土地使用规则和设计标准结合在一起。除了州政府关心结构美学以外，联邦政府将主要精力集中在考虑人工环境对人类生活的影响上，以及制定准则和规范以指导设计者在设计过程中改进质量和外观。从为了改进结构整体外观而进行的桥型评估中可以看出，提高桥梁结构美学质量的潜力还是很大的。

BRIDGE ENGINEERING AND AESTHETICS

Evolvement of bridge Engineering,brief review

Among the early documented reviews of construction materials and structure types are the books of Marcus Vitruvios Pollio in the first century B.C.The basic principles of statics w ere developed by the Greeks , and were exemplified in works and applications by Leonardo da Vinci,Cardeno,and Galileo.In the fifteenth and sixteenth century, engineers seemed to be unaware of this record , and relied solely on experience and tradition for building bridges and aqueducts .The state of the art changed rapidly toward the end of the seventeent h century when Leibnitz, Newton, and Bernoulli introduced m athematical formulations. Published works by Lahire (1695)and Belidor (1792) about the theoretical analysis of structures p rovided the basis in the field of mechanics of materials . Kuzmanovic(1977) focuses on stone and wood as the first brid ge-building materials. Iron was introduced during the transiti onal period from wood to steel .According to recent records , concrete was used in France as early as 1840 for a br idge 39 feet (12 m) long to span the Garoyne Canal at Gri soles, but reinforced concrete was not introduced in bridge construction until the beginning of this century . Prestresse d concrete was first used in 1927.

Stone bridges of the arch type (integrated superstructure and substructure) were constructed in Rome and other European c ities in the middle ages . These arches were half-circular ,with flat arches beginning to dominate bridge work during t he Renaissance period.This concept was markedly improved at t he end of the eighteenth century and found structurally adeq uate to accommodate future railroad loads .In terms of analy sis and use of materials , stone bridges have not changed much ,but the theoretical treatment was improved by introduci ng the pressure-line concept in the early 1670s(Lahire, 1695) . The arch theory was documented in model tests where typ ical failure modes were considered (Frezier,1739).Culmann(1851) introduced the elastic center method for fixed-end arches, and showed that three redundant parameters can be found by the use of three equations of coMPatibility.

Wooden trusses were used in bridges during the sixteenth cen tury when Palladio built triangular frames for bridge spans 10 feet long . This effort also focused on the three basic principles og bridge design : convenience(serviceability) ,ap pearance , and endurance(strength) . several timber truss bri

dges were constructed in western Europe beginning in the 175 0s with spans up to 200 feet (61m) supported on stone subs tructures .Significant progress was possible in the United St ates and Russia during the nineteenth century ,prompted by t he need to cross major rivers and by an abundance of suita ble timber . Favorable economic considerations included initia l low cost and fast construction .

The transition from wooden bridges to steel types probably d id not begin until about 1840 ,although the first documented use of iron in bridges was the chain bridge built in 173 4 across the Oder River in Prussia . The first truss compl etely made of iron was in 1840 in the United States , f ollowed by England in 1845 , Germany in 1853 , and Russia in 1857 . In 1840 , the first iron arch truss bridge wa s built across the Erie Canal at Utica .

The Impetus of Analysis

The theory of structures

The theory of structures ,developed mainly in the ninetheenth century,focused on truss analysis, with the first book on bridges written in 1811. The Warren triangular truss was int roduced in 1846 , supplemented by a method for calculating the correcet forces .I-beams fabricated from plates became po pular in England and were used in short-span bridges.

In 1866, Culmann explained the principles of cantilever truss bridges, and one year later the first cantilever bridge wa s built across the Main River in Hassfurt, Germany, with a center span of 425 feet (130m) . The first cantilever bri dge in the United States was built in 1875 across the Ke ntucky River.A most impressive railway cantilever bridge in t he nineteenth century was the First of Forth bridge , built between 1883 and 1893 , with span magnitudes of 1711 feet (521.5m).

At about the same time , structural steel was introduced as a prime material in bridge work , although its quality wa s often poor . Several early examples are the Eads bridge in St.Louis ; the Brooklyn bridge in New York ; and the G lasgow bridge in Missouri , all completed between 1874 and 1883.

Among the analytical and design progress to be mentioned are the contributions of Maxwell , particularly for certain sta tically indeterminate trusses ; the books by Cremona (1872) on graphical statics; the force method redefined by Mohr; an d the works by Clapeyron who introduced the three-moment equ ations.

The Impetus of New Materials

Since the beginning of the twentieth century , concrete has taken its place as one of the most useful and important structural materials . Because of the coMParative ease with which it can be molded into any desired shape , its struct ural uses are almost unlimited . Wherever Portland cement an d suitable aggregates are available , it can replace other materials for certain types of structures, such as bridge su bstructure and foundation elements .

In addition , the introduction of reinforced concrete in mul tispan frames at the beginning of this century imposed new analytical requirements . Structures of a high order of redu ndancy could not be analyzed with the classical methods of the nineteenth century .The importance of joint rotation was already demonstrated by Manderla (1880) and Bendixen (1914) , who developed relationships between joint moments and ang ular rotations from which the unknown moments can be obtaine d ,the so called slope-deflection method .More simplifications in frame analysis were made possible by the work of Calis ev (1923) , who used successive approximations to reduce the system of equations to one simple expression for each iter ation step . This approach was further refined and integrate d by Cross (1930) in what is known as the method of momen t distribution .

One of the most import important recent developments in the area of analytical procedures is the extension of design t o cover the elastic-plastic range , also known as load fact or or ultimate design. Plastic analysis was introduced with some practical observations by Tresca (1846) ; and was formu lated by Saint-Venant (1870) , The concept of plasticity att racted researchers and engineers after World War Ⅰ, mainly in Germany , with the center of activity shifting to Engl and and the United States after World War Ⅱ.The probabilist ic approach is a new design concept that is expected to re place the classical deterministic methodology.

A main step forward was the 1969 addition of the Federal H ighway Adiministration (FHWA)”Criteria for Reinforced Concrete Bridge Members “that covers strength and serviceability a t ultimate design . This was prepared for use in conjunctio n with the 1969 American Association of State Highway Offfic ials (AASHO) Standard Specification, and was presented in a format that is readily adaptable to the development of ultim ate design specifications .According to this document , the proportioning of reinforced concrete members ( including colum

ns ) may be limited by various stages of behavior : elasti c , cracked , and ultimate . Design axial loads , or desi gn shears.Structural capacity is the reaction phase , and al l calculated modified strength values derived from theoretical strengths are the capacity values , such as moment capacit

y ,axial load capacity ,or shear capacity .At serviceability states , investigations may also be necessary for deflectio ns , maximum crack width , and fatigue .

Bridge Types

A notable bridge type is the suspension bridge , with the first example built in the United States in 1796. Problems

of dynamic stability were investigated after the Tacoma bridg e collapse , and this work led to significant theoretical c ontributions Steinman ( 1929 ) summarizes about 250 suspensio n bridges built throughout the world between 1741 and 1928 . With the introduction of the interstate system and the need

to provide structures at grade separations , certain bridge types have taken a strong place in bridge practice. These include concrete superstructures (slab ,T-beams,concrete box girders ), steel beam and plate girders , steel box girders , composite construction , orthotropic plates , segmental c onstruction , curved girders ,and cable-stayed bridges . Pref abricated members are given serious consideration , while int erest in box sections remains strong .

Bridge Appearance and Aesthetics

Grimm ( 1975 ) documents the first recorded legislative effo rt to control the appearance of the built environment . Thi s occurred in 1647 when the Council of New Amsterdam appoin ted three officials . In 1954 , the Supreme Court of the United States held that it is within the power of the legi slature to determine that communities should be attractive as well as healthy , spacious as well as clean , and balanc ed as well as patrolled . The Environmental Policy Act of 1969 directs all agencies of the federal government to ident ify and develop methods and procedures to ensure that presen tly unquantified environmental amentities and values are given appropriate consideration in decision making along with econ omic and technical aspects .

Although in many civil engineering works aesthetics has been practiced almost intuitively , particularly in the past , bridge engineers have not ignored or neglected the aesthetic disciplines .Recent research on the subject appears to lead to a rationalized aesthetic design methodology (Grimm and P reiser , 1976 ) .Work has been done on the aesthetics of

color ,light ,texture , shape , and proportions , as well as other perceptual modalities , and this direction is both theoretically and empirically oriented .

Aesthetic control mechanisms are commonly integrated into the land-use regulations and design standards . In addition to concern for aesthetics at the state level , federal concer n focuses also on the effects of man-constructed environment on human life , with guidelines and criteria directed towa rd improving quality and appearance in the design process . Good potential for the upgrading of aesthetic quality in bridge superstructures and substructures can be seen in the evaluation structure types aimed at improving overall appear ance .