土木工程文献外文翻译(中英互译版)

使用加固纤维聚合物增强混凝土梁的延性作者：Nabil F. Grace, George Abel-Sayed, Wael F. Ragheb

摘要：

一种为加强结构延性的新型单轴柔软加强质地的聚合物(FRP)已在被研究，开发和生产(在结构测试的中心在劳伦斯技术大学)。这种织物是两种碳纤维和一种玻璃纤维的混合物，而且经过设计它们在受拉屈服时应变值较低，从而体现出伪延性的性能。通过对八根混凝土梁在弯曲荷载作用下的加固和检测对研制中的织物的效果和延性进行了研究。用现在常用的单向碳纤维薄片、织物和板进行加固的相似梁也进行了检测，以便同用研制中的织物加固梁进行性能上的比较。这种织物经过设计具有和加固梁中的钢筋同时屈服的潜力，从而和未加固梁一样，它也能得到屈服台阶。相对于那些用现在常用的碳纤维加固体系进行加固的梁，这种研制中的织物加固的梁承受更高的屈服荷载，并且有更高的延性指标。这种研制中的织物对加固机制体现出更大的贡献。

关键词：混凝土，延性，纤维加固，变形

介绍

外贴粘合纤维增强聚合物（FRP）片和条带近来已经被确定是一种对钢筋混凝土结构进行修复和加固的有效手段。关于应用外贴粘合FRP板、薄片和织物对混凝土梁进行变形加固的钢筋混凝土梁的性能，一些试验研究调查已经进行过报告。Saadatmanesh和Ehsani（1991）检测了应用玻璃纤维增强聚合物(GFRP)板进行变形加固的钢筋混凝土梁的性能。Ritchie等人（1991）检测了应用GFRP，碳纤维增强聚合物（CFRP）和G/CFRP板进行变形加固的钢筋混凝土梁的性能。Grace等人（1999）和Triantafillou（1992）研究了应用CFRP薄片进行变形加固的钢筋混凝土梁的性能。Norris，Saadatmanesh和Ehsani（1997）研究了应用单向CFRP薄片和CFRP织物进行加固的混凝土梁的性能。在所有的这些研究中，加固的梁比未加固的梁承受更高的极限荷载。这些梁中大多数出现的一个缺陷是梁的延性有很大的损失。然而通过对梁的荷载-挠度性能的测试，可以发现大多数荷载的增加是在钢筋屈服后发生的。也就是说，极限荷载明显提高，然而屈服荷载却没有太大提高。因此在正常使用水平荷载的明显增加很难实现。

除去加固前混凝土构件条件的影响，钢筋对加固梁的弯曲反应有明显的贡献。而可惜的是，现有的FRP加固材料和钢材性能不同。虽然FRP有很高的强度，但是它们多数在提高足够的强度之前被拉伸而产生很大的应变。因为同大多数FRP材料的极限应变相比，钢材的屈服应变相对较低，所以随着加固构件的变形，钢材和FRP加固材料的贡献发生了变化。结果，钢筋可能会在加固构件取得任何可测荷载增加值之前就屈服了。一些研究者在横截面布置了更强的FRP，这通常会增加加固的成本，进而提供可测的贡献，尽管这时变形是受限制的（在钢筋屈服之前）。但是，加固材料从混凝土表面的剥落更多的时候是由于应力集中的原因发生的。剥落是这项加固技术中不出现的一种脆性破坏。尽管使用一些类似超高模量碳纤维的特别的低应变纤维看起来是一种解决方法，但这可能导致由于纤维破坏而产生脆性破坏。本文旨在介绍一种新型伪延性FRP织物，它在屈服时应变低从而具有与钢筋同时屈服的潜力，能够实现期望中的加固水准。

研究意义

FRP已经被越来越多地用做钢筋混凝土结构修复和加固的材料。但是现在常用的FRP材料缺少延性，并且与钢筋性能不一致。结果，经过加固处理的梁会体现出延性降低，不能达到期待中的水平，或者二者兼有。本项研究介绍了一种新型的伪延性FRP加固织物。这种织物可以使加固梁承受更高的屈服荷载，并且有助于避免延性的损失，而这在使用目前常用的FRP进行加固中是常见的。

混杂织物的研制

为了克服前面所提的缺陷，一种具有低屈服应变值的延性FRP材料是很必要的。

混杂的文献回顾

为了研制这种材料，考虑了各种不同纤维的混杂。多于一种纤维材料的混杂是许多材料科学研究的兴趣所在。他们的工作多数集中于结合两种纤维以提高每种材料单独工作时的力学特性并且降低成本。这已经在几本出版物中报道过,例如Bunsel和Harris（1974），Philips（1976），Manders和Bader（1981），Chow和Kelly（1980），以及Fukuda和Chow（1978）。做为一种能够克服FRP 加固棒延性不足问题的工具，混杂吸引了结构工程师。Nanni,Henneke和Okamoto（1994）研究了用编织芳香尼龙纤维绕在钢筋核心的短棒。Tamuzs和Tepfors报道了关于使用碳和芳香阻尼纤维进行组合而成的混合纤维棒的试验调查。Somboonsong，Frank和Harris（1998）研制了一种用编织芳香尼龙纤维缠绕在碳纤维核心的混合FRP加固棒。Harris，somboonsong和Frank（1998）使用这些棒对混凝土梁进行加固，以得到用常规钢筋进行加固的混凝土梁的普通荷载-挠度特性。

设计思想和材料

为了产生延性，一种使用不同种类纤维的混杂技术已经被采用。选用了在破坏时有不同延长量级的三种纤维。图1显示了这些复合纤维在拉伸时的应力-应变曲线，表1显示了它们的力学特性。

这项技术是建立在将这些纤维结合起来并控制配合比例的基础上的，这样当它们被拉伸时共同承受荷载，延伸小（LE）的纤维先破坏，允许一定的应变

松弛（应变增加而混合材料的荷载却并未增加）。余下的延伸大（HE）的纤维被分配承担所有的荷载直到破坏。延伸小的纤维破坏时的应变值体现了混合材料屈服应变值，而延伸大的纤维破坏时的应变值体现的是极限应变值。延伸小的纤维破坏时对应的荷载体现的是屈服荷载值，而延伸大的纤维承担的最大荷载体现的是极限荷载值。超高模量碳纤维（1号碳）被用做延伸小的纤维，它应有尽可能低的应变，但不得小于钢筋的屈服应变（60级钢筋大约为0.2%）。另一方面，Ｅ型玻璃纤维被用做延伸大的纤维，应能提供尽可能高的应变而产生高延性指标（破坏时的变形和屈服时的变形的比例）。高模量碳纤维（２号碳）被选做了延伸中等（ME）纤维，它使在延伸小的纤维破坏后发生应变松弛时荷载的降低最小化，并且能够提供从延伸小的纤维向延伸大的纤维逐渐传递荷载的途径。基于这种思想，生产了一种单向织物，并进行了测试，将它在拉伸时的性能和理论预测的承载性能做了对比。理论上的性能建立在混合物规则上，根据这种规则，混合物的轴向刚度是将各组成部分的相对刚度进行总合计算得到的。这种织物的生产过程是，将不同的纤维做为相邻的纱线结合起来，并将它们用环氧树脂注入模具中。图２就是一个生产样品的照片。编织而成的玻璃纤维片布置在试样的两端，以消除测试中固定端的应力集中。试样厚２mm （0.08in），宽25.4mm（1in），在拉伸时根据美国材料实验协会Ｄ3039规范进行测试。四个测试样品的平均荷载-应变曲线见图3，上面还有理论预测的曲线。应该注意到直到应变值达到0.35%，荷载-应变性能都是线性的，这时延伸小的纤维开始破坏。在这一点上应变增长的速率高于荷载。当应变值达到0.90%时，中等延伸的纤维开始破坏，导致应变有附加的增长，直到由于延伸大的纤维破坏带来试样的彻底破坏。可以测试到屈服荷载（荷载-应变曲线上性能去不再为线性的第一点）为0.46kN/mm（2.6kips/in）,极限荷载为0.78kN/mm（4.4kips/in）。

梁的测试

梁的详细情况

一共浇筑了13根钢筋混凝土梁，横截面尺寸为152×254mm（6×10in），长2744mm（108in）。梁的受弯钢筋由底部的两根5号（16mm）受拉钢筋和顶部的两根3号（9.5mm）的受压钢筋组成。为防止发生剪切破坏，使用162mm 长的3号钢筋扎成闭合镫形对梁的抗剪进行进一步的加固。有5根梁浇筑时角

部做成半径25mm（1in）的圆角，从而易于加固材料的安置。图4显示了梁的尺度、钢筋详图、支座和加载点的位置。使用的钢筋为60等级，屈服强度415MPa （800psi）。

加固材料

研制中的混合织物用于加固8根梁。使用了两种不同厚度的织物。第一种（H体系，t=1.0mm）厚度1.0mm（0.04in），第二种（H-体系，t=1.5mm）厚度1.5mm（0.06in）。其他四根梁使用现在常用的碳纤维加固材料进行加固：1）一层单向碳纤维薄片，极限荷载0.34kN/mm（1.95kips/in）；2）两层单向碳纤维织物，极限荷载1.31kN/mm（7.5kips/in）；3）一层固体玻璃谈碳纤维板，极限荷载为2.8kN/mm（16kips/in）。对这些材料测试得到的荷载-应变图见图5。表2给出了包括研制中的织物在内的加固材料的特性。

粘结材料

对这种混合织物，使用一种环氧树脂（环氧A）注入纤维，并做为织物和混凝土表面的粘结材料。这种环氧材料极限应变为4.4%，从而保证不至于在纤维破坏之前破坏。对于使用碳纤维薄片、板和织物加固的梁，使用的是极限应变为2.0%的环氧树脂（环氧B）。由生产商提供的粘结材料的力学特性见表3。加固

在梁的底部和两侧喷砂以使其表面粗糙。然后使用丙酮除去污物对梁进行清洁。采用两种加固构造：1）只在梁底面布置加固材料（A组梁）；2）除对梁底部外，在梁两侧各伸长152mm（16in），大概能覆盖住梁的受弯拉伸部分（B 组梁）。加固材料沿梁长度布置在中心，长达 2.24m（88in）。环氧在对梁进行测试前要进行两周的养护。对研制中的混合织物（H-体系）加固的梁，制备了两根，并对各种构造进行测试来证实结果。表4对梁的检测进行了汇总。

仪器

跨中FRP的应变通过布置在梁底面的三个应变片测量。测量A组梁钢筋拉伸应变是通过监控在梁的侧面与钢筋棒平行处测量点设置的DEMC（可拆式机械计量器），而B组梁使用的是应变片。跨中挠度是通过使用串行电位计测量的。使用液压器对梁加载。荷载有一种荷载电池测量。所有的传感器同数据采集系统相连以扫描并记录读数。

试验结果和讨论

控制梁

控制梁的屈服荷载82.3kN（18.5kips），极限荷载95.7kN（21.5kips）。梁由于钢筋屈服而破坏，随之跨中混凝土受压破坏。控制梁的试验结果见加固梁的试验成果图上（图6至15）。

A组梁

A组梁已在底面进行了加固。图6至11显示了这些梁的试验结果。H-50-1梁和H-75-1梁分别和H-50-2梁和H-75-2梁各自的结果非常接近，因此关于这些梁的讨论就集中于后两者，以避免重复。梁的延性通过计算延性指数来考察，即计算破坏时与屈服时的挠度之比。

图6（a）显示了C-1梁的荷载-跨中挠度关系图，C-1梁使用碳纤维薄片进行加固。梁在荷载为85.9kN（19.3kips）时屈服，在荷载为101.9kN（22.9kips）时由于碳纤维薄片的开裂而破坏。值得注意的是，从这幅图中看来，虽然有了延性性能，但是同控制梁比起来，屈服荷载只提高了4%。延性指数为2.15。图6（b）显示了跨中荷载-碳纤维应变关系图。

图7（a）显示了C-2梁对应的荷载-挠度曲线。这根梁使用固体玻璃碳纤维板进行加固。它没有屈服台阶（延性指数为1），在荷载为132.6kN（29.8kips）时由于板端部的受剪-受拉破坏而突然破坏。尽管荷载提高了61%，但破坏仍是脆性的。图7（b）显示了跨中荷载-碳纤维应变关系。碳纤维破坏时记录的最大应变为0.33%，这意味着板的承载力发挥了24%。

C-3梁的荷载-挠度关系见图8（a）。该梁由两层碳纤维织物加固。它在荷载为107.7kN（24.2kips）时屈服，在荷载为134.4kN（30.21kips）时由于织物的剥落而破坏，此时它并未如控制梁那样显示出任何明显的屈服台阶。延性指数是1.64。值得注意的是，在图8（b）中破坏时记录到的碳纤维应变的最大值为0.67%，这意味着纤维承载力大约发挥了48%。

图9（a）显示了H-50-2梁的荷载-挠度关系。这根梁使用研制中的厚度为1mm厚的混合织物进行加固。屈服荷载为97.9Kn（22.0kips）（同控制梁比起来提高了19%）。在图9（b）中值得注意的是，当梁屈服时织物应变为0.40%。它的延性指数为2.33，当荷载最终达到114.8kN（25.8kips）时由于织物的彻底开裂而破坏。图9（c）即为破坏时的梁。

图10（a）显示了H-75-2梁的荷载-屈服关系。这根梁使用厚度为1.5mm厚

的研制中的混合织物。它在荷载为113.9kN（25.6kips）时屈服，在130.8kN （29.4kips）的极限荷载下由于织物剥落而导致彻底破坏之前体现出的延性指数为2.13。值得注意的是，尽管最终破坏是由于织物的剥落，但这是在取得了令人满意的延性之后发生的。从图10（b）中可见当梁屈服时的应变为0.35%。图10（c）是梁破坏时的照片。

图11和表5对A组梁的试验结果进行了比较。可以观察出如下现象：

1．C-1梁和H-50-2梁体现了较好的延性特征。但是H-50-1梁比C-1梁体现了更高的屈服荷载。这是因为，经过设计这种研制中的混合织物比碳纤维片有更高的初始刚度；因此，在钢筋屈服前它比碳纤维对加固的贡献更大。

2．尽管碳纤维织物的极限荷载比1.5mm厚的混合织物屈服时对应的荷载大几倍，但是直到屈服时，H-75-2体现着和C-3相似的性能。但是H-75-2梁有令人满意的屈服台阶，而C-3梁却没有。

3．相对于现在常用的碳纤维加固材料，这种研制中的织物屈服时的应变和钢筋的屈服应变接近。尽管仍然较高，但是混合织物的应变值和梁屈服时的应变值接近，这意味这它和钢筋同时屈服。这一部分要归功于将植物安置在梁的外表面，这样比安置在梁的内部要承受更大的拉应变。结果织物的屈服应变设计值看起来是可以接受的。

4．当使用有较高承载能力的碳纤维板（正如在C-2梁中使用的）时，能够提供高的破坏荷载，同时也会产生脆性破坏。

B组梁

这组梁除对梁底部外，在梁两侧向上延伸152mm（16in）的范围也进行了加固。改组试验结果见表5和图12至15。H-S50-1梁和H-S75-1梁分别和H-S50-2梁和H-S75-2梁各自的结果非常接近，因此关于这些梁的讨论就集中于后两者，以避免重复。

图12（a）显示了CS梁的荷载-挠度关系。这根梁是使用碳纤维薄片体系加固的。它在荷载达到99.2kN（22.3kips）时由于钢筋的屈服而屈服。屈服荷载增加了20%。梁在达到123.3kN（27.7kips）的极限荷载时由于跨中混凝土的受压破坏而破坏。从图12（b）可以看出当梁屈服时，碳纤维的应变为0.35%，因此在这段承载阶段发挥了它的大约30%的能力。在梁破坏之前记录到的最大应变为1.0%。取得的延性指数为2.04。

H-S50-2的试验结果见图13。这根梁使用研制中的厚度为1mm厚的混合织物进行加固。图13（a）显示了它的荷载-挠度曲线。当荷载达到113.9kN（25.6kips）时由于钢筋和织物的破坏，梁发生破坏。屈服荷载增加了38%。梁在达到146.6kN（32.9kips）的极限荷载时由于混凝土的受压破坏而破坏。延性指数为2.25。图13（b）显示了跨中荷载和织物应变的关系。梁屈服时记录到的应变值是0.35%，在梁破坏前记录到的最大应变值是1.2%。梁的破坏情形见图13（c）。

图14即H-S75-2的试验结果。这根梁也是用研制中的混合织物加固的，但是厚度为1.5mm。从图14（a）可见梁在荷载为127.3kN（28.6kips）时屈服，由于钢筋和织物的屈服，屈服荷载增加了55%。当荷载达到162.0kN（36.4kips）时，这根梁由于跨中混凝土的受压破坏而破坏。它的延性指数为1.89。图14（b）显示了跨中荷载和织物应变的关系。在梁破坏前记录到的最大应变是0.74%。该梁的破坏情形见图14（c）。

图15显示了B组各梁试验结果的比较。从试验结果可以观察到如下现象：1．虽然混合织物的屈服荷载低于碳纤维板的极限荷载，但是H-S50-2梁比CS梁体现出了更高的延性。这是因为同碳纤维薄片相比，这种混合织物有更高的初始刚度。

2．用研制中的混合织物加固的梁屈服荷载更大，并且有令人满意的屈服台阶。

这种研制中的混合织物的一个优点是它易于通过视觉观察判断织物是否屈服，因为任何破坏的碳纤维纱线都是可见的。而且，这种混合织物比目前常用的碳纤维材料便宜，因为这些纤维中超过75%的使用的是玻璃纤维，而这要比碳纤维成本低。

结论

基于本研究所介绍的研究调查，可以得出如下结论：

1．目前常用的FRP材料作为弯曲加固体系用于混凝土结构并不能总是在加固梁中提供类似未加固梁的屈服时的屈服台阶。在一些情况下，加固可能导致加固梁的脆性破坏或着是屈服荷载增加很不明显，或者是二者兼有。

2．选择的几种类型的纤维的混杂被用于研制伪延性的织物，它在屈服时的应变低（0.35%）。经过设计，这种织物具有同加固梁中的钢筋同时屈服的潜力。

3．同那些应用碳纤维进行加固体系相比，使用研制中的混合织物进行加固的梁通常会显示出在屈服荷载上有更高的增长。有些用混合织物进行加固的梁会显示出类似未加固梁的屈服台阶。这在结构破坏之前保证足够的警示作用是特别重要的。

4．使用研制中的混合织物体系进行加固的梁并没有显示出明显的延性损失。使用碳纤维加固的梁也没有明显的延性损失，但是屈服荷载较低。

参考文献

ASTM D 3039, 2000, “Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials,” Annual Book of ASTM Standards, V. 15.03, pp. 106-118.

Bunsell, A. R., and Harris, B., 1974, “Hybrid Carbon and Glass Fibre Composites,” Composites, V. 5, pp. 157-164.

C how, T. W., and Kelly, A., 1980, “Mechanical Properties of Composites,”Annual Review of Composite Science, V. 10, pp. 229-259.

Fukuda, H., and Chow T. W., 1981, “Monte Carlo Simulation of Strength of Hybrid Composites,” Journal of Composite Materials, V. 16, pp. 371-385.

Grace, N. F.; Soliman, K.; Abdel-Sayed, G.; and Saleh, K., 1999,

“Strengthening Reinforced Concrete Beams Using Fiber Reinforced Polymer CFRP Laminates,” Journal of Composites for Construction, ASCE, V. 2, No. 4.

Harris, H. G.; Somboonsong, W.; and Frank, K. K., 1998, “New Ductile Hybrid FRP Reinforcement Bar for Concrete Structures,” Journal of Composites for Construction, ASCE, V. 2, No. 1, pp. 28-37.

Manders, P. W., and Bader, M. G., 1981, “The Strength of Hybrid Glass/Carbon Fibre Composites: Part 1—Failure Strain Enhancement and Failure Mode,” Journal of Materials Science, V. 16, pp. 2233-2245.

Nanni, A.; Henneke, M. J.; and Okamoto, T., 1994, “Tensile Properties of Hybrid Rods for Concrete Reinforcement,” Construction and Building Materials, V. 8, No. 1, pp. 27-34.

Norris, T.; Saadatmanesh, H.; and Ehsani, M. R., 1997, “Shear and Flexure Strengthening of R/C Beams with Carbon Fiber Sheets,” Journa of Structural Engineering, ASCE, V. 123, No. 7, pp. 903-911.

Philips, L. N., 1976, “ The H ybrid Effect—Does it Exist?” Composites, V. 7, pp. 7-8.

Ritchie, P. A.; Thomas, D. A.; Lu, L.; and Connelly, G. M., 1991, “External Reinforcement of Concrete Beams using Fiber Reinforced Plastics,” ACI Structural Journal, V. 88, No. 4, July-Aug., pp. 490-500.

Saadatmanesh, H., and Ehsani, M. R., 1991, “RC Beams Strengthening with GFRP Plates I: Experimental Study,” Journal of Structural Engineering, ASCE, V. 117, No. 11, pp. 3417-3433.

Somboonsong, W.; Frank, K. K.; and Harris, H. G., 1998, “Ductile Hybrid Fiber Reinforced Plastic Reinforcing,” ACI Materials Journal, V. 95, No. 6, Nov.-Dec., pp. 655-666.

Tamuzs, V., and Tepfers, R., 1995, “Ductility of Nonmetallic Hybrid Fiber Composite Reinforcement for Concrete,” Proceedings, 2nd International RILEM Symposium (FRPRCS-2), pp. 18-25.

Triantafillou, N. P., 1992, “Strengthening of RC Beams with Epoxy-Bonded

Fiber-Composite Materials,” Materials and Structures, V. 25, pp. 201-211.

附录表1 复合纤维的力学特性

表2 加固材料的特性

表3 环氧粘结材料特性

表4 试验梁的汇总

表5 试验结果汇总

ACI STRUCTURAL JOURNAL TECHNICAL PAPER

Title no：99-S71

Strengthening of Concrete Beams Using Innovative Ductile Fiber-Reinforced Polymer Fabric

By Nabil F. Grace, George Abel-Sayed, Wael F. Ragheb

abstract

An innovative, uniaxial ductile fiber-reinforced polymer (FRP) fabric has been researched, developed, and manufactured (in the Structural Testing Center at Lawrence Technological University) for strengthening structures. The fabric is a hybrid of two types of carbon fibers and one type of glass fiber, and has been designed to provide a pseudo-ductile behavior with a low yield-equivalent strain value in tension. The effectiveness and ductility of the developed fabric has been investigated by strengthening and testing eight concrete beams under flexural load. Similar beams strengthened with currently available uniaxial carbon fiber sheets, fabrics, and plates were also tested to compare their behavior with those strengthened with the developed fabric. The fabric has been designed so that it has the potential to yield simultaneously with the steel reinforcement of strengthened beams and hence, a ductile plateau similar to that for the nonstrengthened beams can be achieved. The beams strengthened with the developed fabric exhibited higher yield loads and achieved higher ductility indexes than those strengthened with the currently available carbon fiber strengthening systems. The developed fabric shows a more effective contribution to the strengthening mechanism. keyword：Concrete, ductility, textile fiber reinforcement, distortion

INTRODUCTION

The use of externally bonded fibcr-rcinforccd polymer (FRP) sheets and strips has recently been established as an effective tool for rehabilitating and strengthening reinforced concrete structures. Several experimental investigations have been reported on the behavior of concrete beams strengthened for flexure using externally bonded FRP plates, sheets, or fabrics. Saadatmancsh and Ehsani (1991) examined the behavior of concrete beams strengthened for flexure using glass fiber-reinforced polymer (GFRP) plates. Ritchie ct al. (1991) tested reinforced concrete beams strengthened for flexure using GFRP. carbon fibcr-rcinforccd polymer (CFRP). and G/CFRP plates. Grace et al. (1999) and Trian- tafillou (1992) studied the behavior of reinforced concrete beams strengthened for flexure using CFRP sheets. Norris. Saadatmancsh. and Fhsani (1997) investigated the behavior of concrete beams strengthened using CFRP unidirectional sheets and CFRP woven fabrics. In all of these investigations, the strengthened beams showed higher ultimate loads compared to the nonstrcngthcncd ones. One of the drawbacks experienced by most of these strengthened beams was a considerable loss in beam ductility. An examination of the load- deflection behavior of the beams, however, showed that the majority of the gained increase in load was experienced after the yield of the steel reinforcement. In other words, a significant increase in ultimate load was experienced without much increase in yield load. Hence, a significant increase in service level loads could hardly be gained. Apart from the condition of the concrete element before strengthening, the steel reinforcement contributes significantly to the flcxural response of the strengthened beam. Unfortunately, available FRP strengthening

materials have a behavior that is different from steel. Although FRP materials have high strengths, most of them stretch to relatively high strain values before providing their full strength. Because steel has a relatively low yield strain value when compared with the ultimate strains of most of the FRP materials, the contribution of both the steel and the strengthening FRP materials differ with the deformation of the strengthened element. As a result, steel reinforcement may yield before the strengthened element gains any measurable load increase. Some designers place a greater FRP cross section, which generally increases the cost of the strengthening, to provide a measurable contribution. even when deformations arc limited (before the yield of steel). Debonding of the strengthening material from the surface of the concrete, however, is more likely to happen in these cases due to higher stress concentrations. Debonding is one of the nondesired brittle failures involved with this technique of strengthening. Although using some special low-strain fibers such as ultra-high-modulus carbon fibers may appear to be a solution, it would result in brittle failures due to the failure of fibers. The objective of this paper is to introduce a new pseudo-ductile FRP fabric that has a low strain at yield so that it has the potential to yield simultaneously with the steel reinforcement, yet provide the desired strengthening level. RESEARCH SIGNIFICANCE

FRPs have been increasingly used as materials for rehabilitating and strengthening reinforced concrete structures. Currently available FRP materials, however, lack the ductility and have dissimilar behaviors to steel reinforcement. As a result, the strengthened beams may exhibit a reduced ductility, lack the desired strengthening level, or both. This study presents an innovative pseudo-ductile FRP strengthening fabric. The fabric provides measurably higher yield loads for the strengthened beams and helps to avoid the loss of ductility that is common with the use of currently available FRP. DEVELOPMENT OF HYBRID FABRIC To overcome the drawbacks mentioned previously, a ductile FRP material with low yield strain value is needed.

ACI Structural Journal, V. 99, No. 5, September-October 2002.

MS No. 01-349 received October 23, 2001, and reviewed under Institute publication policies. Copyright €) 2002, American Concrete Institute. All rights reserved, includ-ing the making of copies unless permission is obtained from the copyright proprietors. Pertinent discussion will be published in the July-August 2003ACl Structural Journal if received by March 1, 2003.

ACI StructuralJournal/September-October 2002

ACI member Nabil F. Grace is a professor and Chair of the Structural Testing Center, Department of Civil Engineering, Lawrence Technological University, Southfield, Mich. He is a member of ACI Committee 440, Fiber Reinforced Polymer Reinforcement; and Joint ACI-ASCE Committee 343, Concrete Bridge Design. His research interests include the use of fiber-reinforced polymer in reinforced and pre stressed concrete structures.

George Abdel-Sayed is Professor Emeritus in

the Department of Civil and Environmental Engineering, University of Windsor, Windsor, Ontario, Canada. His research interests include soil-structure interaction.

Wael F. Ragheb is a research assistant in the

Department of Civil Engineering at Lawrence Technological University. He is a PhD candidate in the Department of Civil and Environmental Engineering, University of Windsor, Windsor, Ontario, Canada.

Table 1—Mechanical properties of composite fibers*

* Composite properties are based on 60% fiber volume fraction.

Literature review on

hybridization

To develop this material, hybridization for

different fibers was considered. Hybridization of more than one type of fibrous materials was the interest of many materials science researchers. Most of their work was concerned with combining two types of fibers to enhance the mechanical properties of either type acting alone and to reduce the cost. This has been reported in several publications such as Bunsell and Harris (1974), Philips (1976), Manders and Bader (1981), Chow and Kelly (1980), and Fukuda and Chow (1981). Hybridization interested structural engineers as a tool to overcome the problem of a lack of ductility in FRF reinforcing bars. Nanni, Henneke, and Okamoto (1994) studied bars of braided aramid fibers around a steel core. Tamuzs and Tcpfcrs (1995) reported experimental investigations for hybrid fiber bars using different combinations of carbon and aramid fibers. Somboonsong, Frank, and Harris (1998) developed a hybrid FRP reinforcing bar using braided aramid fibers around a carbon fiber core. Harris, Somboonsong, and Frank (1998) used these bars in reinforcing concrete beams to achieve the general load- deflection behavior of concrete beams reinforced with conventional steel.

Design concept and materials To generate ductility, a hybridization technique of different types of fibers has been implemented. Three fibers have been selected with a different magnitude of elongations at failure. Figure 1 shows the stress-strain curves in tension for the selected composite fibers, and Table 1 shows their mechanical properties.

The technique is based on combining these fibers together and controlling the mixture ratio so that when they arc loaded together in tension, the fibers with the lowest elongation (LE) fail first, allowing a strain relaxation (an increase in strain without an increase in load for the hybrid). The remaining high-elongation (HE) fibers are proportioned to sustain the total load up to failure. The strain value at failure of the LE fibers presents the value of the yield-equivalent strain of the hybrid, while the HE fiber strain at failure presents the value of ultimate strain. The load corresponding to failure of LE fibers presents the yield-equivalent load value, and the maximum load carried by the HE fibers is the ultimate load value. Ultra-high-modulus carbon fibers (Carbon No.

1) have been used as LE fibers to have as low a strain as possible, but not less than the yield strain of steel (approximately 0.2% for Grade 60 steel). On the other hand. E-glass fibers were used as HE fibers to provide as high a strain as possible to produce a high-ductility index (the ratio between deformation at failure and deformation at yield). High-modulus carbon fibers (Carbon No. 2) were selected as medium-elongation (ME) fibers to minimize the possible load drop during the strain relaxation that occurs after failure of the LE fibers, and also to provide a gradual load transition from the LE fibers to the HE fibers. Based on this concept, a uniaxial fabric was fabricated and tested to compare its behavior in tension with the theoretical predicted loading behavior. The theoretical behavior is based on the rule of mixtures, in which the axial stiffness of the hybrid is calculated by a summation of the relative stiffness of each of its components. The fabric was manufactured by combining different fibers as adjacent yarns and impregnating them inside a mold by an epoxy resin. Figure 2 shows a photo of one of the fabricated samples. Woven glass fiber tabs were provided at both ends of the test coupons to eliminate stress concentrations at end fixtures during testing. The coupons had a thickness of 2 mm (0.08 in.) and a width of 25.4 mm

ACI StructuralJournal/September-October 2002

(1 in.) and were tested in tension according to ASTM D 3039 specifications. The average load-strain curve for four tested samples is shown in Fig. 3 together with the theoretical prediction. It should be noted that the behavior is linear up to a strain of 0.35%, when the LE fibers started to fail. At this point, the strain increased at a faster rate than the load. When the strain reached 0.90t h e ME fibers started to fail, resulting in an additional increase in strain without a significant increase in load, up to the total failure of the coupon by failure of the HE fibers. A yield-equivalent load (the first point on the load-strain curve where the behavior becomes nonlinear) of 0.46 kN/mm

width (2.6 kips/in.) and an ultimate load of 0.78 kN/mm (4.4 kips/in.) arc observed.

BEAM TESTS

Beam detail s

Thirteen reinforced concrete beams with cross-sectional dimensions of 152 x 254 mm (6x10 in.) and lengths of 2744 mm (108 in.) were cast. The flexure reinforcement of the beams consisted of two No. 5(16 mm) tension bars near the bottom, and two No. 3 (9.5 mm) compression

bars near the top. To avoid shear failure, the beams were over- reinforced for shear with No. 3 (9.5 mm) closed stirrups spaced at 102 mm (4.0 in.). Five beams were formed with rounded corners of 25 mm (1 in.) radius to facilitate the installation of the strengthening material on their sides and bottom faces without stress concentrations. Figure 4 shows the beam dimensions, reinforcement details, support locations, and location of loading points. The

steel used was Grade 60 with a yield strength of 415 MPa (60.000 psi), while the concrete compressive strength at the time of testing the beams was 55.2 MPa (8000 psi).

Strengthening materials

The developed hybrid fabric was used lo strengthen eight beams. Two different thicknesses of fabric were used. The first (H-systcm, t = 1.0 mm) had a thickness of 1.0 mm (0.04 in.), and the second (H-systcm, / = 1.5 mm) had a thickncss of 1.5 mm (0.06 in.). Four other beams were strengthened with three currently available carbon fiber strengthening materials: 1) a uniaxial carbon fiber sheet with an ultimate load of 0.34 kN/mm (1.95 kips/in.);

土木工程外文翻译.doc

项目成本控制一、引言项目是企业形象的窗口和效益的源泉。随着市场竞争日趋激烈，工程质量、文明施工要求不断提高，材料价格波动起伏，以及其他种种不确定因素的影响，使得项目运作处于较为严峻的环境之中。由此可见项目的成本控制是贯穿在工程建设自招投标阶段直到竣工验收的全过程，它是企业全面成本管理的重要环节，必须在组织和控制措施上给于高度的重视，以期达到提高企业经济效益的目的。二、概述工程施工项目成本控制，指在项目成本在成本发生和形成过程中，对生产经营所消耗的人力资源、物资资源和费用开支，进行指导、监督、调节和限制，及时预防、发现和纠正偏差从而把各项费用控制在计划成本的预定目标之内，以达到保证企业生产经营效益的目的。三、施工企业成本控制原则施工企业的成本控制是以施工项目成本控制为中心，施工项目成本控制原则是企业成本管理的基础和核心，施工企业项目经理部在对项目施工过程进行成本控制时，必须遵循以下基本原则。 3.1 成本最低化原则。施工项目成本控制的根本目的，在于通过成本管理的各种手段，促进不断降低施工项目成本，以达到可能实现最低的目标成本的要求。在实行成本最低化原则时，应注意降低成本的可能性和合理的成本最低化。一方面挖掘各种降低成本的能力，使可能性变为现实；另一方面要从实际出发，制定通过主观努力可能达到合理的最低成本水平。 3.2 全面成本控制原则。全面成本管理是全企业、全员和全过程的管理，亦称“三全”管理。项目成本的全员控制有一个系统的实质性内容，包括各部门、各单位的责任网络和班组经济核算等等，应防止成本控制人人有责，人人不管。项目成本的全过程控制要求成本控制工作要随着项目施工进展的各个阶段连续进行，既不能疏漏，又不能时紧时松，应使施工项目成本自始至终置于有效的控制之下。 3.3 动态控制原则。施工项目是一次性的，成本控制应强调项目的中间控制，即动态控制。因为施工准备阶段的成本控制只是根据施工组织设计的具体内容确

土木工程类专业英文文献及翻译

PA VEMENT PROBLEMS CAUSED BY COLLAPSIBLE SUBGRADES By Sandra L. Houston,1 Associate Member, ASCE (Reviewed by the Highway Division) ABSTRACT: Problem subgrade materials consisting of collapsible soils are com- mon in arid environments, which have climatic conditions and depositional and weathering processes favorable to their formation. Included herein is a discussion of predictive techniques that use commonly available laboratory equipment and testing methods for obtaining reliable estimates of the volume change for these problem soils. A method for predicting relevant stresses and corresponding collapse strains for typical pavement subgrades is presented. Relatively simple methods of evaluating potential volume change, based on results of familiar laboratory tests, are used. INTRODUCTION When a soil is given free access to water, it may decrease in volume, increase in volume, or do nothing. A soil that increases in volume is called a swelling or expansive soil, and a soil that decreases in volume is called a collapsible soil. The amount of volume change that occurs depends on the soil type and structure, the initial soil density, the imposed stress state, and the degree and extent of wetting. Subgrade materials comprised of soils that change volume upon wetting have caused distress to highways since the be- ginning of the professional practice and have cost many millions of dollars in roadway repairs. The prediction of the volume changes that may occur in the field is the first step in making an economic decision for dealing with these problem subgrade materials. Each project will have different design considerations, economic con- straints, and risk factors that will have to be taken into account. However, with a reliable method for making volume change predictions, the best design relative to the subgrade soils becomes a matter of economic comparison, and a much more rational design approach may be made. For example, typical techniques for dealing with expansive clays include: (1) In situ treatments with substances such as lime, cement, or fly-ash; (2) seepage barriers and/ or drainage systems; or (3) a computing of the serviceability loss and a mod- ification of the design to "accept" the anticipated expansion. In order to make the most economical decision, the amount of volume change (especially non- uniform volume change) must be accurately estimated, and the degree of road roughness evaluated from these data. Similarly, alternative design techniques are available for any roadway problem. The emphasis here will be placed on presenting economical and simple methods for: (1) Determining whether the subgrade materials are collapsible; and (2) estimating the amount of volume change that is likely to occur in the 'Asst. Prof., Ctr. for Advanced Res. in Transp., Arizona State Univ., Tempe, AZ 85287. Note. Discussion open until April 1, 1989. To extend the closing date one month,

土木工程外文翻译

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附件1：外文资料翻译译文抗侧向荷载的结构体系常用的结构体系若已测出荷载量达数千万磅重，那么在高层建筑设计中就没有多少可以进行极其复杂的构思余地了。确实，较好的高层建筑普遍具有构思简单、表现明晰的特点。这并不是说没有进行宏观构思的余地。实际上，正是因为有了这种宏观的构思，新奇的高层建筑体系才得以发展，可能更重要的是：几年以前才出现的一些新概念在今天的技术中已经变得平常了。如果忽略一些与建筑材料密切相关的概念不谈，高层建筑里最为常用的结构体系便可分为如下几类： 1.抗弯矩框架。 2.支撑框架，包括偏心支撑框架。 3.剪力墙，包括钢板剪力墙。 4.筒中框架。 5.筒中筒结构。 6.核心交互结构。 7. 框格体系或束筒体系。特别是由于最近趋向于更复杂的建筑形式，同时也需要增加刚度以抵抗几力和地震力，大多数高层建筑都具有由框架、支撑构架、剪力墙和相关体系相结合而构成的体系。而且，就较高的建筑物而言，大多数都是由交互式构件组成三维陈列。将这些构件结合起来的方法正是高层建筑设计方法的本质。其结合方式需要在考虑环境、功能和费用后再发展，以便提供促使建筑发展达到新高度的有效结构。这并

不是说富于想象力的结构设计就能够创造出伟大建筑。正相反，有许多例优美的建筑仅得到结构工程师适当的支持就被创造出来了，然而，如果没有天赋甚厚的建筑师的创造力的指导，那么，得以发展的就只能是好的结构，并非是伟大的建筑。无论如何，要想创造出高层建筑真正非凡的设计，两者都需要最好的。虽然在文献中通常可以见到有关这七种体系的全面性讨论，但是在这里还值得进一步讨论。设计方法的本质贯穿于整个讨论。设计方法的本质贯穿于整个讨论中。抗弯矩框架抗弯矩框架也许是低，中高度的建筑中常用的体系，它具有线性水平构件和垂直构件在接头处基本刚接之特点。这种框架用作独立的体系，或者和其他体系结合起来使用，以便提供所需要水平荷载抵抗力。对于较高的高层建筑，可能会发现该本系不宜作为独立体系，这是因为在侧向力的作用下难以调动足够的刚度。我们可以利用STRESS，STRUDL 或者其他大量合适的计算机程序进行结构分析。所谓的门架法分析或悬臂法分析在当今的技术中无一席之地，由于柱梁节点固有柔性，并且由于初步设计应该力求突出体系的弱点，所以在初析中使用框架的中心距尺寸设计是司空惯的。当然，在设计的后期阶段，实际地评价结点的变形很有必要。支撑框架支撑框架实际上刚度比抗弯矩框架强，在高层建筑中也得到更广泛的应用。这种体系以其结点处铰接或则接的线性水平构件、垂直构件和斜撑构件而具特色，它通常与其他体系共同用于较高的建筑，并且作为一种独立的体系用在低、中高度的建筑中。

土木工程岩土类毕业设计外文翻译

姓名：学号： 10447425 X X 大学毕业设计（论文）外文翻译（2014届）外文题目Developments in excavation bracing systems 译文题目开挖工程支撑体系的发展外文出处Tunnelling and Underground Space Technology 31 (2012) 107–116 学生XXX 学院XXXX 专业班级XXXXX 校内指导教师XXX 专业技术职务XXXXX 校外指导老师专业技术职务二○一三年十二月

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（二〇一二年六月外文文献及翻译题目： About Buiding on the Structure Design 学生姓名：学院：土木工程学院系别：建筑工程系专业：土木工程(建筑工程方向) 班级：土木08-4班指导教师：

英文原文： Building construction concrete crack of prevention and processing Abstract The crack problem of concrete is a widespread existence but again difficult in solve of engineering actual problem, this text carried on a study analysis to a little bit familiar crack problem in the concrete engineering, and aim at concrete the circumstance put forward some prevention, processing measure. Keyword:Concrete crack prevention processing Foreword Concrete's ising 1 kind is anticipate by the freestone bone, cement, water and other mixture but formation of the in addition material of quality brittleness not and all material.Because the concrete construction transform with oneself, control etc. a series problem, harden model of in the concrete existence numerous tiny hole, spirit cave and tiny crack, is exactly because these beginning start blemish of existence just make the concrete present one some not and all the characteristic of quality.The tiny crack is a kind of harmless crack and accept concrete heavy, defend Shen and a little bit other use function not a creation to endanger.But after the concrete be subjected to lotus carry, difference in temperature etc. function, tiny crack would continuously of expand with connect, end formation we can see without the

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土木工程毕业设计外文文献翻译修订版 IBMT standardization office【IBMT5AB-IBMT08-IBMT2C-ZZT18】

外文文献翻译 Reinforced Concrete （来自《土木工程英语》） Concrete and reinforced concrete are used as building materials in every country. In many, including the United States and Canada, reinforced concrete is a dominant structural material in engineered construction. The universal nature of reinforced concrete construction stems from the wide availability of reinforcing bars and the constituents of concrete, gravel, sand, and cement, the relatively simple skills required in concrete construction, and the economy of reinforced concrete compared to other forms of construction. Concrete and reinforced concrete are used in bridges, buildings of all sorts underground structures, water tanks, television towers, offshore oil exploration and production structures, dams, and even in ships. Reinforced concrete structures may be cast-in-place concrete, constructed in their final location, or they may be precast concrete produced in a factory and erected at the construction site. Concrete structures may be severe and functional in design, or the shape and layout and be whimsical and artistic. Few other building materials off the architect and engineer such versatility and scope. Concrete is strong in compression but weak in tension. As a result, cracks develop whenever loads, or restrained shrinkage of temperature changes, give rise to tensile stresses in excess of the tensile strength of the concrete. In

土木工程外文翻译参考3篇

学校毕业设计（论文）附件外文文献翻译学号： xxxxx 姓名： xxx 所在系别： xxxxx 专业班级： xxx 指导教师： xxxx 原文标题： Building construction concrete crack of prevention and processing 2012年月日 .

建筑施工混凝土裂缝的预防与处理1 摘要混凝土的裂缝问题是一个普遍存在而又难于解决的工程实际问题，本文对混凝土工程中常见的一些裂缝问题进行了探讨分析，并针对具体情况提出了一些预防、处理措施。关键词：混凝土裂缝预防处理前言混凝土是一种由砂石骨料、水泥、水及其他外加材料混合而形成的非均质脆性材料。由于混凝土施工和本身变形、约束等一系列问题，硬化成型的混凝土中存在着众多的微孔隙、气穴和微裂缝，正是由于这些初始缺陷的存在才使混凝土呈现出一些非均质的特性。微裂缝通常是一种无害裂缝，对混凝土的承重、防渗及其他一些使用功能不产生危害。但是在混凝土受到荷载、温差等作用之后，微裂缝就会不断的扩展和连通，最终形成我们肉眼可见的宏观裂缝，也就是混凝土工程中常说的裂缝。混凝土建筑和构件通常都是带缝工作的，由于裂缝的存在和发展通常会使内部的钢筋等材料产生腐蚀，降低钢筋混凝土材料的承载能力、耐久性及抗渗能力，影响建筑物的外观、使用寿命，严重者将会威胁到人们的生命和财产安全。很多工程的失事都是由于裂缝的不稳定发展所致。近代科学研究和大量的混凝土工程实践证明，在混凝土工程中裂缝问题是不可避免的，在一定的范围内也是可以接受的，只是要采取有效的措施将其危害程度控制在一定的范围之内。钢筋混凝土规范也明确规定：有些结构在所处的不同条件下，允许存在一定宽度的裂缝。但在施工中应尽量采取有效措施控制裂缝产生，使结构尽可能不出现裂缝或尽量减少裂缝的数量和宽度，尤其要尽量避免有害裂缝的出现，从而确保工程质量。混凝土裂缝产生的原因很多，有变形引起的裂缝：如温度变化、收缩、膨胀、不均匀沉陷等原因引起的裂缝；有外载作用引起的裂缝；有养护环境不当和化学作用引起的裂缝等等。在实际工程中要区别对待，根据实际情况解决问题。混凝土工程中常见裂缝及预防: 1.干缩裂缝及预防干缩裂缝多出现在混凝土养护结束后的一段时间或是混凝土浇筑完毕后的一周左右。水泥浆中水分的蒸发会产生干缩，且这种收缩是不可逆的。干缩裂缝的产生主要是由于混凝土内外水分蒸发程度不同而导致变形不同的结果：混凝土受外部条件的影响，表面水分损失过快，变形较大，内部湿度变化较小变形较小，较大的表面干缩变形受到混凝土内部约束，产生较大拉应力而产生裂缝。相对湿度越低，水泥浆体干缩越大，干缩裂缝越易产 1原文出处及作者：《加拿大土木工程学报》

土木工程毕业设计外文翻译最终中英文

7 Rigid-Frame Structures A rigid-frame high-rise structure typically comprises parallel or orthogonally arranged bents consisting of columns and girders with moment resistant joints. Resistance to horizontal loading is provided by the bending resistance of the columns, girders, and joints. The continuity of the frame also contributes to resisting gravity loading, by reducing the moments in the girders. The advantages of a rigid frame are the simplicity and convenience of its rectangular form.Its unobstructed arrangement, clear of bracing members and structural walls, allows freedom internally for the layout and externally for the fenestration. Rig id frames are considered economical for buildings of up to' about 25 stories, above which their drift resistance is costly to control. If, however, a rigid frame is combined with shear walls or cores, the resulting structure is very much stiffer so that its height potential may extend up to 50 stories or more. A flat plate structure is very similar to a rigid frame, but with slabs replacing the girders As with a rigid frame, horizontal and vertical loadings are resisted in a flat plate structure by the flexural continuity between the vertical and horizontal components. As highly redundant structures, rigid frames are designed initially on the basis of approximate analyses, after which more rigorous analyses and checks can be made. The procedure may typically inc lude the following stages: 1. Estimation of gravity load forces in girders and columns by approximate method. 2. Preliminary estimate of member sizes based on gravity load forces with arbitrary increase in sizes to allow for horizontal loading. 3. Approximate allocation of horizontal loading to bents and preliminary analysis of member forces in bents. 4. Check on drift and adjustment of member sizes if necessary. 5. Check on strength of members for worst combination of gravity and horizontal loading, and adjustment of member sizes if necessary. 6. Computer analysis of total structure for more accurate check on member strengths and drift, with further adjustment of sizes where required. This stage may include the second-order P-Delta effects of gravity loading on the member forces and drift.. 7. Detailed design of members and connections.

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PROJECTCOSTCONTROL INTRODUCTION project a corporate image window and effectiveness of the source. With increasingly fierce market competition, the quality of work and the construction of civilizations rising material prices fluctuations. uncertainties and other factors, make the project operational in a relatively tough environment. So the cost of control is through the building of the project since the bidding phase of acceptance until the completion of the entire process, It is a comprehensive enterprise cost management an important part, we must organize and control measures in height to the attention with a view to improving the economic efficiency of enterprises to achieve the purpose. 2, outlining the construction project cost control, the cost of the project refers to the cost and process of formation occurred, on the production and operation of the amount of human resources, material resources and expenses, guidance, supervision, regulation and restrictions, in a timely manner to prevent, detect and correct errors in order to control costs in all project costs within the intended target. to guarantee the production and operation of enterprises benefits. 4, the construction cost control measures cost control measures. Reduce the cost of construction projects means, we should not only increase revenue is also reducing expenditure, or both also increase savings. Cutting expenditure is not only revenue, or revenue not only to cut expenditure, it is impossible to achieve the aim of reducing costs, at least there is no ideal lower cost effective.

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附录：中英文翻译英文部分： LOADS Loads that act on structures are usually classified as dead loads or live loads are fixed in location and constant in magnitude throughout the life of the the self-weight of a structure is the most important part of the structure and the unit weight of the density varies from about 90 to 120 pcf (14 to 19 KN/m)for lightweight concrete,and is about 145 pcf (23 KN/m)for normal calculating the dead load of structural concrete,usually a 5 pcf (1 KN/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 may be either fully or partially in place,or not present at 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 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 is oftern important to distinguish between the

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