专业外语英译汉

大作业课程名称：专业外语

题目：英译汉"Destructive Testing of a Decommissioned Reinforced Concrete Bridge"

院系：土木工程系

专业：

年级：

姓名：

指导教师：

西南交通大学峨眉校区

2012 年 6 月8 日

原文：

Destructive Testing of a Decommissioned Reinforced Concrete Bridge Abstract: A destructive field testing of a simply-supported channel-beam bridge was carried out to gain insight into the ultimate load-carrying capacity of existing reinforced concrete bridges. Based on a field inspection and assessment of the material strength, structural damage, and the testing that the field bridge exhibited local nonlinearities due to its beam-to-beam bolted structural degradation before testing, a detailed test program was developed. It was observed from connections and nitial damages. The failure mode of the tested bridge was the typical flexural failure characterized by yielding of rebars and concrete crushing. Some concrete failures were also observed at the location of bridge bearings. The observed load carrying capacity was much higher than that of the original design of the tested bridge and much more studies are needed to understand the real performance of field bridges.

Keywords: Existing RC bridge; Destructive testing; Damages; Ultimate load-carrying capacity, field testing

Introduction

The serviceability and ultimate load carrying capacity of old bridges were concerned by researchers and engineers. In recent years, with the increase of bridge collapses especially in developing countries such as in China, these problems have received even more attention. The ultimate load carrying capacity of old bridges were studied by some researchers (Azizinamini et al. 1994; Miller et al. 1994; Aktan et al. 1993; Bakht and Jaeger 1992; Allbright et al. 1994; Roschke and Pruski 2000). However, only a few destructive testings were conducted due to many reasons such as the high testing expenses and rare availabilities of testing subjects (Chajes et al. 2006, Bergstr?m et al. 2009).

In this study, a destructive testing was performed on a decommissioned bridge. The objectives of the testing were to better understand the load-carrying mechanism, gain insight into the ultimate load-carrying capacities of existing reinforced concrete (RC) bridges, and study the structural response of RC bridges during their whole loading process.

Description of Bridge and Testing Procedure

The Nanping Bridge, located at the 209 Hunan provincial highway, China, was built in 1964 and decommissioned in 2007. As shown in Fig. 1, it is a three-span simply-supported RC bridge with an equal span length of 13.3 m. Each single span of the Nanping Bridge consisted of 6 channel beams that were defined as beam I to beam VI from the upstream to the downstream as shown in Fig. (c). Due to the angle of the creek running underneath the bridge, the bridge abutments and piers were skewed at 25 度to the direction of roadway. For each beam, with the dimensions shown in Fig. 1(d), the rib at the upstream side was denoted as “rib A” and the downstream one as “rib B.” The notation of Ф in the figure corresponds to plain rebars with a smooth surface and a mean yield strength of 235 MPa, and the number following the Ф sign is the diameter of rebars in mm. There were six diaphragms in a simple span with two end diaphragms and four intermediate ones as shown in Fig. 1(e). The diaphragms did not continue across the two adjacent channel beams. However, the ribs of adjacent channel beams were connected by 20 bolts with a diameter of 25.0 mm (See Fig. 1 (b)).

The bridge was designed for Vehicle-15 truck loads (JTJ 021-89). The Vehicle-15 is a two-axle vehicle, with an axle distance of 1.8 m and a total weight of 196 kN, slightly heavier than

the US H20 truck (178 kN). However, the bridge was overloaded frequently by numerous trucks during its service time, which resulted in accumulated damages to the bridge. A detailed inspection and investigation was conducted on the Nanping Bridge before the destructive testing, including measuring the dimensions, concrete strength, reinforcement parameters, structural damage etc. Results of the prior testing inspection indicated that a side span was more significantly damaged and was selected as a representative structure to test the ultimate load-carrying capacity of RC bridges. This bridge was also tested for overload effects and the results were reported by Zhang et al. (2011).

A number of samples of concrete cylinders with a 100 mm in diameter and 100 mm in height were cored from the beams in the tested span for concrete compressive strength testing after the destructive testing, showing an average concrete compressive strength of 37.4 MPa by following the Chinese test standard (CECS 03-2007). A number of steel samples were also taken for mechanical testing, showing an average yield strength of 224 MPa, an ultimate strength of 306 MPa, and an average modulus of elasticity of 184 GPa.

The field inspection before testing showed that the beams in the tested span had significantly cracked. There appeared more cracks in beam III and beam IV than the other beams. Because of the relatively weak transverse connection between the beam ribs, the transverse distribution of vehicle loads was relatively limited. Therefore, beams III and IV carried most vehicle loads since they are located near the central line of the bridge section, which resulted in more cracks in the two beams.

The ultimate load of the bridge was numerically predicted as 2,400 kN, corresponding to a bending moment of 7,980 kN.m under the live load if a single-point loading system was employed at the midspan. Considering the possible error of prediction, a loading system with a bending capacity of 9,980 kN.m was planned in the testing. One of the key issues was how to design a safe and reliable loading system to produce such a large bending moment at the bridge site. Many loading systems were considered such as heaping a heavy weight, placing a water tank, constructing rock anchors as the reactive foundation, and using a reaction beam. Finally, the loading system as shown in Fig 2 was selected to load the bridge.

The selected reaction foundation of the loading system consisted of a swage box that was placed under the bridge with dimensions of 9m×9m×2.5m as shown in Fig. 3. A total weight of 3,100 kN gravels was put in the box as a counterweight. Eight high-strength bolts with a length of 9 m and a diameter of 50 mm were drilled through the bridge deck and anchored on the reaction foundation. Three steel box girders were used in the loading system. A 1500 mm×1400 mm×7000 mm steel box girder was placed on the bridge deck to distribute the loads to the six channel beams. The other two 1200 mm×450 mm×5600 mm steel box girders, connected with the swage box through the eight high-strength bolts, were used as reaction girders. Two hydraulic jacks with a capacity of 5,000 kN each were employed to produce the loading applied to the bridge.

To obtain both the local and global structural responses, approximately 400 gauges were used to measure the structural displacements, strains in reinforcement, and strains in concrete (See Fig. 4 and Fig. 5). When the strain gauges were attached to the rebars, the concrete cover was removed and rebars were polished to remove the rust. Deflections were measured using electronic displacement gauges and dial indicators and relative deflections are reported later by removing the support settlement. In order to assure that the data obtained from the testing is useful for analyzing the structural behavior, all measurement locations had two types of gauges so that

the test results could be cross-checked each other. Two digital levels were also employed to measure the structural deflections of beams near the midspan.

The parapets of the bridge were cut off and 50% deck pavements were removed before the testing. As a result, their contributions to the flexural capacity of the bridge could be excluded during testing. The joints between the test span and adjacent span were cleaned to make the test beams deform freely. Furthermore, rubber bearings and steel plates were assembled between the bridge deck and the distribution girder to distribute the loading more uniformly to each beam.

The loading increments were kept at 200 kN and reduced to 100 kN until a total load reached 1600 kN. Due to the fact that there were many initial cracks from the long time service and overloaded vehicles all over the bridge, the structural response remained linear only when the applied load is less than 1,600 kN. When the bridge was loaded up to 2,400kN, the structural response under the same loading increment increased significantly, indicating the yielding of reinforcement. Correspondingly, a maximum deflection of 43.62 mm was measured at the midspan of beam VI as shown in Fig. 6. Hence, the tested bridge was unloaded to zero to conduct a modal test that was intended for the purpose of parameter identifications and is not reported here. After the modal test, the bridge was reloaded. When the applied load was about 2,600 kN the concrete of the side beam was crushed with a maximum midspan deflection of 174 mm. The test bridge was continuously loaded (but the load remained about 2600 kN) till the concrete of all beams were crushed as shown in Fig. 7, corresponding to a maximum deflection of 240 mm at the midspan of beam VI. The total force 2,600 kN represents the weight of 13 design vehicles (196 kN for each Vehicle 15).

Analysis of Test Results

Fig. 8 shows the deflections along the transverse direction under the two hydraulic jack loadings. The weak transverse connections of the bridge resulted in obvious deformation differences of individual members, though the distribution girder with a strong flexural stiffness was used to distribute the jack loads. The shoulders on the bridge deck were usually treated as nonstructural elements, but they appeared to contribute to the stif fness of the bridge at the early stages of loading. This resulted in the deflections of the two edge ribs being significantly smaller than those of the other ribs for the first few loading steps. With the increase of loading and deflection, the bonding between the bridge shoulder and deck was weakened, and correspondingly, cracks on their interface were observed as shown in Fig. 9. Therefore, the contributions of shoulders to the structural ultimate capacity could be neglected. Fig. 10 describes the deflection along the span length for beam IV and they were symmetric about the midspan, and the curves were relatively smooth.

Fig. 11 shows the load versus the compressive strains of the concrete flange of beams I and IV at the mid-span. It is observed from Fig. 11 that the concrete strains of beam I under the applied loads was linear before the yielding point. In contrast, the strains of beam IV showed an abrupt increase at the applied 1oad of 1,700 kN. Furthermore, the concrete strains of beam IV are always higher than those of beam I. This phenomenon agrees with the deflection data very well because: (1) The deflection of beam IV is about 49% higher than that of beam I before the yielding point, and (2) The shoulder located at the top of rib A of beam I would undertake part of the compressive stress and consequently reduce the compressive strains in concrete.

Fig. 12 shows the transverse distribution of the concrete compressive strains at the mid-span of all beams under the applied loads. The uneven distribution of concrete strains

between structural members due to the weak lateral connections is also observed in Fig. 12. Because of the loading distribution and the contribution of shoulder to the structural stiffness, at the beginning the compressive strains of beam VI was very close to that of beam I. The concrete compressive strains of beam VI propagated rapidly, resulting from the corrosion of rebar and the weak bonding between the concrete and rebars.

Fig. 13 shows the applied loads versus tensile strains in concrete at the bottom of the ribs at the mid-span measured by surface strain gauges and micrometers. The mean tensile strain of concrete over the gauge length measured at the yielding load of 2400 kN is about 1,356×10-6

. It can be seen in the figure that the strains in the concrete recorded by two types of gauges match each other very well. The strain of beam VI exceeded that of the other beams rapidly after a load of 1,400 kN was applied, which did not match the structural deflection of this beam. However, the quick increase of tensile strains in the concrete agreed with the nonlinear increase of deflection for beam VI at an applied load of 1900 kN.

Fig. 14 shows the applied load versus the rebar strains at the mid-span of some beams. As shown in the figure, the measured strains of the rebars located at the mid-span of beams III and V under the observed yielding load (2,400 kN) are about 1,217×10-6and 1,401×10-6 respectively. However, the corresponding strains of beams I and II rebars are significantly less. It is noted that the measured strains do not include the strain due to the bridge’s self - weight and therefore are less than the steel’s yield strain. Moreover, the rebar strain increments of some test points show a sudden decline at the applied loads of 1,800 kN and 1,900 kN. This might be resulted from the slippage between the rebars and concrete.

The investigation after the destructive testing showed that the failure modes of this structure included not only the crushed concrete in the compressive zones but also the obvious inclined cracks of concrete near the bearing of the tested bridge toward the end of beam. Moreover, the cracks penetrating the section completely were also observed at the place of connection between the ribs and diaphragms. Because the ultimate load was just slightly higher than the load of rebar yielding, these various failure modes possibly had affected the ultimate loads. Conclusions

In this study, a destructive test was performed on a simply-supported RC channel-beam bridge that had been in service for more than 43-years. Although the bridge was deteriorated severely, it held a total load of 2,600 kN before it totally failed. This ultimate load produced approximately a bending moment equivalent to that caused by 16 two-axle trucks (Vehicle 15) being vertically placed at the most unfavorable position of the test span, while it represented the weight of 13 design vehicles (196 kN for each Vehicle 15).

The response of the bridge exhibited some significant nonlinear behaviors that occurred in almost all beams at different times in the expected linear stage. It is also found that there existed large differences in mechanical properties of each simply-supported channel beam under live load due to the weak lateral connections.

There appeared to be different types of failure modes at various parts of the field bridge. This means that the flexural failure at the midspan is not the only failure mode. The failure mode and ultimate load carrying capacity of existing RC bridges may be affected by various influencing factors. This study can help provide references in evaluating the safety of similar types of bridges.

译文：

一座退役钢筋混凝土桥的破坏性试验

摘要：（作者）对一座简支梁桥做了一次现场破坏性试验来观察既有钢筋混凝土桥的极限承载能力。根据对材料强度、结构破坏情况的现场观察和评估以及由于在实验前梁与梁连接部分功能退化使得桥非线性变化的试验，一个详细的测试项目产生了。它是从初始破坏时开始观察的。所测试桥梁的失效正是典型的以钢筋屈服和混凝土压碎为特征的失效。在桥梁的支承处也观察到了混凝土开裂。观测到的承载能力比桥的初始设计值高许多，需要做更多的研究来理解桥梁的工作机理。

关键字：既有钢筋混凝土桥；破坏性试验；破坏；极限承载能力；现场试验

简介：专家和工程师对古老的桥梁的正常使用承载能力和极限承载能力很重视。近年来，随着桥梁倒塌案例的增加，特别是在像中国一样的发展中国家，这些问题已越来越受到重视。有一些专家研究过古老桥梁的极限承载能力，但是由于许多原因，比如，试验的高昂费用，稀少的可供试验的目标，仅仅做了一些破坏性试验。

在本研究中，对一座退役的桥梁做了破坏性试验。本次试验的目的是为了更好地理解承载机理，观察既有钢筋混凝土桥的极限承载能力，研究在整个加载过程中钢筋混凝土桥结构的响应。

桥梁试验程序的描述：

南平桥位于中国湖南省公路209道，建于1964年并与2007年退出使用。如图1所示，它是一座三跨钢筋混凝土简支梁桥，每跨长度为13.3m。南平桥每一跨由六根横梁构成，从上游至下游为I-VI，如图（c）所示。由于小溪的转角在梁的下方，桥墩偏离道路方向25度。对于每一片梁，其尺寸规格如图1（d）所示。在上游的肋梁记为“A肋梁”，下游的记为“B肋梁”。表中的符号Φ对应光面钢筋，平均屈服强度为235MPa，符号Φ后面的数字表示钢筋的直径，其单位是毫米。一个单跨有六块横隔板，其中有两块端横隔板，四块中横隔板，如图1（e）所示。横隔板并不穿过两块相邻的梁，但是相邻梁的肋板是用直径为25mm 的20颗螺栓连接在一起的。（见图1（b））

这座桥是按V-15卡车的荷载设计的，V-15是双车轮，车轮间距1.8m，总重为196KN，比USH20卡车（178KN）稍重。然而，在桥的使用期内，许多卡车造成频繁的超载，这就对桥梁产生累积损害。在破坏性试验之前，（专家）对南平桥做了一次详细的检查，包括测量尺寸、混凝土强度、钢筋参数、结构破坏等。前期测试观察结果表明边跨破坏得更加严重，

因此选其作为代表结构来测试钢筋混凝土桥的极限承载能力。该桥也用来测试超载效应。

在破坏性试验后，许多直径为100mm ，高度为100mm 的混凝土柱面试样被从所试验梁跨中钻取出来用以测定混凝土的抗压强度，根据中华人民共和国试验标准，得出混凝土平均抗压强度为37.4MPa 。许多钢筋试样也被用作力学测试，得出平均屈服强度为224MPa ，极限强度为306MPa ，平均弹性模量为184GPa 。

实验之前的观察表明在测试梁跨段的梁已经有严重的开裂。Ⅲ号梁和Ⅳ号梁较其他梁出现更多的裂缝。由于梁肋间的横向连接相对较弱，车辆荷载的横向分布受到相对的限制。因此，Ⅲ号梁和Ⅳ号梁承担最多的车辆荷载，因为它们位于桥截面中心线附近，这就导致在这两片梁中产生更多的裂缝。

如果集中力作用在跨中预计桥的的极限荷载数值上为2400KN ，对应活载作用下的弯矩为7980KN.m 。考虑到预测的可能的错误，一能提供9980KN.m 弯矩的加载系统被用于试验中。关键问题之一是如何设计一套既安全又可靠的加载系统来在桥上产生这么大的弯矩。许多加载系统都考虑了比如堆积重物、放置水箱、抛锚作反应基础、用反应梁。最后选择加载桥梁的加载系统如图2.

被选择的加载系统的反应基础为一个铁箱模，该铁箱模放置在桥下，尺寸为m m m 5.299??，如图3所示，将一个总重3100KN 的碎石放在箱子里面作为平衡物。八根长为9m ，直径为50mm 的高强螺栓钻过桥面板并固定在反应基础上。三根钢箱梁被用在了加载系统中。一根mm mm mm 700014001500??钢箱梁放置在桥面板上来将荷载分给六根横梁。其他两根mm mm mm 56004501200??钢箱梁通过八根高强螺栓与铁箱模相连被用作反应梁。两个每个承载力为5000KN 的液压千斤顶用来产生荷载。

为了获得局部的和整体的结构响应，试验人员用了近400支仪表来测量结构的位移、钢筋的应变、混凝土的应变（见图4和图5），当测应变的仪表与钢筋项链是，移动混凝土面，擦亮钢筋以除去铁锈。用电子移位仪和刻度盘指示器测量挠曲变形，通过移动支座沉降读出相对位移。为了确保从试验中获得的数据对分析结构行为有用，每个测点有两类仪表以便测试结果能相互对照检验。两数字也被用来测量跨中附近梁的结构变形。

在试验前切断桥上的栏杆，移除一半的路面。所以，在试验过程中，它们对桥的抗弯能力的影响可以排除。将试验量跨与相邻梁跨间的接头清理干净以使测试梁自由变形。并且，橡胶支座和钢垫块同桥面与分布梁统一分布荷载相类似。

加载增量维持在200KN ，当总荷载达到1600KN 时，减少到100KN 。由于有许多因长时间使用和全桥超载产生的初裂缝，结构响应只在荷载小于1600KN 时保持线性。当桥梁加载到

2400KN 时，在相同荷载增量下，结构相应严重增加，表明钢筋屈服了。相应地，如图6所示，Ⅵ号梁跨中测得的最大挠度为43.62mm 。因此，桥梁卸载到0以测试参数，这里不再叙述。在模态测试之后，桥梁重新加载，当荷载大约为2600KN 时，边梁混凝土开裂且跨中最大变形为174mm 。对桥继续加载（但荷载维持在2600KN 左右）直到所有梁出现图7所示的裂缝，对应Ⅵ号梁跨中的最大挠度为240mm.总荷载2600KN 代表13设计车辆的重量（每辆196KN ）。

试验结果的分析：

图8反映了在两台液压千斤顶下沿桥横向的挠曲变形。桥的弱横向连接导致各单元变形明显不同，即使用强抗弯刚度的分布梁来分布千斤顶荷载。通常，桥面板肩头被当做非结构单元，但是在加载初始阶段它们提高了桥的刚度。这就导致在前几步加载阶段两边肋梁的挠曲变形比其他肋梁小很多。随着荷载和变形的增大，桥肩头与桥面板间的粘合变弱。相应地，在它们分界面观察到的裂缝如图9所示。因此，肩头对结构极限承载能力的贡献可以忽略。图10描述了Ⅳ号梁沿桥跨长度的挠曲变形，它们关于跨中对称，曲线图相对平滑。

图11反映了I 号梁和Ⅳ号梁边缘混凝土的压应变。从图11可以得出在荷载作用下，I 号梁混凝土中的应变在屈服点之前是线性的。相反，当何在为1700KN 时，Ⅳ号梁中的应变出现突然地增加。并且Ⅳ号梁中的混凝土应变总是比I 号梁高。这种现象与挠曲变形数据非常吻合，因为：（1）在屈服点之前，Ⅳ号梁的挠曲变形比I 号梁大大约49%；（2）I 号梁的A 肋梁顶部的肩头会承担部分压应力并最终减小了混凝土中的压应变。

图12反映了在荷载作用下，所有梁梁跨中部混凝土压应变的横向分布。结构单元间由于较弱的侧向连接导致混凝土应变的不均匀分布，在图12中也可以看到。由于荷载分布以及肩头对结构刚度的贡献，刚开始Ⅵ号梁的压应变与I 号梁很接近。因为钢筋的锈蚀以及混凝土和钢筋间较弱的链接，Ⅵ号梁的混凝土压应变发展迅速。

图13反映了通过表面应变仪器和千分尺测得的跨中肋梁底部混凝土中的拉应变。在2400KN 的屈服荷载下测得的平均拉应变为6

101356-?。可以看出两种类型的仪表记录的混凝土中的应变数据非常吻合。当加载1400KN 的荷载后，Ⅵ号梁的应变扩展同其他梁一样快，这不符合这片梁的结构变形。然而，在1900KN 荷载作用下时，混凝土中拉应变的快速增加同Ⅵ号梁变形的非线性增加相符。

图14反映了一些梁的跨中钢筋的应变。如数据显示，在观测屈服荷载（2400KN ）作用下，测得Ⅲ号梁和Ⅴ号梁跨中的钢筋应变为6

6101401101217--??，。然而，对应的Ⅰ号梁

和Ⅱ号梁中的钢筋应变很小。所测的应变不包括由于桥的自重产生的应变，因此小于钢筋的屈服应变。在1800KN和1900KN荷载作用下，一些测点的钢筋应变表现为突然减小。这可能是因为钢筋和混凝土间的滑移造成的。

破坏性试验后的检查表明结构的失效模式不仅包括受压区混凝土开裂，而且包括测试桥梁支承附近的混凝土斜裂缝。在肋梁和缀板间连接位置处观察到裂缝贯穿整个截面。因为极限荷载仅仅比钢筋屈服荷载高一点儿，所以这些各种失效模式可能对极限荷载有影响。

结论：

本研究对一座已经服役超过43年的钢筋混凝土简支梁桥做破坏性试验，虽然这座桥严重恶化，但在它完全失效前它仍能承受2600KN的荷载。极限荷载产生的弯矩几乎等价于将16辆双轮卡车放置在测试桥跨的最不利位置产生的弯矩，它代表13设计车辆的重量（每辆196KN）。

桥梁的响应表现出一些在预期线性阶段的不同时期几乎所有梁中发生的大的非线性行为。也发现，在活载作用下，由于较弱的横向连接，每片简支梁的力学性能存在很大的不同。

在桥梁的各个部分出现了不同类型的失效模式，这就意味着跨中弯曲失效不是唯一的失效模式。既有钢筋混凝土桥的失效模式和极限承载能力受到各种影响因素影响。本研究能够为评估相似类型桥梁的安全提供参考。