Discussion on Detection and Evaluation of Simply Supported Prestressed Concrete Small Box Girder Bridge After a Fire

The article takes a simply supported prestressed concrete small box girder bridge project as an example for inspection and evaluation after a fire incident.This includes appearance detection,concrete color hardness detection,concrete strength detection,concrete surface damage layer detection,reinforcement protective layer detection,and concrete carbonation detection.It is hoped that this analysis can be used as a reference for the detection and evaluation of future bridge projects with fire incidents to smoothen its subsequent repair and maintenance.

Dynamic finite element model updating of prestressed concrete continuous box-girder bridge

The dynamic finite element model （FEM） of a prestressed concrete continuous box-girder bridge, called the Tongyang Canal Bridge, is built and updated based on the results of ambient vibration testing （AVT） using a real-coded accelerating genetic algorithm （RAGA）. The objective functions are defined based on natural frequency and modal assurance criterion （MAC） metrics to evaluate the updated FEM. Two objective functions are defined to fully account for the relative errors and standard deviations of the natural frequencies and MAC between the AVT results and the updated FEM predictions. The dynamically updated FEM of the bridge can better represent its structural dynamics and serve as a baseline in long-term health monitoring, condition assessment and damage identification over the service life of the bridge .

Full-scale model tests and nonlinear analysis of prestressed concrete simply supported box girders

Full-scale model tests were carried out on a 30 m span prestressed concrete box girder and a 20 m span prestressed concrete hollow slab. Failure models were prestressed reinforcement tensile failure and crashing of roof concrete, respectively. The ductility indexes of the box girder and hollow slab were 1.99 and 1.23, respectively, according to the energy viewpoint. Based on the horizontal section hypothesis, the nonlinear computation procedure was established using the limited banding law, and it could carry out the entire performance analysis including the unloading, mainly focusing on the ways to achieve the unloading curves computation through stress-strain, moment-curvature and load-displacement curves. Through the procedure, parameters that influence on the bearing capacity, deformation performance and ductility of the structures were analyzed. Those parameters were quantity of prestressed reinforcement and tension coefficients of prestressed reinforcement. From the analysis, some useful conclusions can be obtained.

Finite element failure analysis of continuous prestressed concrete box girders

In order to analyze the load carrying capacity of prestressed concrete box girders, failure behaviors of in-situ deteriorated continuous prestressed concrete box girders under loading are experimentally observed and a finite failure analysis method for predicting behaviors of box girders is developed. A degenerated solid shell element is used to simulate box girders and material nonlinearity is considered. Since pre-stressed concrete box girders usually have a large number of curve prestressed tendons, a type of combined element is presented to simulate the prestressed tendons of box girders, and then the number of elements can be significantly reduced. The analytical results are compared with full-scale failure test results. The comparison shows that the presented method can be effectively applied to the failure analysis of in-situ continuous prestressed concrete box girders, and it also shows that the studied old bridge still has enough load carrying capacity.

Shear design of high strength concrete prestressed girders

Normal strength prestressed concrete I-girders are commonly used as the primary superstructure components in highway bridges. However, shear design guidelines for high strength PC girders are not available in the current structural codes. Recently, ten 7.62 m （25 feet） long girders made with high strength concrete were designed, cast, and tested at the University of Houston （UH） to study the ultimate shear strength and the shear concrete contribution （Vc） as a function of concrete strength （f＇c）. A simple semi-empirical set of equations was developed based on the test results to predict the ultimate shear strength of prestressed concrete I-girders. The UH-developed set of equations is a function of concrete strength （√f＇c）, web area （bwd）, shear span to effective depth ratio （a/d）, and percentage of transverse steel （Pt）. The proposed UH-Method was found to accurately predict the ultimate shear strength of PC girders with concrete strength up to 117 MPa （17000 psi） ensuring satisfactory ductility. The UH-Method was found to be not as overly conservative as the ACI-318 （2011） code provisions, and also not to overestimate the ultimate shear strength of high strength PC girders as the AASHTO LRFD （2010） code provisions. Moreover, the proposed UH-Method was found fairly accurate and not exceedingly conservative in predicting the concrete contribution to shear for concrete strength up to 117 MPa （17000 psi）.

Approach for analyzing the ultimate strength of concrete filled steel tubular arch bridges with stiffening girder

A convenient approach is proposed for analyzing the ultimate load carrying capacity of concrete filled steel tubular (CFST) arch bridge with stiffening girders. A fiber model beam element is specially used to simulate the stiffening girder and CFST arch rib. The geometric nonlinearity, material nonlinearity, influence of the construction process and the contribution of prestressing reinforcement are all taken into consideration. The accuracy of this method is validated by comparing its results with experimental results. Finally, the ultimate strength of an abnormal CFST arch bridge with stiffening girders is investigated and the effect of construction method is discussed. It is concluded that the construction process has little effect on the ultimate strength of the bridge.

Weakening effect of vertical prestress ducts on web sections in prestressed concrete box girder bridges

Based on experimental study result of two simply supported beams,which were prestressed by vertical tendons,the research on the weakening effect of vertical prestress ducts on web sections of prestressed concrete box girder was carried out. The test result shows that in the condition without grouting into the ducts,the cracking load is evidently lower than that with full grouting,and stirrup stress and principal tension stress at the surface of concrete will increase obviously. Meanwhile,the finite element analysis has been done to the test beams. The research is consistent with the analysis of finite element. The research tells that strengthening the detection and management for the vertical prestress grouting quality have an important meaning to prevent cracking of the prestressed concrete box girder bridge and provide one theoretical and testing basis for analyzing the cracking reason of such bridges.

Influences of Installment Tensioning Technology on Bearing Capacity of Rectangular Prestressed Concrete Beam

To obtain the relationship between use of installment tensioning technology and the bearing capacity of prestressed concrete beams, tensile and cyclic loading tests are conducted on five rectangular prestressed concreted specimens. Two types of prestressed tensioning methods are adopted in the tests, one uses installment tensioning technology to tension beams on days 4, 12, and 8, 12, respectively, and the other adopts the conventional method to tension the beam on day 28 only. The age of concrete, number of times tensioned, and the prestress value of early tensioning are considered in tests. Results show that use of installment tensioning technology has no effect on the bending failure pattern of prestressed concrete beams, but it reduces prestress loss and increases crack and yield loads. © 2017, Tianjin University and Springer-Verlag Berlin Heidelberg.

Detection and Genesis Analysis of Cracks in Prestressed Box Girder of a Certain Project

This paper introduces a crack detection example of the prestressed box girder in a certain project. The morphology of the box girder cracks was surveyed and mapped. The length, width, and depth of the cracks were inspected, and the strength and reinforcement configuration of the components were tested. The test results indicate that the strength and reinforcement configuration of the inspected components meet the design requirements. The crack at the end of the top plate of the box girder is a local compressive crack at the anchorage end. The width and length of the crack on the bottom surface of the top plate are not significant, and the depth is relatively shallow. Judging from the crack morphology, this crack is identified as a temperature crack. Additionally, based on the treatment measures for cracks of different widths, the treatment measures for the cracks of the components in this project are derived, providing a reference basis for similar projects in the future.

预应力UHPC槽形节段与整体式混凝土板组合梁受剪性能

将预制的UHPC槽形节段通过干缝连接和预应力张拉形成槽形梁,再与整体现浇的混凝土板组合成的组合梁,称为预应力UHPC槽形节段与整体式混凝土板组合梁(PUCS-MCS组合梁)。它是一种能充分发挥不同材料的性能、施工方便且整体性能好的新型桥梁结构。为探究其抗剪性能,开展了9根模型梁的试验。分析了接缝数、接缝处剪力键数、剪跨比、UHPC钢纤维体积率、配箍率和纵筋率等参数对试件变形、破坏模式、抗剪承载力的影响;基于试验研究结果,提出了PUCS-MCS组合梁抗剪承载力计算方法。结果表明:PUCS-MCS组合梁均为剪压破坏,所有梁在开裂前的荷载-挠度曲线差异不大,在开裂后刚度不断下降;PUCS-MCS组合梁的抗剪承载力随接缝处剪力键数、UHPC钢纤维掺量、配箍率和纵筋率的增大而增大,随干接缝数量增加和剪跨比的增大而减小,其中影响最显著的是干接缝和剪力键,影响最小的是钢纤维掺量和配箍率,因此PUCS-MCS组合梁可不配箍筋,并可采用较低钢纤维掺量的UHPC。

The Layout and Simulation of Logarithmic Spiral Double Curved Arch Dam Transverse Joints

Because of its good condition with mechanics, logarithmic spiral double curve arch bam has been widely used in the practical engineering. The introduction of a new method in how to divide transverse joint in arch dam will be given and the further research of its calculation has been done. The C＋＋ is used in electronic procedure and the 3D simulation has been finished with AutoCAD, which will provide the object model for computer simulation of the arch dam and the division of finite element mesh. Meanwhile, this method in dividing the transverse joint in arch dam also can be taken as the calculated basis for the design and calculation of arch dam, construction lofting and the calculation of the work amount.

简支变结构连续小箱梁桥负弯矩区UHPC-NC组合桥面板抗裂性研究

针对当前简支变结构连续小箱梁桥负弯矩区钢束易堵孔、运营中桥面开裂病害等问题,提出一种无负弯矩钢束的UHPC-NC组合桥面板结构。以一座3×30 m简支变结构连续小箱梁桥为研究对象,以正常使用极限状态梁体不开裂为控制准则确定UHPC合理构造尺寸,对所提出的负弯矩组合桥面板结构进行1∶2的缩尺模型试验。试验显示:裂缝首先出现于UHPC-NC交界面处的普通混凝土部分,随后逐渐向UHPC层沿伸,且C50混凝土开裂、梁体破坏对应的截面弯矩分别为3 520,9 152 kN·m(考虑1∶8弯矩缩尺比),大于正常使用极限状态、承载能力极限状态梁体截面弯矩3 300,5 838 kN·m,即该组合桥面板结构满足小箱梁的抗裂与承载能力要求。基于试验结果建立精细化有限元模型,采用参数分析法研究UHPC厚度对梁体开裂荷载、极限承载力等方面的影响。结果表明:梁体开裂弯矩主要由UHPC上覆层厚度决定,相较于普通钢筋混凝土梁,5 cm厚的UHPC上覆层可将梁体开裂弯矩提高28.9%,7.5 cm厚的UHPC上覆层可将梁体开裂弯矩提高41.6%;在配筋率不变的情况下,增大UHPC层厚度对梁体承载力无显著提升。综合考虑梁体受力性能以及施工便利性,建议背景工程UHPC厚度取10 cm。

预应力UHPC-RC无腹筋组合梁足尺模型抗弯试验及极限弯矩计算研究

为了解预应力UHPC-RC无腹筋组合梁(简称组合梁)的抗弯性能,以2座组合梁桥实际工程为背景,分别制作25 m长工字形组合梁及30 m长箱形组合梁足尺模型进行抗弯试验,研究组合梁在弯曲荷载下的裂缝发展形态、荷载~挠度曲线及不同截面高度应变等。结果表明:2种组合梁最终受弯破坏时,1条主裂缝快速发展为贯穿弯曲裂缝,组合梁裂缝细密;荷载~挠度曲线较为饱满,刚度折减较普通预应力混凝土梁明显推迟,结构性能更为优良;开裂前组合梁截面受力发展满足平截面假定,出现主裂缝后逐渐不满足平截面假定。为考虑组合梁截面在极限状态不满足平截面假定的情形,基于UHPC材料本构关系,提出采用体外预应力筋极限理论推导组合梁极限弯矩计算方法,并将该方法与平截面假定理论计算结果及试验结果进行对比。结果表明:提出的组合梁极限弯矩计算方法较平截面假定理论计算方法能更好地反映结构受力。

预应力效应对中速磁浮线路简支梁车-桥耦合振动响应的影响

以长沙磁浮线路简支梁桥为研究对象,建立考虑不同预应力效应的磁浮线路简支梁桥车-桥耦合振动模型,分析预应力效应对中速磁浮线路车-桥耦合振动响应的影响。结果表明:预应力效应的变化对桥梁动力响应影响明显,预应力增加显著加剧桥梁竖向振动加速度,预应力由0.67P0(P0为张拉控制应力)增加到1.33P0时,桥梁跨中竖向最大加速度从0.21 m/s^(2)增至0.44 m/s^(2);车速增加会加剧预应力效应的影响,对桥梁竖向振动加速度的影响尤为明显,车速由20 km/h增加到200 km/h时,在1.00P0作用下,桥梁跨中竖向最大加速度从0.15 m/s^(2)增至0.76 m/s^(2);箱壁局部变形对车-桥耦合竖向振动响应有显著影响,预应力导致的箱壁局部变形不可忽略。

大跨公铁两用钢桁拱桥边跨施工关键技术

常泰长江大桥天星洲专用航道桥为(168+388+168)m大跨重载公铁两用钢桁拱桥。主梁采用2片主桁双层板桁组合结构,边跨钢梁施工采用架梁吊机悬臂散件拼装。为确保边跨钢梁架设轴线和竖曲线线形,按照最快形成稳定桁片结构原则拼装,上墩前悬臂拼装并形成三角桁片稳定结构后再实施抄垫;在钢梁架设过程中对钢梁标高进行调整,精确控制钢梁上墩标高;为确保边跨钢梁架设结构受力满足要求,通过有限元理论分析比选,确定临时墩最优脱空时机;采用“基于空间六点调位法”对边跨钢梁进行整体精确定位;主墩支座采用重力法灌浆;基于多点变形协调,通过优化杆件安装工艺,解决了超静定结构杆件带力安装难题。

预应力混凝土拱板屋架检测鉴定与加固

预应力混凝土拱板屋架结构在我国粮食仓储领域扮演着举足轻重的角色,作为主要的粮仓顶部结构形式,对其检测鉴定进行研究具有重要的实际指导意义。从我国研究现状来看,大多数研究都聚焦于施工工艺和施工设计,在检测鉴定及加固技术方面的探讨相对较少。选取罗山国家粮食储备库的预应力混凝土拱板屋架作为研究对象,从工程检测、承载力验算、数值模拟及加固设计等多个环节开展研究,最后,针对不符合承载力要求的下弦板,提出体外预应力加固的设计方案。这一系列研究成果不仅对预应力拱板的检测鉴定提供科学可靠的理论基础及参数化模型,也为同类工程的加固设计提供新的借鉴。

30 m预应力UHPC箱梁抗弯性能试验及结构优化研究

为了解大尺寸预应力UHPC箱梁的抗弯性能,以预应力UHPC公路桥——河北石磁跨线桥为背景,设计、制作1片长30 m的足尺预应力UHPC箱梁模型进行四点弯曲试验,结合有限元计算结果,分析试验现象及裂缝分布、跨中荷载~位移曲线、受拉区UHPC及筋材应力~应变曲线。在此基础上分别考虑普通钢筋配筋情况、预应力筋数、腹板厚度和底板厚度等参数对预应力UHPC箱梁进行结构优化设计研究。结果表明:箱梁破坏时受压区UHPC未压溃、受拉区钢纤维被拔出,裂缝贯通底板;根据荷载~位移曲线,箱梁受力可分为弹性阶段、裂缝发展阶段、裂缝快速发展阶段和破坏阶段;根据应力~应变曲线,受拉区UHPC在纵筋屈服时仍能贡献抗拉能力;试验现象及力学指标实测值均说明了预应力UHPC箱梁抗弯能力还有很大富裕空间,可进一步优化。完全不配置普通钢筋的预应力UHPC箱梁仍能满足抗弯承载能力极限状态设计要求;底部预应力筋数增多可有效提高受压区UHPC的抗压强度利用率;腹板厚度过薄会造成腹板主拉应力过大问题,不宜薄于8 cm;采用体外预应力的方法可有效减薄底板所需厚度。

武汉市江汉四桥拓宽工程主桥设计关键技术

武汉市江汉四桥拓宽工程主桥采用与旧桥外形一致、呈反对称布置的主跨232 m独塔混合梁斜拉桥,跨径布置为(232+70+40+20)m,采用刚构体系。主梁采用钢-混叠合梁与预应力混凝土梁组成的混合梁,钢-混结合面位于主跨距桥塔中心线9 m处,主跨采用双边工字形叠合梁,桥面宽23.5 m,标准梁高1.6 m;边跨采用预应力混凝土边主梁和箱形截面主梁,桥面宽23.5~27.0 m,标准梁高2.1 m。桥塔采用“A”形混凝土塔,塔高114.5 m,其下布置整体式承台,采用18根ϕ2.8 m的群桩基础。斜拉索按空间扇形双索面布置,共104根斜拉索,采用标准强度1770 MPa高强平行钢丝索,主跨梁端采用锚拉板锚固,边跨梁端设置槽口锚固,塔端采用锚固齿块锚固,主塔斜拉索锚固区纵、横桥向均配置有无粘结预应力钢棒。汉阳岸边墩采用T形钢筋混凝土板墩及钻孔桩基础;汉口岸边墩、辅助墩均采用钢筋混凝土独柱墩及钻孔桩基础。桥塔塔柱采用爬模施工;边跨主梁采用支架现浇施工,主跨主梁采用悬臂拼装施工。结构计算结果表明,大桥结构刚度及应力均满足要求。

悬臂拼装施工的预制节段箱梁桥预应力参数优化

为揭示预制节段箱梁桥预应力相关参数对悬臂拼装阶段和合龙阶段箱梁横截面应力及施工期线形的影响,选取某工程一联三跨预制节段箱梁桥,针对悬臂拼装阶段和合龙阶段不同预应力参数取值对桥梁受力状态及变形特征的影响进行数值模拟。研究结果表明:预制节段箱梁桥顶板钢束最优张拉控制应力为预应力钢束抗拉强度标准值的0.70~0.75倍,与此同时应控制预应力钢束截面积不低于0.000 98 m^(2)(7Ф15.2 mm)。顶板单侧钢束组预应力合力作用线与顶板中轴线之间的距离,即顶板预应力合力偏心距宜取箱梁宽度的0.22~0.26倍。合龙阶段采用先张拉底板、腹板通长钢束,再张拉中、边跨局部钢束的方式可使桥梁在不同张拉阶段之间的线形及横截面应力变化更加平缓,有利于施工期间结构的安全控制。

济南齐鲁黄河大桥网状吊杆系杆拱桥施工关键技术

济南齐鲁黄河大桥主桥为(95+280) m+420 m+(280+95) m五跨三连拱下承式网状吊杆系杆拱桥,主梁采用钢-混组合梁,梁宽60.7 m,采用“先梁后拱”的施工工艺。钢箱梁采用“静动结合”的吊装技术,解决了有限作业空间下超重、超宽钢箱梁节段上桥的难题,钢箱梁采用智能化步履式顶推设备与坦克轮相结合的方式顶推施工,提高了顶推过程的可控性、安全性和高效性。3跨拱肋中2个280 m跨采用满堂支架法施工,420 m跨采用“三段法”施工,即通过满堂支架法安装两端60 m边拱肋,300 m中拱段采用在钢箱梁上低位拼装,然后整体提升中拱段,使其与边拱肋配切合龙。对吊杆张拉方案进行对比,基于有限元分析,以吊杆内力控制为原则,最终选择吊杆应力水平更低的从跨中向拱脚对称张拉的吊杆张拉方案,张拉过程中采用接长杆减少张拉工作量,使吊杆张拉更高效、安全。