Controlling deflection of long steel I-shaped girder bridge using two V-shaped pre-tensioning cables

Despite appropriate design of girder under bending and shear,the deflection of long steel girders usually exceeds the allowable range,and therefore the structural designers encounter challenges in this regard.Considering significant features of the cables,namely,low weight,small cross section,and high tensile strength,they are used in this research so as to control the deflection of long girder bridges,rather than increasing their heights.In this study,theoretical relations are developed to calculate the increase in pre-tensioning force of V-shaped steel cables under external loading as well as the deflection of steel girder bridges with V-shaped cables and different support conditions.To verify the theoretical relations,the steel girder bridge is modeled in the finite element ABAQUS software with different support conditions without cable and with V-shaped cables.The obtained results show that the theoretical relations can appropriately predict the deflection of girder bridge with V-shaped cables and different support conditions.In this study,the effects of the distance from support on the deflection of mid span are studied in both simply supported and fixed supported girder bridge so as to obtain the appropriate distance from support causing the minimum deflection.

Explosion resistance performance of reinforced concrete box girder coated with polyurea:Model test and numerical simulation

To study the anti-explosion protection effect of polyurea coating on reinforced concrete box girder,two segmental girder specimens were made at a scale of 1:3,numbered as G(without polyurea coating)and PCG(with polyurea coating).The failure characteristics and dynamic responses of the specimens were compared through conducting explosion tests.The reliability of the numerical simulation using LS-DYNA software was verified by the test results.The effects of different scaled distances,reinforcement ratios,concrete strengths,coating thicknesses and ranges of polyurea were studied.The results show that the polyurea coating can effectively enhance the anti-explosion performance of the girder.The top plate of middle chamber in specimen G forms an elliptical penetrating hole,while that in specimen PCG only shows a very slight local dent.The peak vertical displacement and residual displacement of PCG decrease by 74.8% and 73.7%,respectively,compared with those of specimen G.For the TNT explosion with small equivalent,the polyurea coating has a more significant protective effect on reducing the size of fracture.With the increase of TNT equivalent,the protective effect of polyurea on reducing girder displacement becomes more significant.The optimal reinforcement ratio,concrete strength,thickness and range of polyurea coating were also drawn.

Fatigue Crack Propagation Law of Corroded Steel Box Girders in Long Span Bridges

In order to investigate the fatigue performance of orthotropic anisotropic steel bridge decks,this study realizes the simulation of the welding process through elastic-plastic finite element theory,thermal-structural sequential coupling,and the birth-death element method.The simulated welding residual stresses are introduced into the multiscale finite element model of the bridge as the initial stress.Furthermore,the study explores the impact of residual stress on crack propagation in the fatigue-vulnerable components of the corroded steel box girder.The results indicate that fatigue cracks at the weld toe of the top deck,the weld root of the top deck,and the opening of the transverse diaphragm will not propagate under the action of a standard vehicle load.However,the inclusion of residual stress leads to the propagation of these cracks.When considering residual stress,the fatigue crack propagation paths at the weld toe of the transverse diaphragm and the U-rib weld toe align with those observed in actual bridges.In the absence of residual stress,the cracks at the toe of the transverse diaphragm with a 15%mass loss rate are categorized as type I cracks.Conversely,when residual stress is considered,these cracks become I-II composite cracks.Residual stress significantly alters the cumulative energy release rate of the three fracturemodes.Therefore,incorporating the influence of residual stress is essential when assessing the fatigue performance of corroded steel box girders in long-span bridges.

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.

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.

落石撞击钢筋混凝土箱梁数值仿真与损伤分析

为研究落石撞击对钢筋混凝土箱梁的影响,通过ANSYS/LS-DYNA有限元软件对落石撞击某匝道桥箱梁的过程进行数值模拟,计算竖直方向的落石撞击力,分析桥面破损情况和箱梁开裂形态,并与现场检测结果进行对比。结果表明:落石与箱梁发生了5次撞击,产生了多个撞击力峰值,桥面出现5处凹坑;落石撞击力类似三角形脉冲荷载,瞬时峰值大,持续时间短;首次撞击时落石撞击力最大,瞬时峰值达到10705 kN,基于瑞士公式和日本道路公团公式计算的最大落石撞击力比模拟值小,将其直接用于落石-箱梁碰撞计算是偏不安全的;有限元计算得到的桥面凹坑分布和箱梁开裂破损情况与事故测量结果吻合较好,再现了落石撞击钢筋混凝土箱梁的过程;落石撞击箱梁所造成病害主要是碰撞接触区域的局部损伤,首次撞击时病害最严重,桥面破损范围大,箱梁翼缘板上表面混凝土开裂并向下延伸至翼缘与腹板交界处。

考虑腐蚀效应的锚箱式索梁锚固结构疲劳性能分析

锚箱式索梁锚固结构作为大跨斜拉桥常用的锚固形式之一,其结构复杂、焊缝众多,在车辆、风等疲劳荷载作用下易于发生疲劳破坏。同时,锚箱内部形成的盐雾腐蚀环境会进一步加速锚固区疲劳性能的劣化。为研究腐蚀效应对锚箱式索梁锚固结构疲劳性能的影响,该文采用能反映腐蚀电化学机理的元胞自动机模型获得了锚固区典型构件的表面点蚀坑模型,并以润扬长江北汊斜拉桥为工程背景建立了考虑腐蚀表面粗糙度的大跨斜拉桥的有限元模型。基于现场实测的车辆数据建立了疲劳车辆模型,考察了在疲劳车辆模型作用下典型的锚箱构件腐蚀对索梁锚固结构疲劳性能的影响。通过采用可反映电化学本质的元胞自动机模型代替了工程上传统的均匀折减厚度的方式来考虑腐蚀效应,可充分考虑表面粗糙度和点蚀坑底部的应力集中对腐蚀构件性能劣化的影响。面向大跨斜拉桥整体结构进行受力分析可确保锚固区部位应力分布的准确性。该研究方法充分考虑了腐蚀的电化学效应和实际的通行车辆荷载对索梁锚固区力学性能的影响。研究结果表明:与未考虑腐蚀效应相比,锚箱底板、上腹板和下腹板构件分别在10%的质量损失率下,锚箱式索梁锚固结构的疲劳寿命分别降低了21.18%、26.99%和6.3%。因此,腐蚀效应会大幅降低锚箱式锚固结构的疲劳寿命,需充分予以关注。

基于车桥耦合振动的双层钢桁梁斜拉桥行车舒适度分析

探究车辆在双层钢桁梁斜拉桥的行车舒适性,为优化双层桥梁结构设计理论提供依据。以车桥耦合振动理论为基础,利用ANSYS分析软件进行数值模拟,通过求解车体的振动加速度,并根据《机械振动和冲击—评估人体暴露于全身振动的情况》(ISO2631-1)中均方根乘值法对乘车舒适性进行评价,探究了单(双)层加载、车速、车载质量、桥面不平顺度、车辆间距、车辆数目等因素对行车舒适性的影响。相较于单层通车,上下层同时通车时车体的振动强度略微降低;当车载质量越小或车速越大时,车体的加速度均方根值会逐渐增大;路面对车体振动强度影响较大,当路面等级处于较差的D级和E级时,车体振动强度会成倍增加。双层同时加载时,车辆的行车舒适性略优于单层通车;保持适当的车速或增大车载质量可以提高司乘人员的行车舒适性;行车舒适性对于路面等级较为敏感,当路面等级较差时,车内司乘人员受其影响无法长时间乘车。

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.

THEORETICAL ANALYSIS AND EXPERIMENTAL RESEARCH FOR ULTIMATE LOAD-CARRYING CAPACITY OF WEB PLATES OF Ⅰ-SECTION PLATE GIRDERS

The post buckling strength of web plate of I section plate girders is considered to resist the shear force in many other countries code for design of steel structures,while it has not been considered in the Chinese code GB J17-88.For the code revising,some important conclusions have been drawn through the theoretical analysis and experimental research of the post buckling strength of web plate of I section plate girders.

Application of LRB isolation technology in continuous girder bridges

This paper summarizes the superiority of lead-rubber beating （LRB） continuous girder bridges. The research method for isolation performance is discussed when pile-soil interaction is considered. By the finite element method and self-compiling program, a systematic study of the reliability of LRB continuous girder bridges is given by the use of different indicators, including the riding comfort of the LRB system, the pounding and dynamic stability when the LRB system is subjected to seismic excitations, and the reliability of the LRB system when subjected to other common horizontal loads. The results show that the LRB system has obvious advantages over the traditional continuous girder structure. The LRB isolation effect remains good even when pile-soil interaction is considered; the vertical rigidity of the LRB guarantees desirable riding comfort. The LRB demonstrates good reliability when subjected to the effects of braking, wind loads and temperature. However, it is also pointed out that the pounding of the LRB system subjected to earthquakes must be avoided, and the dynamic stability may be reduced when the LRB system has higher piers and generates a larger displacement in a strong earthquake. Useful advice and guidance are proposed for engineering application.

A Method in Mixed Frequency-time domain for Fatigue Life Estimation of Steel Girders of Cable-stayed Bridges Due to Buffeting

发展了斜拉桥钢主梁抖振疲劳寿命的混合时－频域方法．在本方法中，首先建立了桥面处的风速风向概率密度函数，导出的应力谱因其包括背景分量而不再是窄带谱．据应力谱模拟出了疲劳应力的时间历程，并用雨流计数法统计了其幅值特性．基于修正的Ｍｉｎｅｒ定理导出了考虑风速风向作用的桥梁主梁抖振疲劳寿命的估算公式，并用此分析了杨浦大桥钢主梁的抖振疲劳寿命．结果表明，风向对抖振疲劳寿命有很大影响；杨浦大桥主梁的疲劳寿命远大于设计寿命．

考虑风-温耦合的钢箱梁外形对温度效应影响研究

为了准确分析钢箱梁外形对截面温度特性的影响规律,提出了一种考虑钢箱梁周围局部风场与温度场相互作用的有限元分析方法,采用折减系数k来建立钢箱梁周围热边界层高度处风速U_(a)与远处气象站实测风速U的对应关系,对比分析了是否考虑风-温耦合对钢箱梁截面温度分布的影响,探讨了不同风嘴形式、截面宽高比、不同栏杆形式以及铺装厚度对钢箱梁截面温度分布的影响规律。研究表明:钢箱梁周围热边界层厚度处的风速U_(a)呈不均匀分布,且与远处风速U呈线性正相关;不考虑风-温耦合会明显低估钢箱梁顶板表面温度;钢箱梁截面的风嘴、截面宽高比、栏杆参数以及铺装厚度均会影响钢箱梁横截面的温度分布,改变截面的温差,因此,在桥梁的设计中,钢箱梁外形对截面温度分布的影响不可忽视。

基于激光-位置传感器的简支梁桥挠度测量方法研究

挠度变形监测是桥梁健康监测的重要组成部分,该文提出了一种基于激光-位置传感器(position sensitive detectors,PSD)的简支梁桥高精度挠度测量系统。该系统采用激光反射偏转位移放大简支梁桥挠度,实现微米级精度的桥梁挠度静、动态监测。介绍了该系统的组成及工作原理,通过激光反射偏转原理可以将桥梁跨中挠度放大7倍以上,实现高精度挠度测量;通过理论推导与误差分析,讨论了激光发射接收器与反射器放置位置对挠度放大倍率的影响;通过试验验证了该体系的测量效果。该体系可在毫米级量程内,准确测量高于1μm的简支梁桥跨中挠度,并且可以对挠度进行动态测量,识别桥梁的自振周期等动力参数。该文提出的激光-PSD测量体系具有精度高、响应速度快、价格低、易于开展长期动态监测的特点。以期为中小跨径简支梁桥的挠度健康监测提供参考。

基于Python的ABAQUS华伦形钢桁梁多尺度模型二次开发

华伦形钢桁梁是目前大跨度铁路悬索桥应用最多的加劲梁形式,但由于结构形式复杂且桥梁跨度不断增加,导致建模过程繁琐。为提高多尺度模型前处理效率,基于Python语言开发了华伦形钢桁梁与桥面板快速建模插件,通过内核执行代码与ABAQUS GUI图形界面交互实现了钢桁梁节段的参数化建模。以我国西南峡谷地区在建SQ铁路悬索桥为例,建立了全桥的多尺度有限元模型,对典型钢梁节段吊装过程进行了抗风验算,并与MIDAS、ANSYS两类有限元软件的计算结果进行了对比,风致位移响应在不同吊装高度的趋势基本一致且误差较小。研究结果表明:所开发的快速建模插件各预设功能均可正常实现,在确保计算精度的同时极大地提高了复杂钢桁梁结构的建模效率。

基于点云配准的钢箱梁数字化拼装方法

基于全站仪检测结果修正钢箱梁模型并生成对应三维点云模型,利用RANSAC聚类算法,实现钢箱梁的拼接控制截面点云数据提取,并通过利用边缘准则(Angle Criterion)算法实现截面点云的边缘提取。结合拼接控制点集的快速四点一致配准(4PCS)和快速全局配准(FGR)算法,完成钢箱梁拼接的配准拼装。结合实验室试验,通过拼装具有典型钢箱梁特征的钢结构试件,验证了本文提出钢箱梁智能化虚拟预拼装方法的精度和可行性。通过对比实体预拼装与虚拟预拼装在拼装效率和检测结果上的差异,分析了基于三维点云的装配式钢箱梁虚拟预拼装方法的诸多优势。

带悬臂板单箱双室薄壁箱梁畸变效应分析

为研究带悬臂板单箱双室薄壁箱梁的畸变效应,基于板梁框架法建立了畸变控制微分方程,给出竖向偏心集中荷载作用下该方程的初参数解,同时还导出了带悬臂板单箱双室截面箱梁畸变框架惯性矩的具体解析式.利用解析理论对悬臂梁和简支梁算例进行分析,研究结果表明:解析解与已有文献和有限元计算结果均吻合良好,验证了解析理论的正确性;通过参数分析可知,中腹板厚度越大,双室箱梁的抗畸变变形能力越强,中腹板厚度的变化对边腹板横向弯矩的影响很小,但中腹板的横向弯矩随其板厚的增大而增大,当中腹板厚度与边腹板厚度相等时,中腹板的横向弯矩可近似等于边腹板横向弯矩的2倍.

泥石流中细粒石直径对小箱梁桥桥墩冲击力影响

我国部分地区经常遭受泥石流影响,桥梁经常会倒塌,桥梁受到泥石流冲击的过程中其受到的冲击力有很大的不确定性。为研究小箱梁桥上部结构在泥石流冲击下的动力学影响,本文基于欧拉-拉格朗日流固耦合理论,建立了泥石流浆体、粒状泥石流、小箱梁桥梁有限元模型。以广东罗定市罗镜桥为研究对象,分析泥石流冲击下桥梁。分析结果显示:泥石流浆液中粒状石的直径对桥墩的冲击力具有显著影响。

基于气象参数的钢箱梁竖向温度梯度模式

【目标】基于气象参数,利用统计分析和数值模拟相结合的方法,确定钢箱梁在日照环境下的温度梯度模式,以解决传统实桥温度试验方法工作量大、成本高的问题。【方法】以浙江省杭州江东大桥为例,根据热传导原理,借助有限元软件,建立了包含铺装层的钢箱梁二维数值模型,并将模型计算结果与实桥获取的少量温度测量数据进行对比,以验证模型的准确性和可靠性。【数据】基于杭州地区2014年至2016年夏季晴天及多云天的气象数据,借助有限元软件计算得到江东大桥带铺装层钢箱梁的日最大竖向正温差样本数据,并对样本数据进行统计分析,最终得到钢箱梁具有50 a重现期的竖向正温差标准值。【结果】温度计算值与实测值吻合较好,两者最大差值不超过1.5℃;江东大桥钢箱梁夏季晴天及多云天的日最大竖向正温差服从广义极值分布;江东大桥带铺装层钢箱梁竖向正温差标准值为16.82℃,该值小于按照相关桥梁设计规范计算得到的取值。【应用】不同地区气象条件差异使得规范统一的温度梯度模式无法完全涵盖中国所有区域,本研究方法为根据当地气象条件,得到适用于该地区钢箱梁的温度梯度模式提供了参考。

SIMPLIFIED ANALYSIS METHOD FOR ULTIMATE LOAD CAPACITY OF WEB PLATES OF BOX GIRDERS

The prosperous post buckling load capacity of web plates of box girders can be used.In this article,the post buckling behaviour of web plates of box girders under different loading conditions is theoretically analyzed and on the basis of domestic and overseas design codes of steel structures,the corresponding simplified analysis methods are put forward for the engineering design or code revision.It is proved that the simplified methods are safe,efficient and practicable through the comparison between several results.