Analysis of free vibration characteristic of steel-concrete composite box-girder considering shear lag and slip

Based on Hamilton principle,the governing differential equations and the corresponding boundary conditions of steel-concrete composite box girder with consideration of the shear lag effect meeting self equilibrated stress,shear deformation,slip,as well as rotational inertia were induced.Therefore,natural frequency equations were obtained for the boundary types,such as simple support,cantilever,continuous girder and fixed support at two ends.The ANSYS finite element solutions were compared with the analytical solutions by calculation examples and the validity of the proposed approach was verified,which also shows the correctness of longitudinal warping displacement functions.Some meaningful conclusions for engineering design were obtained.The decrease extent of each order natural frequency of the steel-concrete composite box-girder is great under action of the shear lag effect.The shear-lag effect of steel-concrete composite box girder increases when frequency order rises,and increases while span-width ratio decreases.The proposed approach provides theoretical basis for further research of free vibration characteristics of steel-concrete composite box-girder.

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 .

Free Vibration Analysis of RC Box-Girder Bridges Using FEM

The free vibration analysis of simply supported box-girder bridges is carried out using the finite element method.The fundamental frequency is determined in straight,skew,curved and skew-curved box-girder bridges.It is important to analyse the combined effect of skewness and curvature because skew-curved box-girder bridge behaviour cannot be predicted by simply adding the individual effects of skewness and curvature.At first,an existing model is considered to validate the present approach.A convergence study is carried out to decide the mesh size in the finite element method.An exhaustive parametric study is conducted to determine the fundamental frequency of box-girder bridges with varying skew angle,curve angle,span,span-depth ratio and cell number.The skew angle is varied from 0°to 60°,curve angle is varied from 0°to 60°,span is changed from 25 to 50 m,span-depth ratio is varied from 10 to 16,and single cell&double cell are used in the present study.A total of 420 bridge models are used for parametric study in the investigation.Mode shapes of the skew-curved bridge are also presented.The fundamental frequency of the skew-curved box-girder bridge is found to be more than the straight bridge,so,the skew-curved box-girder bridge is preferable.The present study may be useful in the design of box-girder bridges.

Simulation of Temperature Field in Original Segment of Concrete Box-Girder Bridge

Temperature field and its variation with time are necessary for analyzing the thermo-mechanical performance of mass concrete structures at their early ages. This paper carries out a temperature field simulation analysis for an original segment of a real box girder bridge with the finite element software ANSYS. Two representative exothermic rate models are used to describe the heat- releasing process caused by the cement hydration in concrete. The exothermic rate model that conforms to reality more closely is recognized by comparing the simulation results with the data gathered from the optical fiber temperature sensors pre-embedded in the original segment. The air temperature and wind velocity that constitute thermal boundary conditions are determined in the light of the local meteorological department and correlative research achievements of recent years. Moreover, the consideration for the steel formwork acting as a barrier to heat loss is also proved to be beneficial to improve the simulation effect.

Design and Research of Class 900 t Railway Box-girder Bridge Erecting Machine

In this article, the current railway box girder bridge erecting machines at home and abroad are briefly introduced and analyzed, the research & design situation of class 900t railway box girder bridge erecting machines is described, and also the principle for determining the overall plan and a series of issues much concerning the design of key components of class 900t railway box girder bridge erecting machines are described.

Noise reduction mechanism of high-speed railway box-girder bridges installed with MTMDs on top plate

The issue of low-frequency structural noise radiated from high-speed railway(HSR) box-girder bridges(BGBs) is a significant challenge worldwide. Although it is known that vibrations in BGBs caused by moving trains can be reduced by installing multiple tuned mass dampers(MTMDs) on the top plate, there is limited research on the noise reduction achieved by this method. This study aims to investigate the noise reduction mechanism of BGBs installed with MTMDs on the top plate. A sound radiation prediction model for the BGB installed with MTMDs is developed, based on the vehicle–track–bridge coupled dynamics and acoustics boundary element method. After being verified by field tested results, the prediction model is employed to study the reduction of vibration and noise of BGBs caused by the MTMDs. It is found that installing MTMDs on top plate can significantly affect the vibration distribution and sound radiation law of BGBs. However, its impact on the sound radiation caused by vibrations dominated by the global modes of BGBs is minimal. The noise reduction achieved by MTMDs is mainly through changing the acoustic radiation contributions of each plate of the bridge. In the lower frequency range, the noise reduction of BGB caused by MTMDs can be more effective if the installation of MTMDs can modify the vibration frequency and distribution of the BGB to avoid the influence of small vibrations and disperse the sound radiation from each plate.

Field test on temperature field and thermal stress for prestressed concrete box-girder bridge

A field test was conducted to investigate the distribution of temperature field and the variation of thermal stress for a prestressed concrete(PC)box-girder bridge.The change of hydration heat temperature consists of four periods:temperature rising period,constant temperature period,rapid temperature fall period and stow temperature fall period.The peak value of hydration heat temperature increases with the increasing casting temperature of concrete;the relation between them is approximately linear.According to field tests,the thermal stress incurred by hydration heat may induce temperature cracks on the PC box-girder.Furthermore,the nonlinear distribution of temperature gradient and the fluctuation of thermal stress induced by exposure to sunlight were also obtained based on continuous in-situ monitoring.Such results show that the prevailing Chinese Code(2004)is insufficient since it does not take into account the temperature gradient of the bottom slab.Finally,some preventive measures against temperature cracks were proposed based on related studies.The conclusions can provide valuable reference for the design and construction of PC box-girder bridges.

南京仙新路长江大桥主桥结构设计

南京仙新路长江大桥主桥为跨径1760 m的单跨钢箱梁悬索桥,主缆垂跨比1/9,边跨跨径580 m,边中跨比0.33。该桥上、下游各设1根主缆,单根主缆由169股127∅5.4 mm镀锌铝高强钢丝索股组成,采用PPWS法施工,钢丝标准抗拉强度2100 MPa。吊索与索夹采用销接式结构,跨中设置柔性中央扣索,短吊索设置关节轴承。主索鞍采用宽鞍槽单纵肋铸焊结合构造,散索鞍采用底座式全铸结构。加劲梁采用扁平流线型封闭整体钢箱梁,总宽31.5 m,梁高4 m,顶板与U肋之间采用双面埋弧全熔透焊接。桥塔采用门形混凝土结构,总高277.3 m,其上横梁为预应力混凝土结构,外包N字造型钢结构;桥塔基础采用直径2.8 m钻孔灌注桩。南锚碇采用外径65 m圆形地下连续墙基础;北锚碇采用沉井基础,平面尺寸70 m×50 m,高50 m。对结构进行静力分析及抗风性能理论和试验研究,结果表明:结构强度、刚度均满足规范要求;在加劲梁上设置0.67 m高中央稳定板、两侧风嘴处设置1 m宽水平稳定板后,大桥的颤振、涡振等抗风性能均满足要求,且具备一定的阻尼储备。

基于贝叶斯优化支持向量回归的流线型箱梁颤振气动外形优化方法

为解决风洞试验耗时费力和计算流体动力学(CFD)计算量大的问题,提出了一套新型流线型箱梁断面颤振性能气动外形优化方法.以风嘴参数为设计变量,利用CFD获取断面三分力系数,以准定常理论估算的颤振临界风速为优化目标.根据贝叶斯优化支持向量回归构建代理模型,利用混合加点法更新模型,通过寻优算法确定最优断面.以虎门大桥为例,得到桥梁在可行域内颤振性能最佳的断面方案.结果表明,风嘴升高,颤振临界风速先增后减,相对高度为0.6时整体性能较优,相对高度为0.7时可获得最优断面.底板宽增加,颤振性能显著降低,下斜腹板倾角为14°~16°时颤振性能最优.断面优化后桥梁颤振临界风速相比原始断面提升约31%.

三星堆古蜀文化遗址博物馆大型螺旋坡道结构设计与分析

三星堆古蜀文化遗址博物馆中庭的螺旋坡道采用钢箱梁结构体系,最大半径28.7m,水平投影长度118.5m。介绍了大型螺旋坡道结构体系选型和边界条件的对比过程,采用通用计算软件MIDAS Gen建立多尺度整体模型考虑螺旋坡道和主体结构的相互作用,通过静力分析和反应谱分析考察螺旋坡道在不同荷载作用下的承载能力和变形,并采用有限元软件ANSYS建立分析模型进行连续倒塌分析。结果表明,螺旋坡道采用钢箱梁结构具有较好的整体刚度,静力荷载和地震作用下坡道的应力和变形均满足规范要求,并具有较好的抗连续倒塌能力。

偏载作用下薄壁箱梁空间整体效应的综合分析

为了研究斜腹板箱梁在竖向偏心荷载作用下的受力性能,在合理构造各翘曲位移函数的基础上,用能量变分法建立全面反映竖向弯曲变形以及剪力滞、约束扭转、畸变等翘曲变形的控制微分方程,通过对既有文献中的模型梁进行计算分析,明确剪力滞、约束扭转及畸变翘曲应力在竖向弯曲应力中的占比情况,并揭示各翘曲广义内力的分布规律。结果表明:按文章解析法求得的模型梁应力理论值与实测值吻合良好,从而验证文章方法的合理性;在偏载作用下箱梁的约束扭转微分方程与畸变微分方程是相互耦联的,这在已有文献中往往被忽略;在剪力滞、约束扭转及畸变翘曲应力中,畸变翘曲应力占据主导地位,剪力滞和约束扭转翘曲应力相对较小,但仍不可忽略,在控制截面上因各种翘曲变形引起的应力放大系数达到1.362;偏心集中荷载引起的各翘曲广义内力均具有快速衰减的分布规律,剪力滞和约束扭转广义内力分布范围很小,而畸变广义内力分布范围广阔。建议在桥梁设计规范相关条文及实际箱梁桥设计中,对畸变效应给予充分重视。

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。

主跨330 m高速铁路无砟轨道混合梁斜拉桥设计

研究目的:为满足防洪及通航要求,南玉高铁百合郁江特大桥采用(36+40+64+330+64+40+36)m钢箱-混凝土混合梁斜拉桥跨越郁江。该桥为目前国内在建最大跨度的高速铁路无砟轨道钢箱-混凝土混合梁斜拉桥。本文主要基于百合郁江特大桥的设计与受力特点,通过多种评价方法,探讨在大跨度钢混斜拉桥上铺设无砟轨道适应性,为后续建造同类型无砟轨道桥梁提供理论参考。研究结论:(1)主桥采用钢箱梁与混凝土箱梁,并在钢箱梁顶板上现浇混凝土桥面板,为无砟轨道铺设创造了良好条件,并且能很好地控制后期主梁的收缩徐变变形,提高大跨桥梁对无砟轨道适应性;(2)百合郁江特大桥具有良好的静力性能和刚度条件;(3)主桥将轨道结构高度由725 mm调整为775 mm,分别为底座板和道床板预留了20 mm和30 mm的纠偏量,为后续无砟轨道分级施工和纠偏提供了基础,能更好地将施工与测量误差逐级消除,提高无砟轨道铺设精度;(4)采用多种无砟轨道适应性评价方法对主桥无砟轨道线形进行分析,结论均满足设计要求;(5)该桥的成功实施,为国内外高速铁路无砟轨道桥梁建设提供了宝贵的经验,将进一步推动高速铁路无砟轨道大跨度桥梁的技术发展。

考虑弯曲空间效应影响的箱梁强迫振动分析

选取附加挠度为剪力滞广义位移,箱梁体系总动能中计入剪力滞附加变形的影响,综合运用薄壁结构弹性理论和Hamilton原理,建立考虑弯曲空间效应影响的箱梁强迫振动控制微分方程及边界条件,并给出任意简谐荷载作用下简支和连续箱梁的强迫振动解析解。引入振动频率影响的应力和挠度放大系数,详细分析简支、连续箱梁剪切剪力滞效应在初等梁结果中的占比及放大系数分布规律。算例分析表明:考虑弯曲空间效应影响的箱梁截面纵向动应力与有限元结果吻合良好;振动频率越大,应力和挠度放大系数、剪切效应占比越大,剪力滞效应占比越小;同频率振动时,简支箱梁放大系数远大于两跨连续箱梁(单跨长等于简支跨长),且频率越高,差值比越大;基频内振动时,箱梁纵向应力计算可忽略剪力滞效应,挠度计算需考虑剪切变形的影响。

冲击下箱型梁弯曲失效临界载荷的评估方法研究

箱型梁作为工程应用最广泛结构之一,其结构安全裕度需得到清晰表达。箱型梁通常具有纵横加筋结构,冲击载荷下容易发生局部结构屈曲,但是箱型梁后屈曲失稳路径相对稳定,难以采用现有方法确定其失效对应的临界载荷。以简支钢质箱型梁为研究对象,首先研究了非线性有限元建模方法因素的影响,分析不同冲击载荷下箱型梁动态响应的变化规律;其次,根据不同冲击载荷工况计算结果,绘制冲击载荷与箱型梁位移曲线,提出了振幅极值准则和曲率极值准则两种新准则用于箱型梁动态失效临界载荷下限值与上限值的评估;最后,将该准则推广应用于三角形、矩形冲击载荷与落锤冲击作用下箱型梁弯曲失效的临界载荷评估,以及不同梁截面、边界条件和载荷工况下箱型梁弯曲失效临界载荷的评估。该研究结论可为冲击载荷下箱型梁结构安全评估提供基础支撑。

基于翼板横向位移模式的箱梁剪力滞效应分析

以剪翘变形状态为分析对象,综合运用广义坐标法、剪翘变形协调条件和平衡微分方程,提出箱梁的翼板横向位移模式。基于最小势能驻值原理,推导考虑翼板横向位移影响的箱梁剪力滞解析解。引入翼板横向位移对剪力滞影响的差值比参数,详细分析截面参数及梁端约束条件对剪力滞差值比的影响。算例分析表明:翼板横向位移对剪力滞有一定的削弱作用,考虑横向位移的纵向应力与有限元解、实测值吻合更好;跨宽比、高宽比越大,剪力滞差值比越小;悬臂板宽度越大,剪力滞系数差值比越小;梁端约束条件越强,剪力滞差值比分布曲线越陡峭,约束条件较强时需考虑横向位移的影响。

大跨度铁路桥附属构件对不同宽高比矩形断面涡振性能的影响

在已建成的大跨度鳊鱼洲长江大桥原设计宽高比为6.7∶1的四线铁路桥矩形箱型主梁断面的基础上,通过调整断面宽高比,设计宽高比为4∶1的二线铁路和宽高比为9∶1的六线铁路桥矩形箱梁断面。通过节段模型风洞试验,在0°,±3°和±5°风攻角的均匀来流下,对以上3种常用二线、四线和六线铁路桥矩形箱梁断面与对应相同宽高比纯矩形断面之间的涡振特性关系,以及铁路桥附属构件对不同宽高比矩形断面涡振性能的影响进行研究。结果表明:在宽高比分别为4∶1和6.7∶1的矩形断面上布置铁路桥附属构件能增大断面在负风攻角下的涡振振幅,在-5°风攻角下竖向涡振振幅增大率高达277.5%,但对正风攻角下的涡振响应起到一定的抑制作用,而在宽高比为9∶1的矩形断面布置六线铁路桥附属构件则能明显增大该断面在各风攻角下的涡振振幅,其扭转涡振振幅增大率均在48.3%以上;铁路桥附属构件对矩形断面涡振性能的降低作用随着断面宽高比的增大而提升,针对气动外形较钝的二线和四线铁路桥箱梁,可参考相似宽高比矩形断面涡振特性,并重点考察箱梁在负风攻角下的涡振响应,而针对宽高比较大的六线铁路桥箱梁,由于附属构件影响较大,参考相似宽高比矩形断面涡振特性的意义较小,均应详细研究其在各风攻角下的涡振性能。

基于多目标优化的箱梁渡槽结构设计研究

针对箱梁渡槽所受水荷载远大于同等跨径箱梁桥所受汽车荷载导致槽身纵向受力突出的问题,在渡槽结构设计中统筹考虑箱梁纵向应力储备和造价,构建了以截面尺寸、钢筋用量等6个参数为设计变量,以渡槽边缘正应力和造价为目标函数,以槽身挠度、法向应力等9个验算指标为约束条件的多目标优化模型,并基于支持向量机近似模型和NSGA2遗传算法求解多目标优化模型的Pareto最优解集,然后综合专家打分、COWA算子、博弈论综合赋权与TOPSIS法从Pareto最优解集中选出最佳方案。结果表明:与初始方案相比,最佳方案的渡槽边缘正应力储备提高了17.55%,渡槽上部结构总造价降低8.84%;与有限元分析相比,该方法在保持较高计算精度的同时节省了65.42%的计算时间成本。

考虑约束扭转二次剪力流影响的箱梁畸变效应分析

为了揭示箱梁约束扭转和畸变之间的耦联关系,研究约束扭转对箱梁畸变效应的影响,根据约束扭转二次剪力流形成的畸变荷载,建立了考虑约束扭转的箱梁畸变控制微分方程.基于乌曼斯基第二理论,提出约束扭转剪力流是基于约束扭转引起的畸变效应修正后的总扭矩布雷特剪力流,并通过Ansys有限元模型和能量法计算结果对理论公式进行了验证.数值算例结果表明:2种不同约束扭转剪力流分解方法计算所得结果完全一致;不同计算点处的约束扭转剪应力与Ansys有限元法计算结果吻合良好;扭转畸变翘曲总正应力、畸变翘曲正应力均与按能量法计算所得结果吻合良好,误差不超过10%.计入约束扭转二次剪应力的影响能够更准确地计算箱梁畸变效应.

带挑臂PK箱梁涡振性能及优化措施机理研究

为研究带挑臂PK箱梁的涡振性能及气动优化措施,通过节段模型风洞试验研究了PK箱梁在0°、±3°风攻角下的涡振性能,并测试了人行道高度、封闭挑臂底部、栏杆透风率改变、不同倾角抑流板等气动措施对PK箱梁气动稳定性的影响,研究表明:主梁在0°、+3°风攻角下出现强烈的竖向涡激共振,并出现多个竖向涡振区间,同时在高风速下主梁出现了明显的扭转涡振;抬高人行道高度能降低各攻角下主梁的竖弯涡振响应,同时高风速下的扭转涡振得到极大程度的改善;通过封闭栏杆来改变栏杆透风率的研究发现,竖向间隔封闭人行道外侧护栏能破坏涡激气动力在展向的相关性,将主梁涡振峰值响应降低至规范限值的55.8%;0.25 m宽抑流板能有效改善主梁气动稳定性,抑流板倾角变化在20°~75°之间时,其均能完全抑制主梁涡振响应;气流在迎风侧人行道护栏处发生分离,在上表面卷起形成规律的大尺度旋涡,从而造成主梁剧烈的涡激振动,抑流板明显破坏了挑臂附近旋涡的形成,无法向下游发展形成规律的大尺度旋涡,从而能有效抑制主梁涡振。