Dynamic Response Impact of Vehicle Braking on Simply Supported Beam Bridges with Corrugated Steel Webs Based on Vehicle-Bridge Coupled Vibration Analysis

A novel approach for analyzing coupled vibrations between vehicles and bridges is presented,taking into account spatiotemporal effects and mechanical phenomena resulting fromvehicle braking.Efficient modeling and solution of bridge vibrations induced by vehicle deceleration are realized using this method.The method’s validity and reliability are substantiated through numerical examples.A simply supported beam bridge with a corrugated steel web is taken as an example and the effects of parameters such as the initial vehicle speed,braking acceleration,braking location,and road surface roughness on the mid-span displacement and impact factor of the bridge are analyzed.The results show that vehicle braking significantly amplifies mid-span displacement and impact factor responses in comparison to uniform vehicular motion across the bridge.Notably,the influence of wheelto-bridge friction forces is of particular significance and cannot be overlooked.When the vehicle initiates braking near the middle of the span,both the mid-span displacement and impact factor of the bridge exhibit substantial increases,further escalating with higher braking acceleration.Under favorable road surface conditions,the midspan displacement and the impact factor during vehicle braking may exceed the design values stipulated by codes.It is important to note that road surface roughness exerts a more pronounced effect on the impact factor of the bridge in comparison to the effects of vehicle braking.

Experimental and Numerical Investigation on the Aerodynamic Characteristics of High-Speed Pantographs with Supporting Beam Wind Deflectors

Aiming to mitigate the aerodynamic lift force imbalance between pantograph strips,which exacerbates wear and affects the current collection performance of the pantograph-catenary system,a study has been conducted to support the beam deflector optimization using a combination of experimental measurements and computational fluid dynamics(CFD)simulations.The results demonstrate that the size,position,and installation orientation of the wind deflectors significantly influence the amount of force compensation.They also indicate that the front strip deflectors should be installed downwards and the rear strip deflectors upwards,thereby forming a“π”shape.Moreover,the lift force compensation provided by the wind deflectors increases with the size of the deflector.Alternative wind compensation strategies,such as control circuits,are also discussed,putting emphasis on the pros and cons of various pantograph types and wind compensation approaches.

Effect of temperature difference load of 32 m simply supported box beam bridge on track vertical irregularity

In order to study the effect of temperature difference load （TDL） along the vertical direction of a simply supported beam bridge section on the vertical irregularity, a rail-bridge-piers calculation model was established. Taking 32 m simply supported box beam bridge which is widely used in the construction of pas- senger dedicated line in China as an example, influences of the temperature variation between the bottom and top of the bridge, temperature curve index, type of temperature gradient, and beam height on track vertical irregularity were analyzed with the model. The results show that TDL has more effects on long wave track irregularity than on short one, and the wavelength mainly affected is approxi- mately equal to the beam span. The amplitude of irregu- larity caused by TDL is largely affected by the temperature variation, temperature curve index, and type of temperature gradient, so it is necessary to monitor the temperaturedistribution of bridges in different regions to provide accurate calculation parameters. In order to avoid the irregularity exceeding the limit values, the height of 32, 48, and 64 m simply supported box beam bridges must not be less than 2.15, 3.2, and 4.05 m, respectively.

ANALYTICAL SOLUTION OF A SIMPLY SUPPORTED PIEZOELECTRIC BEAM SUBJECTED TO A UNIFORMLY DISTRIBUTED LOADING

Using the inverse method, the analytical solution of a simply supported piezoelectric beam subjected to a uniformly distributed loading has been studied.First,the polynomials of stress function and induction function are given.Then, considering the gradient properties of the elastic parameter and the potential funciton as well as the piezoelectric parameter,the analytical solution of a simply supported beam subjected to a uniformly distributed loading is obtained and discussed.

STABILITY AND LOCAL BIFURCATION IN A SIMPLY-SUPPORTED BEAM CARRYING A MOVING MASS

The stability and local bifurcation of a simply-supported flexible beam （Bernoulli- Euler type） carrying a moving mass and subjected to harmonic axial excitation are investigated. In the theoretical analysis, the partial differential equation of motion with the fifth-order nonlinear term is solved using the method of multiple scales （a perturbation technique）. The stability and local bifurcation of the beam are analyzed for 1/2 sub harmonic resonance. The results show that some of the parameters, especially the velocity of moving mass and external excitation, affect the local bifurcation significantly. Therefore, these parameters play important roles in the system stability.

Buckling of stepped beams with elastic supports

The tangent stiffness matrix of Timoshenko beam element is applied in the buckling of multi-step beams under several concentrated axial forces with elastic supports. From the governing differential equation of lateral deflection including second-order effects,the relationship of force versus displacement is established. In the formulation of finite element method (FEM),the stiffness matrix developed has the same accuracy with the solution of exact differential equations. The proposed tangent stiffness matrix will degenerate into the Bernoulli-Euler beam without the effects of shear deformation. The critical buckling force can be determined from the determinant element assemblage by FEM. The equivalent stiffness matrix constructed by the topmost deflection and slope is established by static condensation method,and then a recurrence formula is proposed. The validity and efficiency of the proposed method are shown by solving various numerical examples found in the literature.

Finite Element Modeling of Stability of Beam-Column Supports for Field Fabricated Spherical Storage Pressure Vessels

Spherical pressure vessels in large sizes are generally supported on legs or columns evenly spaced around the circumference. The legs are attached at or near the equator of the sphere. This research work focussed on flexural-torsional buckling of beam-column supports of field fabricated spherical pressure vessels using finite element analysis. Flexuraltorsional buckling is an important limit state that must be considered in structural steel design and it occurs when a structural member experiences significant out-of-plane bending and twisting. This research has therefore considered the total potential energy equation for the flexural-torsional buckling of a beam-column element. The energy equation was formulated by summing the strain energy and the potential energy of the external loads. The finite element method was applied in conjunction with the energy method to analyze the flexural-torsional buckling of beam-column supports. To apply the finite element method, the displacement functions are assumed to be cubic polynomials, and the shape functions used to derive the element stiffness and element geometric stiffness matrices. The element stiffness and geometric stiffness matrices were assembled to obtain the global stiffness matrices of the structure. The final finite element equation obtained was in the form of an eigenvalue problem. The flexural-torsional buckling loads of the structure were determined by solving for the eigenvalue of the equation. The resulting eigenvalue equation from the finite element analysis was coded using FORTRAN 90 programming language to aid in the analysis process. To validate FORTRAN 90 coding developed for the finite element analysis and the methodology, the results given by the software were compared to existing solutions and showed no significant difference P > 0.05.

FE Dynamic Analysis Using Moving Support Element on Multi-Span Beams Subjected to Support Motions

In the present study, finite element dynamic analysis or time history analysis of two-span beams subjected to asynchronous multi-support motions is carried out by using the moving support finite element. The elemental equation of the element is based on total displacements and is derived under the concept of the quasi-static displacement decomposition. The use of moving support element shows that the element is very simple and convenient to represent continuous beam moving, deforming and vibrating simultaneously due to support motions. The comparison between the numerical results and analytical solutions indicates that the FE result agrees with the analytical solution.

邻近既有桥梁的路基结构设计与研究

某铁路在既有铁路路桥衔接段出岔,为避免新建铁路道岔上桥,以路基结构与既有桥梁相邻建造,从而出现横向结构尺寸和变形受限的问题。设计采用一种能够承受竖向和横向荷载,且能有效控制结构变形的桩基托梁冠梁挡墙路基结构,研究解决新建路基与既有桥梁相衔接的问题。

基于煤矸振动特性的放顶煤支架传感器优化布置策略研究

针对放顶煤煤矸智能识别研究,为提供完整且有效的煤矸振动信号采集方案,提出了一种基于煤矸振动特性的放顶煤液压支架尾梁传感器优化布置策略。首先,对尾梁模型进行模态分析,提取振型矩阵,利用有效独立法初选测点;其次,获取尾梁试验台相应初选测点的落煤和落矸振动信号,进行特征提取;然后,对所提取特征进行t分布式随机邻域嵌入(t-distributed Stochastic Neighbor Embedding,t-SNE)降维可视化,筛选出5个对落煤和落矸信号区分敏感的特征,并以此作为目标特征;最后,经核密度估计法估算目标特征的概率密度函数,利用K-L(Kullback-Leibler)散度评估各测点组合信号与完整信号的近似性和煤矸特征的差异性,构建煤矸振动信号评价指标,结合Fisher信息矩阵准则,形成综合评价指标,确定尾梁的传感器布置最优方案。结果表明,该方法在满足模态可观测性的基础上不仅减少了传感器数量,还使得所测振动信号具有更好的煤矸差异性和信息完整性。

钢-混工字组合简支梁桥静动载试验及冲击系数研究

近年来钢-混工字组合简支梁桥因其能充分发挥不同材料特性而被广泛应用,但评价动力特性的重要指标———冲击系数的计算尚缺少相关试验积累和理论研究。以一座新建钢-混工字组合简支梁桥为依托,详细介绍了该桥的静载试验以及脉动、跑车、跳车等动载试验过程,探讨了此类结构冲击系数的试验计算值,并与各规范计算值进行了对比。结果表明:该桥整体刚度好,承载安全度高;冲击系数的试验计算值多数大于各规范计算值,采用规范设计相对不安全;跨中冲击系数试验计算平均值等于我国规范《公路桥涵设计通用规范》(JTG D60—2015)计算值,但也出现了试验值大于规范值的情况。因此,今后进行高速公路30m跨径钢-混工字组合简支梁桥设计时,应对桥梁跨中冲击系数适当放大。

煤矿液压支架顶梁的耐久性分析及结构优化

在概述液压支架及顶梁结构的基础上,利用SolidWorks和ANSYS软件构建了液压支架的有限元模型,通过耐久性分析发现顶梁在高位姿态下的最小寿命为2554次,低位姿态时的寿命为2151次。选择顶梁的15个关键结构为优化对象,以耐久性为优化目标,利用ANSYS开展结构优化改进工作,使得高位和低位姿态下的耐久性分别提升了23.31%和28.07%。将新的顶梁结构应用到ZY9000/45/22D型液压支架中,经过一段时间的现场应用其发现达到了预期效果,结构的耐久性预计能提升20%左右。

煤矿液压支架顶梁结构优化设计

液压支架是采煤工作面支护设备,也是保证煤炭安全生产的关键设备,其结构质量较大,会对自身的承载能力产生一定影响。为优化液压支架的顶梁结构,文章采用MATLAB软件进行优化处理,并验证其优化结果的合理性及可行性。此次优化设计在确保液压支架满足工作需求的前提下,最大限度地减轻了顶梁的质量,研究内容可为液压支架的优化设计和工程应用提供参考。

钢管柱支架在运梁过站结构加固中的应用

随着轨道交通的快速发展,高架桥梁预制梁板的运输和架设逐步得到广泛应用,在预制梁架设运输过程中,主体结构的承载能力对运输安全性及结构自身稳定性而言至关重要。为此,在运输前往往对主体结构进行数值模拟分析,评估其承受运梁荷载的安全性,并据此决定是否采取加固措施。文章对主体结构加固前后的力学特性进行模拟分析,旨在验证加固方案的有效性与可行性。

煤层群采空区下回采巷道锚网索梁支护技术研究

为实现采空区下回采巷道围岩的有效控制,以9303运输巷为研究对象,提出采用锚网索梁方式支护围岩,并对工程应用进行了分析。分析了7#煤层回采后底板的破坏范围,发现9303运输巷处于底板破坏范围内,是导致运输巷掘进期间围岩破碎的主要原因。因此,采用了高预紧力锚杆、短锚索对围岩进行支护,并配合W型钢带、金属网、钢梁及钢带托盘等,为围岩提供了较大的支护作用力。同时,还通过强化顶板7#煤层采空区的积水疏排能力,降低了顶板淋水对支护的影响。应用结果表明,9303运输巷围岩控制效果显著,采用的支护方案可有效控制顶板离层和围岩变形情况,确保了9303运输巷后续的使用需求。

大悬臂现浇盖梁支架体系受力有限元分析

桥梁工程中,盖梁通常采用现浇施工,因此合理设计支架对保障施工安全、提高施工质量具有重要意义。本文以太浏公路大桥为研究背景,对现浇大悬臂盖梁支架体系进行设计,采用有限元计算软件MIDAS Civil建立支架体系的三维有限元分析模型,对支架的受力、变形和稳定性进行计算分析。结果表明,考虑不同荷载组合条件下,支架各部分的受力、变形以及支架体系稳定性均满足相关设计要求,表明该支架体系可满足桥梁施工的相关需求。此外,研究还表明有限元数值计算可有效应用于相关工程的设计和施工中。

不挖掘覆土下地下室顶板梁支座正截面增大截面加固法研究

为降低地下室顶板梁支座正截面承载力加固的施工难度、造价、工期和渗水风险,本研究分析了不涉及梁顶施工的三种增大梁宽的增大截面加固形式,分析发现:三种加固形式均对梁支座正截面承载力有较大提升,提升幅度在梁底增设纵筋后考虑塑性内力重分布时最大,板底增设负筋方式相较于不增设钢筋方式有一定承载力提升。

斜撑贝雷梁组合支架研发及其在跨浅埋地铁现浇箱梁中的应用

高架结构在既有交通线路上方进行现浇梁施工时,将对线路的正常运行产生扰动,软土地质的存在将会进一步加剧此类影响。为解决类似技术难题,文章结合在建的上海松江高铁南站简支箱梁施工工程实例,设计一种可跨越既有交通线路直接施工的新型支架体系——斜向支撑体系与贝雷梁组合支架。结合支架部件组成及实际施工过程出现的荷载工况,通过MIDAS Civil有限元分析软件建模分析支架的应力及位移,确保支架在施工过程中的受力安全、结构稳定。结果表明,设计的斜撑贝雷梁支架结构,能在不影响既有线路运行的情况下进行施工,支架结构强度、刚度及稳定性均能满足规范要求,可为同类型桥梁的支架设计、计算提供可行性思路。

黄陵一号煤矿“110工法”工程实践应用

黄陵一号煤矿通过1006综采工作面300 m沿空留巷工业试验、1009综采工作面实施“110工法”回采期间,沿空留巷段顶板下沉、底鼓严重等现象凸显,顶板支护成为井工煤矿实施“110工法”的一项技术攻关。该矿通过提前对沿空留巷段顶板进行锚梁补强支护,尾巷支护方式由“U29挡矸柱+单体支护”创新性升级为“U29挡矸柱+单体+垛式支架双重支护”,辅运部分端头支架优化调整为特殊支架支护,通过一个工作面的实践、应用,有效控制了沿空留巷段受采动影响顶板压力过大、底鼓严重等造成的影响,成功实现留巷的完整,保证了1006、1009这2个工作面的顺利回采,为后续“N00工法”的进一步实施积累了丰富的作业经验,为“110-N00工法”开采新技术的成功实施应用提供、融合了黄陵经验。

Ⅷ度区连续钢混组合梁桥抗震支座选型

以(42+60+42)m跨径的变截面钢混组合梁为例,采用MIDAS Civil有限元软件对桥梁进行时程分析,在桥梁设置有效防落梁设施的前提条件下,对桥梁边墩的抗震支座进行比选,涉及板式橡胶支座、滑板支座、高阻尼支座3种类型支座,以墩柱内力、梁端位移、工程费为评判标准,得到最合适的边墩支座,为同类桥梁的合理抗震设计提供参考。