无背索斜拉桥主塔受力及抗震性能分析

为探讨主塔横梁对无背索斜拉桥结构的静动力特性影响,以某无背索斜拉桥为原型,采用三维静\,动力有限元计算方法,分析了实心横梁、大空心横梁、小空心横梁与无横梁四种主塔横梁方案的静、动力结构特性。静力计算结果表明:在最不利荷载作用下,四种对比方案中,实心横梁的拉索应力接近安全系数临界值;横梁重量越大,主梁挠度及主塔顺桥向变形值越小,且未设置横梁的方案在长期荷载作用下产生主跨侧的收缩徐变变形值。动力计算结果表明:大空心横梁方案结构横桥向刚度最大塔底轴力最大、横桥向弯矩值最大;无横梁时横桥向剪力最大,且无横梁方案使得主塔刚度较小,阵型易出现主塔横向失稳。综合考虑结构静、动力特性与施工便利性和后期维护,建议该结构采用实心主塔横梁。     

ANSYS在直流电法正演中的应用

以点电源场为例,详细叙述了直流电法正演在ANSYS上的实现过程.通过正演模型ANSYS模拟解与理论值的对比分析,验证了应用ANSYS进行直流电法正演模拟的正确性.鉴于ANSYS强大的分析功能,快速、准确的模拟以及便于操作等优点,对ANSYS在地球物理正演中的应用的研究是有重大意义的.     

带地形高频大地电磁法有限元数值模拟

随着中深度地球物理勘探的迫切需要,以美国EH-4电导率成像系统为代表的高频大地电磁法在我国地球物理勘探行业应用越来越广泛,其勘探深度在地下1000 m以浅,频率范围10 Hz～100 KHz.本文研究了带地形的高频率大地电磁法有限元高精度、快速数值模拟.首先利用广义变分原理推导出电磁场的有限元方程,编制了双线性和双二次插值有限元程序,对典型山谷和山脊地形的数值模拟结果进行了分析,得出了一些有意义的结论.     

基于ANSYS的矿井直流电场研究

矿井直流电阻率法超前探测是预测掘进工作面前方潜在灾害体的一种物探方法,该方法具有经济、快捷、方便及施工效率高等优点,但其在在理论研究方面还不是很成熟.本文利用ANSYS软件通过有限元数值模拟方法对典型的地电模型的全空间的巷道影响等问题进行了研究.结果表明:巷道空腔的存在使稳定电流场的分布发生改变,尤其在巷道迎头附近影响极为严重,但随着电极距的增大巷道影响明显减小.层状介质模型中的异常特征不仅与层状介质各层间电性、层厚有关,还与异常体的导电性、尺寸、形状以及巷道迎头的距离等因素有关.     

有限元数值模拟方法在华北地区地震地质研究中的应用进展

文中综述了近30年来有限元数值模拟方法在华北地区地震地质研究中的应用和发展情况,从华北地区地震地质数值模拟的有限元模型、有限元数值模拟所采用的实测资料以及模拟结果3方面进行了讨论,综合分析了华北地区有限元数值模拟从弹性到弹塑性、黏弹性和蠕变性,从二维线性到三维非线性,从连续变形到非连续变形,从个别资料的应用到GPS网络观测资料拟合的发展过程。简单阐述了华北地区有限元数值模拟工作的意义、存在问题和发展趋势     

地震波作用下地下管道试验的数值模拟方法

以模型试验几何尺寸建立有限元数值模拟模型,全面给出了地下管道地震动作用的三维有限元建模及分析研究的主要步骤,建立柔-柔接触面来反映管-土相互作用,利用拉格朗日乘子法求解接触效应;通过ANSYS和MATLAB的交互使用,对土体四周及底部定义的粘弹性边界实现能量辐射,减小边界效应;考虑试验模型与实际模型的比例,对原始地震波加速度时程曲线进行缩尺处理,模拟得到的管道响应规律与试验结果吻合较好,表明该数值模型是合理的。在此基础上讨论了管道在地震波作用下的位移、加速度和应力的动力响应,并提出了相关实用的工程建议,为地下管线等长线型地下结构的地震响应理论分析提供参考。     

深软场地上考虑土-结构相互作用的斜拉桥被动控制分析

结合某一工程,采用软土粘塑性动力本构模型,在合理模拟深软场地非线性基础上讨论土-结构动力相互作用对斜拉桥被动控制效果的影响.利用软件ABAQUS建立了深软场地-桩基-斜拉桥三维有限元模型,作为对比,建立了深软场地上不考虑土-结构动力相互作用的常规刚性地基模型,通过时程分析法计算斜拉桥地震反应.计算结果表明:深软场地上考虑土-结构动力相互作用后,斜拉桥被动控制效果下降;在刚性地基上取得良好减震效果的被动控制手段若照搬至柔性地基上,可能不仅减震效果不好,还会给桥梁结构增加内力负担.     

润扬斜拉桥有限元模拟及模态分析

本文主要研究润扬长江大桥北汊斜拉桥以结构健康监测和状态评估为目标的空间有限元模型建立过程中的一些基础性问题。在建模过程中,尽可能多地考虑了一些影响全桥有限元模型精度的因素:如斜拉索的几何非线性(重力垂度和初始应力),将构造正交各向异性钢箱梁桥面板用复合材料力学的方法等效为物理正交各向异性板等。然后应用所建立的有限元模型进行模态分析,最后将有限元模态计算结果与环境振动试验结果进行比较,验证了润扬斜拉桥有限元模型的有效性。由此建立的有限元模型可以为该桥的结构健康监测和状态评估提供分析的基础。     

基于电场矢量波动方程的三维可控源电磁法有限单元法数值模拟

从可控源电磁法的基本原理出发,推导了基于电场矢量波动方程的三维边值问题,利用广义变分原理,把边值问题转换为变分问题,并引入散度条件,避免了伪解的出现,使有限元计算在理论上更加完备.在准静态近似条件下,把水平电偶极子在空中和大地的远区电场闭合表达式作为有限元计算中的区域外边界条件,解决了边界条件加载的困难;把应用于地震模拟中的伪delta函数引入到可控源电磁法中的三维有限元模拟中,消除了源点的奇异性,提高了方程组的稳定性.通过对均匀大地和层状介质模型的模拟,检验了程序的正确性,并对典型的地质体模型进行了数值模拟,分析了其变化规律.     

钢框架后张抗震梁柱节点的非线性分析

推导了后张顶底角钢梁柱节点的初始刚度及极限承载力的一般公式,并利用ANSYS建立了其三维有限元模型,模拟该节点在地震荷载下的受力特征.分析表明,后张顶底梁柱节点具有与传统焊接刚性节点相近的刚度,能够充分发挥各个组成构件的性能,且残余变形较小.对比证明,角钢厚度和后张力大小是影响节点性能的主要因素.最后针对后张节点的薄弱环节提出了适合应用的改进形式.     

Nonlinear FE model updating and reconstruction of the response of an instrumented seismic isolated bridge to the 2010 Maule Chile earthquake

Nonlinear finite element (FE) modeling has been widely used to investigate the effects of seismic isolation on the response of bridges to earthquakes. However, most FE models of seismic isolated bridges (SIB) have used seismic isolator models calibrated from component test data, while the prediction accuracy of nonlinear FE models of SIB is rarely addressed by using data recorded from instrumented bridges. In this paper, the accuracy of a state‐of‐the‐art FE model is studied through nonlinear FE model updating (FEMU) of an existing instrumented SIB, the Marga‐Marga Bridge located in Viña del Mar, Chile. The seismic isolator models are updated in 2 phases: component‐wise and system‐wise FEMU. The isolator model parameters obtained from 23 isolator component tests show large scatter, and poor goodness of fit of the FE‐predicted bridge response to the 2010 Mw 8.8 Maule, Chile Earthquake is obtained when most of those parameter sets are used for the isolator elements of the bridge model. In contrast, good agreement is obtained between the FE‐predicted and measured bridge response when the isolator model parameters are calibrated using the bridge response data recorded during the mega‐earthquake. Nonlinear FEMU is conducted by solving single‐ and multiobjective optimization problems using high‐throughput cloud computing. The updated FE model is then used to reconstruct response quantities not recorded during the earthquake, gaining more insight into the effects of seismic isolation on the response of the bridge during the strong earthquake.     

Comparison of finite difference and finite element solutions to the variably saturated flow equation

Numerical solutions to the equation governing variably saturated flow are usually obtained using either the finite difference (FD) method or the finite element (FE) method. A detailed comparison of these methods shows that the main difference between them is in how the numerical schemes spatially average the variation of material properties. Further differences are also observed in the way that flux boundaries are represented in FE and FD methods. A modified finite element (MFE) algorithm is used to explore the significance of these differences. The MFE algorithm enables a direct comparison with a typical FD solution scheme, and explicitly demonstrates the differences between FE and FD methods. The MFE algorithm provides an improved approximation to the partial differential equation over the usual FD approach while being computationally simpler to implement than the standard FE solution. One of the main limitations of the MFE algorithm is that the algorithm was developed by imposing several restrictions upon the more general FE solution; however, the MFE is shown to be preferable over the usual FE and FD solutions for some of the test problems considered in this study. The comparison results show that the FE (or MFE) solution can avoid the erroneous results encountered in the FD solution for coarsely discretized problems. The improvement in the FE solution is attributed to the broader hydraulic conductivity averaging and differences in the representation of flux type boundaries.     

考虑流固耦合作用的深水桥墩地震响应分析

地震作用下,深水桥墩与周围水体的耦合振动是一个非常复杂的动力相互作用问题。本文基于非线性Morison方程,采用Airy波浪理论,建立了深水桥墩考虑流固耦合作用的有限元模型,应用Newmark—β法提出了求解该耦合非线性方程的算法,并用ANSYS软件和Matlab软件自编了求解程序。以某跨海大桥深水桥墩为算例,对其进行在地震作用下的非线性动力分析,并与已有计算方法进行对比。结果表明：按本文方法计算的墩顶最大位移、墩底最大剪力及墩底最大弯矩均较大,差异最大达到12．5％。因此在极端海况条件下,对深水桥墩进行地震作用下的动力分析时,建议采用本文考虑流固耦合的方法。     

Seismic response of skewed RC box-girder bridges

It is critical to ensure the functionality of highway bridges after earthquakes to provide access to important facilities. Since the 1971 San Fernando earthquake, there has been a better understanding of the seismic performance of bridges. Nonetheless, there are no detailed guidelines addressing the performance of skewed highway bridges. Several parameters affect the response of skewed highway bridges under both service and seismic loads which makes their behavior complex. Therefore, there is a need for more research to study the effect of skew angle and other related factors on the performance of highway bridges. This paper examines the seismic performance of a three-span continuous concrete box girder bridge with skew angles from 0 to 60 degrees, analytically. Finite element （FE） and simplified beam-stick （BS） models of the bridge were developed using SAP2000. Different types of analysis were considered on both models such as： nonlinear static pushover, and linear and nonlinear time history analyses. A comparison was conducted between FE and BS, different skew angles, abutment support conditions, and time history and pushover analysis. It is shown that the BS model has the capability to capture the coupling due to skew and the significant modes for moderate skew angles. Boundary conditions and pushover load profile are determined to have a major effect on pushover analysis. Pushover analysis may be used to predict the maximum deformation and hinge formation adequately.     

Numerical failure analysis of a continuous reinforced concrete bridge under strong earthquakes using multi-scale models

Previous failure analyses of bridges typically focus on substructure failure or superstructure failure separately. However, in an actual bridge, the seismic induced substructure failure and superstructure failure may influence each other. Moreover, previous studies typically use simplified models to analyze the bridge failure; however, there are inherent defects in the calculation accuracy compared with using a detailed three-dimensional (3D) finite element (FE) model. Conversely, a detailed 3D FE model requires more computational costs, and a proper erosion criterion of the 3D elements is necessary. In this paper, a multi-scale FE model, including a corresponding erosion criterion, is proposed and validated that can significantly reduce computational costs with high precision by modelling a pseudo-dynamic test of an reinforced concrete (RC) pier. Numerical simulations of the seismic failures of a continuous RC bridge based on the multi-scale FE modeling method using LS-DYNA are performed. The nonlinear properties of the bridge, various connection strengths and bidirectional excitations are considered. The numerical results demonstrate that the failure of the connections will induce large pounding responses of the girders. The nonlinear deformation of the piers will aggravate the pounding damages. Furthermore, bidirectional earthquakes will induce eccentric poundings to the girders and different failure modes to the adjacent piers.     

可控源电磁三维频率域有限元模拟

本文采用电磁场的磁矢量位和电标量势,将Maxwell方程组化为位势的类似于Helmholtz型方程,并引入罚项及稳定化方法克服了电磁三维有限元算法中的伪解及数值不稳定性;采用人工边界把计算区域局域化,将均匀半空间中水平电偶极子源产生的位势值作为人工边界上的第一类边界条件以表示源的作用,减少了实际的计算区域.理论模型和复杂模型的计算结果均表明,可控源电磁三维有限元数值模拟给出了稳定、可靠的电磁场分布.     

基于光流法的稀疏光场稠密重建算法

光场成像在三维重建、合成孔径去遮挡和全息成像等应用中具有重要作用.光场稠密重建算法能够弥补光场成像硬件的不足,实现稀疏光场的稠密重建.本文从二维光流基本原理出发,以光场双平面模型为基础,提出一种新的四维光场光流约束方程数学模型,利用该约束方程求解得到的光场光流确定新视角的位置坐标,并通过插值计算及图像反演逐点获得新坐标...     

Cluster computing-aided model updating for a high-fidelity finite element model of a long-span cable-stayed bridge

Accurate and high-fidelity finite element (FE) models are in great demand in the design, performance assessment, and life-cycle maintenance of long-span cable-stayed bridges. The structural system of a long-span cable-stayed bridge is often huge in size and complex with many components connected and various materials constituted. Therefore, the FE model of a long-span cable-stayed bridge involves a large number of elements and nodes with many uncertainties. The model updating of the FE model to best represent a real bridge is necessary but very challenging. One of the challenging issues is that the numerical computation needed for searching the global optimum of a large set of structural parameters is so extensive that the existing FE (not surrogate) model-based updating methods cannot fulfill this task. In this study, a cluster computing-aided FE model updating framework is proposed for the high-performance FE model updating of large and complex structures. In the framework, several computer software packages, including MSC.Marc, Python, and MATLAB, are interconnected for making use of their respective functions of strength. The shake table test of a scaled physical structure of the Sutong cable-stayed bridge in China is used to validate the accuracy and efficiency of the proposed framework. The simulated bridge responses based on the updated FE model are in good agreement with the measured ones from the shake table test. The successful application of the proposed framework provides a reference for the model updating of other types of large and complex structures.     

地震作用下曲线梁桥双向碰撞作用影响分析

碰撞作用直接影响到桥梁不同构件的地震响应,是桥梁抗震研究中一直关注的问题。针对地震作用下曲线梁桥因主梁面内转动而发生主梁与切向桥台和径向挡块碰撞的现象,以1座3跨预应力混凝土连续梁桥为例,采用非线性时程分析方法,对曲线连续梁桥的双向碰撞作用影响进行研究,并分析了不同减撞措施的效果。结果表明:考虑双向碰撞作用后,下部结构响应有明显增加,主梁转动现象变得复杂,曲线梁桥地震响应分析中应通过建立精细化模型来考虑主梁双向碰撞作用的影响;在切向桥台处设置限位拉锁装置能起到较好的减轻双向碰撞作用的影响,以及采用减隔震设计后,减撞效果更明显,桥梁抗震性能明显改善,但合理减撞措施设计参数应结合曲线梁桥约束体系及结构设计参数进行体系分析确定。     

钢筋混凝土箱型高墩双向拟静力试验研究

随着高墩大跨桥梁的广泛应用,其抗震问题也越来越突出。本文主要考虑轴压比、长细比的影响,进行了6个钢筋混凝土薄壁箱型高墩缩尺模型的双向拟静力试验,以及反复荷载作用下的非线性分析。研究表明：①钢筋混凝土薄壁箱型高墩柱在多维荷载共同作用下,主要发生典型的弯曲破坏,但剪切作用也不容忽视;②墩枉的破坏受到不同方向耦合作用的显著影响,尤其是抗弯刚度小的一侧受到的影响更大,较早就出现开裂,提前进入塑性发展阶段;③非线性有限元计算的滞回曲线、骨架曲线等与试验结果基本吻合;④建立了考虑轴压比、长细比影响的钢筋混凝土薄壁箱型高墩的双向荷载一位移恢复力模型,该模型基本能够反映钢筋混凝土薄壁箱型高墩的抗震性能,可供钢筋混凝土箱型高墩柱及高墩桥梁结构的抗震设计和动力计算参考。