非保守弹性动力系统两类变量的广义拟变分原理及其应用

按照广义力和广义位移之间的对应关系,将弹性动力学的各基本方程分别乘上相应的虚量,然后在相应的体积域和面积域上积分,将积分式代数相加,再将代数和在时间域上积分,代入本构关系,并考虑到体积力和面积力均为伴生力,进而建立了非保守弹性动力系统的第1类两类变量的广义拟变分原理;再应用类似的方法,通过代入另一类本构关系,建立了非保守弹性动力系统的第2类两类变量广义拟变分原理.应用第1类两类变量广义拟余能原理给出同时求解1个典型的非保守弹性动力系统的固有频率、变形和内力的计算方法.最后,讨论了有关问题.     

大跨度柔性屋盖风振中流固耦合分析的强耦合方法

本文针对大跨度柔性屋盖风振中流固耦合作用的特点,介绍了一种计算黏性不可压缩流体与经历大变形非线性结构之间流固耦合作用的强耦合方法。本文将伪实体弹性模型引入到流固耦合问题的流体域中处理其变形,使流体和固体形成整体耦合,推导了计算流固耦合问题的整体式方程,并用Newton—Raphson法求解。文中首先用经典圆柱绕流证明了该方法的有效性,并利用该方法计算了一大跨度柔性屋盖风振的流固耦合问题,结果与已有文献中的结果符合良好。因此证明本文提出的强耦合方法用于计算大跨度柔性屋盖风振流固耦合问题是准确可行的。     

致密砂岩水压瞬态致裂液化格子波尔兹曼及有限元数值研究

水压瞬态致裂液化在地应力测量、 地震破坏评估和机理研究、 油气(天然气、 页岩气)及地热资源开发等地学领域都具有重要的理论和应用价值。 自20世纪60年代至今在理论和实际应用方面取得了一些奠基性和开创性成果, 但鉴于问题复杂性, 瞬态致裂液化机理至今尚不清楚。 本研究应用格子波尔兹曼及有限元多孔介质流固耦合物理模型, 对地震波载荷作用下致密砂岩水压瞬态致裂液化过程进行数值模拟研究。 首先, 以鄂尔多斯盆地某油田延长组致密砂岩为例, 利用X射线CT断层成像技术, 应用基于量子力学第一性原理格子波尔兹曼方法, 建立致密砂岩数字岩芯模型。 进而, 推导格子波尔兹曼及有限元多孔介质流固耦合数值模型公式, 建立致密砂岩水压致裂液化物理模型。 最后, 应用地震波载荷边界和初始条件, 模拟瞬态致裂液化流固耦合过程, 讨论了地震波载荷幅值、 频率及作用时间对致密砂岩孔隙结构(孔隙度大小及连通性)、 致密砂岩破裂最大主应力之间关系, 得到了地震波作用下致密砂岩致裂液化准则。     

随机地震动场多点激励下大跨度桥梁地震反应分析方法

地震输入问题一直是工程结构抗震研究关注的焦点。对大跨度桥梁结构，考虑随机地震动场的多点激励而进行地震反应分析较为合理。本文结合大跨度桥梁抗震设计，系统地介绍了随机地震动场的模型以及随机地震动场多点激励下大跨度桥梁地震反应分析的方法。     

平面S波在饱和多孔热弹性介质边界的反射问题研究

针对饱和多孔介质中热弹性波的传播特性问题,基于多孔介质理论和广义的热弹性模型,研究平面S波在饱和多孔热弹性介质边界上的反射问题。以考虑流-固耦合的饱和多孔介质波动方程和热-弹耦合的广义热弹性基本方程出发,建立饱和多孔介质的热-流-固耦合弹性波动模型。通过引入势函数并考虑自由透水和绝热的边界条件,经过理论推导最终给出在饱和多孔热弹性介质边界上的四种反射波的振幅反射率的理论表达式。在此基础上进行数值计算,分别讨论平面S波的入射频率、入射角和热膨胀系数等参数对四种反射波的振幅反射率的影响情况。结果表明:各反射波的振幅反射率分别随频率和热膨胀系数的增大而增大,同时也受到平面S波入射角变化的影响。该结论对于土动力学的理论研究及其相关的工程勘探具有一定的指导意义。     

大跨度拱桥地震动输入模式研究

地震动输入是大跨度桥梁地震反应分析的重要一环。从明确大跨度拱桥的临界跨度入手,探讨了大跨度拱桥地震动输入模式中的行波效应、三向输入及其地震动选取问题。基于某大跨度钢管混凝土拱桥,建立了有限元分析模型,考查了行波效应及三向地震动输入对拱关键截面内力、减隔震支座位移及粘滞阻尼器冲程的影响。结果表明:给出的大跨度拱桥临界跨度确定方法合理,行波效应对拱顶轴力有重要影响,不考虑三向地震动同时作用会明显低估大跨度拱桥的地震反应。确定大跨度拱桥地震动输入模式时需考虑行波效应与三向地震动同时输入。     

基于桥梁抖振分析的自激力计算方法

抖振是桥梁在风荷载作用下的一种经常性的限幅振动。对于长大跨度桥梁在计算其抖振响应时不得不考虑自激力的影响，而自激力的计算方法不一，且其计算过程复杂，繁琐。本文根据抖振计算理论，研究一种自激力的实用计算方法，并对军山斜拉桥进行自激力计算。     

地震动空间效应对大跨度桥梁非线性地震响应的影响

由于大跨度桥梁的桥墩间距离较大,其地震响应分析应考虑地震动输入的空间效应。本文建立了多点激励下大跨度桥梁地震响应分析方法,采用损伤塑性本构模型模拟混凝土材料特性,考虑地震动空间效应对大跨度连续刚构桥进行非线性地震响应分析,从而分析地震动空间效应对大跨度桥梁地震响应的影响。研究表明:考虑行波激励或多点激励时桥梁地震响应较一致激励而言有所差异,考虑地震动空间效应时可能会夸大或减小桥梁结构的动力响应;多点激励时桥梁地震响应会随视波速的改变而变化。由此得出结论,对于大跨度桥梁地震响应分析应合理的考虑地震动空间效应。     

结构拟动力试验力控制实现技术

本文研究了大刚度结构拟动力实验的有关技术问题，基于结构动力分析和电液伺服作动器工作原理，阐述了作动器在力控制方式下实现大刚主结构拟动力实验的可行性，提出了减小实验误差的若干处理技术。通过作者所完成的四个自由度１：３钢筋混凝土结构模型拟动力实验，说明所述方法的有效性。     

无源伺服技术拓展振动速度传感器量程的研究

介绍了采用无源伺服技术进行位移摆式速度计测量量程扩展的研究。首先对传统速度计的原理进行分析;其次通过介绍无源伺服技术的原理,给出了采用无源伺服技术扩展速度计位移测量量程的方法,并给出实测结果,且线性相对误差小于1%。实验证明,以无源伺服反馈的方式扩展了传感器的位移量程,实现了高层建筑和大跨度桥梁的超低频大位移的有效测量。     

Ductile steel plate external end diaphragms for steel tub girder straight highway bridges

The end diaphragm of bridges are normally designed to resist lateral seismic forces imposed on the superstructure in earthquake prone regions. Using ductile diaphragms with high deformation capacity could reduce the seismic demands on the substructure and prevent costly damage under strong ground motions. The end diaphragms of steel tub girder bridges with high lateral stiffness and dominant shear behavior have a potential to be used as ductile fuse elements. In this study, a steel plate shear diaphragm(SPSD) is introduced as an external end diaphragm of tub girder steel bridges to reduce the seismic demands imposed on the substructure. Quasi static nonlinear analyses were conducted to evaluate responses of sixteen SPSDs with different boundary conditions, aspect ratios and diaphragm plate thicknesses. Moreover, nonlinear time history analyses were performed using three different ground motions corresponding to DBE and MCE level spectrums. Cyclic and time history analyses proved the proper behavior of SPSD and its efficiency to reduce seismic demands by more than 25%.     

Seismic performance of cable-sliding friction bearing system for isolated bridges

During past strong earthquakes, highway bridges have sustained severe damage or even collapse due to excessive displacements and/or very large lateral forces. For commonly used isolation bearings with a pure friction sliding surface, seismic forces may be reduced but displacements are often unconstrained. In this paper, an alternative seismic bearing system, called the cable-sliding friction bearing system, is developed by integrating seismic isolation devices with displacement restrainers consisting of cables attached to the upper and lower plates of the bearing. Restoring forces are provided to limit the displacements of the sliding component. Design parameters including the length and stiffness of the cables, friction coefficient, strength of the shear bolt in a fixed-type bearing, and movements under earthquake excitations are discussed. Laboratory testing of a prototype bearing subjected to vertical loads and quasi-static cyclic lateral loads, and corresponding numerical finite element simulation analysis, were carried out. It is shown that the numerical simulation shows good agreement with the experimental force-displacement hysteretic response, indicating the viability of the new bearing system. In addition, practical application of this bearing system to a multi-span bridge in China and its design advantages are discussed.     

Effects of isolation on the seismic response of bridges designed for two different soil types

The objective of this study was to investigate the effect of lead rubber isolators on the seismic response of bridges designed according to current codes for two different soil conditions: hard and medium type soils, in order to assess their applicability for the design of new bridges or retrofit of existing ones. The study was conducted for two levels of earthquake, one corresponding to a return period of 50 years and a service limit state, the other with a return period of 1,000 years and a failure limit state. Twenty one subduction earthquake records on the two types of soil were used to evaluate the linear and nonlinear dynamic response of a set of bridges designed for this purpose with and without base isolation. The response parameters evaluated are the maximum relative displacement on top of the piers, the maximum pier distortion, the maximum shear forces in the piers and the ductility demands for the isolators. The results presented are the average of these maxima for the various earthquakes. This study is an expansion of a previous one in which the seismic response of 36 bridges considering models with and without base isolators, structures with linear base isolators and bridges with nonlinear isolators. The results of this study confirm the conclusions previously obtained and show that the isolation can have beneficial effects even for bridges located in medium soil types.     

Seismic fragility curves of as-built single-span masonry arch bridges

Masonry arch bridges are crucial elements in the railway transportation network throughout Europe. Although significant advances in seismic risk assessment of various bridge types have been made by developing fragility curves of generalized classes of structures, there are no comparable tools for masonry arch structures. In this context, this paper presents the construction of seismic fragility curves of single-span masonry bridges according to the limit analysis method. An iterative procedure is implemented to define the capacity curve of the equivalent single degree of freedom system through non-linear kinematic analysis. The process involves determination of the collapse mechanism, calculation of the limit load multiplier, and definition of the thrust line. The intrinsic variability of the seismic action is incorporated with the use of different sets of elastic spectra compatible with EC 8 Type-1 spectrum for various types of soil, with peak ground acceleration varying over the range 0.05–1.5 g. The fragility curves of the generalized classes of single-span masonry bridges are finally obtained from the effective ranges of the main geometric and material parameters affecting arch bridge capacity.     

Dynamic behaviour of R/C highway bridges under the combined effect of vertical and horizontal earthquake motions

Measurements of ground motions during past earthquakes indicate that the vertical acceleration can reach values comparable to horizontal accelerations or may even exceed these accelerations. Furthermore, measurements of structural response show the possibility of significant amplification in the response of bridges in the vertical direction that can be attributed to the vertical component of ground motion. In this study, the relative importance of the vertical component of ground motion on the inelastic response of R/C highway bridges is investigated. Particular emphasis is placed on modelling of the deck and piers to account for complex loading histories under combined vertical and horizontal earthquake motions. Analyses of actual bridges indicate that, in general, the vertical motion will increase the level of response and the amount of damage sustained by a highway bridge. Vertical motion generates fluctuating axial forces in the columns, which cause unstability of the hysteresis loops and increase the ductility demand. Furthermore, vertical motion can generate forces of high magnitude in the abutments and foundations that are not accounted for by the current seismic design guidelines. Thus, it is important to consider this component of the ground motion in the design of highway bridges, especially for those located in regions near seismic faults.     

A comparative study between China and U.S. on seismic design philosophy and practice of a long span arch bridge

This paper presents the first of a series of case studies on the seismic design of long span bridges （cable-stayed bridges, suspension bridges and arch bridges） under a cooperative research project on seismic behavior and design of highway bridges between the State Key Laboratory for Disaster Reduction in Civil Engineering, Tongji University and the Multidisciplinary Center for Earthquake Engineering Research, University at Buffalo. The objective of this series of case studies is to examine the differences and similarities on the seismic design practice of long span bridges in China and the U.S., to identify research needs and to develop design guidelines beneficial to bridge engineers in both countries. Unlike short to medium span bridges, long span bridges are not included in most seismic design specifications, mainly because they are location dependent and structurally unique. In this paper, an available model of a steel tied half through arch bridge with a main span of 550m in China is discussed. Analysis is focused on comparisons of the seismic responses due to different ground motions. Seismic design criteria and seismic performance requirements for long span bridges in both countries were first introduced and compared, and then three near field earthquake records with large vertical components were selected as the excitations to examine the seismic behavior and seismic vulnerability of the bridge. Results show that （1） the selected near field ground motions cause larger responses to key components （critical sections） of the bridge （such as arch rib ends） with a maximum increase of more than twice those caused by the site specific ground motions; （2） piers, longitudinal girders and arch crowns are more vulnerable to vertical motions, especially their axial forces; and （3） large vertical components of near field ground motions may not significantly affect the bridge＇s internal forces provided that their peak acceleration spectra ordinates only appear at periods of less than 0.2s. However, they may have more influence on the longitudinal displacements of sliding bearings due to their large displacement spectra ordinates at the fundamental period of the bridge.     

减隔震桥梁设计方法及抗震性能研究综述

桥梁作为交通系统中的生命线工程,其抗震性能问题尤为重要。桥梁减隔震技术主要通过减隔震装置来降低结构的地震损伤,目前已发展成为提高强震区桥梁抗震能力的重要措施。为促进减隔震技术在中国桥梁工程领域的进一步发展,首先总结减隔震桥梁的设计方法,归纳其地震反应和震害情况,对采用不同减隔震装置桥梁的非线性动力性能、减隔震效果、地震随机响应、易损性及性能优化方法等研究情况进行梳理;其次,概述减隔震技术在斜交桥、曲线桥及铁路桥梁中的应用情况与研究进展,并介绍新型韧性抗震设计理念在桥梁工程领域中的应用情况和发展前景;最后,总结减隔震桥梁的试验研究情况,指出目前减隔震桥梁研究中的不足和发展趋势。     

Seismic energy dissipation for cable-stayed bridges using passive devices

This study assesses analytically the effectiveness, feasibility and limitations of elastic and hysteretic damping augmentation devices, such as elastomeric and lead–rubber bearings, with respect to the dynamic and seismic performance of cable-stayed bridges. This type of bridge, which has relatively greater flexibility, is more susceptible to undesirable vibrations due to service and environmental loadings than are conventional bridges. Therefore, damping is a very important property. Supplementary damping devices based on the plastic deformation of lead and steel are proposed at critical zones, such as the deck–abutment and deck–tower connections, to concentrate hysteretic behaviour in these specially designed energy absorbers. Inelastic behaviour in primary structural elements of the bridge can therefore be avoided, assuring the serviceability of these cable-supported bridges. Analytically, three-dimensional modelling is developed for the bridge and the damping devices, including the bridge geometrical large-displacement non-linearity and the local material and geometric non-linearities of the energy dissipation devices. The effects of various modelling and design parameters of the bridge response are also studied, including the properties, modelling accuracy and location of the devices along the bridge superstructure. It is shown that an optimum model of the seismic performance of the bridges with these passive control devices can be obtained by balancing the reduction in forces along the bridge against tolerable displacements. Appropriate locations and hysteretic energy dissipation properties of the devices can achieve a significant reduction in seismic-induced forces, as compared to the case with no dampers added, and relatively better control of displacements. In addition, proper selection of the location of the passive control systems can help redistribute forces along the structure which may provide solutions for retrofitting some existing bridges. However, caution should be exercised in simulating the device response for a reliable bridge structural performance. Moreover, while seismic response of the bridge can be significantly improved with added dampers, their degree of effectiveness also depends on the energy absorption characteristics of the dampers.     

铁路桥梁抗震规范与新版公路桥梁抗震规范的比较

2020年6月交通运输部发布了新版《公路桥梁抗震设计规范》（JTG/T 2231-01-2020）（简称"《公规》"）。本文比较了现行《铁路工程抗震设计规范》（GB 50111-2006）（2009年版）（以下简称"《铁规》"）与《公规》的抗震设计相关内容,并分别采用两本规范对25m墩高（D类）、35m墩高（C类）和40m墩高（B类）简支梁进行抗震设计,比较二者地震力和配筋设计结果差异。结果表明:《公规》和《铁规》的抗震设计框架和内容基本一致,在具体规定上如E2或罕遇地震设计最大加速度响应值以及桥墩强度和延性验算方法等方面不同;D类桥梁《铁规》地震力明显大于《公规》,C类和B类桥梁《铁规》和《公规》地震力相当;地震力相同时,《铁规》配筋率计算值大于《公规》,因《铁规》配筋设计基于容许应力法,而《公规》基于极限状态法。