桥梁结构弹塑性地震反应分析新进展

介绍了地震反应分析理论和方法发展的基本概况,并对弹塑性地震反应分析中采用的纤维梁柱单元及国外新近出现的IDA方法进行了详细的说明。在此基础上,对能够有效解决弹塑性地震反应分析计算的OpenSEES软件系统做了介绍。     

基于IDA的高墩大跨桥梁地震易损性分析

针对目前我国桥梁抗震设计规范仅适用于墩高40m以下规则桥梁的现状,以一常见山区高墩大跨连续刚构桥为研究对象,采用IDA方法分析了桥梁结构在15条地震动下的动态响应,得到桥墩各截面在所有地震动作用下的曲率包络图。以高墩最不利截面的材料损伤应变所对应的截面曲率为损伤指标,结合能力需求比对数回归分析,计算了高墩在不同损伤状态下的破坏概率,建立了墩柱易损性曲线,同时还建立了梁端支座的易损性曲线。基于联合失效概率分析方法,形成了桥梁系统易损性曲线。分析结果表明:薄壁空心墩连续刚构桥在强地震作用下高墩发生破坏的部位主要集中在墩顶和墩底区域;墩柱发生完全破坏的概率极小,但桥台处梁端活动支座的地震损伤概率较高;桥梁系统损伤概率能够更加准确地反映高墩大跨桥梁的真实抗震性能。     

特殊复杂场地条件下桥梁结构地震易损性研究现状及发展趋势分析

考虑到桥梁地震易损性分析中场地条件影响的不确定性,本文主要针对流水冲刷环境、可液化场地、近断层场地、氯盐侵蚀环境和冻土场地等特殊复杂场地条件对桥梁结构地震易损性的影响特征和机理进行了总结归纳,并提出了尚待进一步研究的关键问题.结果 表明:特殊场地地震响应的复杂性和桥梁结构的特殊性相叠加,给复杂场地条件下桥梁的抗震性能评...     

Displacement-based seismic design of multi-degree-of-freedom bridge structures

The concept of displacement-based design is attractive for seismic design, primarily because it places the focus of design directly on displacement demand, and hence damage, rather than on force-reduction or behaviour factors. A procedure is presented which extends the simple concept of displacement-based design to complex multi-degree-of-freedom (MDOF) bridge structures. The procedure is based on the assumption of a displaced shape for the structure, and the subsequent reduction of the system to an equivalent single-degree-of-freedom (SDOF) system. The process is shown to work well for the design of a symmetrical bridge, while suffering some shortcomings when applied to a highly irregular bridge. The topic of design-oriented displacement response spectra is also briefly addressed.     

高架桥地震反应半主动控制分析

本文探讨了高架桥结构地震反应LQR(Linear Quadratic Regulator)半主动控制算法以及考虑刚度退化的桥墩非线性计算模型，并利用Matlab语言编制的程序对其进行了数值仿真计算。结果表明，将隔震技术与利用MR阻尼器的半主动控制技术相结合，能够有效地减小高架桥的地震反应；MR阻尼器的设置位置以及结构的参数对控制效果有较大影响。考虑桥墩非线性影响将能得到更为接近实际的计算结果。     

基于砌体结构破坏损伤的地震烈度物理标准研究

为了研究基于砌体结构破坏的地震烈度物理标准,将15个地震动参数按属性(峰值、频率、持时和能量)分成4类,将地震记录按地震动三要素(峰值、频率、持时)分成3组,求出每组记录作用下砌体结构的延性系数,计算出各个参数值和延性系数的相关系数,比较分析这些相关系数发现地震动峰值加速度、有效峰值加速度、地震动输入能量和滞回耗能都能表征地震动对砌体的破坏势,并且这4个参数都和烈度有很好的相关性,可以作为烈度的物理标准。     

黏滞阻尼器对高层钢结构地震易损性的影响

为研究黏滞阻尼器对高层钢结构地震易损性的影响,基于Open SEES有限元分析平台,建立一个25层钢框架结构以及同尺寸附着黏滞阻尼器的钢框架结构,对两个钢框架结构以地震动峰值加速度(PGA)作为地震动强度指标,以结构最大层间位移角θmax为工程需求参数,从太平洋地震工程研究中心(PEER)中选取了15条地震动记录,分别对两个结构进行增量动力分析(Incremental Dynamic Analysis,IDA),建立结构的IDA曲线簇。结合地震易损性分析,对分析结果进行对数拟合,构筑两个结构的连续易损性曲线,并进一步提出用贝塔分布函数将结果转化为地震动参数-震害指数概率密度函数的概率表达方式,可以更加直观简便地观察到黏滞阻尼器显著的减震效果。该表达方法具有直观性,研究成果可为既有结构的地震灾害风险评估等提供简明且有力的分析方法。     

基于推覆分析的RC框架地震倒塌易损性预测

基于倒塌率的结构倒塌易损性分析是目前评价结构抗倒塌能力最合理的方法.但是,目前基于增量动力分析(IDA)的倒塌率分析方法,工作量和实施难度大,很难直接用于工程设计,因此有必要研究便于工程应用的新方法.本文基于18个典型多层RC框架结构的IDA倒塌率分析和静力推覆分析,发现RC框架在大震下的倒塌率及抗倒塌安全储备(CMR)与静力推覆得到的结构位移安全储备之间存在较好的相关关系.依据此关系,建议了保证大震倒塌率的推覆位移安全储备,并通过9个RC框架结构算例进行了验证.本文方法简单易行,可供规则多层RC框架结构抗倒塌设计参考.     

高墩大跨连续刚构桥梁地震易损性分析

基于增量动力分析方法,通过非线性地震反应分析,得到整体结构的破坏特征和易损位置,分析适用于高墩大跨连续刚构桥的损伤指标.对高墩大跨连续刚构桥进行整体结构的地震易损性分析时,采用应变作为墩柱损伤指标,位移作为支座损伤指标,绘制了基于整体性能的全桥易损性曲线.     

Modelling of shear keys in bridge structures under seismic loads

Shear keys are used in the bridge abutments and piers to provide transverse restraints for bridge superstructures. Owing to the relatively small dimensions compared to the main bridge components (girders, piers, abutments, piles), shear keys are normally regarded as secondary component of a bridge structure, and their influences on bridge seismic responses are normally neglected. In reality, shear keys are designed to restrain the lateral displacements of bridge girders, which will affect the transverse response of the bridge deck, thus influence the overall structural responses. To study the influences of shear keys on bridge responses to seismic ground excitations, this paper performs numerical simulations of the seismic responses of a two-span simply-supported bridge model without or with shear keys in the abutments and the central pier. A detailed 3D finite element (FE) model is developed by using the explicit FE code LS-DYNA. The bridge components including bridge girders, piers, abutments, bearings, shear keys and reinforcement bars are included in the model. The non-linear material behaviour including the strain rate effects of concrete and steel rebar are considered. The seismic responses of bridge structures without and with shear keys subjected to bi-axial spatially varying horizontal ground motions are calculated and compared. The failure mode and damage mechanism of shear keys are discussed in detail. Numerical results show that shear keys restrain transverse movements of bridge decks, which influence the torsional–lateral responses of the decks under bi-axial spatially varying ground excitations; neglecting shear keys in bridge response analysis may lead to inaccurate predictions of seismic responses of bridge structures.     

Optimal vector-valued intensity measure for seismic collapse assessment of structures

The present study is aimed to investigate the ability of different intensity measures(IMs), including response spectral acceleration at the fundamental period of the structure, S a(T1), as a common scalar IM and twelve vector-valued IMs for seismic collapse assessment of structures. The vector-valued IMs consist of two components, with S a(T1) as the first component and different parameters that are ratios of scalar IMs, as well as the spectral shape proxies εSa and N p, as the second component. After investigating the properties of an optimal IM, a new vector-valued IM that includes the ratio of S a(T1) to the displacement spectrum intensity(DSI) as the second component is proposed. The new IM is more efficient than other IMs for predicting the collapse capacity of structures. It is also sufficient with respect to magnitude, source-to-site distance, and scale factor for collapse capacity prediction of structures. To satisfy the predictability criterion, a ground motion prediction equation(GMPE) is determined for S a(T1)/DSI by using the existing GMPEs. Furthermore, an empirical equation is proposed for obtaining the correlation between the components of the proposed IM. The results of this study show that using the new vector-valued IM leads to a more reliable seismic collapse assessment of structures.     

Highway bridge seismic design: Summary of FHWA/MCEER project on seismic vulnerability of new highway construction

The Federal Highway Administration (FHWA) sponsored a large, multi-year project conducted by the Multidisciplinary Center for Earthquake Engineering Research (MCEER) titled “Seismic Vulnerability of New Highway Construction” (MCEER Project 112), which was completed in 1998. MCEER coordinated the work of many researchers, who performed studies on the seismic design and vulnerability analysis of highway bridges, tunnels, and retaining structures. Extensive research was conducted to provide revisions and improvements to current design and detailing approaches and national design specifications for highway bridges. The program included both analytical and experimental studies, and addressed seismic hazard exposure and ground motion input for the U.S. highway system; foundation design and soil behavior; structural importance, analysis, and response; structural design issues and details; and structural design criteria. Supported by: the Federal Highway Administration under contract number DTFH61-92-C-00112.     

Empirical seismic vulnerability analysis for masonry buildings based on school buildings survey in Iran

School facilities in Iran, in particular masonry schools, have shown poor performance during past earthquakes and can be identified as one of the parts of the country’s infrastructure that is most vulnerable to earthquakes. Hence, in this paper a method to perform index-based damage assessment for brick masonry schools located in the province of Yazd, the central region of Iran, using a comprehensive database of school buildings, is proposed. The database was obtained from the field survey forms applied for each observed school to collect the features of and damage to the structure. The results of a vulnerability index method developed in Iran are employed as input data to obtain empirical fragility curves for the school inventory. The Macroseismic model and GNDT II level method are two empirical methods combined in this procedure. Finally, the procedure is verified using damage survey data obtained after recent earthquakes (1990 Manjil–Rudbar earthquake and 2003 Bam earthquake) that occurred in Iran.     

Effect of abutment modeling on the seismic response of bridge structures

Abutment behavior significantly influences the seismic response of certain bridge structures. Specifically in the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture the critical components and modes of abutment response without the need to generate continuum models of the embankment, approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model types of increasing complexity are developed for each bridge, denoted as roller, simplified, and spring abutments. The roller model contains only single-point constraints. The spring model contains discrete representations of backfill, bearing pad, shear key, and back wall behavior. The simplified model is a compromise between the efficient roller model and the comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation. The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is evaluated. Recommendations for abutment modeling are made.     

渡口河大桥地震响应分析

渡口河大桥为在建宜万线上的一座高墩大跨度连续刚构桥,为了研究其地震响应特性,分别按桩土连续梁模式、桩土空间刚架模式来模拟桩土共同作用,建立了相应的空间有限元模型,采用数值模拟方法合成了桥址处地震动时程。研究比较了这两种模型和不考虑桩土作用模型按反应谱输入方式下结构的地震响应,并对地震竖向分量的影响、不同波速的行波效应进行了探讨。通过分析计算,得出了一些对实际工程有意义的结论。     

Effects of deep excavation on seismic vulnerability of existing reinforced concrete framed structures

In this paper the effects of deep excavation on seismic vulnerability of existing buildings are investigated. It is well known that deep excavations induce significant changes both in stress and strain fields of the soil around them, causing a displacement field which can modify both the static and dynamic responses of existing buildings. A FEM model of a real case study, which takes into account geometry, non-linear soil behavior, live and dead loads, boundary conditions and soil–structure interaction, has been developed in order to estimate the soil displacements and their effects on seismic behavior of a reinforced concrete framed system close to deep excavation. Considering a significant accelerometric seismic input, the non-linear dynamic responses of the reinforced concrete framed structure, both in the pre and post-excavation configurations, have been evaluated and, then, compared to estimate the modification in seismic vulnerability, by means of different seismic damage indices and inter-story drifts.     

基于改进云图法的结构概率地震需求分析

概率地震需求分析是美国太平洋地震工程研究中心(Pacific Earthquake Engineering ResearchCenter,PEER)提出的新一代"性能化地震工程(Performance-Based Earthquake Engineering,PBEE)"理论框架的重要一环。传统的概率地震需求分析方法称为"云图法",这种方法针对确定性结构进行一系列地震动作用下的非线性动力分析,从而得到地震动强度参数与结构地震需求的"云图"。然而,传统的云图法只能考虑地震动的不确定性,而无法考虑结构的不确定性。为此,结合拉丁超立方体抽样技术,提出一种能综合考虑地震动不确定性和结构不确定性的改进云图法,并将传统的概率地震需求分析内容拓展为概率地震需求模型、概率地震需求易损性分析、概率地震需求危险性分析三个层次。以一榀五层三跨钢筋混凝土框架结构为例,分别采用传统云图法和改进云图法对其进行概率地震需求分析,得到了该结构的概率地震需求模型、地震需求易损性曲线和地震需求危险性曲线。分析结果表明:提出的方法可以有效地考虑地震动与结构的不确定性,避免不考虑结构的不确定性而低估结构的地震风险性。     

Fuzzy logic control of bridge structures using intelligent semi-active seismic isolation systems

Passive supplemental damping in a seismically isolated structure provides the necessary energy dissipation to limit the isolation system displacement. However, damper forces can become quite large as the passive damping level is increased, resulting in the requirement to transfer large forces at the damper connections to the structure which may be particularly difficult to accommodate in retrofit applications. One method to limit the level of damping force while simultaneously controlling the isolation system displacement is to utilize an intelligent hybrid isolation system containing semi-active dampers in which the damping coeffic ient can be modulated. The effectiveness of such a hybrid seismic isolation system for earthquake hazard mitigation is investigated in this paper. The system is examined through an analytical and computational study of the seismic response of a bridge structure containing a hybrid isolation system consisting of elastomeric bearings and semi-active dampers. Control algorithms for operation of the semi-active dampers are developed based on fuzzy logic control theory. Practical limits on the response of the isolation system are considered and utilized in the evaluation of the control algorithms. The results of the study show that both passive and semi-active hybrid seismic isolation systems consisting of combined base isolation bearings and supplemental energy dissipation devices can be beneficial in reducing the seismic response of structures. These hybrid systems may prevent or significantly reduce structural damage during a seismic event. Furthermore, it is shown that intelligent semi-active seismic isolation systems are capable of controlling the peak deck displacement of bridges, and thus reducing the required length of expansion joints, while simultaneously limiting peak damper forces. Copyright © 1999 John Wiley & Sons, Ltd.     

悬摆隔震结构动力分析方法初探

本文对悬摆隔震结构力学模型作等效处理,探索利用常规计算程序对其进行动力分析的有效方法,同时验证了悬摆隔震指施对于减弱结构地震反应的效果是明显的。     

Simplified transverse seismic analysis of buried structures

This paper presents a simplified method for the analysis of square cross-section buried structures (tunnel) subjected to seismic motion. Finite element analyses are performed to assess the fundamental modes of vibration of the soil layer with and without the tunnel. The influence of the tunnel on the modes of vibrations is taken into account by comparing the modal deformations in the free-field to those in the presence of the tunnel. From this comparison the zone of influence of the modal displacements due to the presence of the structure is determined. The resulting model is subjected to horizontal and vertical excitation of statistically independent accelerograms compatible with the response spectra of the Regulatory Guide 1.6 of the Nuclear Energy Commission. The free-field displacement is introduced at the boundaries of the zone of influence. The proposed simplified static analysis yields a state of stresses similar to that obtained from a full dynamic analysis of the complete soil–tunnel system. Several examples are solved to corroborate the validity of the method.