Seismic response of long multiple-span highway bridges

Non-linear seismic responses are described for three prototype, long, multiple-span, reinforced concrete, modern highway bridge structures, namely the 5/14 South Connector Overcrossing and the curved Figueroa Street Under-crossing as designed by the California Department of Transportation, and a straight version of the Figueroa Street Undercrossing. The analytical seismic responses are discussed and are correlated with the apparent prototype behaviour experienced during the San Fernando, California, earthquake of 9 February 1971. In particular, the causes of collapse of the 5/14 South Connector Overcrossing are identified and examined. Finally, based on parameter studies of the seismic responses of these structures, general conclusions and recommendations related to seismic design methodology are presented.     

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.     

Seismic response of bridges with massive foundations

The dynamic response of vehicular overpasses with massive foundations built in highly populated earthquake prone regions is studied to assess the massive foundation potential of being a technically sound mean to reduce the structural response during major earthquakes. The study consists on numerical simulations using 3-D finite element models. Two typical supports of a major 23 km long vehicular overpass recently built in the north east part of Mexico City valley were considered in this research. This zone is characterized by the presence of stiff soils comprised by dense and very dense silty sands and sandy silts, randomly intercalated by stiff clays layers of variable thickness. Initially, a conventional raft foundation structurally connected to four precast closed-end concrete piles was considered. Then, the potential beneficial effect of a massive foundation of variable depth was assessed. Sets of 3-D finite element models were developed and the response of the systems was evaluated for a typical seismic scenario such as that prevailing at the zone, assuming a potential 8.1 M_w seismic event, and for a hypothetical 8.7 M_w extreme event. Important attenuations of about 39% to 48% at the upper deck spectral accelerations and of 21% to 30% in maximum lateral foundation displacements were achieved with the massive soil improvement for the cases analyzed. Thus, the massive foundations seem to be a convenient alternative to reduce the overall structural seismic response.     

多年冻土区桥梁的地震反应

首先研究了冻土区桥梁的抗震计算方法,对波动法和惯性力法的计算结果进行厂对比分析。对比结果表明惯性力法的计算结果偏大,但当基岩的剪切波速很大时,两种方法的结果接近。然后,采用波动法对季节性冻土区和多年冻土区桥梁结构进行了地震反应分析,研究了冻土层的变化对桥梁结构地震反应的影响,得到了不同冻土厚度、不同墩高时桥墩地震内力分布的规律。计算结果表明,冻土层的存在对桥梁的地震反应具有显著影响,桥墩的地震反应在冬夏两季具有显著区别。     

海底地震动作用下近海桥梁地震响应研究

以某近海大桥引桥段连续梁桥为工程背景,建立考虑海底地震动特性和腐蚀效应的近海桥梁地震反应分析模型。采用增量动力分析方法分析腐蚀效应以及海底地震动作用对近海桥梁地震响应的影响。研究结果表明:腐蚀效应与海底地震动作用都会不同程度影响近海桥梁结构的抗震性能。其中:腐蚀效应会增大近海桥梁的破坏指标,降低最大墩底剪力和弯矩值,从而降低桥梁的抗震性能;海底地震动作用会增大近海桥梁的破坏指标及最大墩底剪力、弯矩值;在2种因素耦合作用下,桥梁的抗震性能将会进一步降低。     

高墩梁桥地震响应分析

本文将对两座高墩桥梁的地震响应进行分析,一座是连续-刚构组合梁桥,另一座是刚构桥。这两种是高墩桥梁普遍采用的桥型,对其进行详细的动力分析对此类桥梁的抗震设计具有一定的指导作用。针对这两种桥梁结构,本文首先分析直接影响结构动力响应的自振特性,从中总结高墩桥梁的特点,然后采用反应谱法、时程分析法分析结构地震响应,并对其结果进行比较,同时讨论桩-土相互作用对高墩桥梁地震响应的影响。     

Seismic response analysis of bridges isolated with friction pendulum bearings

A systematic method is developed for the dynamic analysis of the structures with sliding isolation which is a highly non-linear dynamic problem. According to the proposed method, a unified motion equation can be adapted for both stick and slip modes of the system. Unlike the traditional methods by which the integration interval has to be chopped into infinitesimal pieces during the transition of sliding and non-sliding modes, the integration interval remains constant throughout the whole process of the dynamic analysis by the proposed method so that accuracy and efficiency in the analysis of the non-linear system can be enhanced to a large extent. Moreover, the proposed method is general enough to be adapted for the analysis of the structures with multiple sliding isolators undergoing independent motion conditions simultaneously. The superiority of the proposed method for the analysis of sliding supported structures is verified by a three-span continuous bridge subjected to harmonic motions and real earthquakes. In addition, the side effect of excessive displacement of the superstructure induced by the sliding isolation is eliminated by replacing one of the roller supports on the abutments with hinge support. Therefore, both reductions in the forces of the substructure and the displacements of the superstructure can be achieved simultaneously. © 1998 John Wiley & Sons, Ltd.     

Seismic response of continuous span bridges through fiber-based finite element analysis

1 Introduction Older design codes based on equivalent elastic force approaches proved to be ineffective in preventing damage caused by destructive earthquakes. After recent major earthquakes (e.g. Northridge 1994, Kobe 1995, and Kocaeli 1999 etc.), the necessity for using more accurate methods, which explicitly account for geometrical nonlinearities and material inelasticity, to evaluate seismic demand on structures, became evident. Within this framework, two analysis tools are currently offe…     

Seismic response of isolated bridges with soil–structure interaction

The modern transportation facilities demand that the bridges are to be constructed across the gorges that are located in seismically active areas and at the same time the site conditions compel the engineers to rest the pier foundation on soil. The purpose of this study is to assess the effects of soil–structure interaction (SSI) on the peak responses of three-span continuous deck bridge seismically isolated by the elastomeric bearings. The emphasis has been placed on gauging the significance of physical parameters that affect the response of the system and identify the circumstances under which it is necessary to include the SSI effects in the design of seismically isolated bridges. The soil surrounding the foundation of pier is modelled by frequency independent coefficients and the complete dynamic analysis is carried out in time domain using complex modal analysis method. In order to quantify the effects of SSI, the peak responses of isolated and non-isolated bridge (i.e. bridge without isolation device) are compared with the corresponding bridge ignoring these effects. A parametric study is also conducted to investigate the effects of soil flexibility and bearing parameters (such as stiffness and damping) on the response of isolated bridge system. It is observed that the soil surrounding the pier has significant effects on the response of the isolated bridges and under certain circumstances the bearing displacements at abutment locations may be underestimated if the SSI effects are not considered in the response analysis of the system.     

近断层地震动下设置BRB的双向减隔震桥梁地震反应

在近断层地震动下桥梁结构将发生较大反应,减隔震设计是减轻地震损伤的重要手段。提出了在桥梁双柱墩横桥向设置防屈曲支撑(BRB),在纵桥向设置铅芯橡胶支座(LRB)的双向减隔震体系。利用Midas Civil软件建立3种不同减隔震方式的桥梁结构模型:LRB仅单向,LRB双向与LRB联合BRB,运用非线性时程分析方法计算了桥墩反应(墩顶侧移角、残余位移角和曲率延性)、LRB支座变形和BRB的耗能特性等。结果表明:在近断层地震动输入下联合设置LRB和BRB的双向减隔震桥梁减震效果明显,相比其它2种方式,能有效降低墩柱的塑性变形及起到保护桥墩的作用。在横桥向,桥墩最大侧移角、残余位移角和最大曲率延性系数都显著降低。     

强震区轻骨料混凝土桥梁地震响应研究

为研究轻骨料混凝土桥梁的地震响应,以一座强震区典型连续梁桥为研究对象,在考虑轻骨料混凝土材料特性基础上建立桥梁结构有限元分析模型,采用非线性动力时程分析法进行结构地震响应分析,研究轻骨料混凝土材料布设位置对桥梁结构动力特性和地震响应的影响,并从内力和位移响应方面与普通混凝土桥梁进行对比。结果表明:与普通混凝土桥梁相比,仅上部结构或仅下部结构采用轻骨料混凝土对降低桥墩内力并不明显,而全桥采用轻骨料混凝土能够显著降低桥墩内力。轻骨料混凝土桥梁与普通混凝土桥梁地震内力和位移响应变化趋势不同,桥墩塑性发展程度和时间存在差异。采用轻骨料混凝土桥梁方案时,应综合考虑结构质量、刚度分布及材料塑性特性与普通混凝土桥梁的不同,合理确定抗震设计方案。     

Seismic response predictions of multi‐span steel bridges through pushover analysis

In the new trend of seismic design methodology, the static pushover analysis is recommended for simple or regular structures whilst the time‐history analysis is recommended for complex structures. To this end, the applicable range of the pushover analysis has to be clarified. This study aims at investigating the applicability of pushover analysis to multi‐span continuous bridge systems with thin‐walled steel piers. The focus is concentrated on the response demand predictions in longitudinal or transverse directions. The pushover analysis procedure for such structures is firstly summarized and then parametric studies are carried out on bridges with different types of superstructure‐pier bearing connections. The considered parameters, such as piers' stiffness distribution and pier–0.5ptdeck stiffness ratio, are varied to cover both regular and irregular structures. Finally, the relation of the applicability of pushover analysis to different structural formats is demonstrated and a criterion based on the higher modal contribution is proposed to quantitatively specify the applicable range. Copyright © 2003 John Wiley & Sons, Ltd.     

考虑支座摩擦滑移及结构碰撞的非规则人字形桥梁地震响应分析

针对非规则人字形桥梁在地震作用下灾变严重的问题,以一座非规则人字形桥梁为研究对象,建立其空间分析模型,研究综合考虑支座摩擦滑移、结构碰撞对非规则人字形桥梁地震响应的影响。结果表明:邻梁间的碰撞作用可使得桥梁墩顶位移及内力相比不考虑时有所减小,但同时也使梁体产生了较大的加速度脉冲效应;当考虑支座摩擦滑移和结构碰撞时,固定墩墩顶位移和邻梁相对位移峰值有一定程度增大,然而对梁体加速度脉冲效应结果影响并无统一规律;纵向地震波作用下,非规则人字形桥梁不仅存在顺桥向的碰撞,横桥向的碰撞响应也不容忽视。非规则人字形桥梁进行抗震设计计算时应选取符合实际情况的计算模型,考虑支座摩擦滑移及结构间的碰撞。     

考虑轨道约束的连续梁拱桥地震反应及减震控制研究

以一座大跨度单线铁路连续梁拱桥为背景,建立了考虑轨道约束和相邻构件碰撞效应的动力分析模型;通过输入40组水平双向地震动记录进行非线性时程分析,探究轨道约束和拱肋对桥梁地震响应的影响,采用"减震榫-拉索限位器"与"自恢复耗能支撑(SCEDB)-屈曲约束支撑(BRB)"控制水平向地震反应,并对比两种组合减震控制系统的减震效...     

行波激励下大跨度连续刚构桥的地震反应分析

地晨输入问题一直是工程结构抗震研究所关注的焦点。大跨度桥梁结构各地面支承距离较大、延伸较长，进行地震反应分析时应考虑地震波有限波速传播所引起的行波效应。本文基于行波激励下大跨度桥梁地震反应分析的方法，对某一大跨度的四跨预应力混凝土连续刚构桥进行了行波激励下地震反应的数值模拟，并与一致地震激励下的计算结果进行了比较，对该四跨预应力混凝土连续刚构桥的工程建设具有直接的指导意义。     

隔震桥梁减震效果分析

本文根据隔震桥梁的设计特点，分别利用非线性水平和转动弹簧单元来模拟减、隔震支座的桥梁延性塑性铰的非线性性能，计及隔震器与减震器的作用对桥梁结构非线性弹塑性动力反应进行了研究。在把桥梁结构和减震器作为整体考虑的情况下，用算例分析了隔震桥梁的减震效果。     

Seismic responses of deck-type arch bridges

The dynamic responses of three deck-type arch bridges, with main spans of 59,213 and 518m, are presented. The ratios of natural period to arch span were found to be quite close for all three bridges. Artificial ground motions were applied separately in three directions to finite-element models of each bridge. Three acceleration levels were considered—0.09g, 0.22g and 0.50g—corresponding to the AASHTO Seismic Risk Zones I, II and III, respectively. Responses to uniform lateral motion were generally the largest, while the responses to vertical motion were generally lower than those due to lateral or longitudinal motion. In all cases considered, none of the total stresses in the main members exceeded the yield stress. Connection and secondary member responses were also calculated and are presented. In addition, the effects of unequal motions at the supports were sampled by various deterministic inputs. While the effects of such motions in the vertical and lateral directions were less than the responses to uniform motion, the effects of unequal longitudinal motions at the supports were substantial.     

Seismic spatial effects on dynamic response of long-span bridges in stationary inhomogeneous random fields

The seismic analysis of long-span bridges subjected to multiple ground excitations is an important problem.The conventional response spectrum method neglects the spatial effects of ground motion, and therefore may result in questionable conclusions. The random vibration approach has been regarded as more reliable. Unfortunately, so far,computational difficulties have not yet been satisfactorily resolved. In this paper, an accurate and efficient random vibration approach -- pseudo excitation method (PEM), by which the above difficulties are overcome, is presented. It has been successfully used in the three dimensional seismic analysis of a number of long-span bridges with thousands of degrees of freedom and dozens of supports. The numerical results of a typical bridge show that the seismic spatial effects, particularly the wave passage effect, are sometimes quite important in evaluating the safety of long-span bridges.     

山区桥梁的抗震概念设计

山区桥梁因为地形和施工条件等的限制,给设计带来很大的问题,使得结构不规则,影响了桥梁的抗震能力。且由于山地震动效应等复杂因素的影响,该类桥梁的抗震计算往往不能很好地反映真实的地震反应。概念设计通过长期积累的实际设计经验和理论研究的成果,从总体上把握设计的原则,是非常重要和有意义的。本文针对山区桥梁的特点,对山区桥梁的抗震概念设计方法进行了探讨。     

交通系统中桥梁的抗震分析

桥梁抗震防灾研究也可以说是桥梁易损性分析问题,Pushover分析方法具有表达非线性静力分析的特性,而在桥梁抗震分析和计算方面也表现出较好的适应能力,阐述该方法的基本原理,并用桥梁实际震害样本与Pushover分析方法计算结果进行对比,其对比结果表明,用Pushover分析方法计算出的结果比较符合实际震害情况,显然该法对处理一般性桥梁问题是可行和有效的。