Seismic demand evaluation of medium ductility RC moment frames using nonlinear procedures

Performance-based earthquake engineering is a recent focus of research that has resulted in widely developed design methodologies due to its ability to realistically simulate structural response characteristics.Precise prediction of seismic demands is a key component of performance-based design methodologies.This paper presents a seismic demand evaluation of reinforced concrete moment frames with medium ductility.The accuracy of utilizing simplified nonlinear static analysis is assessed by comparison against the results of time history analysis on a number of frames.Displacement profiles,drift demand and maximum plastic rotation were computed to assess seismic demands.Estimated seismic demands were compared to acceptance criteria in FEMA 356.The results indicate that these frames have sufficient capacity to resist interstory drifts that are greater than the limit value.     

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。     

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。     

行波效应对铁路大跨长联连续刚构桥地震反应的影响

介绍了多点激励下结构运动方程的求解方法。以某大跨度铁路连续刚构桥为工程背景,用有限元软件MIDAS建立了结构有限元模型,选取地震波波速为主要参数,对某铁路大跨长联连续刚构桥进行了考虑行波效应的时程反应分析,并与一致激励下的结果进行了对比。结果表明:考虑行波效应后,跨中截面的弯矩增大,而墩底截面的弯矩减小。在梁部结构的抗震设计中应考虑行波效应的影响。     

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.     

澳门澳凼第三大桥斜拉桥地震反应分析

结合一座澳门澳凼第三大桥斜拉桥的工程设计实例,采用大型有限元分析程序ANSYS,选取空间BEAM188、BEAM4及SHELL63单元建立动力计算模型,对比研究了主塔墩底在假定固结和考虑桩土共同工作这两种边界约束处理方式下的动力特性;并选取三条地震波在桥的纵、横向分别进行桥梁地震作用下的时程分析,给出了主梁和中塔的内力、位移及时程响应。     

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。     

Inelastic response of RC frame buildings with seismic isolation

A comprehensive parametric study on the inelastic seismic response of seismically isolated RC frame buildings, designed for gravity loads only, is presented. Four building prototypes, with 23 m × 10 m floor plan dimensions and number of storeys ranging from 2 to 8, are considered. All the buildings present internal resistant frames in one direction only, identified as the strong direction of the building. In the orthogonal weak direction, the buildings present outer resistant frames only, with infilled masonry panels. This structural configuration is typical of many existing RC buildings, realized in Italy and other European countries in the 60s and 70s. The parametric study is based on the results of extensive nonlinear response‐time history analyses of 2‐DOF systems, using a set of seven artificial and natural seismic ground motions. In the parametric study, buildings with strength ratio (F_y/W) ranging from 0.03 to 0.15 and post‐yield stiffness ratio ranging from 0% to 6% are examined. Three different types of isolation systems are considered, that is, high damping rubber bearings, lead rubber bearings and friction pendulum bearings. The isolation systems have been designed accepting the occurrence of plastic hinges in the superstructure during the design earthquake. The nonlinear response‐time history analyses results show that structures with seismic isolation experience fewer inelastic cycles compared with fixed‐base structures. As a consequence, although limited plastic deformations can be accepted, the collapse limit state of seismically isolated structures should be based on the lateral capacity of the superstructure without significant reliance on its inherent hysteretic damping or ductility capacity. Copyright © 2012 John Wiley & Sons, Ltd.     

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...     

Non-linear buffeting response analysis of long-span suspension bridges with central buckle

The rigid central buckle employed in the Runyang Suspension Bridge (RSB) was the first time it was used in a suspension bridge in China. By using a spectral representation method and FFT technique combined with measured data,a 3D fluctuating wind field considering the tower wind effect is simulated. A novel FE model for buffeting analysis is then presented,in which a specific user-defined Matrix27 element in ANSYS is employed to simulate the aeroelastic forces and its stiffness or damping matrices are parameterized by wind velocity and vibration frequency. A nonlinear time history analysis is carried out to study the influence of the rigid central buckle on the wind-induced buffeting response of a long-span suspension bridge. The results can be used as a reference for wind resistance design of long-span suspension bridges with a rigid central buckle in the future.     

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.     

大型双槽渡槽地震反应分析

为了得到比较精确的大型双槽渡槽结构的地震反应，根据渡槽结构复杂、影响动力因素较多等特点，采用8结点空间块体单元对渡槽槽身和槽墩进行有限元离散，分别用耦合自由度和多个弹簧单元分别模拟渡槽槽身横向拉杆、加劲肋和盆式橡胶支座，建立了大型双槽渡槽结构地层反应分析的有限元模型，计算了南水北调水利工程中的双洎河大型双槽渡槽的振动特性，并分别用反应谱法和时程分析法对该渡槽进行了地震反应分析，计算结果可为该渡槽的抗震设计提供参考。     

考虑桩土效应的天津站交通枢纽地震反应分析

为弄清楚带有地下室大型复杂结构的抗震性能,本文针对天津站交通枢纽工程,分别取结构典型的横向及纵向剖面,应用大型通用有限元分析软件ANSYS,建立了结构-桩-土体系相互作用的有限元模型,采用动力时程分析方法,研究体系在水平地震作用下的弹塑性动力反应规律,分析结构在地震动作用下的位移和内力的分布;并与假定刚性基础周边土简化为弹簧的结构模型的计算结果进行比较,通过两种模型的地震反应的对比分析,得到了一些有益的结论。     

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.     

考虑双向碰撞效应的连续斜交桥地震响应研究

为研究双向碰撞效应对连续斜交桥地震响应的影响,采用Kelvin-Voigt模型模拟桥台伸缩缝处的纵向碰撞现象,采用简化滞回模型模拟挡块与主梁的横向碰撞过程,针对某三跨连续斜交桥进行参数对比研究。研究表明,双向碰撞对主梁横向位移的影响远比纵向位移大,其中桥台间隙对主梁平面转角的影响最大,且平面转角随桥台间隙的增大而减小;横向碰撞对墩柱曲率变形的影响远比纵向碰撞大,其中挡块强度的影响特别大,当挡块强度由0%增至50%时,墩柱纵、横向曲率均值分别增大13.43倍、7.21倍。随着斜交角的增大,梁端纵向位移不断增大,横向位移和平面转角则先增后减;墩底纵向曲率不断增大,横向曲率经历先增后减\,再增的过程;纵向碰撞效应先减弱后增强,而横向碰撞效应则先增强后减弱。由于横向碰撞对墩柱的影响远大于纵向碰撞,因此在斜交角为15°～45°时,宜设法降低横向碰撞效应。     

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。     

大跨度斜拉管线桥地震反应分析

首先利用Newmark-β法和修正的Newton-Raphson法，提出并推导了一种求解几何非线性地震反应方程的方法。利用该方法对大跨度斜拉管线桥进行了线性和非线性地震响应分析。通过结果比较，得出一些有意义的结论：几何非线性效应对斜拉管线桥的地震反应分析影响很大，在分析中不能忽略，尤其是恒载初始内力。     

随机地震动场多点激励下大跨度连续刚构桥的地震反应分析

本文基于随机地震动场的功率谱模型和多点地震激励，建立了大跨度桥梁在随机地震动场多点激励的地震反应分析方法，并数值模拟了某四跨预应力混凝土连续刚构桥的地震反应，考虑了行波效应、部分相干效应和局部场地效应等因素的影响，并与确定性地震一致激励下的计算结果进行了比较。对工程建设具有参考意义。     

Seismic performance evaluation of steel arch bridges against major earthquakes. Part 1: dynamic analysis approach

In this study the inelastic behavior of steel arch bridges subjected to strong ground motions from major earthquakes is investigated by dynamic analyses of a typical steel arch bridge using a three‐dimensional (3D) analytical model, since checking seismic performance against severe earthquakes is not usually performed when designing such kinds of bridge. The bridge considered is an upper‐deck steel arch bridge having a reinforced concrete (RC) deck, steel I‐section girders and steel arch ribs. The input ground motions are accelerograms which are modified ground motions based on the records from the 1995 Hyogoken‐Nanbu earthquake. Both the longitudinal and transverse dynamic characteristics of the bridge are studied by investigation of time‐history responses of the main parameters. It is found that seismic responses are small when subjected to the longitudinal excitation, but significantly large under the transverse ground motion due to plasticization formed in some segments such as arch rib ends and side pier bases where axial force levels are very high. Finally, a seismic performance evaluation method based on the response strain index is proposed for such steel bridge structures. Copyright © 2004 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…