近断层脉冲型地震动作用下隔震结构地震反应分析

隔震结构在远震场地减震效果良好，但是近断层地震动的明显的长周期速度和位移脉冲运动可能对隔震建筑等长周期结构的抗震性能和设计带来不利影响，需要深入探讨。本文首先讨论近断层地震动的长周期脉冲运动特征，然后以台湾集集地震8条典型近震记录和其它4条常用近震记录以及4条远震记录作为地震动输入，对两幢安装铅芯橡胶隔震支座的钢筋混凝土框架隔震结构进行非线性地震反应时程分析，通过比较探讨了算例计算结果，定量说明隔震结构的近震脉冲效应显著，是隔震设计不容忽视的问题。     

近断层脉冲型地震动作用下高层摩擦摆基础隔震结构的减震性能研究

近断层地震动中长周期、短持时和高能量的加速度脉冲将对高层摩擦摆基础隔震结构的减震性能产生不利影响,考虑土-结构相互作用（SSI效应）后的隔震结构将产生动力耦合效应,可能进一步放大隔震结构地震响应。为此,通过一幢框架-核心筒高层摩擦摆基础隔震结构的非线性地震响应分析,考察近断层脉冲型地震动作用下框架-核心筒摩擦摆基础隔震结构的层间位移角、楼层加速度和隔震层变形等响应规律,揭示隔震体系的损伤机理。基于集总参数SR （sway-rocking）模型,分析不同场地类别与不同地震动类型对隔震体系动力响应影响规律。结果表明:高层摩擦摆基础隔震结构在近断层脉冲型地震动作用下的减震效果相比普通地震动减震效果变差,楼层剪力、层间位移角和隔震层变形等超越普通地震动作用下的1.5倍;对于Ⅲ和Ⅳ类场地类别,考虑SSI效应使隔震结构的地震响应进一步放大,弹塑性层间位移角随着土质变软增大尤为明显。     

脉冲型地震动作用下隔震结构动力响应的影响参数研究

通过对隔震结构进行非线性动力响应分析,分别研究地震动参数和支座参数对结构地震响应的影响。首先,建立铅芯橡胶支座基础隔震结构的非线性运动方程;然后,以人工合成脉冲型地震动作为输入,运用MATLAB进行编程并求解结构在脉冲型地震动作用下的地震响应;最后,分别研究速度脉冲周期、支座屈服力、屈服后与屈服前的刚度比对隔震支座最大位移和上部结构层间位移的影响。研究结果表明,脉冲周期对结构地震响应影响很大,在进行隔震设计时应使结构自振周期远离脉冲周期;支座刚度比对结构地震响应影响较大,在进行支座选型时应重点关注;支座屈服力对支座位移的影响显著,屈服力越大,支座位移越小。     

地震动速度脉冲对巨型结构体系地震响应影响研究

以巨-子结构抗震体系、隔震体系以及智能隔震体系为研究对象,选择4组具有速度脉冲特性的实际地震动加速度记录及人工模拟的具有相同加速度反应谱而无速度脉冲的地震动时程分别作为地震动输入,采用数值分析方法分别计算在有、无速度脉冲的地震动激励下三种结构体系的地震响应,探讨地震动的速度脉冲对巨型结构体系在不同控制策略下地震响应的影响。研究结果表明:三种结构体系在速度脉冲型地震动作用下的地震响应大部分要大于无速度脉冲型的地震响应,近断层地震动的速度脉冲对巨-子结构抗震体系、隔震体系以及智能隔震体系的地震响应均有一定的不利影响。智能隔震体系对速度脉冲地震动较为敏感,但能有效地减小隔震层位移。     

近断层地震作用下设备-结构耦合隔震体系动力响应分析

建立设备-结构耦合隔震体系模型,选取近断层脉冲型和非脉冲型地震波各50条,计算耦合隔震体系的动力响应。分析表明,近断层脉冲型地震动对耦合隔震体系的影响大于非脉冲型地震动,且对主体结构的影响大于对设备的影响;近断层脉冲型地震作用下的隔震层位移、层间位移、楼层加速度、设备加速度和设备位移的平均响应分别达到非脉冲型地震作用的2.25倍、2.17倍、2.24倍、1.17倍和1.20倍。进行设备-结构耦合隔震体系设计时,需考虑近断层地震动脉冲作用的影响,同时需注意引起主体结构和设备最大响应的地震动不一定相同。     

长周期地震动参数与隔震结构响应参数的相关性研究

从Chi-Chi地震动数据中选取20条近场长周期地震记录和20条远场长周期地震记录,再从汶川地震渭河地震动数据中选取20条远场长周期地震记录作为输入,研究各个地震动记录相对应的地震动强度参数及其之间的相关性,筛选出了适合于长周期地震动的地震动强度指标,采用Pearson相关系数对筛选出的地震动强度指标与隔震体系的隔震层位移响应之间的相关性进行分析。结果表明:①在近、远场长周期地震动作用下,中长周期隔震结构的隔震层位移响应与频谱特征参数的相关性比较好,在进行中长周期隔震结构的抗震性能研究时,PGD、Sd_avg及DSI与隔震结构的相关性较好,地震动强度指标在集集近场建议选取PGD和Sd_avg,集集远场建议选取DSI和D/V,渭河远场建议选取Sd_avg和DSI;②在强相关范围内考虑相关性的高低,近场和远场的长周期地震动强度指标建议分别选取PGD和DSI。     

近断层地震动破裂向前方向性与滑冲效应对隔震建筑结构抗震性能的影响

选择台湾集集地震和美国北岭地震的近断层地震动记录作为输入,考察了近断层地震动破裂向前方向性与滑冲效应引起的两种不同速度脉冲运动对单自由度体系和长周期橡胶支座隔震建筑结构抗震性能的影响.反应谱分析表明,破裂向前方向性与滑冲效应对工程结构地震响应的影响是随结构周期变化的.在中短周期段,含破裂向前方向性效应地震动的谱加速度值大于含滑冲效应地震动的谱加速度值;而在长周期段,含滑冲效应地震动的谱加速度大于含破裂向前方向性效应的谱加速度值.并且,与无脉冲地震动作用相比,含破裂向前方向性与滑冲效应脉冲的近断层地震动作用下隔震建筑的地震响应显著增大.滑冲效应引起的速度脉冲使隔震建筑底部的层间变形和楼层剪力明显增大,这意味着滑冲效应脉冲比向前方向性效应脉冲对长周期建筑结构的破坏更具危害性.     

近断层地震动作用下LRB隔震储罐地震反应特征研究

采用Bouc-Wen模型模拟铅芯橡胶支座(LRB)非线性力学性能,建立LRB基础隔震储罐地震反应的数值模型.利用叠加原理得到人工合成近断层脉冲型地震动,从实际典型近断层地震动和人工近断层脉冲地震动输入两个角度出发,以远场地震反应为参照,系统探讨了近断层地震动作用下LRB隔震储罐地震反应特点以及近断层地震动运动特征的影响规律.研究发现,近断层地震动作用下LRB隔震储罐地震反应明显大于远场地震反应值,显著的近断层脉冲效应是隔震储罐设计不容忽视的问题.近断层地震动的PGV/PGA值是决定隔震储罐地震反应的综合指标,PGV/PGA值较大时,隔震储罐地震反应脉冲效应突出.另外,脉冲周期、脉冲参与系数以及脉冲类型也是影响LRB隔震储罐地震反应的重要因素.在脉冲参与系数越大、含有脉冲数量越多的近断层地震动作用下,隔震储罐地震反应越强烈.当脉冲周期接近储罐晃动周期时,晃动波高会出现峰值.     

考虑SSI效应的层间隔震结构在三维地震下的响应研究

为探讨三维地震下层间隔震结构考虑土-结构相互作用(SSI效应)时的地震响应,建立了考虑SSI效应的层间隔震结构模型,分别输入一维、二维、三维地震动,比较层间隔震结构在不同维度地震波输入工况下的地震响应。针对三维地震动输入下隔震支座拉压应力超限问题,添加三维隔震装置,并与传统水平隔震结构地震响应结果进行对比分析。结果表明:三维地震动输入下的结构地震响应大于一维和二维;加入三维隔震支座后,竖向地震动被有效隔离,结构地震响应减小,优化了支座受力,支座拉压破坏问题得以解决,地基土体应力小于设置传统水平隔震支座下的土体应力,对地基和基础设计有利。     

双向耦合地震作用下滑移隔震结构振动控制及其优化研究

目前,滑移隔震结构的分析通常只考虑水平地震动而不考虑竖向地震动的影响,有关多向地震动及其相关性的研究也很少。水平与竖向地面运动具有相关性,从而影响控制效果,因此对双向耦合地震作用下滑移隔震结构模型的理论进行研究,建立动力分析模型并得出运动微分方程。以6层滑移隔震结构为例,对其进行地震反应分析。研究表明,在考虑竖向地震作用的情况下,滑移隔震结构也具有良好的控制作用,但是竖向地震作用的存在使结构的地震反应有不同程度的增加,其增量随着竖向地震作用的增加而增加。因此,在高烈度地区的滑移隔震结构应该考虑竖向地震作用对结构的影响。建立滑移隔震装置的参数优化设计模型,采用IHGA程序对结构的重要参数进行优化设计。结果表明,滑移隔震结构在各种工况下的各项地震反应均得到更好的控制。     

近断层双向水平地震作用下隔震结构地震反应

近断层地震动脉冲特性在2个水平分量上具有差异,采用平方和开方法分析了近断层脉冲地震动双向地震作用下基础隔震结构和组合隔震结构的隔震层位移,并与近断层脉冲单向地震作用进行了对比分析,结果表明:若仅地震动加速度峰值大的分量或2个方向分量均存在明显速度脉冲,则产生的隔震层位移大于单向地震动;若仅地震动加速度峰值小的分量存在明...     

Damping coefficients for soil–structure systems and evaluation of FEMA 440 subjected to pulse-like near-fault earthquakes

In this study, attempts are made to investigate the effects of inertial soil–structure interaction (SSI) on damping coefficients subjected to pulse-like near-fault ground motions. To this end, a suit of 91 pulse-like near-fault ground motions is adopted. The soil and superstructure are idealized employing cone model and single-degree-of-freedom (SDOF) oscillator, respectively. The results demonstrate that soil flexibility reduces and amplifies the damping coefficients for structural viscous damping levels higher and lower than 5%, respectively. The coefficients reach one for both acceleration and displacement responses in cases of dominant SSI effects. The effect of structure dimensions on damping confidents are found insignificant. Moreover, damping coefficients of displacement responses are higher than those of acceleration responses for both fixed-base and flexible-base systems. Evaluation of damping correction factor introduced by FEMA 440 shows its inefficiency to predict acceleration response of soil–structure systems under pulse-like near-fault ground motions. Soil flexibility makes the damping correction factor of moderate earthquakes more pronounced and a distinctive peak value is reported for cases with dominant SSI effects.     

Intensity measures for the seismic response prediction of base-isolated buildings

Base isolation has become a widely applied technique for protecting buildings located in highly seismic areas. Due to the strongly non-linear constitutive behaviour typical of many isolation devices, the seismic response of base-isolated buildings is usually evaluated through non-linear dynamic analysis. In this type of analysis a suitable set of ground motions is needed for representing the earthquake loads and for exciting the structural model. Many methods can be found in the literature for defining the ground motions. When natural accelerograms are used, the methods mainly differ from each other based on the intensity measures used for scaling the records to the defined earthquake intensity level. Investigations have been carried out for evaluating the predictive capability of the intensity measures used in these methods: while many studies focused on ordinary buildings, only a few focused on base-isolated ones. The objective of this paper is to evaluate the most commonly used intensity measures, which are currently available in the literature, with respect to their capability to predict the seismic response of base-isolated buildings. Selected for the investigation are two frame structures characterized by a different number of storeys and base-isolated with systems having different properties. Two sets of accelerograms, consisting of ordinary and pulse-like near-fault records, are used in the analyses and in the evaluation of the intensity measures. Modified versions of existing intensity measures are also proposed, with the intent of improving the correlations between the considered intensity measures and response quantities.     

Seismic response evaluation of base-isolated reinforced concrete buildings under bidirectional excitation

This paper reports on an investigation of the seismic response of base-isolated reinforced concrete buildings, which considers various isolation system parameters under bidirectional near-fault and far-fault motions. Three-dimensional models of 4-, 8-, and 12-story base-isolated buildings with nonlinear effects in the isolation system and the superstructure are investigated, and nonlinear response history analysis is carried out. The bounding values of isolation system properties that incorporate the aging effect of isolators are also taken into account, as is the current state of practice in the design and analysis of base-isolated buildings. The response indicators of the buildings are studied for near-fault and far-fault motions weight-scaled to represent the design earthquake (DE) level and the risk-targeted maximum considered earthquake (MCE_R) level. Results of the nonlinear response history analyses indicate no structural damage under DE-level motions for near-fault and far-fault motions and for MCE_R-level far-fault motions, whereas minor structural damage is observed under MCE_R-level near-fault motions. Results of the base-isolated buildings are compared with their fixed-base counterparts. Significant reduction of the superstructure response of the 12-story base-isolated building compared to the fixed-base condition indicates that base isolation can be effectively used in taller buildings to enhance performance. Additionally, the applicability of a rigid superstructure to predict the isolator displacement demand is also investigated. It is found that the isolator displacements can be estimated accurately using a rigid body model for the superstructure for the buildings considered.     

一种改进的近断层脉冲型地震动模拟方法

本文基于小波包技术的随机地震动模拟方法,提出一种改进的参数化随机近断层脉冲型地震动模拟方法。然后,通过识别和提取近断层脉冲型地震动数据库中脉冲型地震动的特征参数,建立了基于震源、传播路径和场地特征等参数的脉冲模型参数预测方程。最后,通过模拟实际记录和误差分析检验了改进的模拟方法的有效性。结果表明:应用改进的模拟方法得到的地震动时程无论在波形、频率特性还是峰值上均与实际记录具有较好的一致性。改进的模拟方法在保留地震动时频非平稳性的基础上,能够有效地提高近断层脉冲型地震动的模拟效果,并且能够很好地体现脉冲型地震动的主要特征。     

近断层速度脉冲地震动的三维有限差分模拟

根据台湾西部地质地貌特征和1999年集集M_W7.6地震的研究成果,建立三维速度结构模型和震源模型,并采用三维有限差分法对双冬断层可能产生的近断层脉冲型地震动进行数值模拟。结果表明,方向性效应引起的双向速度脉冲集中在垂直于断层滑动分量的方向上,而滑冲效应引起的单向速度脉冲则集中在平行于断层滑动分量的方向上。受方向性效应和上盘效应的共同调制,近断层脉冲型地震动反映出不对称带状分布的特征,速度脉冲主要分布在距离断层面约10 km的范围内。凹凸体的特性影响着地震动的时空分布,由地震波场显示南投和台中处于强地震动危险区。近场脉冲型地震动的研究对分析速度脉冲形成机理以及地震危险性有一定的参考意义。     

Detection of pulse-like ground motions based on continues wavelet transform

This paper implements a quantitative approach to detect pulse-like ground motions based on continues wavelet transform, which is able to clearly identify sudden jumps in time history of earthquake records by considering contribution of different levels of frequency. These analyses were performed on a set of time series records obtained in near-fault regions of Iran. Pulse-like ground motions frequently resulted from directivity effects in near-fault area and are of interest in the field of seismology and also earthquake engineering for seismic performance evaluation of structures. The results of this study basically help us to establish a suitable platform for selecting pulse-like records, while performance evaluation of structure in near-fault area will need to account. The period of velocity pulses as a key parameter that significantly affects structural response is simply determined by using a pseudo-period of the mother wavelets. In addition, the efficiency of different types of mother wavelets on classification performance and the features of detected pulse are investigated by applying seven different kinds of mother wavelets. The analyses indicate that the selection of most appropriate mother wavelet plays a significant role in effective extraction of ground motion features and consequently in estimation of velocity pulse period. As a result, the user should be aware of what is selected as a mother wavelet in the analysis. The comparisons given here among different mother wavelets also show the better performance of BiorSpline (bior1.3) basis from biorthognal wavelet families for the preferred purpose in this paper.