基于位移设计的钢筋混凝土桥墩抗震性能试验研究(Ⅱ):振动台试验

通过模型振动台试验研究了基于位移设计的钢筋混凝土桥墩的抗震性能。以完成的拟静力试验中的桥墩试件为参考原型,利用基于位移抗震设计方法和现行桥梁抗震规范方法设计了4根1:2的钢筋混凝土桥墩试件并进行了模型振动台试验。对小震、中震和大震作用下桥墩试件的破坏形态、加速度和位移反应、位移延性系数和地震总输入能(耗能)等方面进行了比较分析。综合拟静力试验和振动台试验结果,可以认为基于位移设计的钢筋混凝土桥墩能够达到预期的延性抗震要求。     

A measure of the capacity of earthquake ground motions to damage structures

Even though a number of parameters have been proposed in the literature for measuring the capacity of earthquake ground motions to damage structures, most of them are not consistent with building damage observed during earthquakes. In this study, a parameter for measuring seismic damage capacity is proposed. It uses the energy dissipated by a structure in inelastic deformations and a structural overall drift, and it is evaluated for three typical ground motions recorded in severe earthquakes. By using this parameter, consistent results with building damage observed in these earthquakes are obtained, which indicate the importance of displacement control for minimizing seismic damage.     

Development of damage probability matrices based on Greek earthquake damage data

A comprehensive study is presented for empirical seismic vulnerability assessment of typical structural types, representative of the building stock of Southern Europe, based on a large set of damage statistics. The observational database was obtained from post-earthquake surveys carried out in the area struck by the September 7, 1999 Athens earthquake. After analysis of the collected observational data, a unified damage database has been created which comprises 180,945 damaged buildings from/after the near-field area of the earthquake. The damaged buildings are classified in specific structural types, according to the materials, seismic codes and construction techniques in Southern Europe. The seismic demand is described in terms of both the regional macroseismic intensity and the ratio αg/ao, where αg is the maximum peak ground acceleration (PGA) of the earthquake event and ao is the unique value PGA that characterizes each municipality shown on the Greek hazard map. The relative and cumulative frequencies of the different damage states for each structural type and each intensity level are computed in terms of damage ratio. Damage probability matrices (DPMs) and vulnerability curves are obtained for specific structural types. A comparison analysis is fulfilled between the produced and the existing vulnerability models.     

Correlations between Energy and Displacement Demands for Performance-Based Seismic Engineering

The development of a scientific framework for performance-based seismic engineering requires, among other steps, the evaluation of ground motion intensity measures at a site and the characterization of their relationship with suitable engineering demand parameters (EDPs) which describe the performance of a structure. In order to be able to predict the damage resulting from earthquake ground motions in a structural system, it is first necessary to properly identify ground motion parameters that are well correlated with structural response and, in turn, with damage. Since structural damage during an earthquake ground motion may be due to excessive deformation or to cumulative cyclic damage, reliable methods for estimating displacement demands on structures are needed. Even though the seismic performance is directly related to the global and local deformations of the structure, energy-based methodologies appear more helpful in concept, as they permit a rational assessment of the energy absorption and dissipation mechanisms that can be effectively accomplished to balance the energy imparted to the structure. Moreover, energy-based parameters are directly related to cycles of response of the structure and, therefore, they can implicitly capture the effect of ground motion duration, which is ignored by conventional spectral parameters. Therefore, the identification of reliable relationships between energy and displacement demands represents a fundamental issue in both the development of more reliable seismic code provisions and the evaluation of seismic vulnerability aimed at the upgrading of existing hazardous facilities. As these two aspects could become consistently integrated within a performance-based seismic design methodology, understanding how input and dissipated energy are correlated with displacement demands emerges as a decisive prerequisite. The aim of the present study is the establishment of functional relationships between input and dissipated energy (that can be considered as parameters representative of the amplitude, frequency content and duration of earthquake ground motions) and displacement-based response measures that are well correlated to structural and non-structural damage. For the purpose of quantifying the EDPs to be related to the energy measures, for comprehensive range of ground motion and structural characteristics, both simplified and more accurate numerical models will be used in this study for the estimation of local and global displacement and energy demands. Parametric linear and nonlinear time-history analyses will be performed on elastic and inelastic SDOF and MDOF systems, in order to assume information on the seismic response of a wide range of current structures. Hysteretic models typical of frame force/displacement behavior will be assumed for the local inelastic cyclic response of the systems. A wide range of vibration periods will be taken into account so as to define displacement, interstory drift and energy spectra for MDOF systems. Various scalar measures related to the deformation demand will be used in this research. These include the spectral displacements, the peak roof drift ratio, and the peak interstory drift ratio. A total of about 900 recorded ground motions covering a broad variety of condition in terms of frequency content, duration and amplitude will be used as input in the dynamic analyses. The records are obtained from 40 earthquakes and grouped as a function of magnitude of the event, source-to-site condition and site soil condition. In addition, in the data-set of records a considerable number of near-fault signals is included, in recognition of the particular significance of pulse-like time histories in causing large seismic demands to the structures.     

基于易损性指数的S RC框架核心筒结构地震损伤评估

设计1个20层SRC框架核心筒结构模型,考虑地震的随机性和结构材料的不确定性,采用拉丁超立方体抽取结构-地震动样本,之后对其进行增量动力分析（IDA）,以第1周期谱加速度为强度指标,最大层间位移角为结构需求,定义4个性能水平,研究该结构的易损性。通过引入群体结构震害评估中易损性指数的概念,计算多遇、设防和罕遇地震下的易损性指数。结果表明:以易损性指数作为评价指标,该结构在多遇地震作用下,处于轻微破坏状态;在设防地震作用下,处于中等破坏状态;在罕遇地震作用下,结构处于严重破坏状态。可认为依据我国抗震规范设计的SRC框架核心筒结构能够满足"小震不坏"、"中震可修"和"大震不倒"的抗震设防目标。     

Analytical predictions of the seismic response of friction damped timber shear walls

A new concept for the earthquake resistant design of timber shear wall structures is proposed. By providing friction devices in the corners of the framing system of the shear wall, its earthquake resistance and damage control potential can be enhanced considerably. During severe earthquake excitations, the friction devices slip and a large portion of the seismic energy input is dissipated by friction rather than by inelastic deformation of the sheathing-to-framing connectors. A simple numerical model is developed and results of inelastic time-history dynamic analyses show the superior performance of the friction damped timber shear walls compared to conventional shear wall systems. The proposed friction devices act both as safety valves by limiting the inertia forces transmitted to the structure, and as structural dampers by dissipating a significant portion of the seismic energy input. The devices can be used in any configuration of the framing system to accommodate architectural or construction requirements. The damping system may also be conveniently incorporated in existing timber shear wall buildings to upgrade significantly their earthquake resistance.     

既有钢筋混凝土框架结构的多指标云模型地震损伤评估

目前的既有钢混结构地震损伤研究没有同时考虑不同抗震设计规范差异和耐久性两个因素对结构抗震性能的影响,且损伤指标较简单,在动力损伤分析中也存在局限。基于云模型的特点,提出了包括弹塑性耗能差率、刚度损伤指数、层间位移角和顶点位移角的多元结构损伤状态综合评估方法,能够同时考虑结构各损伤指数的随机性和模糊性。考虑不同版本抗震设计规范造成的结构性能差异和耐久性下降对结构性能的影响,设计3个典型五层钢混框架结构,进行增量动力分析,验证损伤评估方法的准确性。结果表明：随着抗震规范版本的更新,结构的损伤程度有适当减轻;同一结构的损伤程度因混凝土碳化作用先减轻后加重;采用弹塑性耗能差率表征既有结构的地震损伤效果优于刚度损伤指数;基于多指标云模型损伤评估方法获得的云模型综合隶属度和综合损伤值能够更加细化和精确地描述结构损伤状态。     

Seismic response and damage analysis of buildings supported on flexible soils

The investigation reported in this paper studies the effects of soil–structure interaction (SSI) on the seismic response and damage of building–foundation systems. A simple structural model is used for conducting a parametric study using a typical record obtained in the soft soil area of Mexico City during the 1985 earthquake. Peak response parameters chosen for this study were the roof displacement relative to the base and the hysteretic energy dissipated by the simple structural model. A damage parameter is also evaluated for investigating the SSI effects on the seismic damage of buildings. The results indicate that in most cases of inelastic response, SSI effects can be evaluated considering the rigid‐base case and the SSI period. Copyright © 2000 John Wiley & Sons, Ltd.     

川南地区砖混结构房屋典型震害及地震易损性研究

以川南地区为研究区,并以在建造方式上具有明显当地地域特征的砖混结构房屋为研究对象,结合砖混结构房屋建造特点及川南历史地震(如长宁6.0级地震)震害调查结果等,分析砖混结构房屋典型震害特征,统计其在不同烈度下不同破坏等级的比例,采用经验分析法得到初步的易损性矩阵。在此基础上,针对因样本局限性造成的结构在高烈度下破坏比例不全,使实际易损性矩阵缺失的问题,通过插值法,推算高烈度下的破坏比例,补全经验易损性矩阵,拟合出易损性曲线,建立以震害统计为主、数值模拟为辅的砖混结构易损性分析模型;并基于平均震害指数对比分析,对易损性分析的可靠性进行检验。结果表明,构建的易损性矩阵能客观反映川南地区砖混结构房屋的抗震能力,对开展震害预测、灾害损失评估及震害风险评估等工作具有实际应用价值。     

保定市典型多层砖混结构震害预测分析

将保定市42栋典型多层砖混结构分别按照年代、用途、层数分类,采用结构易损性方法进行震害预测分析,得出各自震害矩阵,并以平均抗震能力指数评价其抗震能力。分析结论可为保定市多层砖混群体震害预测提供参考。     

损失分布和非结构损失对房屋建筑地易损性的影响

房屋建筑的地震易损性是地震损失评估和地震巨灾风险模型的基础。作为房屋建筑的重要组成部分,各类非结构构件的损失在现有的易损性模型中并未得到足够重视。本文以一栋典型钢筋混凝土框架结构教学楼为对象,通过将房屋建筑中的各类构件划分为具有不同地震损伤特性和损失后果的易损性组,考察建筑内的损失分布和非结构损失对房屋建筑地震易损性的影响。分析结果表明:由于许多非结构构件在中小地震作用下即可能发生较严重的破坏,房屋建筑在中小地震下的易损性主要受非结构损失控制;随着地震动强度等级的不断提高,结构损伤渐趋严重,结构损失对整体建筑易损性的影响不断增大;在结构进入震后不可修状态之前,建筑不同楼层的损失分布是评估建筑地震损失时不可忽略的因素。     

铁路梁式桥地震灾害损失评估

针对铁路桥梁地震灾害评估中多因素影响问题,结合铁路桥梁地震灾害的复杂特点和各结构层次的震害表现形式,从桥面系、上部结构和下部结构3个方面构建铁路梁式桥地震灾害评估指标体系.基于改进的层次分析法计算了各评估指标的权重,以桥梁承灾系统为研究主体,运用多级综合模糊理论,建立铁路梁式桥震害评估模型.结合汶川地震中一座铁路混凝土...     

Observed and predicted earthquake damage scenarios: the case study of Pettino (L’Aquila) after the 6th April 2009 event

A damage scenario based on observational data collected in L’Aquila Municipality after the 6th April 2009 earthquake is compared with a predicted damage scenario derived from the application of a simplified analytical method for seismic vulnerability assessment of Reinforced Concrete (RC) buildings at large scale. The observational damage scenario is derived from a database of 131 RC buildings located in the Municipality of L’Aquila, which after the 2009 earthquake were subjected to post-earthquake usability assessment procedure. The simplified analytical approach adopted is based on the Capacity Spectrum Method to evaluate seismic capacity at different Damage States (DSs) based on the displacement capacity of structural and non-structural elements. DSs and the corresponding displacement capacity are defined through the interpretation of the observational-based DSs provided by the European Macroseismic Scale EMS-98. Data predicted by the adopted methodology are in good agreement with the observed damage distribution. The observed damage scenario is also compared with predicted scenarios derived from other methodologies from literature.     

基于BP神经网络的有限特征参数砌体结构震害等级推演

详细的建筑结构特征参数是得到合理地震易损性分析结果的基础.本文给出了一种结合已有地震易损性分析成果,在具备有限特征参数的情况下,利用BP神经网络进行单体或群体结构震害等级推演的方法.以陕西省渭南市607栋设防砌体易损性评估结果为样本构建了一个3层BP神经网络模型,并对北京市海淀区近2万栋设防砌体不同地震烈度下的可能破坏...     

罕遇地震下高层RC框架结构双地震动强度参数易损性分析

为研究高层RC框架结构罕遇地震下的易损性,设计了一个7度区典型11层RC框架结构。采用IDA方法进行时程分析,以地震动峰值地面加速度和结构第一自振周期对应的谱加速度为地震动强度指标,最大层间位移角为结构损伤指标,分别得到了单一地震动强度和双地震动强度参数下的IDA曲线和失效概率,绘制了双地震动强度参数下易损性曲面,并对单一地震动强度和双地震动强度参数下的易损性分析结果进行了对比。结果表明:罕遇地震下,采用双地震动强度参数结构失效概率明显低于采用单一地震动强度参数结构失效概率;对高层RC框架结构,采用双地震动强度参数进行易损性分析反映的地震动信息更全面;采用双地震动强度参数得到的结构失效概率公式更能真实量化不同强度地震作用下结构的失效概率。     

Prediction of seismic energy dissipation in SDOF systems

A simple analytical procedure is developed for calculating the seismic energy dissipated by a linear SDOF system under an earthquake ground excitation. The ground excitation is specified by its pseudo-velocity spectra and effective duration whereas the SDOF system is defined by its natural period of vibration and viscous damping ratio. However, the derived relationship for the energy dissipation demand under an earthquake excitation is sensitive neither to the viscous damping ratio nor the ductility ratio when the SDOF system undergoes inelastic response. Accordingly, the proposed relationship can be employed in an energy-based seismic design procedure for determining the required energy dissipation capacity of a structural system.     

Geological Observations of Damage Asymmetry in the Structure of the San Jacinto, San Andreas and Punchbowl Faults in Southern California: A Possible Indicator for Preferred Rupture Propagation Direction

We present new in situ observations of systematic asymmetry in the pattern of damage expressed by fault zone rocks along sections of the San Andreas, San Jacinto, and Punchbowl faults in southern California. The observed structural asymmetry has consistent manifestations at a fault core scale of millimeters to meters, a fault zone scale of meters to tens of meters and related geomorphologic features. The observed asymmetric signals are in agreement with other geological and geophysical observations of structural asymmetry in a damage zone scale of tens to hundreds of meters. In all of those scales, more damage is found on the side of the fault with faster seismic velocities at seismogenic depths. The observed correlation between the damage asymmetry and local seismic velocity structure is compatible with theoretical predictions associated with preferred propagation direction of earthquake ruptures along faults that separate different crustal blocks. The data are consistent with a preferred northwestward propagation direction for ruptures on all three faults. If our results are supported by additional observations, asymmetry of structural properties determined in field studies can be utilized to infer preferred propagation direction of large earthquake ruptures along a given fault section. The property of a preferred rupture direction can explain anomalous behavior of historic rupture events, and may have profound implications for many aspects of earthquake physics on large faults.     

Effects of structural characterizations on fragility functions of bridges subject to seismic shaking and lateral spreading

This paper evaluates the seismic vulnerability of different classes of typical bridges in California when subjected to seismic shaking or liquefaction-induced lateral spreading. The detailed structural configurations in terms of superstructure type, connection, continuity at support and foundation type, etc. render different damage resistant capability. Six classes of bridges are established based on their anticipated failure mechanisms under earthquake shaking. The numerical models that are capable of simulating the complex soil-structure interaction effects, nonlinear behavior of columns and connections are developed for each bridge class. The dynamic responses are obtained using nonlinear time history analyses for a suite of 250 earthquake motions with increasing intensity. An equivalent static analysis procedure is also implemented to evaluate the vulnerability of the bridges when subjected to liquefaction-induced lateral spreading. Fragility functions for each bridge class are derived and compared for both seismic shaking （based on nonlinear dynamic analyses） and lateral spreading （based on equivalent static analyses） for different performance states. The study finds that the fragility functions due to either ground shaking or lateral spreading show significant correlation with the structural characterizations, but differences emerge for ground shaking and lateral spreading conditions. Structural properties that will mostly affect the bridges＇ damage resistant capacity are also identified.     

基于振动台试验的移动通信节点机房蓄电池组地震易损性分析

关键移动通信设备的地震易损性是城市移动通信系统地震灾害预测的基础。本文以移动通信系统节点机房中常用的蓄电池组作为研究对象,通过振动台试验来研究蓄电池组的抗震性能,并获得其地震易损性。试验过程中,首先采用FEMA P695建议的方法从美国PEER强震数据库中遴选出对蓄电池组较为危险的地震动记录作为试验激励,随后逐步增大各条地震动记录的幅值,基于振动台进行增量动力分析。试验后根据蓄电池组的地震损伤特征,定义了其损伤指标和损伤水平,并基于振动台试验数据分析获得了典型蓄电池组的地震易损性曲线。     

汶川地区震后钢筋混凝土框架结构的地震易损性研究

以汶川地震为研究背景,针对震后典型钢筋混凝土框架结构进行地震易损性研究。基于Cornell理论框架结合汶川地质资料,拟合出考虑场地特点的地震危险性模型,同时定义损伤水平状态及限值指标,以概率解析易损性研究方法为基础,运用考虑地震动参数的解析易损性评估方法绘制汶川地区钢筋混凝土框架建筑的地震易损性曲线。研究结果表明:考虑地震动参数的概率解析易损性研究方法是一种有效的地震易损性评估方法;以PGA作为地震强度输入指标的结构反应,随自振周期的增大体系最大响应的相关性降低,结构各个损伤状态的失效概率均随之增大。