抗震设计规范之近断层中小地震影响

近年来发生的中小震级地震中 ,在靠近断层附近观测到的记录中具有显著加速度和速度峰值 ,对结构造成了极大的破坏 ,同时 ,现行抗震设计规范多是以大震级地震记录为基础建立起来的 ,很少考虑断层距对结构地震反应的影响。本文在充分收集近断层地震记录的基础上 ,对近断层中小震级地震动的峰值和反应谱进行了统计分析 ,并和我国的结构抗震设计规范进行了对比 ,指出了现行抗震设计规范的不足之处 ,得出了一些有益的结果 ,为今后抗震设计规范的完善和结构的抗震计算提供了参考。     

结构需求概率危险性分析中强震记录选取研究#br#

目前结构性态地震工程中易损性曲线传统计算流程对强震记录选取不够重视,鲜有对目标场址地震概率危险性的考虑,因而以同时考虑地震概率危险性和结构自振周期特性的条件均值谱作为记录选取依据,将结果应用到IDA方法和条带法中,并与地震事件随机散布的传统云图法进行对比。以某八层平面框架作为算例,将云图法与IDA方法以及条带法在四种极限状态下的结构需求易损性曲线以及结构需求概率危险性曲线进行对比分析。其中,随机选取两组地震事件（M,R）分布范围相仿的强震记录进行云图法计算,二者结果由于不可控的地震动不确定性而存在显著差异,但IDA方法与条带法由于采用条件均值谱对地震动进行了控制,彼此结果基本一致,更符合实际工程场址的危险性需求,同时为后期不同区域的结构性态分析损失评估提供了依据。     

中国广义条件参数目标谱构建方法及地震动输入

为了在时程分析中考虑加速度反应谱之外的强度指标,构建了兼顾危险一致性和参数完备性的广义条件参数目标谱用于地震动记录选取。结合我国地震安全性评价中设定地震解耦的特点,提出利用各个潜源微元的贡献率作为权重计算条件均值向量,进而通过拉丁超立方分层抽样得到多元正态分布假设下的广义强度参数条件分布,即广义条件参数目标谱。通过K-S假设检验的D值法在数据库中搜寻最符合目标分布的记录组合作为选波结果。以我国某工程的地震安全性评价为实例,构建同时考虑幅值、频谱、持时以及谱强度指标的广义条件参数目标谱。结果表明：考虑设定地震贡献率修正的强度指标目标分布与单一设定地震的结果存在差异;广义条件谱记录选取结果的危险性曲线和场址概率危险性分析的结果基本一致;在低超越概率水平下, 广义条件谱下的危险一致性不及仅考虑加速度反应谱指标的条件谱。     

A new proxy for ground motion selection in seismic collapse assessment of tall buildings

Tall buildings are long‐period structures that are sensitive to the long‐period content of ground motions. Selection of appropriate ground motions is an important step in seismic collapse assessment of tall buildings using nonlinear dynamic analyses. Epsilon (ε_Sa) and eta (η) are two spectral shape indicators, which have been recently proposed for ground motion selection in the technical literature. In this study, a new parameter gamma (γ) is proposed, which has considerable correlation with the collapse capacity of long‐period structures having a fundamental period greater than 1 s. This parameter is a linear combination of ε_Sa and the displacement spectrum intensity epsilon (ε_DSI). The parameter γ is obtained and optimized by applying the particle swarm optimization algorithm. Since γ has significant correlation with the collapse capacity of long‐period structures, it can be used as an efficient proxy for ground motion selection in seismic collapse assessment of tall buildings. The results of this study show that ground motion selection considering the new proxy γ causes reduction in the dispersion of structural response and also decrease in the mean annual frequency of collapse, when compared with ground motion selection based on ε_Sa and η. Copyright © 2013 John Wiley & Sons, Ltd.     

核电厂抗震设计谱确定方法分析

抗震设计谱是核电厂抗震设计的主要依据。核电设计谱的表达多采用直线分段式方法,一般由固定的设计谱形与具有一定保证概率的地震动幅值共同组成。简要回顾核电设计谱的发展历程,对核电设计谱的主要确定方法进行比较和分析,探讨统一危险性谱在核电抗震应用中的问题。基于近期发生的强震动数据库,按4种设计谱标定方法分别计算设计谱以及反映设计谱稳定性的规准伪速度谱谱比曲线。分析结果表明,基于双规准反应谱的设计谱在速度控制段的谱值明显偏高,直接基于伪速度谱的设计谱标定方法具有稳定性优势。最后,为我国核电设计谱进一步研究工作的开展提出些许看法和建议。     

基于条件谱记录选取的工程需求概率危险性计算方法

传统云图法和条带法计算工程需求概率危险性曲线(EDHC)时,存在地震危险性水平不可控、理想假设过多和计算成本较大等弊端。在第三代性态地震工程的框架思路下,对现有条带法进行改进,以条件目标谱作为记录选取依据,得到了考虑场址地震危险性特征的EDHC改进计算方法。采用自振周期约为1.0s的10层钢筋混凝土平面框架作为结构算例进行验证。以中国某场址地震安全性评价实例为设定地震解耦依据,构建不同场址地震动危险性水平下条件周期T=1.0s的条件目标谱簇。在进行多危险性水平下的记录选取后,采用改进条带法计算目标结构最大层间位移角和顶层位移的EDHC曲线。与传统云图法的计算结果对比表明,云图法的诸多假设在高地震动输入水平下并不严格成立,最终导致EDHC曲线在年超越概率不大于2%时被显著高估。而采用改进条带法的计算结果表明,即使采用与结构自振周期相关性较弱的0.01s作为条件周期进行后续调幅和选波,与基于Sa(T=1.0s)的EDHC计算结果依然可以保持较好一致性。研究结果证明：该方法可以控制各调幅条带下记录的地震危险性水平一致,且与选择的地震动强度指标无关,可以在计算工程需求概率危险性时合理考虑目标场址的地震危险性特性。     

Numerical and comparative study of earthquake intensity indices in seismic analysis

Elastoplastic and time‐dependent analysis of seismic structures has become a major analysis technique in popularly accepted performance‐based seismic design. However, the primary difficulty in using this technique is the lack of a unified criterion in the selection of various intensity indices of ground motions. Various earthquake factors influencing the elastoplastic response of seismic structures are highly sophisticated. Hence, it is vitally important to choose an appropriate and comprehensive earthquake intensity index to achieve an accurate correlation with the structural performance. In this study, a total of 30 earthquake intensity indices published in the literature are reviewed and are evaluated through correlation analysis based on 60 ground motion records. Examined herein is the correlation between existing earthquake intensity indices and the seismic responses of elastoplastic single degree‐of‐freedom and multi degree‐of‐freedom systems. The characteristics and applicability of such indices are also discussed in some detail, based on which appropriate earthquake intensity indices are recommended. Copyright © 2011 John Wiley & Sons, Ltd.     

隔震结构动力弹塑性分析地震记录选择的波谱分类法研究

高层隔震结构动力弹塑性时程分析地震记录选择是隔震结构地震响应分析的关键,针对地震记录选取提出基于模糊聚类算法结合地震动强度指标进行地震波子集选取的波谱分类法。首先采用动力弹塑性时程方法对隔震结构的等效单自由度简化模型和三维空间模型进行了地震加速度峰值、地震波速度峰值、地震波位移峰值、地震波速度峰值与加速度峰值之比、加速度反应谱、等效速度反应谱6类地震动强度指标与工程需求参数相关性的比较研究,确定了适合隔震结构的有效地震动强度指标。隔震整体结构工程需求参数包含上部结构层间变形、顶层加速度和隔震层位移响应。其后采用构造的地震动指标矩阵应用于地震波样本属性的表征,并基于模糊聚类算法对地震波样本进行了分类。以某15层高层钢框架-混凝土核心筒隔震结构为例,通过将未分类的地震波集合与分类地震波子集作用下结构的地震响应离散性对比研究,确认了波谱分类法在地震动筛选应用中的有效性。     

台湾美浓6.7级地震框架结构震害调查与分析

2016年2月6日我国台湾高雄市美浓地区发生MS 6.7级强地震及多次余震,对台湾南部地区造成严重影响。为了研究台湾美浓地震中框架结构的震害原因,在对台南地区震害调查的基础上,首先,根据新化、草岭、善化、台南市、七股等五个台站的地震动数据,从地面峰值速度、脉冲属性和频谱特性等方面,分析了地震动的主要特征|然后,从整体结构、梁柱构件、填充墙、非结构构件和地基土液化等方面,阐述了其震害特征|最后,结合震害调查工作,从近断层脉冲型地震、地基土液化防治、抗震概念设计及隔震减震技术应用等方面,对建筑抗震设计提出了建议。     

基于总输入能量谱与瞬时输入能量谱的设计谱修正

地震动中的长周期成分对长周期结构的影响不容忽视,现行的设计反应谱为了保证长周期结构抗震设计具备保守性,人为增大了特定频段和特定场地条件的谱值。针对目前设计谱的不足,依据线性单自由度体系的地震动总输入能量谱和瞬时输入能量谱,对规范反应谱5Tg～6s直线下降段提出调整方法。从具有速度 脉冲特征的长周期地震记录中选出能量谱值最大的地震记录加以说明,得到修正后的加速度谱与相应的拟速度谱和位移谱。建议的反应谱修正方法综合体现了总输入能量与瞬时输入能量的特征,对于工程结构设计具有重要的理论意义和实用价值。     

不同震源机制的近断层脉冲型地震动频谱特性及强度指标研究

将不同场地类别和震源机制上的118条近断层地震记录进行分类,基于基础隔震结构的双自由度体系简化模型,利用状态空间法及四阶龙格-库塔法对结构的弹塑性反应谱进行求解,研究了场地类别和震源机制对反应谱频谱特性的影响。通过分析近断层地震记录的3个强度指标与基础隔震结构最大弹塑性响应的相关性,探讨了基础隔震结构地震反应分析时强度指标的选取问题。结果表明,三种场地类别条件中,速度反应谱规律不明显,但逆断层地震动的平均加速度反应谱和逆斜断层地震动的平均位移反应谱均最大。场地类别和震源机制不同,地震动强度指标与结构响应的相关程度不同。因此在进行近断层脉冲型地震动作用下基础隔震结构地震反应分析时,建议考虑结构所在场地及地震动的震源机制后采用不同地震动强度指标来选择和调整地震动输入。     

地震动速度脉冲对不同高宽比基础隔震结构抗震性能的影响

为研究近断层地震动的速度脉冲对基础隔震结构地震反应的影响,建立了不同高宽比的传统抗震及基础隔震框架结构有限元模型,选取了6条具有向前方向性效应和滑冲效应速度脉冲的实际近断层强震记录作为结构基础输入地震动,对8个模型进行了非线性动力时程分析,对比分析了传统抗震及基础隔震框架结构模型的层间位移角、支座位移和基底剪力等反应。结果表明：在近断层速度脉冲型地震动作用下,随着结构高宽比的增加,基础隔震结构的层间位移角和基底最大剪力逐渐增加,而隔震支座位移有先增大后减小的趋势,且随着地震动峰值速度与峰值加速度比值的增大,隔震支座位移也逐步增大;基础隔震对高宽比小于3的结构具有较好的减震效果,且高宽比越小其减震效果越好,但是当结构高宽比为4时,基础隔震效果较差;近断层地震动的速度脉冲对基础隔震结构底部楼层的不利影响会导致结构出现倒塌破坏。     

New insights on effects of directionality and duration of near‐field ground motions on seismic response of tall buildings

The effects of ground motion directionality on seismic response of buildings are at the center of ongoing debate among earthquake engineering professionals and researchers. This has prompted a renewed interest to have a better understanding of directionality effects of near‐field pulse‐like ground motions on seismic response of tall buildings to further improve seismic design in this respect. In particular the prediction of the maximum displacement response along the structural axis which is called the critical displacement response. This paper presents the results from parametric studies that investigate the directionality effects on nonlinear dynamic response of simple structures and a tall building. The outcome of these analyses was the development of a method, which relies on the maximum velocity to provide a good approximation to the critical displacement response. The method developed is computationally efficient and involves less calculation than other methods. In addition, it was determined that the building responses to records rotated to fault‐normal can lead to significant underestimation of the maximum response along the structural axis, using the fault‐parallel ground motion also may lead to large response differences and smaller yet significant differences when using the maximum direction ground motion.     

基于速度脉冲地震动的边坡地震位移统一预测模型

采用基于小波变换的多向地震动速度脉冲特性鉴定方法,从NGA数据库及汶川地震动记录中提取出了196条速度脉冲地震动数据;基于Newmark非耦合滑动模型,考虑土体非线性特征。通过计算速度脉冲地震动作用下不同强度(k_y)及初始自振周期(T_s)边坡模型的地震位移,对比分析了边坡地震位移与速度脉冲地震动参数之间的相关性,并建立了适用于近断层速度脉冲地震动的边坡地震位移统一预测模型。结果表明：既有边坡地震位移预测模型低估了近断层速度脉冲地震动引起的位移值,而用于预测近断层非脉冲地震动引起的边坡地震位移离散较小;近断层速度脉冲地震动引起的边坡地震位移与其速度脉冲特性密切相关,地震位移与速度脉冲地震动参数(峰值速度PGV)相关性最好;采用1.5倍边坡自振周期对应的加速度反应谱(S_a(1.5T_s))和 PGV分别代表速度脉冲地震动的频谱成分及速度脉冲特征,能够综合反映速度脉冲地震动对边坡地震位移的影响;建立了基于边坡参数(k_y, T_s)和脉冲地震动参数(PGV, S_a(1.5T_s))的边坡地震位移预测模型,为考虑近断层地震动速度脉冲特性影响的边坡地震位移概率灾害分析提供了基础。     

设计用地震动总输入能量谱研究

地震动总输入能量的确定是基于能量的设计方法首先要解决的关键问题。本文以单自由度弹性系统为研究对象,分析了地震动三要素和结构自身参数对输入能量谱因素的影响。结果表明,地震动幅值、频谱特性和强震持时都对能量谱值有较大影响,其中频谱特性还影响能量谱峰值出现的结构周期段;结构阻尼比的增大能有效降低能量谱峰值。通过输入160条国内外历次地震中不同场地上的地震动记录,总结能量谱曲线形状规律,提出了设计用三段式简化能量谱曲线。给出了地震动记录所属场地类型的划分标准,建议了确定能量谱峰值的不同场地条件地震动频谱特性V/A和强震持时tD的取值,采用标准化方法提出了4类场地条件的设计用能量谱曲线峰值及其它参数的计算式,给出了结构设计总输入能量计算过程。算例分析结果表明,该输入能量谱形式简单、计算方便,结果安全可靠。     

Method of selecting design earthquake ground motions for tall buildings

In most current seismic design procedures, an earthquake hazard of the design earthquake load is usually defined as a 10% probability of exceedance in 50 years. However, tall buildings and emergency hazard facilities need to be safe against more severe ground shakings than code‐defined design earthquake hazards. Earthquake hazard can be expressed by a 5% damped Linear Elastic Design Response Spectrum (LEDRS) obtained from statistical research using spectral responses of selected EarthQuake Ground Motion (EQGM). In tall buildings that have severe irregularity in plan and elevation or have long natural periods, the use of EQGM records as input loads is recommended instead of using LEDRS. The objectives of this study are to determine the LEDRS considering return periods and to calibrate the EQGM records for making their response spectra fit the determined LEDRS. The parameters of calibration for selecting the EQGMs are investigated. In this study 22, 14 and 8 EQGMs are selected for S₁, S₂, S₃ soil sites, respectively. Selected EQGM records from this study can be used for time‐history analysis as an input earthquake load, especially for low and moderate seismic zone. Copyright © 2000 John Wiley & Sons, Ltd.     

Effectiveness of motion scaling procedures for the seismic assessment of concrete gravity dams for near field motions

With the advent of the time domain analyses, preferred over the design methods based on the response spectrum idea, the use of time histories in the seismic analysis of dams is common practice. Selection of the ground motions to be used in time history analysis is a crucial task as the seismic demands show large variance depending on the chosen records. In order to reduce this variability and predict the ‘true’ demand related to the seismic hazard conditions of the site, the selected ground motions are usually scaled and/or modified. Commonly utilised ground motion scaling techniques (i.e. scaling to the target spectrum, maximum incremental velocity and spectrum matching) are evaluated in this study for determining the efficiency and accuracy of the scaling technique in predicting the target demands on the concrete gravity dams. Different canyon geometries and moduli ratios were considered in a robust soil–structure–reservoir interaction framework including the ground motion variability through the use of a large ensemble of motions. The minimum number of required motions for consistent estimation of seismic demands on gravity dams was determined to be higher than current practice. Demand parameters corresponding to the non-linear response were determined to be underestimated by the scaled sets.     

土-结构相互作用下消能减震结构损伤分析

基于系统化的集总参数模型表征土体动力特性,上部结构每层恢复力模型采用Takeda滞回模型,研究了地震动输入强度和土体剪切波速对消能减震结构损伤指数的影响。研究结果表明：无论是否考虑土-结构相互作用,随着结构阻尼比的增加,消能减震结构的损伤指数都得到了有效降低;考虑土-结构相互作用后,在峰值加速度为0.1g地震动作用下,非减震结构随着土体剪切波速的下降结构损伤指数基本不变,而对于消能减震结构,随着土体剪切波速的下降结构损伤指数会上升;当地震动峰值加速度增加到0.3g时,非减震结构与减震结构随着土体剪切波速的下降,结构损伤指数随之增大。     

Effects of a controlling geological discontinuity on the seismic stability of an underground cavern subjected to near-fault ground motions

The mechanism for the influence of near-fault ground motion on seismic issues for underground rock caverns has seldom been addressed, especially for caverns controlled by large geological discontinuities. In this paper, a nonlinear joint model was used to simulate the effects of unfavorable geological discontinuities under seismic excitation. The influence of near-fault ground motion on unfavorable geological discontinuities was analyzed using a large sample of ground-motion records collected from the NGA-West2 database. A damage potential index (DPI) for unfavorable geological discontinuities was proposed and discussed. The #1 surge chamber of the Baihetan Hydropower Plant, which is dominated by interlayer shear weakness zone (ISWZ) C2, was used as a study case to investigate the differences between pulse-type near-fault ground motion, non-pulse-type near-fault ground motion, and far-field ground motion. The results of the study indicate that (1) significant velocity and displacement as well as a stronger long-period response spectrum are key characteristics of pulse-type near-fault ground motions, whereas non-pulse-type near-fault ground motions display characteristics similar to those of far-field ground motions; (2) the velocity pulse is responsible for the destructive capabilities of near-fault ground motions; (3) the peak ground velocity (PGV) was shown to be the most suitable DPI of several ground-motion parameters for large geological discontinuities under seismic excitation (applicable to both near-fault and far-field ground motions); and (4) PGV was verified to be the most effective DPI for ISWZ C2 at the Baihetan #1 surge chamber. The cavern became fragile when subjected to near-fault ground motions, so special seismic reinforcement measures are recommended. These findings may provide a reference for the seismic design of underground caverns.     

基于系列地震试验基础隔震结构的减震性能及地震波参数的影响研究

为了研究基础隔震结构的减震性能及地震波参数的影响,对1个基础隔震结构模型进行了一系列工况的振动台试验。以隔震结构的减震率为指标,分析近场和远场地震下其减震性能的变化,研究相同地震动强度下平均周期、卓越周期、地震动峰值速度与峰值加速度之比、断层距和地震波方向对其减震性能的影响,分析不同地震动强度和多维地震输入下其减震性能的变化,探讨系列地震下其减震性能的退化。研究结果表明,与远场地震相比,近场地震下基础隔震结构模型的减震率相对较低,其减震性能相对较差;地震波参数中卓越周期、断层距和地震动峰值速度与峰值加速度之比及地震动强度对其减震性能的影响明显,宜作为隔震结构减震性能的主要影响因素;系列地震试验表明铅芯橡胶支座具有良好的抗性能退化能力,可以确保隔震结构的减震性能的稳定性。