近断层区的输入能量设计谱及其在基于能量抗震设计中的应用

研究并确定输入能量设计谱是建立基于性能抗震设计和评估能量方法的必要基础。选取断层15km投影距离内的224条强震记录讨论场地类型和断层距等因素的影响,建议了近场地震的输入能量设计谱(EIDS),在与实际记录及日本等国已有抗震规范比较后表明,所建议的设计能量谱能较好地反映近断层区潜在能量需求,在此基础上形成了基于能量的桥梁结构抗震评估设计方法,并用3座实际RC桥墩进行算例验证证明了所建议方法的可行性,表明基于既有抗震规范设计的桥梁结构仍有必要进行考虑近断层效应的耗能能力验算。     

美国UBC97与中国建筑抗震设计规范近断层系数对比

本文介绍了美国《Uniform Building Code》1997使用Ca和Cv双参数确定抗震设计反应谱的方法。UBC97中规定,同时满足4个方面的条件:(1)建筑位于抗震设防4区;(2)断层是发震断层;(3)断层具备发生不小于M_w6.5级地震的能力;(4)断层距小于15 km,才需考虑近断层系数。近断层反应谱与非近断层反应谱主要有等效峰值加速度、等效峰值速度和反应谱特征周期3个方面的增大。隔震结构的近断层增大系数不小于传统抗震结构的近断层增大系数。中国建筑抗震设计规范只规定了隔震结构和进行性能抗震设计的结构,在同时满足发震断层和断层距2个方面的条件,才需考虑近断层增大系数。通过对比发现,UBC97关于近断层系数的规定更加系统、明确和全面。     

缺乏近断层强震观测资料地区抗震设计规范反应谱研究

根据最近几次的近断层地震观测记录研究显示,在现行结构抗震设计规范中很少考虑近断层效应的影响,对于缺乏近断层强震观测资料地区,抗震设计规范的改进方法及近断层效应的设计参数还没有统一结论. 本文基于UBC97近断层因子设计理念, 在收集世界范围内近断层观测记录的基础上,按场地和震级进行分类,建立了中长周期关键点处的加速度谱需求的衰减关系式,推导给出了缺乏近断层观测资料地区近断层影响因子的震级和断层距的关系式. 并以我国现行的建筑抗震设计规范为基础,建议了近断层影响因子的参考取值和修正后的反应谱曲线,为我国结构抗震设计提供了参考.      

基于现行抗震规范的Kanai-Tajimi模型参数研究

基于我国现行抗震规范(GB50011—2001)并利用随机极值原理对地震动随机模型Kanai—Tajimi功率谱参数进行分析，提出为考虑土体的非线性特性，有必要区分多遇地震作用下和罕遇地震作用下的模型参数；给出了多遇地震作用下与规范相一致的场地土阻尼比和卓越频率，建立了谱强度因子S0与地面最大加速度的关系；对罕遇地震作用下的模型参数进行了初步探讨。     

与建筑抗震设计规范相对应的地面地震动随机模型参数研究

根据《建筑抗震设计规范(GB50011—2001)》的反应谱曲线,确定了基于Clough-Penzien修正过滤白噪声模型的参数取值。采用时间包络函数考虑地震的非平稳特性,根据加速度峰值等效原则迭代计算得到地面的加速度功率谱密度曲线,然后通过曲线拟合得到与规范各种地震烈度、场地类别和设计地震分组相对应的谱参数。计算结果表明,与规范相对应的加速度功率谱密度曲线呈双峰型,Clough-Penzien谱能较好地拟合其曲线形状。最后给出了规范各种工况下的地面加速度功率谱参数值,为随机抗震计算分析提供了依据。     

基于现行抗震规范的胡聿贤模型参数研究

回顾了地震地面加速度随机过程模型,根据随机振动理论采用迭代方法求解出与我国现行《建筑抗震设计规范》(GB50011-2001)设计反应谱相对应的功率谱密度函数,选用胡聿贤功率谱密度函数拟合上述功率谱密度函数,运用非线性拟合技术给出了与规范对应的胡聿贤功率谱参数,可供这种模型作为地震地面运动输入时选用。     

现行抗震规范下地震动随机模型参数研究

以《建筑抗震设计规范》(GB50011─2010)为基础,对地震动过滤有色噪声模型参数的取值进行研究。针对平稳模型和非平稳模型,区分多遇地震和罕遇地震两种情况:给出了与规范场地类别和设计地震分组相对应的场地覆盖层阻尼比和卓越频率;采用随机极值理论,建立了谱强度因子与规范最大地面加速度的对应关系。研究成果为工程结构抗震设计提供了可用的随机地震动荷载标准。     

基于谱速度的近场地震动输入能量计算模型研究

发展基于能量的桥梁结构抗震设计方法首先需要确定地震动的能量输入.对具有显著高能输入的脉冲型近场地震,针对既有的输入能量简化计算方法的不足,通过定义谱速度放大因子,提出了一种基于反应谱速度来计算地震动输入能量的计算模型.以收集到的世界范围内的靠近活动断层15km内的214条近场强震记录为基础,通过近震记录分组和SDOF体系数值计算,进行了谱速度放大因子在不同断层距条件下的分段线性化参数回归,用实际近震记录进行了验证和分组统计对比,和已有的Housner、Manfredi、Chai等代表性模型对比表明文中建议方法具有更高的精度且物理意义明确,能有效考虑结构自振特征的影响,可用于确定在给定断层条件下的结构预期能量输入.     

场地相关设计反应谱特征周期的统计分析

利用近年来的工程场地地震安全性评价和地震小区划工作的成果，对上述工作中得到的场地相关反应谱的特征周期取值进行统计分析，并收集现有的强震记录计算其反应谱，将上述两个结果同两个版本的抗震设计规范(GBJ11-89和GB50011-2001)中的规定进行比较。发现上述两本规范中的特征周期取值在不同程度上小于实际场地情况的统计平均值。其中，虽然GB50011-2001规范相对于GBJ11-89规范更加接近实际场地的情况，但仍然在一些情况下取值偏小。     

不同地震水准反应谱之间的关系和罕遇地震作用设计反应谱的确定

不同地震作用水准的设计反应谱长期以来一直采用各水准谱形完全一致的假定。这与地震危险性分析的一般结论不符。《建筑抗震设计规范》(GB50011-2001)对此作出了修订。本文基于设计反应谱的三参数标定模型推导了罕遇和多遇地震作用设计反应谱的关系，指出两者谱值之比在高频、中频和低频段分别对应于峰值加速度、速度和位移之比。引入地震动衰减规律进行了罕遇和多遇地震作用设计谱关系的近似估计，提出了基于多遇地震作用设计谱确定罕遇地震作用设计谱的调整方案，验证了现行规范将反应谱特征周期适当延长以得到罕遇地震作用设计谱的做法的合理性。     

Testing the acceleration spectra given by China and USA seismic codes based on energy supply in near-fault region

For near-fault ground motion,there should be a remarkable impulsive energy supply. Therefore,it is essential to check the validity of actual seismic design codes with energy balance concept. Based on the relationship between the spectrum velocity and the input energy equivalent velocity with 5% damping ratio,the input energy spectra compatible with main China and USA seismic codes were derived,and the accuracy and applicability were veri-fied by using near-fault records. The recommended energy input design spectrum (EIDS) applicable to the distance of 0～15 km from fault was introduced to check the validity of modern seismic codes. Comparison tests show that the GB50011-2001 Code of China can just match the energy effect of near-fault ground motion to a certain extent only under seldom occurred earthquake with fortification intensity of 9 degree for site soil of Ⅲ and IV,indicating that the impact of near-fault effect has not been embodied in the current code acceleration spectrum. In order to make the design spectrum be applicable to near-fault region,it is necessary to adjust the spectrum platform pa-rameters. On the contrary,for distinct fault distance and site soil,the UBC97 Code of USA can match well with the energy supply of near-fault ground motion except for the site soil of hard rock (SA). Accordingly,correctness of the formula derivation in this paper is certified.     

Failure analysis of one-story precast structures for near-fault and far-fault strong ground motions

Failure of one-story precast structures consisting of cantilever columns connected by simply supported beams was widely reported throughout the epicentral regions of the last devastating earthquakes in Turkey. As a single degree of freedom system, precast columns are designed by using the elastic spectrum given in the seismic code and by considering a seismic load reduction factor which takes into account the inelastic behavior of the columns under seismic loads. Although the existing seismic codes consider near-fault shaking effects in the development of elastic response spectra, they do not currently consider the increased inelastic demands that may occur during near-fault ground motion. The current study consists of nonlinear time history analyses of various hypothetical columns having geometric and mass properties which are being used in Turkish precast industry and the evaluation of damage indexes (DI) in terms of peak ground velocity (PGV) and peak ground acceleration (PGA) of the used strong ground motions. It is achieved that near-fault earthquakes create more damages on the columns. This might be one of the main reasons for the collapse of several one-storey precast buildings which were well designed according to the seismic codes in the district of existing faults. The obtained PGV versus DI charts prove that if one increase the sectional dimensions and/or longitudinal reinforcement ratio of the column, the possible damage from near-fault shaking effects could be reduced.     

近断层速度脉冲型地震动相关问题研究

近断层速度脉冲型地震动研究对揭示建筑结构的破坏机理、开展抗震设防以及抗震设计具有重要价值。首先,对速度脉冲成因进行了系统的总结,并探讨了区分方向性效应速度脉冲和滑冲效应速度脉冲的思路;其次,系统地介绍了近断层速度脉冲的识别方法,评述了各种脉冲识别方法的优缺点;然后,基于速度脉冲特性,探讨了前方向性效应对速度脉冲特性的影响以及速度脉冲对反应谱的放大作用;最后,对速度脉冲型地震动输入方法以及对结构响应研究进行了系统总结,探讨了速度脉冲型地震动输入的关键问题。基于丰富的理论研究,未来对于速度脉冲型地震动研究工作应当充分结合实际工程需求,推进理论成果的规范标准化与工程实践。      

Damping coefficients for near-fault ground motion response spectra

Damping coefficients are frequently used in earthquake engineering as a simple way to adjust the pseudo-acceleration or displacement response spectra associated with a viscous damping ratio of 5% to the higher values of viscous damping needed for design of structures equipped with base isolation and/or supplemental energy dissipation devices. In this study, damping coefficients for the single-degree-of-freedom system subjected to near-fault ground motions are calculated for a large range of periods and damping levels. The results indicate that damping coefficients proposed in design codes and previous studies, based primarily on far-field ground motion records, tend to not be conservative for near-fault seismic excitations. A new approach is recommended for the derivation of damping coefficients appropriate for engineering analysis and design in the immediate vicinity of the earthquake fault. This includes the normalization of the period axis with respect to the duration of the ground velocity pulses recorded in the near-fault region. The pulse duration is controlled by the rise time on the fault plane and scales directly with earthquake magnitude.     

An alternative construction of normalized seismic design spectra for near-fault regions

This paper presents a methodology for constructing seismic design spectra in near-fault regions.By analyzing the characteristics of near-fault pulse-type ground motions,an equivalent pulse model is proposed,which can well represent the characteristics of the near-fault forward-directivity and fling-step pulse-type ground motions.The normalized horizontal seismic design spectra for near-fault regions are presented using recorded near-fault pulse-type ground motions and equivalent pulse-type ground motions,which are derived based on the equivalent pulse model coupled with ground motion parameter attenuation relations.The normalized vertical seismic design spectra for near-fault regions are obtained by scaling the corresponding horizontal spectra with the vertical-to-horizontal acceleration spectral ratios of near-fault pulse-type ground motions.The proposed seismic design spectra appear to have relatively small dispersion in a statistical sense.The seismic design spectra for both horizontal and vertical directions can provide alternative spectral shapes for seismic design codes.     

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。     

Bounding of near-fault ground motion based on radiated seismic energy with a consideration of fault frictional mechanisms

The energy radiated as seismic waves strongly depends on the fault rupture process associated with rupture speed and dynamic frictional mechanisms involved in the fault slip motion.Following McGarr and Fletcher approach,we derived a physics-based relationship of the weighted average fault slip velocity vs apparent stress,rupture speed and static stress drop based on a dynamic circular fault model.The resultant function can be approximately used to bound near-fault ground motion and seismic energy associated with near-fault coseismic deformation.Fault frictional overshoot and undershoot mechanisms governed by a simple slip-weakening constitutive relation are included in our consideration by using dynamic rupture models named as M-and D-models and proposed by Madariaga(1976) and Boatwright.We applied the above function to the 2008 great Wenchuan earthquake and the 1999 Jiji(Chi-Chi) earthquake to infer the near-fault ground motion called slip weighted average particle velocity and obtained that such model-dependent prediction of weighted average ground velocities is consistent to the results derived from the near-fault strong motion observations.Moreover,we compared our results with the results by McGarr and Fletcher approach,and we found that the values of the weighted average particle velocities we obtained for these two earthquakes are generally smaller and closer to the values by direct integration of strong motion recordings of the near-fault particle velocity waveform data.In other words,if this result comes to be true,it would be a straightforward way used to constrain the near-fault ground motion or to estimate source parameters such as rupture speed,static and dynamic stress drops.     

Relative energy zero ratio-based approach for identifying pulse-like ground motions

Pulse-like ground motions are capable of inflicting significant damage to structures. Efficient classification of pulse-like ground motion is of great importance when performing the seismic assessment in near-fault regions. In this study, a new method for identifying the velocity pulses is proposed, based on different trends of two parameters: the short-time energy and the short-time zero crossing rate of a ground motion record. A new pulse indicator, the relative energy zero ratio(REZR), is defined to qualitatively identify pulse-like features. The threshold for pulse-like ground motions is derived and compared with two other identification methods through statistical analysis. The proposed procedure not only shows good accuracy and efficiency when identifying pulse-like ground motions but also exhibits good performance for classifying records with high-frequency noise and discontinuous pulses. The REZR method does not require a waveform formula to express and fit the potential velocity pulses; it is a purely signal-based classification method. Finally, the proposed procedure is used to evaluate the contribution of pulse-like motions to the total input energy of a seismic record, which dramatically increases the seismic damage potential.     

Effects of near-fault ground motions on the nonlinear behaviour of reinforced concrete framed buildings

The design provisions of current seismic codes are generally not very accurate for assessing effects of near-fault ground motions on reinforced concrete(r.c.)spatial frames,because only far-fault ground motions are considered in the seismic codes.Strong near-fault earthquakes are characterized by long-duration(horizontal)pulses and high values of the ratio α_(PGA)of the peak value of the vertical acceleration,PGA_V,to the analogous value of the horizontal acceleration,PGA_H,which can become critical for girders and columns.In this work,six- and twelve-storey r.c.spatial frames are designed according to the provisions of the Italian seismic code,considering the horizontal seismic loads acting(besides the gravity loads)alone or in combination with the vertical ones.The nonlinear seismic analysis of the test structures is performed using a step-by-step procedure based on a two-parameter implicit integration scheme and an initial stress-like iterative procedure.A lumped plasticity model based on the Haar-Karman principle is adopted to model the inelastic behaviour of the frame members.For the numerical investigation,five near-fault ground motions with high values of the acceleration ratio α_(PGA) are considered.Moreover,following recent seismological studies,which allow the extraction of the largest(horizontal) pulse from a near-fault ground motion,five pulse-type(horizontal)ground motions are selected by comparing the original ground motion with the residual motion after the pulse has been extracted.The results of the nonlinear dynamic analysis carried out on the test structures highlighted that horizontal and vertical components of near-fault ground motions may require additional consideration in the seismic codes.     

强震下斜交桥地震反应与减隔震性能分析

针对斜交桥在破坏性地震中发生破坏和损伤的突出问题,采用铅芯橡胶支座(LRB)进行隔震和滞回耗能。基于OpenSees平台建立了不同斜度的传统非隔震和全桥采用LRB隔震的4跨斜交连续梁桥动力分析模型,沿2个水平方向输入远场地震动和具有向前方向性效应、滑冲效应以及无速度脉冲效应的近断层地震动,并进行非线性时程计算,研究桥墩和挡块的损伤状态、主梁旋转度、碰撞力与斜交桥斜度的关系以及LRB对斜交桥抗震性能的影响。结果表明:向前方向性效应和滑冲效应的脉冲型地震动作用下的斜交桥地震反应和损伤明显大于无速度脉冲近断层和远场地震动作用; 采用LRB隔震后,明显降低了固定墩的地震损伤,桥墩位移减震率可达到50%以上; LRB隔震桥主梁与挡块的间隙宜结合桥梁的地震风险和设计位移进行确定。