Evaluation of lateral‐torsional coupling in earthquake response of asymmetric multistory buildings

This paper presents a practical method for evaluating lateral‐torsional coupling in the elastic earthquake response of asymmetric multistory buildings. A transformation technique is first developed to shift the floor centers of mass of an asymmetric building to new reference positions where the sum of the squares of all floor rotations of the building due to lateral inertia loads is a minimum. By setting the locus of the floor centers of mass of the building at the new reference positions, a representative eccentricity and an effectively uncoupled system for the building can be established on the basis which an equivalent eccentric single mass system can be developed. The additional lateral translations caused by seismic torsional effects in the building can be analytically determined and expressed in terms of the representative building eccentricity and the uncoupled periods evaluated using the effectively uncoupled system. The effectiveness and practicality of the proposed method are illustrated with two 30‐story practical buildings. Copyright © 2013 John Wiley & Sons, Ltd.     

Torsional coupling effects in the earthquake response of asymmetric buildings

This paper presents a detailed parametric study of the coupled lateral and torsional response of a partially symmetric single storey building model subjected to both steady state and earthquake base loadings. It is shown that the qualitative effects of the controlling parameters on the maximum translational and torsional responses of the coupled system are not affected by the nature of the loading. The maximum lateral edge displacement of the building arising from the combined response effects is investigated. The related lateral shear forces in vertical resisting elements located on the periphery of the structure may be significantly increased in comparison with the corresponding values for a symmetric building. It is concluded that for particular ranges of the key parameters defining the structural system, typical of the properties of many actual buildings, torsional coupling induces a significant amplification of earthquake forces which should be accounted for in their design.     

Effect of vertical component of earthquake on the response of pure-friction base-isolated asymmetric buildings

This study has been conducted to evaluate the effects of the vertical component of earthquake on the response of pure-friction base-isolated asymmetric buildings. The pure-friction base-isolated asymmetric building is idealized as a three-dimensional single-storey building resting on sliding supports. The sliding surface is modeled by interface rigid contact elements. The response of this idealized system subjected to three-component (including vertical component) and two-component (excluding vertical component) of earthquake excitations is investigated. As an example, the Northridge 1994 earthquake record is used on the structural model. The performance of asymmetric pure-friction base-isolated system is investigated with the help of peak response ratio of sliding to fixed base systems. It is observed that the vertical component of the strong earthquake excitation, significantly affects the response of pure-friction base-isolated torsionally coupled system.     

Collapse behavior evaluation of asymmetric buildings subjected to bi‐directional ground motion

This paper discusses the collapse behavior of low‐rise plan‐asymmetric buildings under bi‐directional horizontal ground motions and utilizing strength and stiffness degrading nonlinear models. For this purpose, three‐dimensional three‐story and six‐story reinforced concrete frame buildings with uni‐directional mass eccentricities equal to 0% (symmetrical), 10%, 20% and 30% are subjected to nonlinear static (pushover) as well as incremental dynamic analyses using a set of far‐field two‐component ground motions and their performance are assessed on the basis of the safety margin against collapse and its probability of occurrence. Comparison of the collapse margin ratios as well as the fragility curves demonstrates significant reduction of the collapse‐level ground motion intensity with increasing eccentricity in plan. Results also indicate that current seismic design parameters including the response modification (R), overstrength (Ω) and ductility (μ) factors are not appropriate for buildings with high levels of plan eccentricity. Buildings with high values of plan eccentricity do not meet the design target life safety performance level on the basis of the calculated probability of collapse and safety margin against collapse. It appears that re‐evaluation of their design parameters is necessary. Copyright © 2015 John Wiley & Sons, Ltd.     

地面运动强度参数的选择对结构地震反应的影响研究及其现状

在基于性能的地震工程学中,采用地面运动强度参数(IM)来量化工程场地的地震活动性。一个理想的IM应该包含足够的关于地面运动特性的信息,可以将地面运动强度水平与结构地震反应水平有效地对应起来,还必须考虑到在地震工程学中,通过概率地震危险性分析进行地面运动危险性水平计算的可行性问题。因此,合理地选择IM,可以更加准确地预计在特定地震灾害环境下结构可能遭受到的最大破坏以及破坏规律,显著提高概率地震需求模型、工程需求参数危险性曲线以及易损性曲线等的精确性和计算效率。     

Optimum design of tuned mass dampers for different earthquake ground motion parameters and models

Tuned mass dampers are frequently used for passive control of vibrations in civil structures subject to seismic and wind actions. Their efficiency depends on selection of their mechanical properties in relation to main system and excitation characteristics. This paper proposes an optimum design strategy of single tuned mass dampers to control vibrations of principal mode of structures excited by earthquake ground motion. The main purpose of the paper is to investigate the influence of the time modulation of earthquake excitation upon the optimal tuned mass dampers design parameters: frequency and damping ratio. The study is based on numerical analyses carried out with different stochastic models for earthquakes: a simple filtered white noise model and two time modulated filtered white noise models. The numerical analyses are carried out to solve an optimization problem with a performance index defined by the reduction of the standard deviation of either the structure displacement or its inertial acceleration as objective function. To complete the work, the influence of the bandwidth excitation over the values of the optimal tuned mass damper parameters is investigated, as well the optimum mass ratio and the structure frequency. The results of the numeral analyses carried out infer that the earthquake excitation characteristics, including its modulation in time domain, highly affect the optimum tuned mass damper design parameters values.     

结构周期延长对倒塌分析中地震动强度指标选择的影响

当结构在强震作用下接近倒塌状态时,其刚度和承载力的退化会导致结构周期延长,为此,研究了周期延长对地震动强度指标选择的影响,将不同周期调整系数β对应的谱加速度(Sa(βT1),T1为弹性基本周期）作为地震动强度指标时,研究其倒塌分析结果的离散性。基于等效单自由度结构周期（Teq）,提出了等效周期谱加速度（Sa(Teq)）。研究结果表明：当周期调整系数β增大时,结构抗倒塌能力分析结果的离散性呈现先减小后增大的趋势。与传统地震动强度指标Sa(T1)相比,所提出的Sa(Teq)可以考虑结构非线性变形引起的周期延长,能有效降低倒塌分析结果的离散性达30%以上。     

论地震地面运动中的持续时间

对地震动持时的宏观影响、影响地震动持时的因素、持时对工程结构的影响进行了阐述,并分析了考虑地震动持时的抗震设计,通过分析,认为对地震动持时的研究可以从持时与其他两个要素的耦合方面去突破,此外结合结构的非线性反应的集中现象,提出了关于间隔薄弱层的抗震设计的设想。     

有关地震烈度与地震动参数联系的探讨

阐述了将地震烈度与地震动参数联系起来的必要性,并详细介绍了地震烈度和地震动单一参数以及多个参数之间的关系,对地震灾害的评估及抗震实践有重要意义。     

影响单层偏心结构地震反应的参数分析

通过单层偏心结构运动方程的解析过程,确立了影响结构弹性反应的主要结构参数,并采用Matlab模拟各参数对结构地震作用效应的影响规律。分析了强度偏心距对偏心结构非弹性地震反应的影响规律,提出在实际结构设计中可以通过提高柔性边抗侧力构件的屈服强度来降低非弹性扭转破坏的影响,为偏心结构的抗震设计提供了有价值的参考依据。     

Modeling of nonstationary ground motion and analysis of inelastic structural response

A new stochastic model of ground excitation is proposed in which both intensity and frequency content are functions of time, and corresponding methods for estimating the model parameters based on actual earthquake records are also given. The proposed ground motion model can be efficiently applied in simulations as well as random vibration vibration and reliability studies of inelastic structures. Responses of single-mass inelastic systems and three-story space frames, with or without deterioration under the nonstationary biaxial ground excitation are investigated via the equivalent linearization method and Monte Carlo simulations. The results show that the time-varying frequency content the dominant frequencies of ground excitation are close to the structural natural frequency. Also biaxial and torsional response may become significant in an unsymmetric structure.     

谈现代混凝土结构抗震设计理念

主要阐述了现代抗震设计的理念及措施,并对目前常用的抗震设计方法的特点、适用范围作了论述分析,经实践证明,建筑结构的抗震设计是实现结构抗震安全目标的重要措施和手段。     

边坡地震动力响应规律及地震动参数影响研究

利用FLAC3D有限差分软件建立了一个边坡动力数值分析模型,用振动台模型试验对数值模拟效果进行了验证。在此基础上,分析了地震作用下边坡的动力响应规律,以及地震动参数对边坡动力响应的影响。结果表明,边坡对输入地震波存在垂直放大和临空面放大作用,边坡土体对输入地震波低频部分存在放大作用,对高频部分存在滤波作用。坡面加速度峰值放大系数随输入地震波振幅、频率的增加而减小,持时对加速度峰值响应的影响不大;坡体位移随振幅、持时的增加而显著增大,随频率的增大而减小。强震作用下剪应变增量最大区域的位置和形状表明,单一均质土层边坡的破坏模式仍是沿着某一弧形潜在滑动面失稳。研究结果有助于进一步揭示边坡在地震作用下的失稳机制。     

超高层建筑场地地震动参数的确定

基于抗震设计的重要性,以厦门某超高层建筑场地为例,在场地地震危险性概率分析的基础上,对场地土层进行了一维地震反应分析计算,确定了该工程场地地震动参数,为抗震设计提供了依据.     

Effect of nonlinearity on site response and ground motion due to earthquake excitation

Ground motions under earthquake loading are influenced by the local soil conditions, but the non-linearity of the soil behavior makes it difficult to estimate the site response. The paper reports a non-linear analysis developed to elucidate the effect of non-linearity on site response, illustrating its applicability with reference to a petroleum storage tank site subjected to earthquake excitation.     

结构耦联周期比影响因素分析

分析了我国规范对于评判和控制偏心结构在地震作用下的扭转效应提出的计算指标,结合对某结构模型的SATWE计算,分析了偏心率、单双向偏心以及扭转刚度对耦联周期比的影响,以使耦联周期比满足规范要求。     

地震动的频谱特性和持时对结构地震反应的影响研究及其现状

多年来,国内外地震工程界存在着一个严重缺陷,即地震学与结构抗震两者之间缺乏联系.随着基于性能的地震工程学(PBEE)的出现以及不断发展,地震学的重要性日益凸显.在结构抗震设计和分析中,强震地面运动特性的变异性对于结构地震需求的影响最大,其主要可以用幅值、频谱特性和持时3个基本要素来表示.震害经验表明,各类结构的震害表现为这3个基本要素综合影响的结果.因此,通过研究强震地面运动特性对于结构地震需求的影响,将地震工程学与结构抗震有机地结合起来是一个必然的发展趋势.     

日本建筑抗震标准的变迁和现行的抗震标准

介绍了日本现行抗震标准及其修订背景。1924年世界上最早的建筑抗震标准在日本诞生,规定了至少取建筑物总重量的0.1倍的力作为设计水平地震荷载。日本现行抗震标准中的抗震设计由两次设计构成,即对在建筑使用年限中发生的中等地震进行第一次设计及对在建筑使用年限中可能发生的罕见大地震进行第二次设计。其现行抗震标准有四个基本的抗震设计方法。     

基于宁洱6．4级地震地震动衰减及场地土层分析

基于宁洱6.4级地震的实际地震台网观测数据,结合云南分区地震动特性,以回归分析的方法对此次地震中地震动大小进行衰减分析,以此衰减到场地基岩的理论地震动值,通过一维场地土层地震反应技术分析,得出场地结构物的地震动大小输入,以期为震害分析做出数据支撑。     

浅谈减轻建筑物地震破坏的综合对策

通过对历次地震震害的调查分析，又针对目前建筑市场存在的若干问题，指出了应尽快改变抗灾意识淡薄的局面以外，还应在工程地质勘察方面采用科学的方法，保证数据的准确性，选择合理的抗震设计结构体系，在施工，使用和维修等方面应采取相应的抗震措施，以最大限度地减轻建筑物在地震时的倒塌破坏。