基于等效单自由度体系的结构地震输入能量的研究

通过对多自由度体系结构在地震作用下的能量分析,考虑地震动因素和结构自身特性,提出一种框架结构地震总输入能量的简化求解方法.实例计算结果表明:基于等效单自由度体系来估计多自由度体系的地震总输入能,是一种计算简便且较为准确的方法.     

单自由度体系地震动输入功率谱的确定

将几种地震动功率谱输入模型换算成和目标反应谱相对应的地震动输入,并应用于单自由度体系分析.结果表明,使用孙景江/江近仁迭代法将目标反应谱换算得到的等价功率谱输入精度较高,建议可以在功率谱分析方法中使用.     

配置自复位耗能跨低多层钢框架体系的能量系数

利用超弹性SMA螺栓梁柱节点的耗能能力和自复位特性,将其引入到耗能跨而构建"自复位耗能跨",基于既有的节点试验研究结果对结构体系的滞回性能进行了探讨。在此基础上,以具有旗形滞回特征的单自由度体系为工具,对配置自复位耗能跨低多层钢框架体系的能量系数进行推导。能量系数可以合理量化具有旗形滞回规则结构的峰值响应需求,能量系数越低,表明地震动下结构的峰值响应越低。为了阐明滞回参数对能量系数的影响,对具有不同滞回参数组合可代表低多层结构的等效SDOF体系进行了非线性动力分析,参数组合包括周期、屈服后刚度比、延性系数及能量比。同时对能量系数的离散性也进行了分析。结果表明:能量系数及能量系数的离散性受结构周期、屈服后刚度比及延性系数影响较大,受能量比的影响较小。     

抗震结构的滞回耗能谱

本文在分析不同类型地面运动引起抗震结构不同类型破坏的基础上，指出结构滞回耗能总量是累积破坏的重要参数，以1735条实际地震记录作为输入计算了不同动力参数单自由度体系弹性及弹塑性总输入能量及滞回耗能量，得出计算弹塑性体系滞回耗能谱的简化公式。     

SSI效应对自复位结构体系延性需求谱的影响分析

为研究土-结构相互作用(soil-structure-interaction, SSI)对自复位结构体系延性需求谱的影响规律,建立了土-自复位结构的数值分析模型,其中上部结构采用旗帜形单自由度滞回系统模拟,并基于锥模型概念模拟土-基础动力相互作用。选取40条Ⅲ类场地远场地震动记录对SSI系统进行非线性时程分析,讨论了刚性地基结构的周期T、强度折减系数R、结构-土体刚度比a₀、结构高宽比s、屈服后刚度比α和耗能系数β对结构延性需求的影响规律。研究结果表明：忽略SSI效应会低估自复位结构的延性需求;对于考虑SSI效应的单自由度自复位结构,延性系数μ与R、a₀的相关性较强,且μ与R和a₀呈正相关,提高R或a₀会增大结构延性需求;延性系数μ与屈服后刚度比α、耗能系数β及结构高宽比s的相关性较弱,其中μ与α和β呈负相关,提高α或β会减小结构延性需求,且随着a₀的增大,α和β对延性需求谱的影响越大;当a₀=1时,s对延性需求谱基本无影响,而a₀取...     

剪切型多自由度体系瞬时输入能量的分布

通过对剪切型多自由度体系的地震能量反应分析,提出了描述多自由度体系整体脉冲能量反应的参数,瞬时输入能量等效平均速度,并在此基础上建立了瞬时输入能量分布系数的概念,提出了估计瞬时输入能量分布的方法。     

地震总输入能量与瞬时输入能量谱的研究

现有的抗震设计理论大多是基于承载力或强度的设计方法,与其相应的反应谱理论最大的缺陷是无法反映地震动持时的影响,而以地震动能量作为设计参数时就能弥补现有抗震理论的不足。本文按照反应谱理论的思路建立了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。研究发现,阻尼比为5%时的地震动总输入能量谱和最大瞬时输入能量谱的等价速度谱可以分别用阻尼比为0.5%和10%下的拟速度谱来近似获得;地震波的V/A值大于0.15时,总输入能量谱的Δt谱峰值与地震波的强震持时呈线性增长关系,V/A值小于0.15时,两者间的关系无规律性。最大瞬时输入能量谱的Δt谱峰值基本不受地震波的V/A值与强震持时的影响;输入能量谱(总输入能量谱与最大瞬时输入能量谱)的特征周期随地震波V/A值的增大而增大,根据分析结果本文提出了线性单自由度体系输入能量谱的简化计算方法,方法简便,计算结果偏安全。     

地震动滞回能量谱衰减规律研究

本文选用美国西部California州15次较大地震中的266条强地震动记录,利用衰减关系建立了滞回能量谱,分析了场地条件、延性系数、震级及距离等参数对滞回能量谱的影响。研究发现,场地条件对滞回能量谱影响很大,随着场地变软,滞回能量谱变大,与A B类场地相比,C类场地的滞回能量谱平均要高出70％左右,D类场地则要高出170％左右。随着延性系数的增大,滞回能量谱有增大的趋势,尤其是当延性系数由2变到4或6时更为明显,但当延性系数增加到一定程度时,滞回能量谱的差别不大,延性系数为4和6时的滞回能量谱差别不大,甚至在周期较大时,延性系数为6的滞回能量谱反而小于延性系数为4时的滞回能量谱。另外,研究结果表明,大的震级和小的距离对结构产生比较大的滞回能量需求。利用本文结果,可以估计未来地震中结构物所遭受滞回能量的大小。     

非对称自复位SMA连接的力学性能研究

提出了一种用于梁柱节点中的非对称自复位形状记忆合金(shape memory alloy, SMA)连接,可有效提高相应钢框架结构的抗震性能和震后功能恢复能力。设计8个考虑SMA面积、SMA预应变、滑移螺杆预拉力的非对称自复位SMA连接,并进行低周循环加载试验研究,得到相应滞回曲线、骨架曲线、割线刚度、耗能能力和复位性能等。研究结果表明：新型连接具有良好的自复位能力和耗能能力,滞回曲线呈明显的旗帜型,最大自复位率达到87.2%,且整个加载过程无任何构件发生损伤。增大SMA面积、SMA预应变可提高连接的承载力、耗能能力和自复位能力,并减小其残余变形;螺杆预拉力取30 N·m时新型连接的性能最佳。基于Umat子程序编制SMA本构模型并用于ABAQUS软件中,可较准确地模拟其力学性能,为相应连接的有限元参数化分析提供理论基础。     

弹性能量半径演化谱及其在多自由度体系地震反应计算中的应用

目前用于结构抗震设计的反应谱仅能反映峰值反应,无法体现反应值随时间的变化。文中提出一种弹性能量半径演化谱,可反映线性单自由度体系弹性能量(即动能与弹性势能之和)随地震持时的变化,且其峰值近似等于结构峰值位移。文中给出了利用地震动演化功率谱得到该演化谱的方法并进一步发展了一种计算线性多自由度体系地震位移反应的新方法。通过两座框架结构的地震反应计算,将新方法与传统振型组合法及时程分析法的计算结果进行对比,发现对于振型稀疏结构,新方法计算结果与SRSS法接近;而对于振型密集结构,新方法计算结果较CQC法更精确,且避免了CQC法相关系数的复杂计算。     

On the estimation of hysteretic energy demands for SDOF systems

Based on a statistical study of the dynamic response of single degree of freedom (SDOF) systems subjected to earthquake ground motions, a rule to estimate hysteretic energy demands is proposed. Expressions for elastic–perfectly plastic, stiffness degrading and pinching SDOF systems were obtained. The proposed rule does not explicitly depend on the period of the system; instead, it depends on the elastic pseudo‐acceleration and elastic velocity spectra. It is shown that the proposed rule can be applied to compute hysteretic energy demands for systems located at different soil conditions. In addition, information about scatter and bias of the proposed rule is also presented. Copyright © 2007 John Wiley & Sons, Ltd.     

Design energy input spectra for moderate‐seismicity regions

This paper proposes energy input spectra applicable to seismic design of structures located in low‐to‐moderate‐seismicity regions. These spectra represent the load effect, in terms of input energy, of the most severe earthquake that the construction might encounter during its lifetime. The spectra have been derived through dynamic response analyses of over 100 ground motion records obtained from 48 earthquakes that have occurred in Spain. An empirical equation for estimating the energy input contributable to damage from the total input energy is also suggested. This equation takes into account both the damping and the degree of plastification of the structure. Finally, the proposed design energy input spectra are compared with the provisions of the current Spanish Seismic Code and with the response spectra of recent earthquakes that have occurred in Turkey and Taiwan. Copyright © 2002 John Wiley & Sons, Ltd.     

Effect of peak ground velocity on deformation demands for SDOF systems

The effect of peak ground velocity (PGV) on single‐degree‐of‐freedom (SDOF) deformation demands and for certain ground‐motion features is described by using a total of 60 soil site records with source‐to‐site distances less than 23 km and moment magnitudes between 5.5 and 7.6. The observations based on these records indicate that PGV correlates well with the earthquake magnitude and provides useful information about the ground‐motion frequency content and strong‐motion duration that can play a role on the seismic demand of structures. The statistical results computed from non‐linear response history analyses of different hysteretic models highlight that PGV correlates better with the deformation demands with respect to other ground motion intensity measures. The choice of PGV as ground motion intensity decreases the dispersion due to record‐to‐record variability of SDOF deformation demands, particularly in the short period range. The central tendencies of deformation demands are sensitive to PGV and they may vary considerably as a function of the hysteretic model and structural period. The results provided in this study suggest a consideration of PGV as a stable candidate for ground motion intensity measure in simplified seismic assessment methods that are used to estimate structural performance for earthquake hazard analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

Incorporating low‐cycle fatigue model into duration‐dependent inelastic design spectra

Seismic performance of structures is related to the damage inflicted on the structure by the earthquake, which means that formulation of performance‐based design is inherently coupled with damage assessment of the structure. Although the potential for cumulative damage during a long‐duration earthquake is generally recognized, most design codes do not explicitly take into account the damage potential of such events. In this paper, the classical low‐cycle fatigue model commonly used for seismic damage assessment is cast in a framework suitable for incorporating cumulative damage into seismic design. The model, in conjunction with a seismic input energy spectrum, may be used to establish an energy‐based seismic design. In order to ensure satisfactory performance in a structure, the cyclic plastic strain energy capacity of the structure is designed to be larger than or equal to the portion of seismic input energy contributing to cumulative damage. The resulting design spectrum, which depends on the duration of the ground motion, indicates that the lateral strength of the structure must be increased in order to compensate for the increased damage due to an increased number of inelastic cycles that occur in a long‐duration ground motion. Examples of duration‐dependent inelastic design spectra are developed using parameters currently available for the low‐cycle fatigue model. The resulting spectra are also compared with spectra developed using a different cumulative damage model. Copyright © 2004 John Wiley & Sons, Ltd.     

Study on comparison between absolute and relative input energy spectra and effects of ductility factor

Introduction Estimation of an attenuation relationship for strong ground motion parameters has been an interesting research subject in the field of engineering seismology and has played a very important role in seismic safety evaluation, seismic zoning, seismic hazard evaluation of major constructions, etc. At present, the generally used parameters include peak acceleration, peak velocity and elastic response spectrum. Such parameters mentioned above are essentially independent of the duration…     

Exact computation of input‐energy spectra from Fourier amplitude spectra

A theoretically exact relation is presented between the Fourier amplitude spectrum and the elastic input‐energy spectrum. This energy spectrum is computed from the Fourier acceleration amplitude spectrum and the real part of the relative velocity transfer function of the single‐degree‐of‐freedom elastic oscillator. Some accelerometric records collected worldwide are used to prove the solution. It is shown that the relation presented in this work opens the door for a better understanding of the relationship between the input‐energy spectrum and other seismological variables, such as magnitude and focal distance. Copyright © 2003 John Wiley & Sons, Ltd.     

Design energy input spectra for moderate-to-high seismicity regions based on Colombian earthquakes

Energy input spectra applicable to the seismic design of structures in moderate-to-high seismicity regions are proposed. Such design inputs are derived from the bilinear envelope of individual spectra obtained for 144 ground motions recorded in Colombia. In the short period region the spectra account for the increase of input energy, due to plastification of the structure, through a new formula derived from extensive nonlinear analyses. The proposed energy input design spectra are compared with the provisions of the Colombian seismic code, and with those proposed for Japan, Spain, Iran and Greece. It is found that the proposed spectra are more demanding than the current Colombian seismic code, and that they agree with those developed recently for six cities in Greece, yet applying a different approach. An empirical equation for estimating the portion of the total seismic input energy that contributes to structural damage is also developed.     

考虑场地类别与强震持时的滞回耗能谱的特征分析

基于力或位移的结构抗震设计方法大多无法反映地震动持时的影响,而能量设计方法则能较好地弥补其不足。按场地类别和强震持时,将302条Northridge地震记录分为15组,对地震记录的峰值进行规一化处理,采用钢筋混凝土退化三线型恢复力模型,对单自由度体系进行弹塑性时程分析,研究场地类别、强震持时、强度屈服水平以及结构周期等因素对滞回耗能的影响。结果表明:在给定地震记录的峰值和屈服强度水平下,结构的滞回耗能依赖于场地条件和强震持时等因素;滞回耗能随强震持时的增加而增大,随场地特征周期的增加而增大。通过非线性回归分析,建立了与峰值加速度、峰值速度、强震持时相对应的简化滞回耗能谱的计算公式。