钢筋混凝土框架非弹性地震反应分析模型研究进展

本文对国内外钢筋混凝土框架非弹性地震反应分析模型的研究进展进行了介绍和评述，指出了这一研究领域中存在的主要问题和值得进一步研究的课题方向。     

空间钢筋混凝土框架结构的非弹性地震反应

对两个缩比为十五分之一的三层、双跨、两开间的钢筋混凝土框架模型进行了振动台试验,一个模型模拟质量中心与刚度中心不一致的偏心结构,另一个模型模拟承受双向地面运动的结构。研究了结构的空间非弹性地震反应。计算结果表明,理论分析与实测结果有较好的吻合性。     

分层弹性地基场地土扭转地震反应分析

本文对场地土按分层弹性地基土建立了合理的力学模型，通过动力分析，给出了分层弹性地基场地土扭转自振特性及在扭转地震载荷作用下强迫反应的解析解，文中的解析公式为分层弹性的基场地土扭转地震反应分析提供了一种新的解析方法．     

等位移理论估计高层建筑结构非弹性地震反应的进一步研究

为进一步研究用等位移理论估计高层建筑结构非弹性地震反应,选用五个钢筋混凝土高层结构实例,输入二十条不同场地条件的地震波,采用结构弹性和非弹性地震时程反应分析方法,研究了结构弹性和非弹性最大顶点位移以及最大层间位移角之间的关系。提出可以直接用弹性最大顶点位移估计非弹性最大顶点位移。对于非弹性层间位移角反应,在中、弱非线陛阶段宜可直接用弹性反应结果估计,而在强非线性阶段则需进行一定修正。     

端承桩基础扭转地震反应分析

端承桩基础扭转地震反应分析刘宗贤，李玉亭，贾相玉，傅文彬（国家地震局工程力学研究所，哈尔滨１５００８０）在某些建筑中，桩是最基本建筑构件，本文重点分析端承桩在扭转地震载荷作用下的动力反应问题。首先将桩头部的各种动力简化成扭转振动载荷，此外，还受到地基     

利用等位移原则估计高层结构的非弹性地震反应(二)

通过高层结构弹性和非弹性地震时程反应分析,研究了两者的位移反应关系。结果表明：结构在不同地震作用下非弹性总位移角反应的平均值与弹性反应十分接近,基本符合等位移原则,可以用后者分析结果直接估计前者;结构最大层间位移角反应的平均值在弱和中等非线性阶段亦与弹性反应十分接近,在强非线性阶段则大于弹性反应,经数据拟合,初步提供了一个在此阶段由弹性最大层间位移角反应估计非弹性反应的近似公式。     

桩基础在分层弹性地基场地土扭转波作用下的扭转地震反应分析

本文对分层弹性地基中单桩基础通过特征分析，建立了合理的力学模型，按分层弹性地基土模型对桩进行扭转振动分析，给出了桩基础扭转自振特性及在扭转地震载荷与扭转振动载荷作用下的强迫反应解析解，文中的解析公式为分层弹性地基中的桩基础扭转地震反应分析提供了一种新的解析方法。     

复杂结构的弹性地震反应分析

目前使用的反应谱振型叠加法在分析复杂结构的地震反应时,可能引起较大的误差。本文提出了一种新的计算处理方法,不论对简单或复杂结构,只要任取两个不同的地震输入方向,仅增加少量的计算工作量,即可得到结构中任一点或截面上的最大应力或内力,且该方法可以很方便地加入到现有计算程序中。文中还提出了结构抗震主轴的概念,定义了结构整体设计合理系数以及结构能质比,为从宏观上比较同一结构在不同、方向以及不同结构之间的抗震性能提供了客观依据。     

利用等位移原则估计高层结构的非弹性地震反应(一)

高层建筑非弹性地震反应估计是当前结构抗震研究迫切希望解决的课题。本文概略介绍了常用非弹性地震反应分析方法在高层结构分析中应用的主要问题,从而引出利用等位移原则(对于长周期体系,弹性与非弹性地震位移反应近似相等)进行高层结构非弹性地震反应估计研究的原因,并以长周期单自由度和多自由度体系弹性与非弹性地震反应之间关系的有关研究结果论述了其可行性。     

On the inelastic seismic response of asymmetric buildings under bi‐axial excitation

The elastic and inelastic seismic response of plan‐asymmetric regular multi‐storey steel‐frame buildings has been investigated under bi‐directional horizontal ground motions. Symmetric variants of these buildings were designed according to Eurocodes 3 and 8. Asymmetric buildings were created by assuming a mass eccentricity in each of the two principal directions. The torsional response in the elastic and inelastic range is qualitatively similar with the exception of the stiff edge in the strong direction of torsionally stiff buildings and the stiff edge in the weak direction of torsionally flexible buildings. The response is influenced by the intensity of ground motion, i.e. by the magnitude of plastic deformation. In the limiting case of very strong ground motion, the behaviour of initially torsionally stiff and initially torsionally flexible buildings may become qualitatively similar. A decrease in stiffness due to plastic deformations in one direction may substantially influence the behaviour in the orthogonal direction. The response strongly depends on the detailed characteristics of the ground motion. On average, torsional effects are reduced with increasing plastic deformations, unless the plastic deformations are small. Taking into account also the dispersion of results which is generally larger in the inelastic range than in the elastic one, it can be concluded that (a) the amplification of displacements determined by the elastic analysis can be used as a rough estimate also in the inelastic range and (b) any favourable torsional effect on the stiff side of torsionally stiff buildings, which may arise from elastic analysis, may disappear in the inelastic range. The conclusions are limited to fairly regular buildings and subject to further investigations. Copyright © 2005 John Wiley & Sons, Ltd.     

Estimation of inelastic seismic deformations in asymmetric multistorey RC buildings

Four real buildings with three to six stories, strong irregularities in plan and little engineered earthquake resistance are subjected to inelastic response‐history analyses under 56 bidirectional EC8‐spectra‐compatible motions. The average chord rotation demand at each member end over the 56 response‐history analyses is compared to the chord rotation from elastic static analysis with inverted triangular lateral forces or modal response spectrum analysis. The storey‐average inelastic‐to‐elastic‐chord‐rotation‐ratio was found fairly constant in all stories, except when static elastic analysis is applied to buildings with large higher mode effects. Except for such buildings, static elastic analysis gives more uniform ratios of inelastic chord rotations to elastic ones within and among stories than modal response spectrum analysis, but generally lower than 1.0. With increasing EPA the building‐average inelastic‐to‐elastic‐chord‐rotation‐ratio decreases but scatter in the results increases. Static elastic analysis tends to overestimate the inelastic torsional effects at the flexible or central part of the torsionally flexible buildings and underestimate them at their stiff side. Modal response spectrum analysis tends to overestimate the inelastic torsional effects at the stiff or central part of the torsionally stiff buildings and underestimate them at the flexible side. Overall, for multistorey RC buildings that typically have fundamental periods in the velocity‐sensitive part of the spectrum, elastic modal response spectrum analysis with 5% damping gives on average unbiased and fairly accurate estimates of member inelastic chord rotations. If higher modes are not significant, elastic static analysis in general overestimates inelastic chord rotations of such buildings, even when torsional effects are present. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of supplemental viscous damping on inelastic seismic response of asymmetric systems

This paper investigates the effects of supplemental viscous damping on the seismic response of one‐storey, asymmetric‐plan systems responding in the inelastic range of behaviour. It was found that addition of the supplemental damping reduces not only deformation demand but also ductility and hysteretic energy dissipation demands on lateral load resisting elements during earthquake loading. However, the level of reduction strongly depends on the plan‐wise distribution of supplemental damping. Nearly optimal reduction in demands on the outermost flexible‐side element, an element generally considered to be the most critical element, was realized when damping was distributed unevenly in the system plan such that the damping eccentricity was equal in magnitude but opposite in algebraic sign to the structural eccentricity of the system. These results are similar to those noted previously for linear elastic systems, indicating that supplemental damping is also effective for systems expected to respond in the inelastic range. Copyright © 2001 John Wiley & Sons, Ltd.     

Seismic reliability analysis of buildings with torsional eccentricities

A study is presented of the influence of stiffness and strength eccentricities on the inelastic torsional response of buildings under the action of two simultaneous orthogonal horizontal ground motion components. Asymmetric buildings were obtained from their respective symmetric systems and were characterized by their stiffness and strength torsional eccentricities in both orthogonal directions. Based on the results of inelastic response of both building types (symmetric and asymmetric), the seismic reliability functions are determined for each system, and their forms of variation with different global system parameters are evaluated. Illustrative examples are presented about the use of this information for the formulation of seismic design criteria for in‐plan asymmetric multistory systems, in order to attain the same reliability levels implicit for symmetric systems designed in accordance with current seismic design codes. Copyright © 2014 John Wiley & Sons, Ltd.     

Inelastic torsional response of buildings to the 1985 Mexican earthquake: a parametric study

This study aims to determine the influence of torsional coupling on the inelastic response of a series of models representing typical structural configurations in real buildings. The lake bed (SCT) east-west component of the 1985 Mexico City earthquake was employed in the analysis, and is representative of a severe ground motion known to have induced large inelastic structural deformations in a high proportion of those buildings having asymmetrical distributions of stiffness and/or strength. Material non-linearity in lateral load-resisting elements has been defined using a hysteretic Ramberg-Osgood model. Structural eccentricities have been introduced into the building models by (i) asymmetrical distributions of stiffness and/or strength, (ii) asymmetrical configuration of lateral load-resisting elements, or (iii) varying post-elastic material behaviour in the resisting elements. The dynamic inelastic response of these models has been obtained by a numerical integration of the relevant equations of motion, expressed in a non-dimensional incremental form.

In the elastic range, the results correlate well with those of previous studies. In the inelastic range, it is concluded that the peak ductility demand of the worst-affected element increases with the ground excitation level across the range of building periods considered, and that the influence of torsional coupling on the key response parameters is model dependent. Most significantly, the strength eccentricity relative to the centre of mass has been shown to influence the peak edge displacement response more than conventionally employed stiffness eccentricity.     

On the inelastic torsional response of single‐storey structures under bi‐axial excitation

An attempt has been made to explore the general trends in the seismic response of plan‐asymmetric structures without any restrictions imposed by a particular code. Systems with structural elements in both orthogonal directions under bi‐directional excitation were studied. Idealized single‐storey models with bi‐axial eccentricity were employed. The systems were torsionally stiff and, in the majority of cases, mass‐eccentric. The main findings are: in general, inelastic torsional response is qualitatively similar to elastic torsional response. Quantitatively, the torsional effect on the flexible side, expressed as an increase of displacements due to torsion, decreases slightly with increasing plastic deformation, unless the plastic deformations are small. The response on the stiff side generally strongly depends on the effect of several modes of vibration and on the influence of the ground motion in the transverse direction. These influences depend on the structural and ground motion characteristics in both directions. Reduction of displacements due to torsion, typical for elastic torsionally stiff structures, usually decreases with increasing plastic deformations. As an additional effect of large plastic deformations, a flattening of the displacement envelopes in the horizontal plane usually occurs, indicating that torsional effects in the inelastic range are generally smaller than in the elastic range. The dispersion of the results of inelastic torsional response analysis is generally larger than that of elastic analysis. Copyright © 2005 John Wiley & Sons, Ltd.     

The role of phase difference components of ground motions in the torsional response of asymmetric buildings

It is demonstrated that the difference in phase content between orthogonal, horizontal, accelerograms can directly influence the effective (band‐limited) torque energy applied to a plan asymmetric structure. This is not the case where a plan asymmetric structure is excited solely by a unidirectional, horizontal, accelerogram ground motion. It is shown that this effective torque energy is well correlated with building torsional (response) acceleration energy and element ductility demands for a broad class of multistorey structures. Nonlinear time‐history analyses employing a database of accelerogram abstracted from USGS are used to quantify the influence of the phase difference content on these building responses. Bias in nonlinear time‐history analyses based on a small sample of accelerograms caused by phase difference content is discussed. Copyright © 2007 John Wiley & Sons, Ltd.     

Estimation of inelastic deformation demands in multistorey RC frame buildings

Estimation of peak inelastic deformation demands is a key component of any displacement-based procedure for earthquake-resistant design of new structures or for seismic evaluation of existing structures. On the basis of the results of over a thousand non-linear dynamic analyses, rules are developed for the estimation of mean and upper-characteristic peak inelastic interstorey drifts and member chord rotations in multistorey RC frame buildings, either bare or infilled in all storeys but the first. For bare frame structures, mean inelastic deformation demands can be estimated from a linear, equivalent static, or preferably multimodal response spectrum analysis with 5 per cent damping and with the RC members considered with their secant stiffness at yielding. 95 per cent characteristic values can be estimated as multiples of the mean deformations. For open-first-storey buildings, the linear analysis can be equivalent static, with the infills modelled as rigid bidiagonal struts and all RC members considered with their secant stiffness to yielding. Copyright © 1999 John Wiley & Sons, Ltd.     

Seismic response of linear and non‐linear asymmetric systems with non‐linear fluid viscous dampers

This investigation is concerned with the seismic response of one‐story, one‐way asymmetric linear and non‐linear systems with non‐linear fluid viscous dampers. The seismic responses are computed for a suite of 20 ground motions developed for the SAC studies and the median values examined. Reviewed first is the behaviour of single‐degree‐of‐freedom systems to harmonic and earthquake loading. The presented results for harmonic loading are used to explain a few peculiar trends—such as reduction in deformation and increase in damper force of short‐period systems with increasing damper non‐linearity—for earthquake loading. Subsequently, the seismic responses of linear and non‐linear asymmetric‐plan systems with non‐linear dampers are compared with those having equivalent linear dampers. The presented results are used to investigate the effects of damper non‐linearity and its influence on the effects of plan asymmetry. Finally, the design implications of the presented results are discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Seismic code analysis of multi-storey asymmetric buildings

Static torsional provisions in most seismic codes require that the lateral force at each floor level be applied at some distance from the reference centre at that floor. However, codes do not specify how to determine the locations of these centres. As a result, several different definitions of the reference centres are being used to implement the code analysis. This investigation examined how the results using various reference centres differ and which of these centres would lead to results that are in agreement with those of dynamic analysis. For this purpose three different buildings ranging form torsionally stiff to torsionally flexible were analysed. It was shown that for the class of buildings studied in this investigation that although the locations of the reference centres were quite different, the results were very similar and nearly independent of the reference centre. Comparison of results calculated from static code equivalent lateral force procedures and results from dynamic response spectrum analyses showed that the static code procedures led to design forces very close (flexible wall) or slightly conservative (stiff wall) when compared to the dynamic analysis for the torsionally stiff building. However, the static code procedures significantly underestimated the design forces of the stiff walls and significantly overestimated the design forces of the flexible walls for the torsionally flexible buildings. © 1998 John Wiley & Sons, Ltd.