SIMPLE PUSH-OVER ANALYSIS OF ASYMMETRIC BUILDINGS

A simple method for the non-linear static analysis of complex building structures subjected to monotonically increasing horizontal loading (push-over analysis) is presented. The method is designed to be a part of new methodologies for the seismic design and evaluation of structures. It is based on the extension of a pseudo-three-dimensional mathematical model of a building structure into the non-linear range. The structure consists of planar macroelements. For each planar macroelement, a simple bilinear or multilinear base shear–top displacement relationship is assumed. By a step-by-step analysis an approximate relationship between the global base shear and top displacement is computed. During the analysis the development of plastic hinges throughout the building can be monitored. The method has been implemented into a prototype computer program. In the paper the mathematical model, the base shear–top displacement relationships for different types of macroelements, and the step-by-step computational procedure are described. The method has been applied for the analysis of a symmetric and an asymmetric variant of a seven-storey reinforced concrete frame–wall building, as well as for the analysis of a complex asymmetric 21-storey reinforced concrete wall building. The influence of torsion on structural behaviour is discussed. © 1997 by John Wiley & Sons, Ltd.     

Dynamic modelling of masonry buildings: Storey mechanism model as a simple alternative

The dynamic behaviour of a four-storeyed masonry building model subjected to simulated earthquake loading has been investigated. The observations of damage propagation during shaking tests indicated the storey mechanism action of model building. Since the predominant effect of the first natural mode of vibrations has been also observed, the idea of simple mathematical modelling has been followed in the calculations. Two simple analytical models have been compared when evaluating the dynamic response of the model building: a four degrees of freedom shear system and an equivalent single degree of freedom system. Three hysteresis rules have been taken into account for modelling the non-linear behaviour of the model. Satisfactory correlation between the measured and calculated response has been obtained in most cases.     

A linear mathematical model for the seismic inplane behaviour of brick masonry walls part 1: Theoretical considerations

In this study two mathematical models are presented for the linear dynamic behaviour of masonry walls. The study is completed in three stages: experimental observations, selection of a mathematical model and the determination of model parameters through optimization analysis. In the present paper (Part 1) the theoretical analysis used in the development of the mathematical models is presented. Part 2 is devoted to the optimization analysis. Evaluation of the experimental data, which is described in detail in Part 2, indicates that the first two modal frequencies of the wall specimen are close to each other. This may be attributed, on physical grounds, to strong interaction between the brick and mortar phases of the wall. Accordingly, a two-phase mathematical model, namely a mixture model (MM), is chosen to describe the wall behaviour because it can differentiate between the two phases of the wall and take into account the interaction between them. The equations of MM are put into a discrete form to simplify the optimization analysis. As a special case, MM contains a simple one-phase model called the effective modulus model (EMM). The equations of EMM are also established. Finally, the theoretical complex frequency response functions (CFRF) predicted by MM and EMM are obtained. CFRF relates the top acceleration of the wall to its base acceleration and is the response quantity chosen to be matched in the optimization analysis.     

An evaluation of force-based design vs. direct displacement-based design of jointed precast post-tensioned wall systems

The unique features of jointed post-tensioned wall systems, which include minimum structural damage and re-centering capability when subjected to earthquake lateral loads, are the result of using unbonded post-tensioning to attach the walls to the foundation, along with employing energy dissipating shear connectors between the walls. Using acceptance criteria defined in terms of inter-story drift, residual drift, and floor acceleration, this study presents a multiplelevel performance-based seismic evaluation of two five-story unbonded post-tensioned jointed precast wall systems. The design and analysis of these two wall systems, established as the direct displacement-based and force-based solutions for a prototype building used in the PREcast Seismic Structural Systems （PRESSS） program, were performed at 60% scale so that the analysis model could be validated using the PRESSS test data. Both buildings satisfied the performance criteria at four levels of earthquake motions although the design base shear of the direct displacement-based jointed wall system was 50% of that demanded by the force-based design method. The study also investigated the feasibility of controlling the maximum transient inter-story drift in a jointed wall system by increasing the number of energy dissipating shear connectors between the walls but without significantly affecting its re-centering capability.     

Linear‐elastic lateral load analysis and seismic design of pin‐supported wall‐frame structures with yielding dampers

This paper describes an analytical investigation on a reinforced concrete lateral load resisting structural system comprising a pin‐supported (base‐rocking) shear wall coupled with a moment frame on 1 or both sides of the wall. Yielding dampers are used to provide supplemental energy dissipation through the relative displacements at the vertical connections between the wall and the frames. The study extends a previous linear‐elastic model for pin‐supported wall‐frame structures by including the effects of the dampers. A closed‐form solution of the lateral load behavior of the structure is derived by approximating the discrete wall‐frame‐damper interactions with distributed (ie, continuous) properties. The validity of the model is verified by comparing the closed‐form results with computational models using OpenSees program. Then, a parametric analysis is conducted to investigate the effects of the wall, frame, and damper stiffness on the behavior of the structure. It is found that the damper stiffness significantly affects the distribution of shear forces and bending moments over the wall height. Finally, the performance‐based plastic design approach extended to the wall‐frame‐damper system is proposed. Case studies are carried out to design 2 damped pin‐supported wall‐frame structures using the proposed approach. Nonlinear dynamic time‐history analyses are conducted to verify the effectiveness of this method. Results indicate that the designed structures can achieve the performance level with the story drift ratios less than target values, and weak‐story failure mechanism is not observed. The approach can be used in engineering applications.     

The pseudo‐viscous frictional energy dissipator: a new device for mitigating seismic effects

Viscous energy dissipators (EDORs) have good suppressing effects on acceleration or base shear and they do not add axial pressure to the column when peak moment in the column occurs at peak displacement. Pall frictional EDORs can dissipate energy even when the compression brace buckles due to a special frictional damping mechanism. Retaining the advantages of viscous and Pall EDORs and overcoming their disadvantages, a pseudo‐viscous frictional energy dissipator (PVEDOR) is developed. PVEDORs use the frictional damping mechanism of Pall EDORs, but the slip force of PVEDORs is made variable so that the slip force reduces with increasing displacement. Behaviour testing of PVEDORs shows that they possess the important hysteretic feature of viscous EDORs, i.e. the restoring force of PVEDORs are out‐of‐phase with displacement. Earthquake simulation tests of a 16‐storey frame structure incorporating PVEDORs and ordinary steel braces and bare frame are carried out. The test results show that PVEDORs have good vibration‐suppressing effects. An analytical hysteretic model of PVEDORs basically agrees with the behaviour testing results. Finally, the parameter influence of PVEDORs on suppressive effectiveness of structural vibration under earthquake conditions is studied. Numerical analyses show that PVEDORs have good control effects on both seismic displacement and acceleration, and that control effects of PVEDORs on base shear are much better than Coulomb‐type frictional EDORs or metallic EDORs. Copyright © 2002 John Wiley & Sons, Ltd.     

航空重力测量的系统误差补偿

基于航空重力测量的基本数学模型,详细分析了航空重力测量的系统误差来源.大致可将系统误差分为三类,即停机坪重力基准值、比力初值的观测误差,格值、交叉耦合系数、摆杆尺度因子的标定误差和水平加速度改正的模型化误差等.然后,对每类系统误差的量级及其补偿方法进行了研究,指出水平加速度改正是引起系统误差的主要因素之一.大同、哈尔滨和渤海湾航空重力测量的实测数据分析均表明,在各项系统误差尤其是水平加速度改正得到有效补偿后,航空重力与地面(或船测)参考值的系统误差将小于1×10^-5m·s^-2.     

钢筋混凝土剪力墙结构基于自平衡力的非线性地震反应分析

本文简要评述了现有钢筋混凝土剪力墙的非线性分析模型，着重介绍了多竖线单元模型，并对其竖向单元的轴向刚度和水平弹簧的剪切刚度分别建议了改进的滞变模型，最后将基于自平衡力的非线性动力反应分析方法应用于求解剪力墙结构的非线性地震反应，并用传统分析方法对其结果进行了检验，表明该分析方法计算简便，而且是有效和可靠的。     

Shaking‐table tests of flat‐bottom circular silos containing grain‐like material

According to Eurocode 8, the seismic design of flat‐bottom circular silos containing grain‐like material is based on a rough estimate of the inertial force imposed on the structure by the ensiled content during an earthquake: 80% of the mass of the content multiplied by the peak ground acceleration. A recent analytical consideration of the horizontal shear force mobilised within the ensiled material during an earthquake proposed by some of the authors has resulted in a radically reduced estimate of this load suggesting that, in practice, the effective mass of the content is significantly less than that specified. This paper describes a series of laboratory tests that featured shaking table and a silo model, which were conducted in order to obtain some experimental data to verify the proposed theoretical formulations and to compare with the established code provisions. Several tests have been performed with different heights of ensiled material – about 0.5 mm diameter Ballotini glass – and different magnitudes of grain–wall friction. The results indicate that in all cases, the effective mass is indeed lower than the Eurocode specification, suggesting that the specification is overly conservative, and that the wall–grain friction coefficient strongly affects the overturning moment at the silo base. At peak ground accelerations up to around 0.35 g, the proposed analytical formulation provides an improved estimate of the inertial force imposed on such structures by their contents. Copyright © 2015 John Wiley & Sons, Ltd.     

Damaging potential of low-magnitude near-field earthquakes on low-rise shear walls

The purpose of this study is to show that small earthquakes close to the site cause less damage in reinforced concrete structure than what is implied by their peak or spectral acceleration, used often as indicators of the destructive potential of earthquake shaking.For this purpose, an important step is to set up a simplified model of a representative reinforced concrete structure, capable of reproducing the global damage. A non-linear single degree of freedom model of a low-rise shear wall, proposed in a previous paper, has been adopted [Eng Struct 25 (2003) 1]. In this paper, the validity of the simplified approach is confirmed by comparing numerical damage predictions engendered by 501 strong motion records with those provided by a finite element approach using local models.Thanks to the drastic reduction of the computation time, the interdependency between the seismic acceleration parameters proposed in the literature and the damage is explored. A spectral intensity, taking into account the degradation of the fundamental frequency, is proposed. The spectral intensity turns out to be much more independent of the distance and magnitude of the causative earthquakes than the PGA and the spectral acceleration at the initial frequency corresponding to the undamaged state.     

Period formulas of shear wall buildings with flexible bases

The evaluation of the fundamental period of shear wall buildings considering the flexibility of the base is investigated in this paper. This research is motivated by the discrepancy reported between the formulas used in different building codes and the measurement of real buildings. Both experimental and analytical approaches are used to assess the effect of the base flexibility on the fundamental period of shear wall structures. In total, twenty buildings built on different types of soil are tested under ambient vibration. The fundamental period is identified using a non‐parametric linear model in the frequency domain. The results show that fundamental period formulas used by UBC‐97 and NBCC‐95 are inadequate since they do not include the effect of the foundation stiffness. To improve the estimation of the fundamental period of shear wall buildings, an analytical approach is presented. The structure and the foundation are represented by a continuous‐discrete system. The stiffnesses of the base are represented by translational and rotational discrete springs. The rigidities of these springs are evaluated from the elastic uniform compression of the soil mass and the size of the foundation. The analytical predictions improve the estimation of the fundamental period and keep the computation simple. The error between the measured period and the analytical results is, on average, less than 10%. Copyright © 2003 John Wiley & Sons, Ltd.     

Evaluation of uniaxial contact models for moat wall pounding simulations

Moat wall pounding occurs when a base-isolated building displaces beyond the provided clearance and collides with the surrounding retaining wall, inducing very high floor accelerations and interstory drifts. Previous studies on moat wall pounding typically employ simplified models of the superstructure, with a uniaxial contact spring used to model the entire moat wall. Consequently, researchers have developed sophisticated contact models to estimate the normal-direction contact force that is generated during seismic pounding. This study examines how the choice in contact model affects the seismic response of a base-isolated building subjected to impact-inducing ground excitation. Five widely used state-of-the-art contact models are summarized and implemented into an experimentally-calibrated numerical model of a base-isolated moment frame. Results of nonlinear dynamic time history analyses are shown in detail for one ground motion, followed by a larger parametric study across 28 near-fault ground motions. This work shows that peak impact force and base acceleration are moderately sensitive to the choice in contact model, while upper floor accelerations and interstory drifts are practically not affected.     

某框架结构基础隔震地震反应对比分析

基于结构动力学原理和有限元基本理论,利用SAP2000有限元分析软件,以某框架结构基础隔震楼和与其相近的非隔震楼为研究对象分别建立分析模型,运用动力时程分析法对两种模型进行水平地震反应分析。结果表明:基础隔震楼的水平向地震反应远小于非隔震楼,其上部结构的自振周期明显大于非隔震楼,其层间剪力和基底剪力、楼层相对位移和加速度低于非隔震楼。总体来说,隔震支座可以显著降低水平向地震对于结构的不良反应,值得推广应用。     

Evaluation of the performance of a suspension isolation system subjected to strong ground motion

This study is concerned with a new isolation device called a Suspended Pendulum Isolation (SPI) system here. Particular attention is given to evaluate the dynamic behaviour of the system under substantial ground motions including the El Centro 1940, Hachinohe 1968 and Kobe 1995 earthquakes. Shaking-table tests have been carried out for a 4 25-scaled model comprising a test structure supported on the SPI system with lead damper. Several yield strengths for the lead damper are examined to investigate its properly designed dimensions. Experimental results show that the SPI system with lead damper has a substantial capability to decrease either peak acceleration or peak base (bearing) displacement responses for broad-band frequency excitations. It also confirms that maximum-storey drift index of isolated structure has been dropped to about one-sixth of its corresponding value at fixed-base condition under strong level of predominant excitation along with considerable decrease of peak acceleration. A non-linear analytical model for an MDOF shear building has been also developed by utilizing the fourth-order Runge–Kutta algorithm. Comparison of analytical and experimental time-history responses for all of the excitations indicates that there is a good agreement in both peak values and shape pattern of the results. Moreover, SPI with an appropriate yield strength of lead damper creates only a very small permanent displacement after strong excitation. © 1998 John Wiley & Sons, Ltd.     

CAP1400核岛结构缩尺模型对地震反应影响分析

针对核电厂CAP1400核岛结构地震反应问题,构建了核岛屏蔽厂房和辅助厂房整体结构的3个分析模型:原型和1/16、1/40缩尺模型,并在AP000谱和RG1.60谱地震动输入下进行了有限元模拟对比分析,探讨了振动台试验模型缩尺处理的合理性和精确性。研究表明,基于缩尺模型得到的结构自振频率相对于原型结构模型有所降低,降低幅度在8.5%以内;结构模型的缩尺对结构反应峰值加速度和高频（大于3Hz）加速度反应谱的影响较为显著,但对较低频（小于3Hz）的加速度反应谱影响较小;模型缩尺对结构不同方向反应的影响中,刚度越大的方向其影响越大。进一步将结构模型数值模拟结果与1/16缩尺模型的振动台试验结果进行了比较分析,试验给出的结构自振频率远低于模型数值模拟结果,但原型和1/16缩尺模型数值模拟得到的结构反应均与试验结果较为接近。基于模型数值模拟和振动台试验研究,认为对于缩尺比1/16或更大的模型可以忽略模型的缩尺效应。     

Dynamics of a sliding-rocking block considering impact with an adjacent wall

A freestanding rigid block subjected to base excitation can exhibit complicated motion described by five response modes: rest, pure rocking, pure sliding, combined sliding-rocking, and free flight. Previous studies on the dynamics of a rocking block have assumed that the block does not interact with neighboring objects. However, there are many applications in which the block may start or come in contact with an adjacent boundary during its motion, for example, a bookcase or cabinet colliding with a partition wall in an earthquake. This paper investigates the dynamics of a sliding-rocking block considering impact with an adjacent wall. A model is developed in which the base and wall are assumed rigid, and impact is treated using the classical impulse and momentum principle. The model is verified by comparing its predictions in numerical simulations against those of an existing general-purpose rigid-body model in which impact is treated using a viscoelastic impact model. The developed model is used to investigate the effects of different parameters on the stability of a block subjected to analytical pulse excitations. It is found that wall placement (left or right) has a dominant effect on the shape of the overturning acceleration spectra for pulse excitations. In general, decreasing the gap distance, base friction coefficient, and wall coefficient of restitution enhance the stability of the block. Similar observations are made when evaluating the overturning probability of a block using earthquake floor motions.     

Shaking table testing and numerical simulation of the seismic response of a typical Mexican colonial temple

A shaking table testing program was undertaken with the main objective of providing basic information for the calibration of analytical models, and procedures for determining seismic response of typical stone masonry temples of the 16–18th centuries stone masonry construction in Mexico. A typical colonial temple was chosen as a prototype. A model at a 1:8 geometric scale was built with the same materials and techniques as the prototype, and was subjected to horizontal and vertical motions of increasing intensities. The maximum applied intensity corresponded to a base shear force of about 58 of the total building weight. Vertical component of the base motion significantly affected the response and increased the damage of the model. Damage patterns were similar to those observed in actual temples. Damping coefficients of the response ranged from 7 for undamaged state, reached about 14 for severe damage. The main features of the measured response were compared with those computed using a nonlinear, finite element model; for the latter, a constitutive law developed for plain concrete was adopted for reproducing cracking and crushing of the irregular stone masonry. Observed damage patterns as well as measured response could be reproduced with reasonable accuracy by the analytical simulation, except for some local vibrations, as those at the top of the bell towers. It can be concluded that the simple constitutive law adopted for the simulation was able to reproduce the experimental response with reasonable level of accuracy. Copyright © 2011 John Wiley & Sons, Ltd.     

钢管混凝土边框高强混凝土组合剪力墙抗震性能试验研究

钢管混凝土边框组合剪力墙是一种新型组合剪力墙。本文进行了2个1/4缩尺的高强混凝土剪力墙模型的低周反复荷载试验,模型1为普通钢筋混凝土剪力墙,模型2为钢管混凝土边框组合剪力墙。在试验研究基础上,对比分析它们的承载力、延性、刚度及其衰减过程、滞回特性、耗能能力及破坏特征,建立了组合剪力墙的承载力计算模型,计算结果与实测结果符合较好。研究表明,钢管混凝土边框高强混凝土组合剪力墙与普通剪力墙相比抗震性能显著提高。     

Static and seismic limit equilibrium analysis of sliding retaining walls under different surcharge conditions

The static and seismic sliding limit equilibrium condition of retaining walls is investigated, and analytical solutions for the angle of the active slip surface, the critical acceleration coefficient and the coefficient of active earth pressure are provided for different surcharge conditions. In particular, walls retaining a horizontal backfill without surcharge, walls supporting an extended uniform surcharge applied at different distances from the wall and walls supporting a limited uniform surcharge or linear uniform surcharge parallel to the wall are considered in the analysis.The solutions have been derived in the framework of the limit equilibrium approach, considering the effect of the wall through its weight, and accounting for the shear resistance at the base of the wall and the inertia force arising in the wall under seismic conditions.For the wall without surcharge the effect of the vertical component of the seismic acceleration as well as the effects of the inclination of the wall internal face and of the soil–wall friction were also investigated.The angle of the slip plane, the critical seismic acceleration coefficient and the coefficient of active earth pressure are given as functions of dimensionless parameters and the boundary conditions for the applicability of each solution are specified. The influence of soil weight, surcharge conditions and inertia forces on the active earth pressure coefficient is analysed.