Effects of hysteretic model on seismic demands: consideration of near‐fault ground motions

This paper summarizes the results of a study that is to evaluate the structural response attributes of near‐fault ground motion. Ground motion recordings from the Chi‐Chi earthquake are used as inputs to the structural system. An improved nonlinear hysteretic model, based on the experimental study, was used to calculate the response of the single degree‐of‐freedom inelastic system. Comparison of the results of analysis with traditional elastic–perfect plastic mode calculations was made. Discussions on the inelastic design spectrum, particularly the code‐specified base shear coefficients, using the improved nonlinear hysteretic model incorporated with the near‐fault input ground motion are made. Copyright © 2002 John Wiley & Sons, Ltd.     

Integrated multi‐type sensor placement and response reconstruction method for high‐rise buildings under unknown seismic loading

Structural health monitoring system has been implemented on high‐rise buildings to provide real‐time measurement of structural responses for evaluating their serviceability, safety, and sustainability. However, because of the complex structural configuration of a high‐rise building and the limited number of sensors installed in the building, the complete evaluation of structural performance of the building in terms of the information directly recorded by a structural health monitoring system is almost impossible. This is particularly true when seismic‐induced ground motion is unknown. This paper thus proposes an integrated method that enables the optimal placement of multi‐type sensors on a high‐rise building on one hand and the reconstruction of structural responses and excitations using the information from the optimally located sensors on the other hand. The structural responses measured from multi‐type sensors are fused to estimate the full state of the building in the modal coordinates using Kalman filters, from which the structural responses at unmeasured locations and the seismic‐induced ground motion can be reconstructed. The optimal multi‐type sensor placement is simultaneously achieved by minimizing the overall estimation errors of structural responses at the locations of interest to a desired target level. A numerical study using a simplified finite element model of a high‐rise building is performed to illustrate the effectiveness and accuracy of the proposed method. The numerical results show that by using 3 types of sensors (inclinometers, Global Positioning System, and accelerometers), the proposed method offers an effective way to design a multi‐type sensor system, and the multi‐type sensors at their optimal locations can produce sufficient information on the response and excitation reconstruction.     

Energy dissipation of tall core‐wall structures with multi‐plastic hinges subjected to forward directivity near‐fault and far‐fault earthquakes

In this study, different energy components in the tall reinforced concrete core‐wall buildings with numerous plastic hinges over the height are investigated using nonlinear time history analysis. The effect of near‐fault and far‐fault earthquakes is compared. The idea of one‐plastic, two‐plastic, three‐plastic and whole‐plastic hinge approaches along the core wall is examined. The input energy, inelastic, damping, kinetic and elastic strain energy during the earthquakes are studied. The results show that a large energy quantity transfers to the structure at the arrival time of the near‐fault motion pulse. Inelastic energy distribution over the height shows a considerable amount of inelastic energy dissipation occurring at the base and above the mid‐height of the walls. Copyright © 2016 John Wiley & Sons, Ltd.     

Nonlinear seismic response of reinforced‐concrete free‐standing towers with application to TV towers on flexible foundations

Reinforced‐concrete (R/C) free‐standing towers such as TV towers are often analysed using elastic analyses as fixed‐base cantilever beams, ignoring the effect of soil–structure interaction. To take the capacity of structures after yielding into account, most designers usually prefer to decrease the peak values of the elastic response spectrum for the maximum credible earthquake (MCE) anticipated at the site by a factor called the ductility capacity factor, which varies with the design earthquake level and the structural characteristics of the structure neglecting the effect of supporting soil. To investigate the effect of foundation flexibility on the response of R/C free‐standing towers deforming into their inelastic range during intense ground shaking, a linear sway‐rocking model is applied in numerical modelling of the soil–structure system. The effect of concrete cracking and reinforcement yielding on the elements used in the structure modelling is taken into account by introducing a nonlinear model for R/C frame elements using the moment–curvature (M–?) relation. A method called pseudo‐dynamic analysis is presented to quantify the inelastic seismic response spectrum of a soil–R/C free‐standing system using response spectrum analysis method and push‐over analysis technique. The earthquake responses of cracked and uncracked systems for a practical TV tower and a practical range of soil shear wave velocity are calculated and compared with the objective of understanding how soil–structure interaction influences structural responses. Copyright © 2002 John Wiley & Sons, Ltd.     

Design and compilation of specifications for a modular‐prefabricated high‐rise steel frame structure with diagonal braces. Part I: Integral structural design

Prefabricated steel structures have certain obvious advantages, that is, rapid construction, industrial production, and environmental protection. Although prefabricated structures have been applied in a number of countries in the world, in most cases, these structures are suitable only for low‐rise buildings, and their applications in high‐rise buildings are nota\bly rare. This paper proposes a new type of prefabricated steel structure called the modular‐prefabricated high‐rise steel frame structure with diagonal braces. Based on the T30 building, which is a hotel building with 30 storeys above the ground, the mechanical properties, failure mode, failure mechanism, and elastic–plastic development laws of the structure were studied via elastic and elastic–plastic design and analyses under various load cases and combinations. The analysis of the internal force and displacement response with frequent earthquakes was performed using the response spectrum and elastic time‐history methods, and an analysis under rare earthquakes is performed via static elastic–plastic pushover analysis. This paper summarizes the elastic and elastic–plastic structural design methods and process. This study provides important references for the design of this kind of modular‐prefabricated high‐rise steel structure, and the design method has been compiled into a design specification named Technical Specifications for Prefabricated Steel Frame Structure with Diagonal Bracing Joints.     

Forward directivity near‐fault and far‐fault ground motion effects on the behavior of reinforced concrete wall tall buildings with one and more plastic hinges

Near‐fault (NF) ground motion having forward directivity and far‐fault (FF) earthquakes can generate different responses on tall reinforced concrete cantilever walls. In this paper, the behavior of the core wall buildings were examined by performing nonlinear time history analyses on 20‐story, 30‐story and 40‐story fiber element models. The concept of one, two, three and extended plastic hinge in the core walls subjected to the NF motions having forward directivity (pulse‐like) and FF motion was studied by carrying out inelastic dynamic analysis. At the upper levels of the walls, NF pulse‐like ground motions can produce considerably larger curvature ductility, inter‐story drift and displacement demands as compared with the FF motions. A new approach was proposed to obtain the moment demand and reinforcement required to balance the curvature ductility demand along the height of a core wall. Copyright © 2015 John Wiley & Sons, Ltd.     

Stochastic seismic collapse and reliability assessment of high‐rise reinforced concrete structures

To provide knowledge beyond the conventional engineering insights, attention in this work is focused on a comprehensive framework for the stochastic seismic collapse analysis and reliability assessment of large complex reinforced concrete (RC) structures. Three key notions are emphasized: the refined finite element modeling and analysis approach towards structural collapse, a physical random ground motion model, and an energy‐based structural collapse criterion. First, the softening of concrete material, which substantially contributes to the collapse of RC structures, is modeled by the stochastic damage constitutive model. Second, the physical random ground motion model is introduced to quantitatively describe the stochastic properties of the earthquake ground motions. And then the collapse‐resistance performance of a certain RC structure can be systematically evaluated on the basis of the probability density evolution method combining with the proposed structural collapse criterion. Numerical results regarding a prototype RC frame‐shear wall structure indicate that the randomness from ground motions dramatically affects the collapse behaviors of the structure and even leads to entirely different collapse modes. The proposed methodology is applicable in better understanding of the anti‐collapse design and collapse prediction of large complex RC buildings.     

Seismic assessment of RC core‐wall building capable of three plastic hinges with outrigger

In a core‐wall structure with buckling restrained braces (BRB) outrigger, locations of the plastic hinges are influenced by the outrigger action. Therefore, the designer should consider the issue and use suitable details in the plastic hinge area. The essential questions that arise here are the plastic hinge location and the design moment demand used for design of this kind of structure. In this paper, responses of the core‐wall buildings with BRB outrigger designed by using the traditional response spectrum analysis procedure are assessed by implementing the nonlinear time history analysis. The result demonstrates that the plasticity can extend over anywhere within the core‐walls specially, at the base and above or below the outrigger levels. Formation of three plastic hinges in the core‐wall is recognized suitable for the system. To control the plasticity extension in the core‐wall, it is recommended that a new modal combination method be applied to calculate the moment strength of the three plastic hinges over the height. A capacity design concept is used to design other regions of the core‐wall where the plasticity does not extend to. The proposed procedure improves behavior of the system by restricting the plasticity extension to the predefined plastic hinge regions. Copyright © 2016 John Wiley & Sons, Ltd.     

Inelastic earthquake control of weld failure Part I: Limit state approach

Active structural control of inelastic response is proposed for the first time on existing buildings. The optimal linear control theory and the force analogy method are combined in state space form to calculate the response of the structure. Application of this combined method is performed to reduce the risk of weld failure in steel buildings. A six‐story moment resisting building damaged during the 1994 Northridge earthquake is used to study the sensitivity of the response and the magnitude of the structural control force to the earthquake ground motion. The limit state approach is used to design the structural control system by limiting the maximum plastic rotations in the building to an acceptable level. In the process, structural control is shown to be very effective in reducing the plastic rotations during excitations, and therefore reducing the risk of weld failure. In addition, structural control is effective in reducing the responses, which include displacement, velocity, acceleration and drift of the structure. Copyright © 1999 John Wiley & Sons, Ltd.     

Shaking table test and numerical analysis of an asymmetrical twin‐tower super high‐rise building connected with long‐span steel truss

The asymmetrical high‐rise building investigated in this paper is composed of a 299.1‐m‐high tower and a 235.2‐m‐high tower, which are diagonally and rigidly connected by two steel truss systems with the maximum span of 65.43 m. Given the great structural irregularities and complexities, the structural seismic performance is necessary to be investigated. A shaking table test of a 1/45 scaled model is conducted in this study, by which the structural damage pattern and dynamic responses are analyzed. The results show that the connecting trusses and rigid connection joints behave well during strong seismic excitations. The damages concentrate on the connecting floors, and the whole structural damage is slight. Most of the lateral resistance components remain elastic. The structure presents high seismic resistance against strong ground motions. Subsequently, a three‐dimensional finite element model of prototype structure is established and validated by the experimental results. The analyses indicate that performance of the connecting trusses is capable of coordinating translational and torsional deformation of the two towers and making them resist lateral seismic force together even subjected to maximum considered earthquakes. And this performance is still reliable although the high torsional modes are triggered.     

Seismic response and fragility analysis of fiber-reinforced concrete frame-shear wall structure

为研究在关键部位采用聚乙烯醇纤维增强混凝土材料的结构的地震反应,利用Perform-3D软件对一栋10层的框架 剪力墙结构进行单向罕遇地震（50年超越概率2%）作用下的非线性动力时程反应分析。结果表明,随着结构地震损伤程度的增加,纤维增强混凝土的优良性能发挥更加充分,对结构的抗震性能改善作用也更加明显;结构基本周期对应的加速度反应谱强度S_a(T₁)能较好地反映结构的损伤程度,适合作为地震动强度衡量指标。依据FEMA P695建议的增量动力分析方法,对22对地震动记录进行标准化处理和调幅,并通过结构地震易损性函数,给出结构在不同强度地震作用下达到“防止倒塌”极限状态的失效概率。对于框架-剪力墙结构,建议可采用墙肢塑性铰转角作为其“防止倒塌”极限状态地震易损性分析的结构反应参数。     

Seismic fragility analysis of concrete encased frame‐reinforced concrete core tube hybrid structure based on quasi‐static cyclic test

Concrete‐encased frame‐core tube hybrid structural system has been widely employed in high‐rise buildings. This paper intends to analyze the seismic fragility of this structural system under ground motion excitation. The quasistatic cyclic test on a 1/5‐scaled, 10‐story three‐bay specimen is introduced. Fiber‐based finite element model is developed and integrated with numerical techniques that would be able to simulate the nonlinear response based on the OpenSees program. As the model is verified by the experimental data, a series of incremental dynamic analyses (IDAs) considering different frame‐tube stiffness ratios are carried out. IDA curves are drawn to describe each structural performance state. Fragility curves and probabilistic demand models are proposed for quantifying failure probability. The collapse margin ratio is employed to evaluate the collapse probability. The result shows that the collapse probability under rare earthquake still meets the requirement of Applied Technology Committee‐63 Report. The hybrid structure is proved to perform superior collapse resistance ability. The proper increase in the stiffness of core tube can reduce the collapse probability and enhance the collapse resistance capacity.     

Fuzzy‐sliding mode control of nonlinear smart base‐isolated building under earthquake excitation

In this paper, the effectiveness of the fuzzy sliding mode control strategy on three‐dimensional benchmark building with smart base isolation under seismic excitation has been examined. One of the appropriate control theories for such this nonlinear system is the sliding mode control theory; discontinuous sliding mode theory has weakness such as chattering phenomena. In this paper, we used a combination of fuzzy logic and sliding mode theory for the deletion of this defect. The proposed control theory has been scrutinized by applying on lately developed nonlinear three‐dimensional base‐isolated benchmark building. This building because of the three‐dimensional nature, coalescing of lateral and torsional responses, continuity of responses of the superstructure, and base is modeled with three degrees of freedom on every floor. In this building eight actuators assigned only at the base level and in the two directions (x, y). In other words, 16 actuators are located underneath the structure. Furthermore, the base isolation system has been modeled by considering lateral coupled equations for a better examination of the performance of the system. The results indicate that reduction of control performance is remarkable. Also, utilizing proposed control theory can decrease the responses of building in two main directions and, particularly, in the rotational degree of freedom.     

An area‐based intensity measure for incremental dynamic analysis under two‐dimensional ground motion input

Incremental dynamic analysis (IDA) is a useful method in performance‐based earthquake engineering. IDA curves combine the intensity measure (IM) of ground motions with structural responses (as measured by engineering demand parameter) from nonlinear dynamic analysis. However, the curves display large record‐to‐record variability. And various IMs can lead to different results. Therefore, it is important to find a desirable IM to reduce the discreteness of the IDA results. So far, the studies on IM for IDA have been carried out by many scholars from scalar‐valued to vector‐valued, but few were based on 2‐dimensional ground motion input. To make the analysis more reasonable and practical as well as investigate the desirable IM under 2‐dimensional ground motion input, incremental dynamic analyses when ground motions are inputted in 2 directions should be investigated. In this paper, 2 combinational types of area‐based IM incorporating the influence of ground motion record components in secondary directions were proposed. To investigate the applicability, efficiency and desirable combinational form of the area‐based IM under 2‐dimensional ground motion input, incremental dynamic analysis were carried out using 2 reinforced concrete frames. Then the efficiency of the IMs was measured by the residual sum of squares and R². It is concluded that the area‐based IM with a combination by the square root of the sum of the squares (SRSS) method is the most efficient for IDA under 2‐dimensional ground motion input. The methods and conclusions will provide significant reference for studying IMs under 2‐dimensional ground motion input. Further research will focus on the applicability of the area‐based IM for tall buildings whose higher modes need to be considered.     

Performance of variable curvature sliding isolators in base‐isolated benchmark building

The performances of variable curvature sliding isolators like variable frequency pendulum isolator (VFPI) and variable curvature friction pendulum system (VCFPS) installed in the base‐isolated benchmark building subjected to bi‐directionally acting seven strong earthquakes have been studied. The shear type base‐isolated benchmark building is modelled as three‐dimensional linear elastic structure having three degrees‐of‐freedom at each floor level. Time domain dynamic analysis of the building has been carried out with the help of constant average acceleration Newmark‐Beta method and non‐linear isolation forces has been taken care by fourth‐order Runge‐Kutta method. The force‐displacement responses of the VFPI and VCFPS are studied under parametric variations of their key characteristics for the comparative performance evaluation. The time history variations of response characteristics and peak response evaluation criteria are also investigated for overall comparison of their performances. The performance of VFPI and VCFPS are observed both in uniform and hybrid isolation systems. The force‐displacement responses of both VFPI and VCFPS subjected to strong near‐field earthquakes show excessively large isolator displacements at higher initial radii of curvature of sliding surface. The large isolator displacements of VFPI and VCFPS can be restrained efficiently by addition of viscous fluid dampers in comparison to the increase in coefficient of friction of isolators. Copyright © 2010 John Wiley & Sons, Ltd.     

Effectiveness of sliding isolators with variable curvature in near‐fault ground motions

Recent studies have revealed that a sliding isolator with variable curvature (SIVC) can mitigate the resonance phenomenon likely to occur in seismic response of a conventional friction pendulum system (FPS) isolator due to its constant isolation frequency. The present study simulates four SIVC isolators and an FPS to find the optimum range of initial isolation period and coefficient of friction and employ them in comparing the effectiveness of SIVC in different peak ground acceleration (PGA) scales of near‐fault earthquakes. Velocity‐dependent coefficient of friction and modified viscoplasticity model have been used to simulate nonlinear friction force of the isolators. Results indicate identical performance of all SIVC isolators in PGA scales up to 0.4 g. When subjected to PGA scales from 0.4 g to 1.0 g, polynomial friction pendulum isolator (PFPI) and variable curvature friction pendulum system (VCFPS) reduce base displacement greatly, while conical friction pendulum isolator (CFPI) and variable frequency pendulum isolator (VFPI) show amplified responses. However, in mitigating structural acceleration, performance of CFPI and VFPI, unlike PFPI and VCFPS, which perform poorly, is excellent. Thus, in a strong near‐fault earthquake, PFPI and VCFPS or CFPI and VFPI can be chosen based on whether reduction of base displacement or super‐structural acceleration is the main concern of designer, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Seismic isolation columns for earthquake‐resistant structures

Seismic isolation is a well‐known trend in earthquake design of structures. It enables a reduction in structural response to earthquakes and minimizes possible damage to buildings. This paper deals with a new constructive solution for seismic isolation, adapted to a structural scheme traditionally used in the Mediterranean region; it is usually presented as an open ground floor with a system of reinforced‐concrete columns, supported on single bases. The best‐known base isolation systems, implemented in existing structures, are elastomeric bearings and friction pendulums. The proposed solution is based on the idea of pendulum suspension brackets installed in seismic isolation columns. The main differences between existing solutions and the proposed one are that the latter requires no additional space for its installation, its lifetime corresponds to that of the structure, and no service is required during the entire period. The proposed solution provides additional damping and, like other base isolation systems, shifts the vibration period of the structure, reducing its spectral response. Since its size is compact, the ground‐floor columns of existing structures with low seismic capacity may easily be replaced by the proposed ones. It yields significant improvement in structural seismic response. Numerical simulation shows that buildings where the proposed system is installed are likely to sustain minimal damage, or none at all, whereas traditionally designed ones may suffer major damage or even collapse due to the same earthquake. Copyright © 2007 John Wiley & Sons, Ltd.     

Design and specification compilation of a modular‐prefabricated high‐rise steel frame structure with diagonal braces part II: Elastic–plastic time‐history analysis and joint design

The use of modular‐prefabricated steel structures has distinct advantages, such as rapid construction, industrial production, and environmental protection. Although this type of structure has been extensively employed around the world, it is primarily used for low‐rise buildings; its application in high‐rise buildings is limited. This paper proposes a new type of modular‐prefabricated high‐rise steel frame structure with diagonal braces. An elastic–plastic time‐history analysis of a 30‐storey building during rare earthquakes was performed. The base shear, storey drift, stress, damage characteristics, and other performances of the structure were investigated. According to the mechanism analysis, finite element simulation, and model test, the formulas for the elastic and elastic–plastic design of the truss–column connection, column–column flange connection, and diagonal brace–truss connection are proposed in this paper. The control parameters for the structural design are also discussed. This study provides an important reference for the research and design of this type of modular‐prefabricated high‐rise steel structure. The design method has been compiled into a design specification named Technical Specifications for Prefabricated Steel Frame Structure with Diagonal Bracing Joints, which is unique for this type of structure.     

Active Tendon Control of Torsionally Irregular Structures under Near‐Fault Ground Motion Excitation

In this study, torsionally irregular single‐story and multistory structures under the effect of near‐fault ground motion excitation were controlled by active tendons. Near‐fault ground motions contain two impulsive characters. These impulsive characters are the directivity effect perpendicular to fault and the flint step parallel to fault. The structural models were simulated under bidirectional earthquake records superimposed with impulsive motions to examine the response of active control under near‐fault effects. Also, the structures were analyzed only under the effect of bidirectional impulsive pulses. The control signals were obtained by Proportional–Integral–Derivative (PID) type controllers and the parameters of the controllers were obtained by using a numerical algorithm depending on time domain analyses. Time delay effect was also considered for active control system. Different cases of orientation of active tendons were examined and the results of the single‐story structure were compared with another control strategy using frequency domain responses in the optimization process. As a conclusion, the control concept is significantly effective on reducing maximum responses in translational and rotational directions and obtaining a steady‐state response.     

非平整场地上输电塔-线体系在多点激励下的地震反应

在以往的大地震中输电塔的破坏时有发生,输电塔倒塌的部分原因是由于相邻塔在地震动多点激励下异相振动产生的导线拉力引起。本文考虑导线的几何非线性,建立了输电塔-线体系三维有限元模型,分析了非平整场地上的结构体系在地震动纵向多点激励下的反应。基于经验相干函数和修正金井清功率谱密度函数模型模拟了空间变化地震动,分别考察了地震波视波速和相干损失对于结构体系地震反应的影响。结果表明,假定地震动一致激励不能准确评估结构体系的反应,地震动空间变化效应放大了输电塔和导线的地震反应,在强震作用下,忽略地震动的空间变化会严重低估输电塔-线体系的反应。