Dynamic characteristics and viscous dampers design for pile‐soil‐structure system

A series of large‐scale shaking table tests are conducted on tall buildings with and without energy dissipation devices on soft soils in pile group foundations, representing pile‐soil‐structure interaction (PSSI) system and the corresponding fixed‐base situations. The superstructure is a 12‐story reinforced concrete (RC) frame. The dynamic characteristics of the test models show that the frequencies decrease and the damping ratio increase in PSSI system by comparison with the fixed‐base structures. The mode shapes of PSSI system are different from that under fixed‐base condition, and the mode shapes of structure without dampers change greater than that with energy dissipation devices under various white noises. An improved method for structural dynamic characteristics, considering the impedance function of piles, is developed to address the issue of modal parameters with PSSI effect. In addition, the structural dynamic parameters of the large‐scale shaking table tests are identified using the modification method and other regulation methods, demonstrating that the improved approach is highly accurate and effective. Subsequently, a design procedure for viscous dampers of structures with PSSI effect is presented based on the dynamic characteristics of the system. Finally, the dynamic responses of the structure with viscous dampers in the practical engineering are decreased effectively, indicating the good performance of designed viscous dampers. The numerical results also show that the damping efficiency of interstory drift is larger than the acceleration and interstory shear force. Therefore, the improved modal parameters method, validated through a series large‐scale shaking table tests, is applicable for identifying dynamic characteristics of pile‐soil‐structure with energy dissipation devices system. The design procedure of viscous dampers, proved by a reinforced concrete frame structure located on a practical Shanghai soft site, can be employed to design the viscous dampers considering seismic PSSI effect.     

中间柱型阻尼器装配式自复位钢框架数值模拟

装配式自复位钢框架具有震后结构自动复位、结构残余变形及损伤较小、可以恢复结构正常使用功能等优势。但是当装配式自复位钢框架跨度较大时,常因刚度不足导致其层间位移角不能满足抗震设计规范限值要求。为此,提出了中间柱型阻尼器装配式自复位钢框架,在拟动力试验研究基础上,通过有限元软件ABAQUS进行数值模拟,并与试验结果进行对比分析;在数值模拟校验的基础上,通过有限元分析研究了施加竖向活荷载对中间柱型阻尼器工作机制的影响。研究结果表明：数值模拟与子结构拟动力试验结果在结构位移峰值、滞回性能、索力变化等方面吻合较好,数值模拟方法可靠;中间柱型阻尼器可提高框架结构的抗侧刚度,有效控制结构层间位移角,同时提高结构耗能能力,延缓主体结构塑性发展进而保护主体结构,减小结构残余变形并控制损伤;中间柱型阻尼器装配式自复位钢框架具有良好的自复位能力,竖向活荷载对中间柱型阻尼器滞回性能及耗能能力影响不大。     

Distribution of Optimum Yield-Strength and Plastic Strain Energy Prediction of Hysteretic Dampers in Coupled Shear Wall Buildings

The structural behavior of reinforced concrete coupled shear wall structures is greatly influenced by the behavior of their coupling beams. This paper presents a process of the seismic analysis of reinforced concrete coupled shear wall-frame system linked by hysteretic dampers at each floor. The hysteretic dampers are located at the middle portion of the linked beams which most of the inelastic damage would be concentrated. This study concerned particularly with wall-frame structures that do not twist. The proposed method, which is based on the energy equilibrium method, offers an important design method by the result of increasing energy dissipation capacity and reducing damage to the wall’s base. The optimum distribution of yield shear force coefficients is to evenly distribute the damage at dampers over the structural height based on the cumulative plastic deformation ratio of the dissipation device. Nonlinear dynamic analysis indicates that, with a proper set of damping parameters, the wall’s dynamic responses can be well controlled. Finally, based on the total plastic strain energy and its trend through the height of the buildings, a prediction equation is suggested.     

An evaluation of energy response and cumulative plastic rotation demand in steel moment‐resisting frames through dynamic/static pushover analyses

In the energy‐based design approach, the seismic design is performed through the balancing of the energy input and the energy dissipation of the structure. The energy dissipation is represented by the hysteretic energy dissipation capacity defined as the total area enclosed in the force–deformation curves under cyclic loading. Thus, the energy‐based design approach considers the cumulative effect of the seismic loading of the structure. The cumulative damage in the structural members can be expressed in terms of cumulative plastic rotation (CPR). The CPR capacity plays an important role in determining the hysteretic energy dissipation capacity of a steel moment connection. This study investigated the energy response and the CPR capacity and demand through dynamic pushover analyses on steel moment‐resisting frames. The results were compared with the ones obtained from the pushover analysis. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental study on a novel replaceable yielding‐based energy dissipater for rocking and seesaw buildings

The use of energy dissipaters for creation of earthquake‐resilient buildings has been paid more and more attention in recent years, and some newly developed structural fuses or dampers have been proposed to be employed in rocking and seesaw buildings. In this study, a new type of yielding‐based dampers, called curved‐yielding‐plates energy dissipater (CYPED), is introduced. CYPEDs are installed at the bottom of rocking or seesaw building's circumferential columns at the lowest story and have hysteretic behavior in their deformation occurring in vertical direction. The initial curvature of the yielding plates prevents them from buckling and gives the device a smooth force–deformation behavior. First, by performing a set of cyclic tests on three specimens of CYPED, their hysteretic force–displacement behavior was investigated. Then, to show the efficiency of this energy dissipating device in reducing the seismic response of buildings, they were employed numerically as multilinear plastic springs in the computer models of a sample seesaw steel building, and a series of nonlinear time history analysis (NLTHA) were performed on both seesaw building and its conventional counterpart. Results of NLTHA show that the proposed seesaw structural system equipped with appropriate CYPEDs not only gives the building a longer natural period, leading to lower seismic demand, but also leads to remarkable energy dissipation capacity in the building structure at base level and, therefore, keeping the seismic drifts in elastic range in all stories of the building. In this way, the building structure does not need any major repair work, even after a large earthquake, while the conventional building suffers from heavy damage and is not usable after the earthquake.     

Seismic analysis for tall and irregular temple buildings: A case study of strong nonlinear viscoelastic dampers

Viscoelastic (VE) dampers, composed of VE layers sandwiched between relative rigid steel plates, have been widely used as dissipation devices to improve performance of structures under dynamic loads. Corresponding analytical and experimental investigations have been carried out by many scholars. However, most of VE dampers studied before are typically traditional dampers applied in regular structures. This paper introduces a new type of VE damper with strong nonlinearity used in the complex and irregular structure of Nanjing Dabaoen Temple. The new VE dampers show obvious nonlinear behavior, improved capacity of dissipation, and larger additional stiffness compared to the traditional ones. Nanjing Dabaoen Temple is a high‐rise steel structure by use of 112 new VE dampers. To investigate dissipation characteristics and control effect of the VE dampers in the complex structure, we established a suitable finite element model using SAP2000 software in which the VE dampers were simulated by Maxwell and Wen models connected in parallel, and then nonlinear time history analysis is executed using seven ground motions of moderate earthquakes and three of major earthquakes. Analytical results indicate that control effect of the VE dampers on structural displacement is preferable to that on structural acceleration and shear force due to dampers' additional stiffness. In addition, owing to incremental deformation of VE dampers under major earthquakes, damping effect of the VE dampers on all structural responses under major earthquakes is more obvious than that under moderate earthquakes. Analytical methods and conclusions in this paper will provide significant reference for analysis, design, and application of complex high‐rise structures added with VE dampers.     

Model‐Reference Health Monitoring of Hysteretic Building Structure Using Acceleration Measurement with Test Validation

A model‐reference health monitoring algorithm with two damage sensitive features is presented in this study, utilizing structural acceleration measurements from earthquake‐damaged building structure. A virtual linear healthy model, representing linear behavior of the instrumented structure, is used to generate real‐time reference response signals for health monitoring during a disastrous earthquake. The tracking error of acceleration and a relevant statistical factor are first proposed for identifying damage occurrence and location at story level. The severity of the hysteretic damage is estimated numerically using a model‐based prediction curve in an equivalent stiffness reduction manner with the implementation of robust Kalman filtering. The performance of damage detection and evaluation in the presented algorithm are illustrated by numerical simulation of structural models with different hysteretic characteristics, and further validated by experimental investigation employing a base‐isolated three‐story structure and real‐world case study of a seven‐story frame structure. The influence of measurement noise and uncertain stiffness in linear healthy model is also discussed through a parametric study.     

A Unified Analysis Model for Energy Dissipation Devices Used in Seismic Structures

Abstract:   To date, various types of energy dissipation devices (EDDs) have been invented and applied to structural systems for mitigating their seismic responses. An elastic structure with EDDs can be treated as a nonlinear dynamic system with hysteretic property. Due to the diversity of the hysteretic properties of various EDDs, it is difficult to obtain a generic analysis method that can be applied to structures with different EDDs. In this study, a unified analysis model containing an internal variable is proposed for simulating the hysteretic behavior of various types of EDDs. By assigning different physical meanings to the internal variable, the model is able to simulate three types of widely used EDDs, namely, yielding, viscoelastic, and friction dampers. The unified model is also able to simulate nonlinear viscous dampers whose velocity terms have an exponential coefficient not equal to 1.0. Furthermore, based on this model, this article also developes a numerical analysis method derived from the discrete-time solution of a state-space equation. Without requiring iteration at each computational time step, the numerical method is able to accurately simulate the hysteretic properties of the three kinds of EDDs. The accuracy and efficiency of the proposed analysis method is investigated by using the analytical solution of a nonlinear system governed by Duffing's equation, and also by using a seismic structure equipped with multiple EDDs.     

Parametric study of the use and optimization of tuned mass dampers to control the wind‐ and seismic‐induced responses of a slender monument

Passive energy dissipation devices have been used around the world to mitigate the response of structures under dynamic excitations, such as wind or seismic loading. The use of tuned mass dampers (TMD) in tall and slender buildings to reduce unwanted responses has proved to be very effective. The main purpose of this work is to study the structural behavior of a 115‐m‐height slender monument fitted with TMDs subjected to simulated wind and seismic loading. Turbulent wind forces were calculated based on samples of turbulent wind speed simulated with an auto regressive and moving average (ARMA) model. Ground motions compatible with a seismic site spectrum were also simulated. An optimization approach is suggested to determine the parameters of the TMDs that reduce the structural response to the maximum. The effectiveness of the TMDs for reducing the structural response of the monument is discussed in detail, and the use of optimally tuned TMDs is emphasized.     

Dynamic experimental and numerical study of double beam–column joints in modern traditional‐style steel buildings with viscous damper

Modern traditional‐style steel (MTS) structure is an innovative architecture structure that is widely used in China. This paper explores the possibility of using viscous damper, which can be conveniently installed between beam and column, to replace “sparrow brace” at beam–column joints to improve its seismic capability. Three 1/2.6 scaled MTS double beam–column joints, one without viscous damper and two with viscous damper, were fabricated and tested under dynamic cyclic loading. The results indicated that the primary failure modes were cracking of base metal and local bucking at the beam ends. The hysteretic curve of specimens with viscous dampers was more plump than the common specimen without viscous dampers, indicating better energy dissipation capacity. The displacement ductility ratio was about 1.79–1.96, indicating the viscous damper has little effect on the ductility, whereas in plastic stage, the energy dissipation of specimens and viscous damper increased rapidly, indicating great energy dissipating function of viscous damper. Meanwhile, the results also proved that finite element analysis may stimulate and predict the mechanical behavior of MTS double beam joints with viscous dampers.     

Self‐centering viscoelastic diagonal brace for the outrigger of supertall buildings: Development and experiment investigation

This paper aims to improve the seismic performance of outriggers within supertall buildings and eliminate the defects of obvious degradation of stiffness, low energy dissipation capacity, and large residual deformation after the buckling of traditional diagonal members by presenting a new type of outrigger. The traditional profiled steel diagonal member is replaced with a self‐centering viscoelastic diagonal brace (SC‐VEDB) in the proposed outrigger, providing enhanced energy dissipation and self‐centering capacity. The new SC‐VEDB is composed of the inner and outer steel tubes, viscoelastic materials, and prestressed tendons. Energy dissipation capacity is produced by the shear deformation of viscoelastic materials, whereas prestressed tendons provide the self‐centering capacity. The working mechanism of SC‐VEDB is first theoretically analyzed. Following this, two specimens with a length of 2.2 m were designed, fabricated, and tested under low cyclic reversed loadings within different frequencies and pretension forces. The results confirm that the hysteretic curve of SC‐VEDB has a typical flag shape, which imparts the stable stiffness, good energy dissipation, and self‐centering capacities. The activation force of SC‐VEDB is mainly determined by the initial pretension force, and the post‐activation stiffness predominantly depends on the stiffness of the prestressed tendons. Moreover, SC‐VEDB has better repairability, and the initial hysteretic behavior of the component can be quickly recovered by replacing the damaged prestressed tendons. A refined finite element model for SC‐VEDB is established to predict its hysteretic behavior, and the numerical simulation corresponds well with the experimental results. The maximum relative error of the initial elastic stiffness and ultimate strength is approximately 4.6% and 1.3%, respectively, which verifies the accuracy of the SC‐VEDB numerical simulation method.     

Serviceability‐based damping optimization of randomly wind‐excited high‐rise buildings

Fluid viscous dampers are proved to be effective for reducing the response of high‐rise buildings subjected to wind excitations so as to enhance structural habitability, which serves as a critical performance in serviceability design. High‐rise buildings attached with fluid viscous dampers, however, exhibit nonlinearity and even act as stiff systems in most cases of wind‐induced vibration mitigation. The traditional equivalent linearization methods employed in practices often fail to obtain an accurate solution. Equivalent linearization methods, including the energy‐dissipation equivalent linearization method and the statistical linearization technique, are first studied and validated in this paper by the backward difference formula, which was verified to be of high accuracy through the nonlinear dynamic analysis. The damping optimization for habitability control is then proceeded. Two families of serviceability criteria, the minimization of standard deviation of roof acceleration employed in traditional habitability analysis and the minimization of failure probability of roof acceleration proposed in the present study, are addressed. For the logical treatment of randomness inherent in wind excitations and its influence upon structural reliability, the probability density evolution method is employed. Numerical results reveal that the criterion of minimizing failure probability of roof acceleration has better performance in habitability enhancement.     

大尺寸超弹性镍钛形状记忆合金螺旋弹簧滞回性能

利用2种镍钛形状记忆合金(SMA)研制了大尺寸超弹性螺旋弹簧,对其进行了单轴反复荷载作用下的滞回性能试验,研究了超弹性SMA螺旋弹簧的恢复力特性与耗能能力,分析了加载频率、位移幅值对2种SMA螺旋弹簧滞回曲线以及等效刚度、单位循环耗能、等效阻尼比和残余位移等力学性能参数的影响;采用刚弹性模型和Bouc-Wen模型,建立了适用于整体结构分析的SMA螺旋弹簧简化恢复力模型,并利用该模型进行了数值模拟。结果表明:超弹性SMA螺旋弹簧具有稳定的滞回曲线,且具有良好的复位性能和大变形能力,可用于结构自复位控制装置的研发;数值模拟结果与试验结果吻合较好,验证了简化恢复力模型的正确性。     

Experimental and analytical investigation on seismic behavior of Q690 circular high‐strength concrete‐filled thin‐walled steel tubular columns

This paper proposed a new Q690 circular high‐strength concrete‐filled thin‐walled steel tubular (HCFTST) column comprising an ultrahigh‐strength steel tube (yield strength f_y ≥ 690 MPa). A quasi‐static cyclic loading test was conducted to examine the seismic behavior, and the obtained lateral load‐displacement hysteresis curves, skeleton curves, and ductility were analyzed in detail. Then, a numerical model based on a nonlinear fiber beam‐column element incorporating the modified uniaxial cyclic constitutive laws for concrete and steel was developed mainly to predict the seismic behavior of the tested Q690 circular HCFTST columns. The effects of the concrete cylinder compressive strength (f_c), steel yield strength (f_y), axial compression ratio (n), and diameter‐to‐thickness (D/t) ratio on the seismic behavior were investigated through a parametric study. Finally, a simplified hysteretic model incorporating the moment‐resisting capacity and deterioration of the unloading stiffness in addition to a normalized skeleton curve and hysteretic criterion was established. The results indicate the following: the proposed Q690 circular HCFTST columns can display reasonable hysteretic behaviors to some extent; the use of high‐strength steel can lead to a significantly larger elasto‐plastic deformation capacity and delay the appearance of post‐peak behavior, even if a lower ductility capacity is provided; moderately loosening the limitations on the D/t ratio can also result in ideal hysteretic behaviors; and the established numerical model and simplified hysteretic model can satisfactorily predict the experimentally observed load‐displacement hysteretic curves, including the deterioration of the strength and stiffness and can, thus, offer design references for the elasto‐plastic analysis of circular HCFTST columns.     

Comprehensive nonlinear seismic performance assessment of MR damper controlled systems using virtual real‐time hybrid simulation

Magnetorheological (MR) dampers have gained significant attention in seismic mitigation of structural systems due to their distinguished characteristics such as inherent stability and minimum power requirements. Their performance in control of nonlinear structural response, however, has not been widely investigated. This paper provides comprehensive nonlinear seismic performance assessment of a three‐story benchmark structure equipped with a large‐scale MR damper using virtual real‐time hybrid simulation to efficiently capture the nonlinear behavior of the damper. The framework is first verified by means of available experimental results of an actual RTHS on the same structural system. A set of 12 earthquake ground motions, each one scaled to have 12 different intensities are then utilized to perform nonlinear dynamic analyses. An energy‐based adaptive passive‐on control strategy is proposed, and its performance is compared with passive‐on, passive‐off, and uncontrolled response of the structure in terms of interstory drifts shown by fragility curves, residual drifts, MR damper control force, and the ability to maintain a uniform interstory drift along the height of the structure.     

Experimental study and numerical analysis on seismic performance of steel beam‐column damping joint in Chinese traditional style buildings

This paper aims to research the seismic performance of steel beam‐column damping joint of Chinese traditional style building. Three specimens of steel beam‐column damping joints with the1:2.6 scale were designed and researched, which included two specimens with viscous damper and one contrast specimen without viscous damper. The experimental study was carried out by cyclic dynamic loading test. The effects of viscous dampers for the steel structure beam‐column joint in Chinese traditional style buildings are analyzed by investigating the hysteretic curves, skeleton curves, strength and stiffness degradation, ductility, overstrength factor, and energy dissipation capacity. The results show that the steel beam‐column joints of Chinese tradition style buildings with viscous damper have better energy dissipation capacity and higher bearing capacity. Based on the experiment, the nonlinear finite element analysis was conducted using the ABAQUS software. The influence of damping coefficient on the behavior of the new damping joint of Chinese tradition style buildings was obtained, and the design suggestions were presented.     

Seismic response of semi‐active friction‐damped reinforced concrete structures with self‐variable stiffness

The influence of structural self‐variable stiffness and semi‐active friction dampers on the behavior of reinforced concrete (RC) buildings during strong earthquakes is discussed. A fully braced six‐story beamless RC frame is analyzed. The effect of concrete braces (with only constructive reinforcement) as a self‐variable mechanism is studied. It is shown that up to a certain limit the frame itself controls its behavior by adapting its dynamic characteristics in the real time of the earthquake. This self‐adaptation is achieved by autonomous disengagement of the braces under tension and their further nonlinear action under compression. The system has several levels of seismic adaptation, and it selects one of them for enhanced response to the given earthquake. However, when the limit is reached, further self‐adaptation of the frame becomes impossible. The occurrence of an earthquake of higher magnitude can then lead to disengagement of the concrete braces under compression, intensifying structural damage and even causing collapse. The use of semi‐active controlled friction dampers is proposed as a means of preventing the collapse of braces under compression, thereby enabling structures to withstand earthquakes. The forces in the friction dampers are regulated according to an optimal control algorithm. Modulation of the friction level in real time during the earthquake yields additional improvement of structural seismic behavior and obviates the need for retrofitting. Copyright © 2007 John Wiley & Sons, Ltd.     

部分输入未知条件下结构参数及激励识别

针对部分输入未知条件下的结构参数和荷载识别问题,提出一种改进的基于最小二乘准则的自适应加权迭代算法。该方法通过引入自适应学习因子和加权正定矩阵,以任意假定的未知外激励作为初始迭代条件,以相邻两次迭代后荷载的识别值的误差作为收敛判断准则,有效地改进了迭代收敛速率、稳定性和识别精度。同时,针对比例阻尼,对现有非线性参数识别的松弛法进行改进,提出一种转换算法。通过一个具有15个自由度的高层数值模型的模拟数据和一个4层结构模型的动力试验实测数据分别验证了该方法有效性,同时,分别探讨了噪声水平、权重系数、学习因子等对算法收敛性的影响。数值算例和基于模型动力测试数据的识别结果表明,该算法具有稳定的收敛特性,参数和荷载识别精度高以及对测量噪声的鲁棒性强的特点。     

Strength and post‐yield behavior of T‐section steel encased by structural concrete

In this study, the seismic performance of unsymmetrical steel–concrete composite precast beams with T‐shaped steel section were numerically explored and validated by their earlier experimental investigation. This design is based on the proposed calibrated finite element model in which key damage parameters for the evaluation of the nonlinear, post‐yield behavior of the precast composite steel beams were identified. The proposed nonlinear finite‐element‐based numerical model uses various parameters, including the dilatation angle and concrete‐damaged plasticity, to simulate the nonlinear behavior of unsymmetrical composite precast beams with T‐section steel. Greater seismic capacity with greater ductility, contributing to a maximized structural capacity within the composite precast beams was introduced by the effective use of the 2 materials, steel and concrete, and shown by the nonlinear hysteretic investigation of unsymmetrical steel–concrete composite precast beams that was validated experimentally. The post‐yield structural capacity found via the numerical analysis agrees with experimental results when the concrete‐damaged plasticity of the plastic‐damaged seismic model for concrete and the von Mises criteria of the steel section were introduced into the finite element model. Practical design parameters and recommendations were eventually suggested by examining the influence of precast composite beams with unsymmetrical steel sections on the concrete degradations and damage evolution.     

Shaking table model test and FE analysis of a reinforced concrete mega‐frame structure with tuned mass dampers

To study the damage characteristics and to evaluate the overall seismic performance of reinforced concrete mega‐frame structures, a shaking table test of a 1/25 scaled model with a rooftop tuned mass damper (TMD) is performed. The maximum deformation and acceleration responses are measured. The dynamic behavior and the damping effect with and without TMD are compared. The results indicate that the mega‐frame structure has excellent seismic performance and the TMD device has a significant vibration reduction effect. A finite element (FE) model simulating the scaled model is also developed, and the numerical and experimental results are compared to provide a better understanding of the overall structural behavior in particular those related to the dynamic characteristics and damping effect. Upon verification of the FE model, other important structural behavior can also be predicted by the FE analysis. Copyright © 2014 John Wiley & Sons, Ltd.