Experimental and analytical study on design performance of full-scale viscoelastic dampers

Viscoelastic (VE) dampers, with their stiffness and energy dissipation capabilities, have been widely used in civil engineering for mitigating wind-induced vibration and seismic responses of structures, thus enhancing the comfort of residents and serviceability of equipment inside. In past relevant research, most analytical models for characterizing the mechanical behavior of VE dampers were verified by comparing their predictions with performance test results from small-scale specimens, which might not adequately or conservatively represent the actual behavior of full-scale dampers, especially with regard to the ambient temperature, temperature rise, and heat convection effects. Thus, in this study, by using a high-performance testing facility with a temperature control system, full-scale VE dampers were dynamically tested with different displacement amplitudes, excitation frequencies, and ambient temperatures. By comparing the analytical predictions with the experimental results, it is demonstrated that adopting the fractional derivative method together with considering the effects of excitation frequencies, ambient temperatures, temperature rises, softening, and hardening, can reproduce the design performance of full-scale VE dampers very well.     

Experimental and analytical studies on the vibration serviceability of long-span prestressed concrete floor

An extensive experimental and theoretical research study was undertaken to study the vibration serviceability of a long-span prestressed concrete floor system to be used in the lounge of a major airport.Specifically,jumping impact tests were carried out to obtain the floor’s modal parameters,followed by an analysis of the distribution of peak accelerations.Running tests were also performed to capture the acceleration responses.The prestressed concrete floor was found to have a low fundamental natural frequency(≈8.86 Hz)corresponding to the average modal damping ratio of≈2.17%.A coefficients plate with simply-supported edges.The calculated analytical results(natural frequencies and root-mean-square acceleration)agree well with the experimental ones.The analytical approach is thus validated.     

Experimental and analytical studies on the response of freestanding laboratory equipment to earthquake shaking

This paper presents results of a comprehensive experimental program on the seismic response of full‐scale freestanding laboratory equipment. First, quasi‐static experiments are conducted to examine the mechanical behavior of the contact interface between the laboratory equipment and floors. Based on the experimental results, the response analysis that follows adopts two idealized contact friction models: the elastoplastic model and the classical Coulomb friction model. Subsequently, the paper presents shake table test results of full‐scale freestanding equipment subjected to ground and floor motions of hazard levels with corresponding displacements that can be accommodated by the shake table at the UC Berkeley Earthquake Engineering Research Center. For the equipment tested, although some rocking is observed, sliding is the predominant mode of response, with sliding displacements reaching up to 60 cm. Numerical simulations with the proposed models are performed. Finally, the paper identifies a physically motivated intensity measure and the associated engineering demand parameter with the help of dimensional analysis and presents ready‐to‐use fragility curves. Copyright © 2008 John Wiley & Sons, Ltd.     

Analytical earthquake response of 1D hybrid base isolation systems

The work presents several dynamic analyses of an actual base isolation system previously identified by using a non-linear 1D model and full scale free vibration tests. After a short introduction to the building and the base isolation system considered, reference is made to previous studies where the model used was developed. The analytical model, originally derived for free vibration analyses and system identification applications, is extended in the present paper to earthquake response simulations. First a theoretical harmonic ground motion is considered, in order to identify resonance conditions for the system and stress how these should be avoided in actual design, by carefully studying the seismological and site conditions. The response of the system to a nearly harmonic natural ground motion is then predicted. Next the performance of the system under several significant ground motions from the Friuli 1976, Irpinia 1980 and L'Aquila 2009 earthquakes is considered, and the reasons for its satisfactory or unsatisfactory behaviour are pointed out and explained. Means for correcting unsatisfactory performances are also suggested and discussed. The behaviour of the system under near fault records from the L'Aquila 2009 earthquake is then considered, the conditions leading to the maximum demands are highlighted and the reasons behind them are clearly explained. Finally the 1D model presented is used to predict the 2D response to 2D ground motions.     

Experimental and analytical study on the performance of particle tuned mass dampers under seismic excitation

A particle tuned mass damper (PTMD), which is a creative integration of a traditional tuned mass damper and an efficient particle damper in the vibration control area, is proposed. This paper presents a comprehensive study that involves experimental, analytical, and computational approaches. The vibration control effects of a PTMD that is attached to a five‐story steel frame under seismic input are investigated by a series of shaking table tests. The influence of some parameters (auxiliary mass ratio, gap clearance, mass ratio of particles to the total auxiliary mass, frequency characteristics, and amplitude level of the input) is explored, and the performance of the PTMD with/without buffered material is compared. The experimental results show that the PTMD can achieve significant damping effects under seismic excitations, and the bandwidth of the suppression frequency is expanded, showing the device's robustness and control efficiency. In addition, an approximately analytical solution that is based on the concept of an equivalent single‐particle damper is presented, and the method to determine the corresponding system parameters is introduced. A comparative study between experimental and numerical results is conducted to verify the feasibility and accuracy of this analytical model. Copyright © 2016 John Wiley & Sons, Ltd.     

Experimental studies on solar stills and their performance characteristics

Summary Demineralization of saline water, using different designs of solar stills, has been considered. The productivity and efficiency of these stills, were determined daily and for a whole year.To investigate the basic principles of the solar distillation process, meteorological measurements concerning the solar intensity the wind speed and the ambient air temperature were undertaken simultaneously together with the temperature measurements of the brine and the glass cover of one of the stills during its operation. The results obtained gave valuable information concerning the construction and design of solar stills.     

Experimental assessment of sliding materials for seismic isolation systems

Novel self-lubricating materials are currently being proposed to be used in sliding isolation systems such as the curved surface sliding isolator system, or pendulum bearing system, for the protection of buildings and structures. The current codes for anti-seismic devices are focused on the evaluation of the performance of the whole isolation system; as a consequence, a reliable procedure for the pre-assessment of the material combinations of sliding interfaces is currently missing. Therefore in this paper, an experimental methodology is proposed for the characterization of self-lubricating materials through tests on small-scale specimens performed using customized equipment able to reproduce the operational conditions of real isolation systems as per contact pressure, sliding velocity, temperature and slide path. The testing sequence has been designed in order to evaluate the sliding properties of the material in terms of static and dynamic coefficient of friction and wear resistance. Examples are reported for the assessment of two self-lubricating materials with different sliding characteristics. In order to validate the method and to confirm the reliability of extrapolating the results to real working conditions, prototypes of pendulum isolation systems incorporating the assessed materials have been tested according to the AASHTO (Guide specifications for seismic isolation design, 2nd edn. American Association of State Highway and Transportation Officials, Washington, DC, 1999) specifications and the relevant dynamic properties assessed from the Horizontal Load—Displacement loops. The experimental outcomes confirmed that the frictional characteristics provided by the proposed procedure can be reliably used in the design of seismically isolated structures.     

Experimental and analytical studies on earthquake resisting behaviour of confined concrete block masonry structures

To improve the seismic performance of masonry structures, confined masonry that improves the seismic resistance of masonry structures by the confining effect of surrounding bond beams and tie columns is constructed. This study investigated the earthquake resisting behaviour of confined masonry structures that are being studied and constructed in China. The structural system consists of unreinforced block masonry walls with surrounding reinforced concrete bond beams and tie columns. The characteristics of the structure include: (1) damage to blocks is reduced and brittle failure is avoided by the comparatively lower strength of the joint mortar than that of the blocks, (2) the masonry walls and surrounding reinforced concrete bond beams and tie columns are securely jointed by the shear keys of the tie columns. In this study, wall specimens made of concrete blocks were tested under a cyclic lateral load and simulated by a rigid body spring model that models non‐linear behaviour by rigid bodies and boundary springs. The results of studies outline the resisting mechanism, indicating that a rigid body spring model is considered appropriate for analysing this type of structure. Copyright © 2006 John Wiley & Sons, Ltd.     

Limiting performance of shock isolation systems by a modal approach

The problem of determining the limiting performance of vibrating systems under shock loading is solved by replacing portions of the system by control forces which can represent any design. For the class of problems treated here, the performance index and the constraints are linear combinations of system response variables such as displacements, velocities and accelerations. Furthermore, the equations of motion are linear, so that it is possible to formulate the optimization procedure as a linear programming problem. In expressing the performance index and the constraints as linear functions of the unknown control forces, a modal approach is used to simplify and improve previous treatments of this problem. In spite of these linearity requirements, the control forces are not required to be linear functions of the response variables.     

Time domain identification of hybrid base isolation systems using free vibration tests

A procedure for the dynamic identification of the physical parameters of coupled base isolation systems is developed in the time domain. The isolation systems considered include high damping rubber bearings (HDRB) and low friction sliding bearings (LFSB). A bi‐linear hysteretic model is used alone or in parallel with a viscous damper to describe the behavior of the HDRB system, while a constant Coulomb friction device is used to model the LFSB system. After deriving the analytical dynamical solution for the coupled system under an imposed initial displacement, this is used in combination with the least‐squares method and an iterative procedure to identify the physical parameters of a given base isolation system belonging to the class described by the models considered. Performance and limitations of the proposed procedure are highlighted by numerical applications. The procedure is then applied to a real base isolation system using data from static and dynamic tests performed on a building at Solarino. The results of the proposed identification procedure have been compared to available laboratory data and the agreement is within ±10%. However, the need for improvement both in models and testing procedures also emerges from the numerical applications and results obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

调谐惯容系统的混合隔震体系一致性优化设计

基础隔震技术广泛应用于建筑结构以减轻结构的地震响应.值得注意的是,在隔震体系中减小主结构的加速度响应是以牺牲隔震器变形为代价的.调谐惯容系统(TID)和隔震器组成的混合隔震体系可减小隔震层的位移响应.与传统调谐质量阻尼器(TMD)结构类似,TID 由惯容、调谐弹簧和阻尼元件组成.因此,可直接利用 TMD减震系统的设计公式来确定 TID 的最优参数.首先基于单自由度体系(SDOF)附加 TID的运动方程,推导分析两种 TID和 TMD设计公式,对两者设计公式的前提条件和适用性进行深入的探讨.其后,借助基础隔震体系的benchmark模型来检验设计 TID的可行性和有效性.数值模拟结果表明,在不增加主结构绝对加速度响应的情况下, TID能够显著减小基础隔震结构的位移响应和基底剪力.     

Experimental performance evaluation of an equipment isolation using MR dampers

Critical non‐structural equipments, including life‐saving equipment in hospitals, circuit breakers, computers, high technology instrumentations, etc., are vulnerable to strong earthquakes, and the failure of these equipments may result in a heavy economic loss. In this connection, innovative control systems and strategies are needed for their seismic protections. This paper presents the performance evaluation of passive and semi‐active control in the equipment isolation system for earthquake protection. Through shaking table tests of a 3‐story steel frame with equipment on the first floor, a magnetorheological (MR)‐damper together with a sliding friction pendulum isolation system is placed between the equipment and floor to reduce the vibration of the equipment. Various control algorithms are used for this semi‐active control studies, including the decentralized sliding mode control (DSMC) and LQR control. The passive‐on and passive‐off control of MR damper is used as a reference for the discussion on the control effectiveness. Copyright © 2008 John Wiley & Sons, Ltd.     

Experimental validation of a simplified model for rolling isolation systems

Rolling isolation systems (RISs) protect mission‐critical equipment and valuable property from earthquake hazards by decoupling the dynamic responses of vibration‐sensitive objects from horizontal floor motions. These responses involve the constrained rolling of steel balls between bowl‐shaped surfaces. The light damping of steel balls rolling between steel plates can be augmented by adhering thin rubber sheets to the plates, thereby increasing the rolling resistance and decreasing the displacement demand on the RIS. An assessment of the ability of lightly‐ and heavily‐damped RISs to mitigate the hazard of seismically induced failures requires high‐fidelity models that can adequately capture the systems' intrinsic nonlinear behavior. The simplified model presented in this paper is applicable to RISs with any potential energy function, is amenable to both lightly‐ and heavily‐damped RISs, and is validated through the successful prediction of peak responses for a wide range of disturbance frequencies and intensities. The validated model can therefore be used to compute the spectra of peak floor motions for which displacement demands equal capacity. These spectra are compared with representative floor motion spectra provided by the American Society of Civil Engineers 7–10. The damping provided by rolling between thin viscoelastic sheets increases the allowable floor motion intensity by a factor of 2–3, depending on the period of motion. Acceleration responses of isolation systems with damping supplied in this fashion do not grow with increased damping, even for short‐period excitations. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparative performance of friction damped systems and base isolation systems for earthquake retrofit and aseismic design

The seismic performance of a steel framed structure equipped with (i) friction damping devices and (ii) base isolators is compared. A parametric study based on energy concepts is performed first using time-history dynamic analysis to determine the optimum properties of the two systems when excited by an earthquake whose energy is distributed over a relatively broad frequency band (1940 El Centro, N-S). Using these same properties, the responses of the two structural systems are then examined when excited by earthquakes whose power content essentially is concentrated at the low frequency end of the energy spectrum (1977 Romania, Bucharest, N-S and 1985 Mexico, SCT E-W). The results of the study show that, while both systems similarly reduce the response of conventional structures to the California earthquake, the friction damped structure exhibits a superior performance under the low frequency earthquakes. Very large shear forces and displacements are observed when the Romania and Mexico earthquakes are applied to the base isolated structure, indicating that the performance of a base isolated structure depends on the characteristics of the site earthquake. By comparison, friction damped structures are shown to behave favourably under the three earthquakes studied; this suggests that friction damping devices offer a more consistent way of protecting structures during earthquakes.     

基础和屋顶隔震混凝土结构的地震振动台实验研究

通过使用平面尺寸为4.0m×4.0m的地震模拟器即振动台,对基础和屋顶隔震体系的控制性能进行了比较研究。试验包括三个三层无隔震、基础隔震和屋顶隔震混凝土框架结构模型。屋顶隔震包括板和叠层橡胶支座(LRB)。输入振动台的模拟地震动分别是1940N-S地震动、人工模拟山东地震动和人工模拟上海地震动。通过分析三个三层模型在白噪音扫描下的动力特性,首先评价了基础隔震与屋顶隔震体系的控制性能。实验结果显示,尽管基础隔震与屋顶隔震有着不同的工作原理,但基础隔震和屋顶隔震体系都能够明显地减小结构的位移和加速度响应(包括层间位移)。而且前者有更好的有效性。值得注意的是,屋顶隔震体系由于实施相对方便,因而可能成为减小中低层建筑结构地震损伤的优先选择。     

Experimental and analytical studies on multiple tuned mass dampers for seismic protection of porcelain electrical equipment

Porcelain electrical equipment (PEE), such as current transformers, is critical to power supply systems, but its seismic performance during past earthquakes has not been satisfactory. This paper studies the seismic performance of two typical types of PEE and proposes a damping method for PEE based on multiple tuned mass dampers (MTMD). An MTMD damping device involving three mass units, named a triple tuned mass damper (TTMD), is designed and manufactured. Through shake table tests and finite element analysis, the dynamic characteristics of the PEE are studied and the effectiveness of the MTMD damping method is verified. The adverse influence of MTMD redundant mass to damping efficiency is studied and relevant equations are derived. MTMD robustness is verified through adjusting TTMD control frequencies. The damping effectiveness of TTMD, when the peak ground acceleration far exceeds the design value, is studied. Both shake table tests and finite element analysis indicate that MTMD is effective and robust in attenuating PEE seismic responses. TTMD remains effective when the PGA far exceeds the design value and when control deviations are considered.     

适用于村镇房屋的新型摩擦摆隔震性能试验研究

针对村镇房屋隔震设施薄弱的问题,本着低成本、易施工的原则,设计了一种玄武岩纤维混凝土材料的摩擦摆隔震支座。将该新型支座与传统钢制摩擦摆支座进行拟静力试验,研究了该新型支座在相同的竖向荷载作用,不同频率下的干摩擦和润滑摩擦两种工况的支座的滞回性能,得出了该新型支座的基本力学性能,通过利用SAP2000有限元模型对采用该新型支座的隔震结构进行了动力时程分析,并且将该新型支座与传统钢制摩擦摆支座在滞回性能、构造方式和经济性三方面进行对比分析。结果表明:玄武岩纤维混凝土摩擦摆支座的滞回性能略低于钢制摩擦摆支座滞回性能,该支座隔震效果显著且易模性好,便于施工,造价低廉,适用于低层村镇房屋隔震设计与施工。     

Experimental and analytical studies of solute transport during run‐off over vegetated surfaces

Solute transport in overland flow is considered as one of the main contributors to water pollution. Although many models of pollutant transport mechanism from soil to run‐off water have been proposed, the characteristics of solute transport accompanying the water run‐off over vegetated surface have not been well studied. In this study, a series of laboratory experiments were conducted to study the solute transport over vegetated surfaces. Based on the experimental results, an idea of the “stationary water layer” in run‐off was proposed. Applying the complete mixing theory in the stationary water layer, an analytical solute transport model was developed with the assumption that the upper run‐off completely mixes with the underlying water in the stationary water layer for each site. The results show that the predictions made by the present model are in good agreement with the measured experimental data. For the vegetated surfaces, the depth of stationary water layer is related to the rainfall intensity, bed slope, and vegetation density. The analytical solution shows that the maximum solute transport occurs at the time of concentration. This study advances our understanding of the mechanisms of solute transport over vegetated areas.     

Experimental studies on the P-T stability conditions and influencing factors of gas hydrate in different systems

The P-T stability conditions of gas hydrate in different systems (i.e., solution, silica sand, and marine sediment) were studied using multi-step decomposition method with our experimental equipment. The effects of different ions with various concentrations and sediment grains on the P-T stability conditions of gas hydrate were investigated. The results show that different ions have different influences on the phase equilibrium of gas hydrate. However, the influence of ions is in a similar trend: the larger the concentration, the bigger the P-T curve shifts to the left. For the silica sand, the influence of pore capillarity of coarse particles (> 460 μm) can be negligible. The P-T curve measured in coarse silica is in agreement with that in pure water. However, the influence of pore capillarity of fine particles (< 35 μm) is significant. The maximum reduction value of temperature is 1.5 K for methane hydrate under stable state. The sediment from the South China Sea significantly affects the P-T stability conditions of methane hydrate, with an average reduction value of 1.9 K within the experimental conditions. This is mainly the result of both the pore water salinity and the pore capillarity of sediment. Because the pore water salinity is keeping diluted by the fresh water released from hydrate dissociation, the measured P-T stability points fall on different P-T curves with the decreasing salinity.     

Effect of variation of normal force on seismic performance of resilient sliding isolation systems in highway bridges

In this study, a series of shaking table tests are carried out on scaled models of two seismically isolated highway bridges to investigate the effect of rocking motion and vertical acceleration on seismic performance of resilient sliding isolators. In addition, performance of RSI is compared with system having solely natural rubber bearings. Test results show that variation of normal force on sliders due to rocking effect and vertical acceleration makes no significant difference in response of RSI systems. In addition, analytical response of prototype isolated bridge and the model used in experiments is obtained analytically by using non‐linear model for isolation systems. It is observed that for seismically isolated bridges, dynamic response of full‐scale complex structures can be predicted with acceptable accuracy by experiments using a simple model of the structure. Copyright © 2005 John Wiley & Sons, Ltd.