Seismic isolation for low‐to‐medium‐rise buildings using granulated rubber–soil mixtures: numerical study

This paper presents the preliminary research works on a potential seismic isolation method that makes use of scrap rubber tires for the protection of low‐to‐medium‐rise buildings. The method involves mixing shredded rubber tire particles with soil materials and placing the mixtures around building foundations, which provides a function similar to that of a cushion. Meanwhile, the stockpiling of scrap tires is a significant threat to our environment, and the engineering community has been looking for long‐term viable solutions to the recycling and reuse of rubber. A finite element program has been developed for modeling the time‐domain dynamic responses of soil–foundation–structure system, by which the effectiveness and robustness of the proposed method have been evaluated. In general, the structural responses, in terms of acceleration and inter‐story drift, can be reduced by 40–60%. Copyright © 2012 John Wiley & Sons, Ltd.     

Lateral load performance and seismic demand of unbonded scrap tire rubber pad base isolators

The scrap tire rubber pad(STRP) made by natural or synthetic rubber and high strength reinforcing cords exhibits substantial vertical stiffness and horizontal flexibility, and these properties can be regarded as suitable for seismic isolators for structures. The use of environmentally burdensome scrap tires as STRP isolators might be convenient as an efficient and low-cost solution for the implementation of aseismic design philosophy for low-to-medium rise buildings, especially in developing countries. Finite element analyses of unbonded square and strip-shaped STRP isolators subjected to a combination of axial and lateral loads are conducted to investigate its lateral deformation performance under seismic loading. The rubber of the isolator is modelled with Mooney-Rivlin hyperelastic and Prony viscoelastic materials, including the Mullins material damage effect. The influence of the length-to-width ratio and bearing height on the isolator performance is assessed in terms of the force-displacement relationship, horizontal stiffness, damping, and isolation periods. It is shown that the dependence of stiffness on the length-to-width ratio is significant in the longitudinal direction and minor in the transverse direction. The STRP isolators following the proposed design criteria are shown to satisfy the performance requirement at different levels of seismic demand specified by the ASCE/SEI 7-2010 seismic provisions.     

Performance improvement studies of masonry houses using elastic post‐tensioning straps

Unreinforced masonry houses are composed of building blocks with weak inter‐binding action between them which commonly possess low tensile strength. The principal tensile stresses generated by out‐of‐plane bending and in‐plane shear forces cannot be tolerated well and leads to heavy structural damage and brittle collapse beyond linear capacity of the material. Remedies such as externally applied mesh reinforcement and post‐tensioning improves post and pre‐cracking performances; however, yielding of reinforcement material or shortening of walls due to cracking causes loss of integrity and post‐tensioning force. This paper discusses a research programme on earthquake strengthening of masonry houses using post‐tensioning by elastomeric straps and related shaking table tests on 1/10 scale single storey rural dwelling models. The aim of the study is to assess the use and effectiveness of post‐tensioning rubber straps at several different configurations especially for houses with heavy earth roofs supported on wooden logs. Full‐scale application can be conducted using scrap automobile tyres, which might be implemented as an economic and environment friendly alternative strengthening technique for poor residents of low‐cost dwellings. The performance and validity of the proposed strengthening techniques were tested on 1/10 scale models using a simplistic shaking table. The structural performance of the reinforced models with vertical post‐tensioning rubber straps was significantly improved as compared to the original specimen; the results were even better when vertical and horizontal straps were used. Obtained results show promise for seismic strengthening using rubber straps for post‐tensioning. Copyright © 2006 John Wiley & Sons, Ltd.     

Seismic isolation using granulated tire–soil mixtures for less‐developed regions: experimental validation

In this study, shaking‐table experiments were conducted with a novel seismic isolation system (Geotechnical Seismic Isolation, GSI) to validate its dynamic performance during earthquakes. This isolation technique uses shredded rubber–soil mixtures to reduce the structural response to earthquakes, and thus may not only provide economical structural safety for buildings in less‐developed regions, but could also consume a large amount of waste tires worldwide. The present experimental results show that the GSI system has potential to significantly mitigate seismic hazards. Copyright © 2013 John Wiley & Sons, Ltd.     

Component and shaking table tests for full‐scale multiple friction pendulum system

The use of base isolation in developed countries including the U.S. and Japan has already been recognized as a very effective method for upgrading the seismic resistance of structures. In this study, an advanced base‐isolation system called the multiple friction pendulum system (MFPS) is investigated to understand its performance on seismic mitigation through full‐scale component and shaking table tests. The component tests of the advanced Teflon composite coated on the sliding surface show that the friction coefficient of the lubricant material is a function of the sliding velocity in the range of 0.03–0.12. The experimental results also indicate that there were no signs of degradation of the sliding interface observed after 2000 cycles of sliding displacements. A full‐scale MFPS isolator under a vertically compressive load of 8830 KN (900 tf) and horizontally cyclic displacements was tested in order to assess the feasibility of the MFPS isolator for its practical use. After 248 cycles of horizontal displacement reversals, the behaviour of the base isolator was almost identical to its behaviour during the first few cycles. The experimental results of the shaking table tests of a full‐scale steel structure isolated with MFPS isolators show that the MFPS device can isolate seismic transmitted energy effectively under soft‐soil‐deposit site earthquakes with long predominant periods as well as strong ground motions with short predominant periods. These test results demonstrate that the MFPS isolator possesses excellent durability and outstanding earthquake‐proof capability. Furthermore, the numerical results show that the mathematical model proposed in this study can well predict the seismic responses of a structure isolated with MFPS isolators. Copyright © 2006 John Wiley & Sons, Ltd.     

Dynamic parameter identification for non-linear isolation systems in response spectrum analysis

The response spectrum method has been widely used in earthquake engineering design, but cannot be directly applied to non-linear systems such as the lead-filled rubber bearing used in base isolation systems. An appraoch to determine the equivalent linearized stiffness and damping coefficient of the lead-filled rubber bearing by use of the results of shaking table tests is developed. Comparisons of time histories for the equivalent linear systems and the actual model show the method gives accurate maxima for displacement and acceleration and at the appropriate times. It is found that the identified parameters vary with the maximum deformation and the simplified formulae that can optimally describe the variations are derived. Using these formulae, an iterative algorithm using the response spectrum method to calculate the dynamic response of buildings isolated by lead-filled rubber bearings is also presented.     

Seismic response estimation method for earthquake‐damaged RC buildings

This study proposes a procedure for identifying spectral response curves for earthquake‐damaged areas in developing countries without seismic records. An earthquake‐damaged reinforced concrete building located in Padang, Indonesia was selected to illustrate the identification of the maximum seismic response during the 2009 West Sumatra earthquake. This paper summarizes the damage incurred by the building; the majority of the damage was observed in the third story in the span direction. The damage was quantitatively evaluated using the damage index R according to the Japanese guidelines for post‐earthquake damage evaluation. The damage index was also applied to the proposed spectral response identification method. The seismic performance of the building was evaluated by a nonlinear static analysis. The analytical results reproduced a drift concentration in the third story. The R‐index decreased with an increase in the story drift, which provided an estimation of the maximum response of the building during the earthquake. The estimation was verified via an earthquake response analysis of the building using ground acceleration data, which were simulated based on acceleration records of engineering bedrock that considered site amplification. The maximum response estimated by the R‐index was consistent with the maximum response obtained from the earthquake response analysis. Therefore, the proposed method enables the construction of spectral response curves by integrating the identification results for the maximum responses in a number of earthquake‐damaged buildings despite a lack of seismic records. Copyright © 2016 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd.     

Study on a new shear wall system with shaking table test and finite element analysis

A new seismic energy dissipation shear wall structure is proposed in this paper. The new shear wall is one with purposely built‐in vertical slits within the wall panel, and rubber belts as seismic energy dissipation devices are installed in the vertical slits. In order to verify this concept, shaking table tests of a 10‐storey shear wall model with rubber belts filled in the vertical slits were carried out, and comparison of seismic behaviour was made between the new shear wall system and a shear wall with reinforced concrete connecting beams as energy dissipation. Furthermore, the seismic behaviour of this new shear wall is analysed by a finite element time history analysis method. The test and analysis show that the new shear wall system has a very good ability to dissipate seismic energy and is easy to use in engineering practice. Copyright © 2000 John Wiley & Sons, Ltd.     

基于振动台试验的移动通信节点机房蓄电池组地震易损性分析

关键移动通信设备的地震易损性是城市移动通信系统地震灾害预测的基础。本文以移动通信系统节点机房中常用的蓄电池组作为研究对象,通过振动台试验来研究蓄电池组的抗震性能,并获得其地震易损性。试验过程中,首先采用FEMA P695建议的方法从美国PEER强震数据库中遴选出对蓄电池组较为危险的地震动记录作为试验激励,随后逐步增大各条地震动记录的幅值,基于振动台进行增量动力分析。试验后根据蓄电池组的地震损伤特征,定义了其损伤指标和损伤水平,并基于振动台试验数据分析获得了典型蓄电池组的地震易损性曲线。     

双场点地震危险性分析方法及其应用

提出了双场点地震危险性分析方法,用以计算在相同地震构造环境中,相同地震作用下的相邻两个工程场点同时超越其给定地震动参数的概率.该方法是确定系统的危险段落、场点遭受的附加地震危险的有效工具.基于汶川MS8.0地震后大渡河干流及邻近地区的地震环境,以大渡河干流梯级水电站系统为例,确定了大渡河干流梯级水电站各个河段的地震危险性.其中危险性最高的3个河段是:龚嘴—铜街子河段、沙坪—龚嘴河段和大岗山—龙头石河段.     

Simulation of the damage to a simple RC structure in the Bhuj,India, earthquake to estimate the level of input‐motion

Analysis of a simple reinforced concrete (RC) structure damaged by the Bhuj, India, earthquake was carried out to estimate the level of shaking in the epicentral region. For this, an attempt was made to estimate the level of input motion to cause inelastic behavior to the extent observed during the field visit. To consider the inelastic effects, both yielding of steel bars as well as crushing of the concrete cover has been investigated employing the hysteretic model known as the Fiber model. The only available record at Ahmedabad of the Bhuj earthquake and four additional earthquake records from Japan and California were used in the analysis. Considering simple scaling of input motion, the level of input motion to cause crushing and spall‐off of the concrete cover as observed in the field was estimated to be of the order of 6 times the original instrumental record obtained at 240 km away from the epicenter. The methodology proposed was promising in providing a useful quantitative indication of the level of shaking when instrumental records are not available. It was also noted that the design response spectrum specified in Indian seismic code IS1893: 1984 appears inadequate compared to the extent of shaking estimated. Copyright © 2005 John Wiley & Sons, Ltd.     

A rapid seismic safety assessment method for mid-rise reinforced concrete buildings

The majority of existing buildings are not safe against earthquakes in most of the developing countries. Existing building stocks should be assessed with a seismic safety assessment method before a devastating earthquake. Cheaper and quicker rapid seismic safety assessment methods can be used instead of code-based assessment methods to determine the seismic performance of existing buildings. In this study, an approach was introduced to determine the seismic performance of existing mid-rise reinforced concrete buildings with fewer parameters and process steps than code-based detailed assessment procedures. Calibration and regulation of the introduced method were conducted on the 39 collapsed buildings’ projects in 1999 Kocaeli, Turkey, earthquake. Finally, 55 existing buildings located in Eskisehir, Turkey, assessed with this calibrated method and the results were compared with the results of a code-based detailed assessment method; the results showed a very good agreement of about 83%. This study shows that the proposed method can be applied for the determination of the seismic performance of existing mid-rise reinforced concrete buildings quickly and without compromising reliability.     

Fundamental study on the response characteristics of drivers during an earthquake based on driving simulator experiments

After the 1995 Kobe earthquake, the expressway structures in Japan were retrofitted and they will not now be seriously damaged under a certain level of strong earthquake motion. However, the stability of a moving vehicle has not been investigated yet. It has been reported that drivers feel seismically induced vibrations, especially in the transverse direction of vehicles. Owing to this phenomenon, drivers have some difficulty in controlling the vehicles during strong shaking. For further safety promotion of the expressway networks, it is important to understand the drivers' reactions to seismic motion. The present authors have performed a series of seismic response analyses of a moving vehicle to investigate its response characteristics based on numerical simulation. However, the responses of the driver were not considered in the simulation process. In order to investigate the drivers' reactions during an earthquake, a series of virtual tests were conducted using a driving simulator. This driving simulator has six servomotor‐powered electric actuators that control its motions. Several types of tests were carried out for different examinees to investigate drivers' responses while controlling the simulator under seismic motion. The results of this study showed that a larger response time lag to strong shaking and over turning of the steering wheel may shift the vehicle into the next lane. According to this finding, trafficaccidents could possibly occur under strong ground shaking in the case of heavy traffic. Copyright © 2004 John Wiley & Sons, Ltd.     

STC加筋砂水平循环剪切与竖向激振特性试验研究

随着中国汽车工业的发展,大量废旧轮胎带来的"黑色污染"问题日益显著。提出一种采用废旧轮胎柱(Scrap tire columns,STC)的加筋土结构,并初步探究其作为基础减隔振材料的可行性。通过室内水平循环剪切试验和竖向激振试验研究STC加筋砂(STCRS)的水平循环剪切和竖向激振特性。结果表明,最大剪应变为1%时STCRS的等效阻尼比未加筋前增加约10%,等效动剪切模量减小20%~25%,水平向减振性能得以提高;STCRS的竖向加速度衰减呈现出速度快、幅值大的特点,竖向减振效果较未加筋砂显著提高。STC加筋砂作为基础减振材料是可行的,且为原形废旧轮胎的资源化利用提供新思路。     

Nonlinear seismic response analysis of arch dam-foundation systems- part II opening and closing contact joints

A time-domain method for the analysis of arch dam-foundation rock dynamic interaction during earthquake was proposed, and the dynamic relaxation technique was adopted to obtain the initial static response for dynamic analysis by [Du et al. (2005). The paper has been contributed to Bulletin of earthquake engineering]. In this paper, a nonlinear explicit method in time domain considering the opening and closing effect of contact joints on arch dam during earthquake is further proposed by introducing the dynamic contact force model into the method. The simulation accuracy of dynamic contact force model is verified by comparing its calculation result and test result of scale model on shaking table. Finally, the influence of joints on the seismic response of Xiaowan arch dam is studied by the proposed method and some conclusions are given.     

七层钢筋混凝土异型柱支撑框架结构模型振动台试验研究

七层钢筋混凝土异型柱支撑框架结构体系的模型，缩尺比为１：３，在振动台上进行了模拟地震动试验，结果表明：该体系的抗震性能较好，可使斜杆在预估地震强度的作用下先开裂并继续工作，从而减轻主体结构的地震破坏。并指出，该体系应进一步实现抗裂抗倒双重设防准则与其设计方法，研究发挥支撑的消能减震作用。这种抗震结构体系，已在天津市的轻质节能建筑中采用。     

基于幂指数法的地震模拟振动台频域前馈补偿方法

针对地震模拟振动台受到系统和试件非线性等因素影响,导致波形再现精度不高的问题,提出基于幂指数法的地震模拟振动台频域前馈补偿方法以提高振动台的控制效果,通过数值仿真和实际振动台试验对该方法的控制性能进行研究。研究结果表明：基于幂指数法的地震模拟振动台频域前馈补偿方法能够快速收敛,迭代次数较少,可以大幅提高振动台的波形复现精度,能够提高振动台的控制性能。     

基于衰减关系的城镇烈度发生概率快速估计

震后快速产出的震动烈度分布是地震应急救援非常有效的依据, 通常由烈度与地震动参数的经验关系给出. 有台站的场点, 地震动参数可以直接由台站数据给出确定性的结果; 而无台站的场点, 地震动参数只能由衰减关系给出估计值. 目前我国台站覆盖有限, 且难于实时获取, 快速生成的地震动参数主要依赖于地震动衰减关系, 再依据烈度与地震动参数的经验关系, 输出确定性的震动烈度分布. 由于衰减关系本身存在着不确定性, 将其估计值用于生成确定性的震动烈度分布是不准确的. 而且实践证明, 震动烈度与实际调查烈度存在差异. 鉴于此, 从衰减关系模型中的ε出发, 提出了场点(城镇)遭遇不同烈度的概率计算方法: 利用衰减关系的估计值与衰减关系的标准差, 构造峰值加速度(PGA)变化的对数正态分布, 然后以烈度分档对应的PGA范围, 计算震区各城镇遭遇不同烈度的概率及各城镇抗震设防烈度被超越的概率. 具体以1966年3月8日河北邢台M_S6.8地震为例, 说明了此方法的可行性, 认为以概率形式给出城镇可能遭遇的烈度在表述上更为合理, 并建议将场点(城镇)遭遇烈度的概率表达方法用于震害快速评估.      

基于位移设计的钢筋混凝土桥墩抗震性能试验研究(Ⅱ):振动台试验

通过模型振动台试验研究了基于位移设计的钢筋混凝土桥墩的抗震性能。以完成的拟静力试验中的桥墩试件为参考原型,利用基于位移抗震设计方法和现行桥梁抗震规范方法设计了4根1:2的钢筋混凝土桥墩试件并进行了模型振动台试验。对小震、中震和大震作用下桥墩试件的破坏形态、加速度和位移反应、位移延性系数和地震总输入能(耗能)等方面进行了比较分析。综合拟静力试验和振动台试验结果,可以认为基于位移设计的钢筋混凝土桥墩能够达到预期的延性抗震要求。