Seismic evaluation of frequency influence and resonant behavior for lead rubber bearing isolated rigid rectangular liquid tanks

The seismic behavior of a partially filled rigid rectangular liquid tank is investigated under short-and longduration ground motions.A finite element model is developed to analyze the liquid domain by using four-noded quadrilateral elements.The competency of the model is verified with the available results.Parametric studies are conducted for the dynamic parameters of the base-isolated tank,using a lead rubber bearing to evaluate the optimum damping and time period of the isolator.The application of base isolation has reduced the total and impulsive hydrodynamic components of pressure by 80 to 90 percent,and base shear by 15 to 95 percent,depending upon the frequency content and duration of the considered earthquakes.The sloshing amplitude of the base-isolated tank is reduced by 18 to 94 percent for most of the short-duration earthquakes,while it is increased by 17 to 60 percent for the majority of the long-duration earthquakes.Furthermore,resonance studies are carried out through a long-duration harmonic excitation to obtain the dynamic behavior of non-isolated and isolated tanks,using a nonlinear sloshing model.The seismic responses of the base-isolated tank are obtained as higher when the excitation frequency matches the fundamental sloshing frequency rather than the isolator frequency.

Influence of Vertical Irregularity on the Seismic Behavior of Base Isolated RC Structures with Lead Rubber Bearings under Pulse-Like Earthquakes

Nowadays,an extensive number of studies related to the performance of base isolation systems implemented in regular reinforced concrete structures subjected to various types of earthquakes can be found in the literature.On the other hand,investigations regarding the irregular base-isolated reinforced concrete structures’performance when subjected to pulse-like earthquakes are very scarce.The severity of pulse-like earthquakes emerges from their ability to destabilize the base-isolated structure by remarkably increasing the displacement demands.Thus,this study is intended to investigate the effects of pulse-like earthquake characteristics on the behavior of low-rise irregular base-isolated reinforced concrete structures.Within the study scope,investigations related to the impact of the pulse-like earthquake characteristics,irregularity type,and isolator properties will be conducted.To do so,different values of damping ratios of the base isolation system were selected to investigate the efficiency of the lead rubber-bearing isolator.In general,the outcomes of the study have shown the significance of vertical irregularity on the performance of base-isolated structures and the considerable effect of pulse-like ground motions on the buildings’behavior.

A Study on the Seismic Isolation Systems of Bridges with Lead Rubber Bearings

This study consists of the development and presentation of example of seismic isolation system analysis and design for a continuous, 3-span, cast-in-place concrete box girder bridge. It is expected that example is developed for all Lead-Rubber Bearing (LRB) seismic isolation system on piers and abutments which placed in between super-structure and sub-structure. Design forces, displacements, and drifts are given distinctive consideration in accordance with Caltrans Seismic Design Criteria (2004). Most of all, total displacement on design for all LRBs case is reduced comparing with combined lead-rubber and elastomeric bearing system . Therefore, this represents substantial reduction in cost because of reduction of expansion joint. This presents a summary of analysis and design of seismic isolation system by energy mitigation with LRB on bridges.

Effect of Alternation of Aging and Seawater Erosion on Properties of Rubber Material Used in Lead Rubber Bearing

An artificially accelerated alternation of aging and seawater erosion test of rubber materials used in lead rubber bearing(LRB)was performed,mainly to study the time-varying laws of rubber materials mechanical properties.Time-varying laws of the Mooney–Rivlin and Neo-Hookean constitutive parameters of rubber materials under the alternation of aging and seawater erosion were also analyzed.Results indicate that the rubber material mechanical properties were significantly affected by alternation of aging and seawater erosion.Hardness and elongation stress increased exponentially with test time.And 120 days after the test,the hardness increased by 14%,the maximum percentage increase in stress of 124.76%occurred at 100%constant elongation and the minimum percentage increase in stress of 68.32%occurred at 300%constant elongation;Tensile strength and elongation at break decreased by 44.96%and 53.09%.Besides,constitutive parameters of Mooney–Rivlin and Neo-Hookean all changed greatly with test duration.Finally,time-varying laws of constitutive parameters were verified by comparing the simulated and experimental results of the lead rubber bearing’s stiffness.Research results are of great significance to the seismic performance research and life-cycle performance analysis of offshore traffic engineering such as cross-sea bridges and bridges in the marine environment.

Effect of Lead-Rubber Bearing Isolators in Reducing Seismic Damage for a High-Rise Building in Comparison with Normal Shear Wall System

Seismic earthquakes are a real danger for the construction evolution of high rise buildings.The rate of earthquakes around the world is noteworthy in a wide range of construction areas.In this study,we present the dynamic behavior of a high-rise RC building with dynamic isolators(lead-rubber-bearing),in comparison with a traditional shear wall system of the same building.Seismic isolation has been introduced in building construction to increase the structural stability and to protect the non-structural components against the damaging effects of an earthquake.In order to clarify the influence of incorporating lead rubber bearing isolators in the seismic response and in reducing seismic damages;a comparative study is performed between a fixed base system(shear wall system)and an isolated base system(Lead Rubber Bearing)on an irregular high rise reinforced concrete(RC)building located in Beirut consisting of 48 storeys almost asymmetric orthogonally.For this purpose,a non-linear analysis of a real earthquake acceleration record(EI Centro seismic signal)is conducted,so that the mode shapes,the damping ratio and the natural frequencies of the two models are obtained using ETABS software.The results prove a substantial elongation of the building period,as well as a reduction in the building displacement,the roof acceleration,the inter-storey drift ratio and the base shear force of isolated building relative to fixed-base building.This study proves that this technology is applicable to high rise buildings with acceptable results.

Experimental and Finite Element Analysis for Multi-lead Rubber Bearings:A Comparative Study

The mechanical properties of multi-lead rubber bearings （MLRBs） were investigated by experiment and finite element analysis. First, the vertical stiffness, horizontal stiffness and yielded shear force were tested for four MLRB specimens and two specimens of the single-lead rubber bearings （ SLRBs）. Then, the MLRBs were modeled by the explicit finite element analysis software ANSYS/ LS-DYNA, in order to evaluate the horizontal force-displacement hysteretic curves under static vertical and dynamical horizontal loadings. The disagreement between the tested and theoretical values was less than 11.4%, and MLRBs and SLRBs were similar in vertical stiffness, pre-yield stiffness and yield stiffness.

柔性直流换流阀LRB隔震性能分析

以一柔性直换流阀为研究对象,进行了铅芯橡胶隔震支座(LRB)基础隔震设计,通过ANSYS有限元模拟得到隔震前后结构的动力响应,对比分析了LRB隔震性能,结果显示:该柔性直流换流阀LRB隔震方案隔震性能优异,可显著降低震中换流阀结构应力和加速度响应,提高柔性直流换流阀结构的安全性。

SMA-LRB隔震连续梁桥地震易损性及寿命周期成本损失评估

为研究采用LRB和SMA-LRB隔震连续梁桥的地震易损性和寿命周期成本损失,对比了采用两种不同隔震支座的桥梁在4种损伤状态下的损伤概率,并采用寿命周期成本损失评估方法计算了桥梁寿命周期内的各种地震损失成本。结果表明:在LRB隔震桥梁的基础上设置SMA既可以降低支座损伤概率,又可以有效降低桥墩在严重损伤和完全损伤状态下的损伤概率;地震动强度较小时,SMA-LRB隔震桥梁在减少桥梁寿命周期成本损失方面的效果更为显著。

铅芯隔震橡胶支座力学性能试验研究

针对铅芯隔震橡胶支座力学性能试验,重点分析橡胶支座结构及粘接试验标准,设计一种新型抗剪粘接模块化试验装置,与现有试验装置进行分析比对,对新型试验装置的结构进行分析计算,对LRB750、LRB900两种支座进行压缩性能、水平性能、水平非破坏粘接性能和破坏粘接性能试验,结果表明:试验设计满足要求,相比垂向压缩、水平剪切对隔震橡胶支座粘接性能影响更明显,且支座压缩刚度、屈服力、屈服刚度、水平等效刚度均满足要求,LRB900初始粘接破坏载荷761 kN、位移735 mm。该研究成果为橡胶支座及同类产品研发和试验提供一定指导作用。

铅芯隔震橡胶支座关键抗震性能参数极低温效应试验研究

中国北方部分地区冬季易受到极寒气候的影响,研究铅芯隔震橡胶支座在此环境下的性能变化规律和规范适用性,对结构抗震安全性具有非常重要的意义。对3种不同形状的铅芯隔震橡胶支座,分别进行了不同温度(-60~40℃)和不同低温暴露时间(1、2、7 d)下的剪切性能试验,得出了支座的关键抗震性能参数(特征强度、水平等效刚度、屈服后刚度和等效阻尼比)随温度和低温暴露时间的变化规律。研究表明:支座形状对铅芯隔震橡胶支座的低温隔震性能影响较小;而橡胶配比在极低温时的影响至关重要;在满足各项性能需求的前提下,低温减隔震支座宜优先选择剪切模量较小的支座;支座的关键抗震性能参数在低温暴露时间约为2 d时达到一个相对稳定的状态。

高速公路多联连续梁桥隔震研究

针对高速公路多联连续梁桥的抗震问题,本文对铅芯橡胶支座和摩擦摆支座进行了隔震效应分析与设计优化。本文基于多联有限元模型和非线性时程分析方法,分析了多联体系下各墩地震响应的差异,及铅芯橡胶支座和摩擦摆支座的隔震和耗能效果,并对隔震支座的参数布置进行了优化。结果表明:多联桥梁交界墩的地震响应较联内墩一般增大20%以上,交界墩上部结构跨径差异较大时甚至可达75%。铅芯橡胶支座位移限制能力和大震耗能更好,且屈服前刚度越大、屈服强度和屈服后刚度越小,滞回耗能能力越强;摩擦摆支座小震时即可发挥其隔震效果,且滑动摩擦系数越小、曲率半径越大,隔震效果越好。通过在交界墩布置更多隔震支座可在保证一定隔震率的同时改善桥墩受力不均匀的问题,具有一定的工程参考价值。

考虑温度相关性的LRB隔震桥梁地震响应分析

系统地研究了铅芯橡胶隔震支座的温度相关性,以及支座温度相关性对隔震桥梁地震响应的影响。试验温度的变化范围为-40℃至50℃,通过拟静力试验的滞回曲线测定了支座在不同温度下的屈前刚度、屈后刚度和屈服剪力。根据所测得的试验数据,采用回归分析,得出了支座的温度影响相关系数函数。建立了LRB隔震桥梁的力学模型,分析了考虑支座温度相关性对隔震桥梁地震响应的影响。比较了不同温度下支座滞回的计算结果。对比分析了不同温度下,隔震梁桥墩顶剪力、梁位移和梁加速度的计算结果,得出了若不考虑支座的温度效应墩顶剪力和梁加速度会有较大的误差,而温度效应对梁位移影响较小的结论。

极低温度下LRB力学性能及对高层结构地震响应的影响

研究极低气温(-40℃)下温度变化对隔震结构中铅芯橡胶支座力学性能的影响及其力学性能变化特征,及﹣40℃至40℃区间支座的温度相关性。选用直径为600 mm的原型铅芯橡胶支座,采用电液伺服加载系统完成剪切应变为100%情况不同恒定温度下的低周反复加载试验。发现支座在极低温度下的力学性能与常温下的力学性能差异显著。提出铅芯橡胶支座屈服后刚度与屈服荷载的温度修正方程,及隔震结构设计中铅芯橡胶支座基于温度的力学参数取值建议。给出考虑温度影响的隔震结构地震反应影响算例,分析结果表明温度对强震下隔震结构的隔震层位移、上部结构层间剪力以及上部结构顶层的加速度响应影响显著。

大型LRB隔震储罐地震反应参数研究

铅芯橡胶支座(LRB)支座参数的最优设计范围是大型隔震储罐研究的关键问题。研究利用Bouc-Wen模型模拟LRB的力-变形非线性行为,结合Newmark增量法和龙格库塔积分法求解隔震储罐非线性动力方程,得到不同类型场地上大型LRB隔震储罐的地震响应特点,总结出LRB参数对大型隔震储罐地震反应(基底剪力、支座位移、晃动波高)的影响规律。研究表明:支座隔震频率是影响大型隔震储罐减震性能的主要参数。I类场地上最优隔震频率范围为0.5～5rad/s,Ⅱ类、Ⅲ类场地上最优隔震频率范围为2～5rad/s,Ⅳ类场地上最优隔震频率范围为1.5～3rad/s。支座屈服强度对储罐地震响应的影响取决于场地类型和隔震频率。在Ⅱ类和Ⅲ类场地上存在最优屈服强度使得基底剪力最小,并且最优屈服强度随隔震频率增加而增大。

LRB支座疲劳温度力学试验及隔震结构地震响应影响分析

对直径为600mm和1100mm的LRB进行循环加载试验,试验结果表明支座在往复运动中产生疲劳温度效应,屈服力下降29%-34%。并进行LRB支座疲劳温度效应理论与试验结果对比,数据表明支座疲劳温度效应引起的支座温度变化量与初始屈服应力成正比,与支座高度成反比。进一步对12层LRB隔震结构在常温和极寒两种环境温度下选用远、近场和双峰值地震波对结构进行动力响应分析,结果表明在超设计0.8g地震作用下,考虑支座疲劳温度效应时,常温工况支座屈服力下降23.5%,极寒工况为19.4%;支座位移增大常温工况为5.8%,极寒工况为26.4%。两种工况下上部结构动力响应最大影响率为9.8%。实际地震的疲劳温度效应对支座力学性能的影响与静力试验80圈结果一致,在设计时应考虑极寒环境在超设计地震作用时支座位移增大带来隔震沟碰撞风险。

建筑LRB橡胶支座的老化和徐变性能研究

老化和徐变性能是LRB橡胶隔震支座重要的长期性能指标,对建筑LRB600原型橡胶支座进行了老化和15MPa持续加载下的徐变性能测试试验。测得了隔震橡胶支座初始状态和相当于60a后的热老化力学特性变化率,以及橡胶支座在1330h持续荷载作用下的徐变量。最后,基于测试结果提出了橡胶支座在正常使用状态下的徐变率预测方程。

考虑双向耦合非线性的LRB隔震桥梁地震反应分析

为了研究铅芯橡胶支座(LRB)隔震桥梁在双向水平地震激励下的非线性地震反应,首先建立了模拟水平正交两向作用力条件下LRB支座非线动力行为的双向耦合弹塑性恢复力模型,这一双向耦合弹塑性模型中的单向力和变形关系的骨架曲线为双线性。在此基础上,提出了一种双向水平地震激励下多跨连续LRB隔震桥梁的非线性地震反应分析模型以及求解方法,并对考虑和忽略LRB支座恢复力的双向耦合作用时隔震桥梁的非线性地震反应进行了算例比较分析。研究表明这种双向耦合作用对隔震桥梁的地震反应有重要影响,如果忽略这些相互作用的影响,支座位移的峰值将被低估,这对隔震桥梁设计是不利的。

SRB与LRB隔震连续梁桥地震响应对比研究

为研究SRB与LRB隔震连续梁桥地震响应的差别,根据G-C模型模拟SMA丝的热力学本构关系,采用Bouc-Wen模型模拟LRB力-位移的滞回非线性特性,通过对结构的离散建立了全桥有限元计算模型,分别编制了求解SRB和LRB隔震结构非线性运动方程的时程分析程序.利用自编程序并结合算例对不同地震激励下的非隔震、SRB和LRB隔震模型进行了时程对比分析.分析结果表明:在非低频脉冲波激励下,采用SRB与LRB隔震,梁体位移虽被放大但均在限值范围内,其它关键部位的地震响应均明显降低;在低频脉冲波激励下,SRB的隔震效果同样显著,但LRB隔震桥梁的地震响应比隔震前有明显放大,梁体位移超出了限值范围.

基于汶川地震的LRB与RB隔震连续梁桥地震响应对比研究

为了研究铅芯橡胶支座(LRB)和板式橡胶支座(RB)对连续梁桥地震响应及隔震效果的影响,分别采用Bouc-Wen滞回恢复力模型模拟LRB的力-位移非线性特性,采用直线型恢复力模型模拟RB的本构关系,通过结构离散建立了非隔震、LRB隔震和RB隔震3种连续梁桥的有限元计算模型,运用四阶显式Runge-Kutta迭代法和Newmark时间积分法联合求解增量形式的全桥动力微分方程,并结合算例对3种连续梁桥有限元计算模型分别输入汶川地震波进行非线性时程对比分析。结果表明:LRB在控制梁体与支座位移,降低结构加速度和墩、台底内力响应方面均比RB的效果要显著;采用RB隔震后,梁体与支座的位移响应均较大,在桥梁隔震设计时要予以充分重视。

LRB隔震桥梁遭受超高车辆撞击时的响应分析

采用线性弹簧碰撞单元,用ANSYS有限元软件建立了超高车辆-桥梁的碰撞模型,对LRB隔震桥梁受到超高车辆正向撞击时的整体响应进行了非线性时程分析。结果表明,车桥碰撞时能产生较大撞击力;铅芯橡胶支座在超高车辆撞击桥梁时能消耗撞击能量,可有效地减小碰撞力向桥墩传播,起到"隔震"作用;影响撞击响应的主要因素是碰撞刚度、超高车辆的质量和速度。最后,为了便于工程设计提出了超高车辆-桥梁碰撞力的计算公式。