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.

Steady Characteristics of the Water-Lubricated Conical Bearings

The water-lubricated conical bearing has attracted attentions of researchers for its simple structure,easily adjusted gap ( film thickness ) , lower friction loss, and less pollution in application. A mathematic model with consideration of the effects of turbulence,two-phase flow,and temperature on the pressure field at bearing surface is proposed here. Using this model,the Reynolds' equation and energy equation are solved in which the thermo-physical properties of the water as lubricant are taken into account. The dependency of characteristics of bearing,such as load-carrying capacity,flow rate ( pumping losses ) ,and frictional losses,on angular velocity, conical angle, and radial eccentricities, is presented. The research results are beneficial to the improvement of the efficiency of conical bearing and the environmental protection.

Development of a modified Mooney-Rivlin constitutive model for rubber to investigate the effects of aging and marine corrosion on seismic isolated bearings

In this study, aging and marine corrosion tests of a large number of rubber material and rubber bearings have been carried out. The constitutive Mooney-Rivlin model parameters for a rubber isolated bearing have been determined. By applying the least-square method to the experimental data, the relationships between the aging time and the marine corrosion time with the constants in the constitutive model for a rubber beating have been derived. Next, the Mooney-Rivlin model has been modified accordingly. Further, using the modified Mooney-Rivlin model and the Abaqus software, the performance of the rubber isolated bearings has been simulated. The simulation results have been compared to the experimental results so as to verify the accuracy of the modified model. The comparison shows that the maximum errors for the vertical and horizontal stiffnesses are 16.8% and 0.49%, respectively. Since these errors are considered acceptable, the accuracy of the modified constitutive model can be considered verified. The results of this study can provide theoretical support for the performance study on rubber isolated bearings under the complex ocean environment and the life-cycle performance evaluation of bridges and other offshore structures.

Vibration Reduction Performance of Damping-Enhanced Water-Lubricated Bearing Using Fluid-Saturated Perforated Slabs

As the first link element for the transmission of shaft vibration to the pedestal and even to the hull,water-lubricated bearing plays a key role in suppressing vibration.Although the porous structure is considered as one of the main methods for improving the wideband vibration and noise reduction performance of materials in many industrial fields,the studies in the field of water-lubricated bearing remain insufficient.To enhance vibration reduction performance,a fluid-saturated perforated slab is designed in this study,and via the establishment of a fluid-solid coupled vibration model,the influence law and impact levels were analyzed and verified by simulation and experiments.The results obtained verified that the total vibration amplitude of damping-enhanced stern bearing in the vertical direction was smaller than that of the normal stern bearing,and the reduction amplitude of the characteristic frequency agreed with the optimal value at approximately 0.1 of the volume fraction of the liquid phase when the solid-fluid phase was rubber–water.Additionally,the increase in fluid fraction did not enhance the damping effect,instead,it unexpectedly reduced the natural frequency of the raw material significantly.This research indicates that the design of the fluid-saturated perforated slab is effective in reducing the transmission of the vibration amplitude from the shaft,and presents the best volume fraction of the liquid phase.

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.

Review of the evolution and prevention of friction,wear,and noise for water-lubricated bearings used in ships

With the development of green tribology in the shipping industry,the application of water lubrication gradually replaces oil lubrication in stern bearings and thrust bearings.In terms of large-scale and high-speed ships,water-lubricated bearings with high performance are more strictly required.However,due to the lubricating medium,water-lubricated bearings have many problems such as friction,wear,vibration,noise,etc.This review focuses on the performance of marine water-lubricated bearings and their failure prevention mechanism.Furthermore,the research of marine water-lubricated bearings is reviewed by discussing its lubrication principle,test technology,friction and wear mechanism,and friction noise generation mechanism.The performance enhancement methods have been overviewed from structure optimization and material modification.Finally,the potential problems and the perspective of water-lubricated bearings are given in detail.

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.

Parameter identification of hysteretic model of rubber-bearing based on sequential nonlinear least-square estimation

In order to evaluate the nonlinear performance and the possible damage to rubber-bearings （RBs） during their normal operation or under strong earthquakes, a simplified Bouc-Wen model is used to describe the nonlinear hysteretic behavior of RBs in this paper, which has the advantages of being smooth-varying and physically motivated. Further, based on the results from experimental tests performed by using a particular type of RB （GZN 110） under different excitation scenarios, including white noise and several earthquakes, a new system identification method, referred to as the sequential nonlinear least- square estimation （SNLSE）, is introduced to identify the model parameters. It is shown that the proposed simplified Bouc- Wen model is capable of describing the nonlinear hysteretic behavior of RBs, and that the SNLSE approach is very effective in identifying the model parameters of RBs.

Insight into the Lubrication Performance of Biomimetic Porous Structure Material for Water-lubricated Bearings

Water-lubricated bearings have great advantages in the application of ship tail bearings due to the characteristics of green,pollution-free,and sustainable.However,the poor wettability of water-lubricated materials,as well as the low viscosity and poor load-carrying capacity of water,resulting in poor lubricating film integrity and short material service life under low-speed,heavy-load,start-stop conditions,which limits its application.To study the relationship between wettability and lubrication state and improve the lubrication performance of Si_(3)N_(4) under water lubrication conditions,the characteristic parameters that determine the hydrophilicity of Sphagnum were detected and extracted,and the bionic Si_(3)N_(4) model was established using Material Studio.Then,the molecular dynamic behavior and tribological properties of different Si_(3)N_(4) models were simulated and analyzed.Pore structure affects the spreading and storage of water on the material surface and changes the wettability of the material.Under the condition of water lubrication,better wettability and water storage promote the formation of water film,effectively improve the lubrication state of the material,and improve its bearing performance.

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.

寒区环境温度对板式橡胶支座连续梁桥地震易损性影响研究

针对现行规范对寒区桥梁减隔震设计中仅考虑橡胶支座力学特性受环境温度作用影响,而忽略桥墩混凝土材料特性受温度影响的不足,以高寒地区一座两联3×30 m混凝土连续梁桥为背景,开展不同环境温度下桥墩混凝土材料抗压性能试验,确定温度对其力学参数的影响,基于试验结果对不同环境温度下的桥墩混凝土力学参数进行修正,从而建立不同环境温度下的全桥精细化非线性有限元模型,并基于增量动力分析(IDA)法探究不同环境温度下该桥的地震易损性。结果表明:极端温度引起桥墩混凝土材料参数和支座刚度的改变,使得该桥自振频率随着温度的升高而降低;地震作用下,极端低温时桥墩墩顶位移较常温增大了26.8%,而极端高温时支座位移增大了19.4%;根据现行规范计算的极端低温时支座和桥梁系统的损伤概率偏小,极端高温时结构和构件的损伤概率偏大,在设计中应予以重视;极端低温下桥墩、支座及桥梁系统的损伤概率,较常温分别增大45.0%、35.2%和27.5%,对于高寒地区该类桥梁设计时需考虑低温对其抗震性能的影响。

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。

钢板削弱型叠层橡胶支座力学性能试验研究

结合厚层橡胶支座和普通叠层橡胶支座的优点设计新型钢板削弱型叠层橡胶支座,通过调节环形钢板的总数和位置进行支座水平和竖向刚度的有效控制.选择3种中心橡胶层厚度的钢板削弱型叠层橡胶支座,分析所设计支座的滞回特性、刚度特性和耗能特性.基于串-并联模型,构建水平和竖向刚度的计算模型.试验结果表明,相比普通叠层橡胶支座,钢板削弱型叠层橡胶支座的水平和竖向刚度更低,水平和竖向耗能比更高,滞回曲线更光滑饱满.所建模型的计算结果与试验结果的一致性较好,误差绝对值不超过10%.所建模型在评估钢板削弱型叠层橡胶支座的水平和竖向刚度方面具有较高的精度和适用性.

自然老化服役后板式橡胶支座摩擦滑移性能试验研究

为了解自然老化服役后板式橡胶支座的摩擦滑移性能,取实际桥梁中服役10年的7个板式橡胶支座进行摩擦滑移试验,分析不同竖向压应力下支座摩擦滑移规律,研究自然老化板式橡胶支座的水平弹性刚度、摩擦系数及耗能能力等,并对比人工热老化支座的相关性能。结果表明:相同服役年限的自然老化板式橡胶支座老化程度并不相同;自然老化板式橡胶支座摩擦系数随着竖向压应力的增大而减小,水平弹性刚度随着竖向压应力的增大而增大;压剪作用对老化板式橡胶支座的耗能能力影响较小,但需要注意累积的摩擦滑移会使支座耗能能力降低。自然老化板式橡胶支座(试验值)相较于未老化支座(理论值)的表面摩擦系数有所降低,但水平弹性刚度明显增大;自然老化板式橡胶支座水平弹性刚度增大幅度远高于人工热老化的板式橡胶支座,人工热老化研究严重低估了自然老化对板式橡胶支座的危害。

工程结构中新型减隔震支座的研究综述

多次震害经验表明,通过在上部结构和地基之间设置减隔震支座,利用橡胶垫的变形使上部结构的振动周期延长,利用钢构件的屈服或者滑动摩擦耗能来达到消能减震的目的,是一项有效的防震减灾措施。论文从减震机理、性质及应用等方面系统阐述和总结了拉索减震支座、叠层橡胶支座、球形抗震支座以及若干新型减震支座的研究成果,对未来新型减隔震支座的研究方向进行了展望。

支座用石墨烯/导电炭黑橡胶材料的制备与性能

以石墨烯和特制导电炭黑为功能填料,溴化丁基橡胶(BIIR)为基胶,制备出阻尼性能较好的导电橡胶材料.针对石墨烯/导电炭黑10种不同的组分,开展了力学性能、动态力学性能与电阻率测试实验,探究了加入石墨烯与导电炭黑对BIIR性能的影响规律.结果表明,导电炭黑对BIIR材料有补强效果,石墨烯/导电炭黑协同并用可以有效提高BIIR的阻尼性能与导电性能.在每100 g总胶料中添加40 g导电炭黑时,BIIR/导电炭黑复合材料的拉伸强度与撕裂强度分别达到20.28 MPa和45.66 kN/m.当导电炭黑和石墨烯并用组分的质量比为40∶10时,BIIR/导电炭黑/石墨烯复合橡胶材料最大损耗因子提升至0.5,电阻率为3 646Ω·cm.复合材料的导电炭黑和石墨烯组分最优质量比为40∶5.制备得到的新型复合材料具有较好的力学性能、阻尼性能与导电性能,可为隔震支座用高阻尼导电橡胶的制备提供参考.

考虑环境温度效应的隔震橡胶支座力学性能试验

为研究环境温度对隔震橡胶支座力学特性的影响,利用高速压剪试验设备针对直径700 mm的隔震橡胶支座(LRB700以及LNR700)开展一系列不同温度(-20、0、23℃)、不同频率(0.2、0.25、0.3 Hz)以及不同剪应变(50%、100%、250%)的压剪试验。鉴于高速高压(15 MPa的竖向压应力)试验设备本身会产生较大的惯性力以及摩擦力,分别提供相应的修正方案以便准确获得支座的力学性能指标。结果表明:随着加载圈数的增加,LRB700内部铅芯的温度变化较为明显,并呈现关于高度的对称性,而LNR700内壁温度变化很小;LRB700及LNR700的相关力学性能指标(如水平屈服剪力、屈服后水平刚度以及水平等效刚度)随环境温度的降低都表现出不同程度的上升趋势,其中,LRB700水平屈服剪力上升15%~32%,LRB700屈服后水平刚度上升7%~16%,LRB700与LNR700水平等效刚度分别上升12%~23%、5%~16%。基于上述结果并结合相关规范针对LRB700以及LNR700提出考虑环境温度效应的力学性能调整系数。

金属橡胶桥梁支座疲劳试验研究

以某公路桥梁为工程背景,设计并制作了两个足尺金属橡胶桥梁支座试件,开展了200万次的竖向疲劳试验,探讨了疲劳前后支座力学性能的变化规律。在疲劳试验过程中每隔20万次进行了一次压缩试验,得到了一组支座竖向压缩滞回曲线。疲劳试验前后分别进行了支座压剪试验,得到了支座水平剪切滞回曲线。引入疲劳损伤因子对金属橡胶桥梁支座的疲劳损伤进行了定量表征。结果表明:金属橡胶桥梁支座疲劳损伤主要表现为内部金属丝之间的磨损、局部断丝、掉丝。疲劳损伤会显著降低支座一侧的水平承载力、屈服后刚度和等效剪切刚度,且使支座的水平剪切滞回曲线变得明显不对称,但会增大支座的整体耗能能力。支座竖向等效刚度及等效阻尼比随着疲劳加载次数先增大后减小然后再趋于稳定。200万次疲劳循环后的剪切等效刚度、竖向等效刚度及竖向等效阻尼比损伤因子均小于0.3,支座具有良好的疲劳性能。

Rubber/UHMWPE复合尾轴承材料及其性能分析

以丁腈橡胶为基体,加入超高分子量聚乙烯(UHMWPE)和石墨等物质进行共混改性,得到一种新型舰船尾管水润滑轴承材料。其物理力学性能达到了我国CB和美国MIL标准,摩擦因数达到了美国军标MIL-DTL-17901C(SH)的标准,在低速下更优于标准。局部最大比压可达0.70 MPa,减振降噪性能优于同类产品,是一种综合性能优异的水润滑轴承材料。