JZUS - Journal of Zhejiang University SCIENCE

Journal of Zhejiang University SCIENCE A 2017 Vol.18 No.5 P.363-376

Explicit finite element analysis and experimental verification of a sliding lead rubber bearing

Author(s): Yi-feng Wu, Hao Wang, Ai-qun Li, Dong-ming Feng, Ben Sha, Yu-ping Zhang
Affiliation(s): School of Civil Engineering, Southeast University, Nanjing 210096, China; more
Corresponding email(s): wyf.07010701@163.com, wanghao1980@seu.edu.cn
Key Words: Explicit analysis, Sliding lead rubber bearing (SLRB), Time step size, Contact relations, Numerical simulation, Experimental verification

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Abstract: Based on the explicit finite element (FE) software ANSYS/LS-DYNA, the FE model for a sliding lead rubber bearing (SLRB) is developed. The design parameters of the laminated steel, including thickness, density, and Young’s modulus, are modified to greatly enlarge the time step size of the model. Three types of contact relations in ANSYS/LS-DYNA are employed to analyze all the contact relations existing in the bearing. Then numerical simulations of the compression tests and a series of correlation tests on compression-shear properties for the bearing are conducted, and the numerical results are further verified by experimental and theoretical ones. Results show that the developed FE model is capable of reproducing the vertical stiffness and the particular hysteresis behavior of the bearing. The shear stresses of the intermediate rubber layer obtained from the numerical simulation agree well with the theoretical results. Moreover, it is observed from the numerical simulation that the lead cylinder undergoes plastic deformation even if no additional lateral load is applied, and an extremely large plastic deformation when a shear displacement of 115 mm is applied. Furthermore, compared with the implicit analysis, the computational cost of the explicit analysis is much more acceptable. Therefore, it can be concluded that the proposed modeling method for the SLRB is accurate and practical.

This paper addresses the issue of efficient finite element (FE) modelling of lead-rubber bearings used for the seismic isolation of building structures. A particular commercial software is used for the task and focus is given on increasing the time step required in conducting non-linear response history analysis without suffering from numerical instabilities due to large deformations expected to develop in the bearings under severe ground excitation intensity. It is proposed by the authors to use artificially small values for the mechanical properties of the steel sheets increasing their thickness such that they become compatible with the properties of the rubber sheets, while increasing the thickness of the steel sheets. Although from a numerical/computational viewpoint the fact that the two materials have now similar properties and therefore a larger time-step can be used in the analysis leading to computational efficiency, this heuristic consideration does not represent reality as the two different materials have very different properties. To this end, the authors undertake verified by experimental data obtained from testing actual bearings in the shaking table to demonstrate that the induced error due to adopting artificially low mechanical properties for the steel sheets do not induce significant errors in predicting the seismic response of the considered specimens tested in the lab. From a technical viewpoint, the paper presents a "smart" way to reduce the time-step in the analysis of lead-rubber bearing which, although raises questions on its rationality, it does seem to yield encouraging results when compared with experimental data. This can be classified as a practical paper which may be of use to practicing engineers undertaking design and verification of base isolated buildings for earthquake resistance. There is always, of course, an issue on whether the proposed heuristic technique is applicable and accurate to different types of lead-rubber bearings not considered in the experimental campaign used in the paper. However, such bearings are always tested in the lab before deployment and, therefore, in each case a similar preliminary analysis can be done by practicing engineers along the lines of the paper to test the validity of the proposed scheme, which may then be used for computationally efficient design verification purposes with confidence.

一种可滑移式铅芯橡胶支座的显式数值模拟与试验验证

目的：随着隔震技术在工程结构中的逐步推广应用，橡胶隔震支座的试验与数值模拟都得到国内外工程研究人员的重视。其中后者因支座大变形时计算较难收敛、铅芯与周边橡胶以及钢板的复杂接触关系较难模拟、采用隐式积分算法时计算规模较难控制等问题，目前仍是这一方向的研究热点。本文旨在探讨基于显式积分算法对一种新型可滑移式铅芯橡胶支座进行准确可行的数值模拟的方法。
创新点：1. 探究基于显式积分算法的隔震支座数值模拟方法；2. 采取多种方法有效地控制了数值模拟计算规模，同时实现了较高的数值模拟精度；3. 采用程序中提供的3种接触方式较好地模拟了支座中存在的复杂接触关系。
方法：本文主要采用4种方法减小数值模拟计算规模：1. 激活程序内置的质量缩放功能；2. 合理增大支座中对支座竖向刚度与水平剪切性能影响较小的非关键部件--叠层钢板的厚度；3. 合理减小叠层钢板的弹性模量；4. 考虑到支座中所有材料均未考虑材料的率变效应，即加载速率对支座的力学性能没有影响，本文数值模拟中所用加载频率为实际加载频率的10倍。此外，本文采用了一般接触、绑定接触与单边接触模拟支座中不同的接触关系。
结论：1. 显式积分的计算时间步长由2.4×10^-7 s增大到3.5×10^-6 s；2. 与试验结果对比验证了本文提出的基于显式积分算法对该新型可滑移式铅芯橡胶支座进行数值模拟的方法的准确实用性；3. 该支座在纯压作用下，部分铅芯发生塑性变形，而在最大剪切位移时，铅芯发生了很大的塑性流动变形；4. 与采用隐式算法对该支座进行数值模拟研究所用时间相比，显式算法所用时间少很多。

关键词：显式算法；可滑移式铅芯支座；计算时间步长；接触关系；试验验证

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一种可滑移式铅芯橡胶支座的显式数值模拟与试验验证

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