Mechanistic Model for Lead Rubber Bearings

Open Access
Author:
Lalwani, Dipesh Suresh
Graduate Program:
Civil Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
March 29, 2017
Committee Members:
  • Dr. Gordon P. Warn, Thesis Advisor
  • Dr. Jeffrey A. Laman, Committee Member
  • Dr. KONSTANTINOS PAPAKONSTANTINOU, Committee Member
Keywords:
  • elastomeric
  • lead rubber bearing
  • seismic isolation
  • seismic isolation bearing model
Abstract:
Seismic isolation is a technique used to shift the fundamental period of a structure to a long range period which reduces the forces a structure attracts during a seismic event. Two, widely used bearings in seismic base isolation of structures are elastomeric and lead rubber bearings. A typical elastomeric bearing consists of a number of layers of rubber alternated with steel shims bonded between two rubber layers. The addition of a lead core inserted in a central mandrel hole results in a lead rubber bearing (LRB). The lead enhances the bearings energy dissipating in an earthquake event. When elastomeric or LRBs are simultaneously subjected to vertical compressive load and increasing lateral displacement, the shear force equilibrium path can exhibit a critical point, beyond which the bearing exhibits negative stiffness. Semi-empirical models to simulate this behavior for elastomeric and LRB have been developed in the past. These models rely on experimentally calibrated parameters, making them impractical for design. Recently, a particular mechanics based model, developed for an elastomeric bearing only, approaches the modelling using vertical springs and a simple bi-linear constitutive relationship to represent the rotational behavior of an elastomeric bearing. Overarching goal of the present study is to build on the mechanics based elastomeric model to develop a LRB model. The elastomeric model is modified to include hysteretic behavior of LRB and also uses a Newton type numerical solution technique to solve for response of the bearing. The model, proposed in this study, utilizing vertical springs approach has shown to be capable of simulating the strength, stiffness and hysteretic behavior of LRB well.