Date of Award

7-7-2020

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Civil and Environmental Engineering

Keywords

elastomeric bearing, FEA, lift-off behaviour, pressure solution, shape factor

Supervisor

Niel Van Engelen

Rights

info:eu-repo/semantics/embargoedAccess

Abstract

Elastomeric bearings are widely used for base isolation as well as accommodating displacements in bridges. Fiber-reinforced elastomeric bearings (FREBs) have been shown to have similar performance as steel-reinforced elastomeric bearings (SREBs). Unbonded FREBs exclude the stiff and heavy steel end plates used to mechanically fasten the bearing to the top and the bottom surfaces. Due to the lack of a connection, lift-off (i.e. the separation between the superstructure and the bearings) could occur under certain combinations of large rotations and relatively low axial stress. This causes the superstructure to partially lose contact with the bearing and thus decreases the effective part of the bearing. Furthermore, nonlinearities are developed during this process which renders the problem to be more complex than the bonded cases. Canadian and American bridge design codes (CSA S6 and AASHTO) have contradicting requirements in the regulation of lift-off. In this thesis, the existing analytical model for bonded FREBs are illustrated and compared with numerical results. The analytical solutions of the lift-off initiation rotation and the moment-rotation relationship for unbonded FREBs are introduced. The shear strain distribution for unbonded FREBs is derived based on the existing analytical solutions. Eight infinite strip-shaped bearings with different number of layers, six bearings with different shape factor values, and four bearings with the same compressibility and extensibility index value but different material properties and geometry are simulated by using ABAQUS to validate the analytical lift-off behaviour. It is concluded that the numerical results fit well with the analytical solutions in terms of moment-rotation relationship, and shear stress and normal stress distribution. The analytical solutions could be used to predict the real behaviour of unbonded FREBs. The numerical results of the moment-rotation relationship agree better with the analytical solutions for the bearings (both bonded and unbonded) with fewer number of layers and under smaller loads. Based on the results, lift-off could be allowed to occur, but the bearings should be carefully designed to avoid shear failure.

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