Thesis
New insights into the mechanical behaviour of rubber bearings
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2023
- Thesis identifier
- T16578
- Person Identifier (Local)
- 201978459
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- This Thesis investigates the mechanical behaviour of elastomeric bearings with a low shape factor (LSF) through the development of advanced and simplified modelling strategies. Such bearings can offer an effective solution for three-dimensional seismic isolation of structures, that is, isolation in vertical as well as horizontal directions. They could also be employed for developing low-cost isolation systems due to their reduced weight and manufacturing cost. The proposed modelling strategies are validated against the results of the experimental tests carried out at Tun Abdul Razak Research Centre (TARRC) on rubber blocks and elastomeric bearings, and at University of Naples Federico II on a prototype building isolated with LSF bearings. The first part of the Thesis investigates the behaviour of rubber blocks bonded between two plates under combined compression and shear loading, using experimental and numerical analyses, and also approximate analytical theories. Numerical simulations are carried out with three-dimensional finite element (FE) models, allowing insight to be gained into the stress and strain fields within the blocks. Existing analytical theories for blocks under compression and combined compressive and shear loading are then reviewed, and their accuracy is evaluated against test and numerical results. The study shows that those theories accounting for the effect of the axial shortening of the blocks provide a better description of the combined compression and shear behaviour, compared to theories, developed for laminated structural bearings with many thin rubber layers, that ignore this effect. An improved theory is also proposed, which better describes the effects of the bulging of the compressed blocks on their shear and flexural parameters and provides a better fit to experimental and numerical results. -The second part of the Thesis describes tests carried out on low-damping natural rubber (NR) double-shear test pieces, LSF bearings and shaking table tests. The material tests are used to inform the development of a FE model of the bearings, which is validated against the bearing test results. It is shown that the proposed FE model can be used to describe accurately the global non-linear horizontal force-displacement behaviour of the compressed bearings, while providing an insight into the local distribution of stresses and strains. It can also be used to investigate the bearing response under boundary conditions that differ from the one considered in the tests. It has been observed that axial loads have a significant influence on the mechanical behavior of the LSF bearings. Most of existing theories and mechanical models for laminated bearings cannot be employed for LSF bearings because they disregard the important effects of axial shortening and bulging of the rubber layers on the horizontal bearing stiffness. Therefore, a simplified model originally developed for slender rubber blocks is also employed for describing the mechanical behavior of LSF bearings and then used for simulating the seismic response of a structural prototype mounted on LSF bearings. In order to further evaluate the effect of axial compliance of the bearings on the dynamic properties of the isolation system and to analyse the effect of variation of axial loads during the motion on the response of the bearing, a FE model of the isolated structure has also been developed. Useful insights are provided into the effect of the vertical bearing flexibility on the response and the attainment of critical conditions of zero tangent horizontal stiffness under horizontal displacements. Elastomeric bearings are widely used also in bridges to support the superstructure, to transfer loads to substructures, and to accommodate movements induced by e.g. temperature changes. Bearing mechanical properties affect the bridge’s performance, and its response to permanent and variable loadings (e.g. traffic). The third part of the Thesis describes the research carried out at Strathclyde towards the development of smart natural rubber bearings that can be used as a low-cost sensing technology for bridge and/or weigh-in-motion monitoring. An experimental campaign was performed, under laboratory conditions, on various natural rubber specimens enhanced with different conductive fillers. Each specimen was characterized under loading conditions that replicated in-situ bearings to determine their mechanical and piezoresistive properties. Relatively simple models can be used to describe the relationship between rubber bearing resistivity and deformation changes. Gauge factors (GFs) in the range between 2 and 11 are obtained, depending on the compound and the applied loading. Experiments were also carried out to show that the developed model can be used to predict the state of deformation of the bearings under random loadings of different amplitudes that are characteristic of the passage of traffic over a bridge.
- Advisor / supervisor
- Tubaldi, Enrico
- Resource Type
- DOI
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