Study On Fire Resistance And Protecion Of Building Seismic Rubber Bearings

Rubber bearings are formed of alternating thin rubber layers and steel shim plates chemically bonded together. They have been in widespread use as seismic isolators in buildings and bridges. However, the rubber bearing have limited fire resistance since vulcanized natural rubber materials used in rubber bearings are susceptible to rapid deterioration of mechanical and bond properties at elevated temperature due to their intrinsic nature of poor thermal stability particularly in oxidative environment. If the seismic rubber bearing are positioned where they are directly subjected to flames, e.g. in storey seismic isolation, significant threat is posed to the safety of the entire building structure. It is therefore of importance to evaluate their fire resistance before rubber bearings could be used with confidence.The fire resistance of rubber bearings, however, has not been sufficiently reported to the best of author's knowledge. This paper outlines an experimental study on fire resistance of Lead Rubber Bearings (LRB) and Natural Rubber Bearings (NRB), carried out recently in South China University of Technology. The differences in fire test program of this paper compared with similar studies carried out by other researchers are as follows: a) the effect of duration of fire exposure on residual mechanical properties is investigated; b) the possible effect of axial load, to which rubber bearings are subjected in fire, on mechanical properties is also accounted for; and c) an economical fire protection solution for building seismic isolators was proposed using a type of cementitious insulation system, with its effectiveness verified in numerical and experimental study.This paper consists of the following four chapters:Chapter I, This chapter gives a brief introduction on the concept, principles, and types of seismic isolation. The structure, mechanical performance, and application of building seismic rubber bearings in seismic isolation are presented. This chapter also makes a literature review on previous studies on thermal properties of rubber materials and fire resistance and temperature-dependent properties of seismic rubber bearings. Chapter II, this chapter presents experimental study on fire resistance of four uninsulated lead rubber bearings and two uninsualted natural rubber bearings. Fire tests on these rubber bearings were conducted individually under ISO834 standard heating process. Their temperature distributions during the fire tests, fire resistance, failure mode, residual mechanical properties, and ultimate lateral deformation capacity after fire were investigated. The effect of duration of fire exposure and vertical load to which bearings were subjected in fire tests on the residual mechanical properties on rubber bearings were also studied.Chapter III, this chapter proposed a unique supplemental cementitious fire insulation for building seismic rubber bearings. A thermal numerical analysis was performed using general-purpose FEM program ANSYS for a) investigating the temperature of distribution with the specimen; and b) verifying the effectiveness of the proposed fire insulation protection and determining the necessary thickness of insulation protection for specimens in fire test.Chapter IV, this chapter presents fire tests on one insulated lead rubber bearing and one insulated natural rubber barings individually under standard heating process. The temperature distribution, failure mode, residual mechanical properties, ultimate lateral deformation capacity of rubber bearings were investigated after fire. Comparison was made between measured results and numerically predicted results. The effectiveness of fire insulation of rubber bearing was verified.