Research On Fire Resistance Of Building Seismic Rubber Bearings

Derham G.J. and Thomas A.G., Kato Michiko, Zhou Fulin, Wu Bo and other scholars or academic teams have explored the fire behavior of building seismic rubber bearings, including the temperature rise during the fire tests, loading capacity under fire, mechanical properties after fire tests and so on. The tested bearings vary in types and sizes, with different fire conditions, making it difficult for the comparison between the results. Instead of the high-priced fire tests, numerical simulation may become a good choice for further research work. However, research work of the temperature-dependent mechanical properties of rubber is insufficiency, thus the numerical simulation stays behind because of the lack of temperature-dependent rubber constitutive model. Tthe author’s research work is described in three aspects:thermal properties of NR and SBR rubbers, basic mechanical properties of rubbers after high temperature and numerical simulation of LNR bearings’ residual mechanical properties by ANSYS after fire. The main research work and results in this paper are as follows:Natural rubber (NR) and styrene butadiene rubber (SBR) are two main rubber materials used in bearings. The thermal properties (thermal conductivity, diffusivity and heat capacity at high temperature) of NR and SBR was measured by the Hot Disk; The thermal stability of NR and SBR was compared through the tested curve relationship between the mass change and the heated temperature by TGA; By exploring the macro and micro (SEM) changes in surface morphology of NR and SBR after high temperatures, a phenomenological explanation for the mechanical properties reduction of NR and SBR was investigated.The mechanical properties of the NR and SBR after high temperatures were explored. Mechanical tests including uniaxial tensile test, simple shear test and uniaxial compression test have been carried out on different samples heated to the target temperatures and cooled for more than 72h. The correlations between the target temperatures and the mechanical properties were investigated.Based on the stress-strain curves tested above, the parameters to establish the hyperelastic material model (Polynomial model, Neo-Hookean model, Ogden model, Yeoh model and HyperFoam model) of NR rubber were obtained through the curve fitting function of ANSYS. Finite element model of the obove different constitutive models was established to simulate the uniaxial tensile and shear behavior of NR, and by comparing the stress-strain curves from FEA with the measured data, the HyperFoam model were proved to be more effective in the simulation of NR to investigate its mechanical behavior.The thermal analysis numerical model of GZP600 by ANSYS was established to explore its temperature distribution during fire tests. The validation of the FEA model was verified by comparing the temperature-rise curves with the test data measured by Wu Bo. Then, the temperature distribution of LNR600 (NR) produced by Haida Rubber & Plastic Co. during 1.0h fire test was investigated with the above FEA model. Based on the maximum temperature NR explored and the tested stress-strain curves, the temperature-dependent constitutive models of NR were introduced in the ANSYS numerical simulation of LNR600, to investigate its residual vertical compressive stiffness (vertical design load=10MPa) and equivalent horizontal stiffness (vertical load=10MPa, shear strain=100%) after 1.0h fire test. The validation of the FEA model for the after-fire residual mechanical properties simulation of seismic rubber bearings was discussed. Based on the above numerial simulation analysis, the fire resistance of LNR bearings made by Haida Rubber & Plastic Co. was explored, and the correlation between the stiffness drop (both vertical and horizontal) and the influence factors (the fire time and the bearing diameter) was investigated.