NUMERICAL ANALYSIS MODELING OF FRICTION TYPE HIGH STRENGTH BOLTED SPLICE CONNECTION EXPOSED TO FIRE

Abstract

In case of fire, in addition to the stress due to permanent load, the thermal stress caused by the thermal expansion occurs in a steel frame. Therefore, if the deformation caused by the thermal stress at fire condition is concentrated at a connection, there is a possibility that the connection will be failed before the steel frame reaches its ultimate state. Considering such a phenomenon, in order to investigate the failure behavior of the steel structure connections exposed to fire in detail, it is necessary to analyze the stress and deformation of a heated steel frame in fire condition using thermal stress analysis. In the meantime, the analytical model that could represent the deformation behavior of the connection in fire is also necessary. Due to the severe high-temperature strength reduction of high-strength bolts, there is a possibility that the friction type high strength bolted splice connection (bolted connection) might be the weakest point of the whole frame in fire condition. In Europe, for a model of the bolted connection using in the frame analysis, the component-based model have been proposed. This model is a model in which each connection component (beam, splice plate and bolt) was defined independently and its characteristics (stiffness and strength) were determined by means of nonlinear load deformation curves. The component-based model is possible to consider both the shear deformation behavior of high-strength bolt and bearing deformation behavior of the bolt hole. This paper discusses a model of bolted connection on the basis of a component-based model. Connection type of a steel structure being used in Japan is different to that in Europe. And the component-based model of friction type bolted splice connection is less researched. Therefore, in order to investigate the deformation behavior of a bolted connection at elevated temperature, high temperature tensile experiments of two-sided friction bolted connections were performed. In this paper, firstly, component-based model outline is introduced. Afterwards, the analysis model based on the high temperature tensile test results of the bolted connection is derived, and is included to thermal stress analysis program. Finally, the suitability of this analytical model is shown by comparing the analysis results using this model with the previous experimental results. The results of this study are shown below. 1) By conducting an analytical study of bearing deformation behavior of steel plate used in a bolted connection at elevated temperature, the curve fit coefficients Ω (reference to the previous studies) were modified as corresponding to the load-deformation relationship of friction type high strength bolted splice connection according to the results of steady temperature tests. 2) The numerical analysis results approximately agreed with deformation behaviors and critical temperatures of elevated temperature tests of the bolted connection under constant load. Also, this analysis method could predict the deformation of each component in bolted splice connection and the failure type of bolted splice connections approximately. 3) The numerical analysis results approximately agreed with the deflection behavior of both ends fixed steel beams with the bolted connection under constant load in fire condition. Moreover, this analytical method could approximate the damage level of each component (beam, splice plate and bolt) at the bolted connection.