Behavior of Steel Beam to Concrete-Filled Steel Tubular Column Connections after Exposure to Fire

A nonlinear finite-element analysis (FEA) model was developed in this paper based on the elastoplastic finite-element theory to analyze the load versus deformation relation of steel beam to concrete-filled steel tubular column connections. Six tests on steel beam to concrete-filled steel tubular (CFST) column connections using external ring after exposure to the ISO-834 standard fire were used to verify the theoretical model. The test parameters included the column cross-sectional type, the fire duration time, the level of axial load in the column, and the beam-column strength ratio. Each test specimen consisted of a CFST column and two steel beam segments in cruciform arrangement to represent an interior joint in a building. Three of the six composite connection specimens had circular cross sections and three had square cross sections. Five of the test specimens were simultaneously exposed to the standard ISO-834 fire condition. After they had cooled down to room temperature, each was tested under a constant axial load and a cyclically increasing flexural load. This paper presents an analysis of the experimental results to validate the FEA model and to evaluate the influences of different testing parameters on various characteristics of the beam-column connection performance. Comparisons between the predicted results and the experimental results indicate that the FEA model can predict the P-(delta) relations of steel beam to CFST column connections and the column lateral load resistance after fire with reasonable accuracy. Finally, the FEA model was used to make a parametric study of the influence of the various factors on the postfire behaviors of steel beam to CFST column connections.