Numerical Investigation of Steel Moment-Resisting Frame with RBS Connections Under Fire Conditions

Recent earthquakes indicate that the welding connections of steel moment-resisting frames (SMRFs) are so brittle. Then, huge damages are generated by cracking the weld between the beam flange and column face. After the 1994 Northridge and the 1995 Kobe earthquakes, reduced beam section (RBS) connections were proposed to reduce the damages by forming a plastic hinge outside the panel zone. Thus, with the great effect of seismic performance and ductility of the panel zone, RBS moves the formation of the plastic hinge at a suitable distance from the column face. In this regard, in order to evaluate the behavior of SMRF with RBS connections under fire conditions, four types of steel frame connections, including RBS with radial, rectangular, triangular, and trapezoidal cuts, were modeled in ABAQUS software. Due to the fact that fire is an unpredictable phenomenon, both in terms of size and fire load, it has special complexities. The fire load was simulated either by a steady state method to reach a fully-developed fire or by a transient state method following the standard temperature–time curve. The results of this study showed that by increasing the temperature of the heated area, the transferring of the plastic hinge is conducted better. Meanwhile, based on the obtained outputs of displacement-time coefficients, the Frame-RBS-01 sample had the most ultimate strength compared to other samples up to 748.34 ° C temperature, and the least ultimate strength is related to the Frame-RBS-Rectangle-02 sample up to 526/90 ° C temperature.