Behavior of beam-to-column moment connections under fire load

The welded flange-bolted web type moment connections are commonly used in the construction of modern steel buildings. The behavior of this type of connection under service load and seismic load has been studied extensively; however, the knowledge of its performance under fire load is limited. In this paper, the experimental studies of the welded flange-bolted web moment connections under fire loads are presented. Four full-size steel beam-to-column assemblages, with and without fire-proofing materials, were selected to simulate the moment connection commonly used in steel buildings. 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. Parametric studies were also conducted to examine the strength degradation of steel moment connection at elevated temperature. From these studies, it was found that the beam-to-column connection is able to retain its design strength up to 650 ^°C. However, the stiffness dropped to 25% of the value at ambient temperature. Ductile behaviors were observed on the connections, with necking and tearing at the top flange and local buckling at the bottom flange. It was also found that the stability and integrity of steel connections can be ensured if proper fire-proofing materials were provided.