Fire response of steel column-tree moment resisting frames

Abstract

The column-tree moment resisting frames are common steel construction design in many countries. Very limited research has been carried out on such systems at elevated temperatures. This paper presents experimental investigations of the performance of beam and its bolted connections in steel column-tree MRF under fire conditions. Six full-scale steel sub-frames with different link-to-stub beam connections were tested under ISO 834 standard fire. The effects of factors, including load level, splice plate’s size, bolt size and bolt grade were studied. The thermal and structural fire behaviors as well as failure modes were investigated. The link-to-stub beam connections failed at temperatures beyond 750 °C, while beam underwent large deflections of more than span/20. It was observed that, bolt shear fracture generally governs the failure of flange connection, whereas bolt hole bearing controls the failure of web connection at elevated temperatures. The results show that the use of stronger bolts in flange splice can significantly enhance the resistance and rotational capacity of the link-to-stub beam connection at high temperatures.