EXPERIMENTAL RESEARCH ON THE BEHAVIOR OF HIGH-STRENGTH BOLTED CONNECTIONS UNDER COMBINED TENSION AND SHEAR IN FIRE

During a fire, the fire resistance of steel connections decreases as temperature increases, and large deformation of beams leads to huge catenary forces within beams. As a result, connections are generally loaded to failure under combined tension and shear forces. Transient fire tests were conducted on eight specimens of two connection types to study their fire-resistance when subjected to different combinations of tension and shear, in which furnace temperature was increased according to a specified bilinear curve. The experimental results indicate that the temperatures of beam endplates, cleat connections, column top flanges and high-strength bolts in the panel zone of high-strength bolted connections were similar, and were about 50℃ lower than that of beams and columns. The stiffness of the connections decreased continuously during the heating, and dropped sharply when the connection temperature exceeded 500℃. The deformation of the 8mm thick flush endplate connection was mainly observed in the endplates and the bolts. When the endplate thickness was 16mm, significant deformations were observed in the column top flanges and the bolts. The double web cleat connections failed because of the excessive deformation of the angles. For all the connections, fire-resistance decreases with an increase in either tension or shear, but the residual deformations were similar among the different connections under a series of tension and shear actions.