Experimental study of fire effects on out-of-plane bending strength/flexibility of steel tubular T-joints

Steel tubular structures are popular in ocean and offshore structures, buildings, bridges, space frames, mining equipment, recreation structures and transportation vehicles. A tubular joint has a critical role in maintaining the integrity of a steel tubular structure under operational and extreme loading conditions. This paper reports the first experimental investigation on the out-of-plane bending (OPB) strength and stiffness of steel tubular T-joints under fire conditions. The tubular specimens were tested to failure under OPB at ambient temperature and under ISO-834 standard fire. The moment rotation response, critical temperature, fire endurance time, structural strength and flexibility of the T-joint specimens were explored. The failure mode of the specimens was noticed to change from "development of a plastic hinge in the brace" at ambient temperature to "the chord face plastification" under fire conditions. Temperature adjustments were made to available parametric equations, basically proposed for the OPB capacity and stiffness of steel tubular joints at ambient temperature. The temperaturemodified OPB capacity equations somewhat under-predicted the test results for OPB strength under fire conditions. The temperature-modified OPB stiffness equations showed satisfactory correlation with the test results under fire conditions.