Experimental study on circular hollow section (CHS) tubular K-joints at elevated temperature

•Experimental tests on two tubular K-joints at elevated temperature are conducted.•Temperature and displacement development for the K-joint specimens are measured.•A deforming rate definition on critical temperature for tubular K-joints is proposed.•Failure process of the K-joint specimens at elevated temperature is analyzed.

This paper is mainly focused on studying fire resistance and failure mode of circular hollow section (CHS) tubular K-joints at elevated temperature under brace axial loading at brace ends. Experimental tests on two full-scale CHS tubular K-joints to investigate the behavior of the specimens at elevated temperature are carried out. A predefined compressive loading is applied at the end of one brace and the other brace end is fixed during the heating procedure until the failure of the specimen occurs. The temperature on the tube surface and the displacement at some critical positions such as crown, saddle and the brace end are measured. Experimental results indicate that the failure of CHS K-joints occurs suddenly when the temperature on the specimens exceeds a critical value. The temperature development at different measurement points on the chord surface is almost same. Comparatively, the temperatures at different time on the brace surface are always higher than the corresponding temperatures on the chord surface. Generally, the failure process can be divided into three distinct stages due to different deforming mechanisms. It can also be observed that the final failure modes of both the K-joint specimens are characterized by local plastic yielding.