Post fire tensile behavior of thread-fixed one-side bolt strengthened by backing plate

Abstract

The post fire tensile behavior of Backing Plates (BP) strengthened Thread-fixed One-side Bolt (TOB) was studied. The full-time test method, which included the before-fire stage, firing stage and the post fire stage, was applied in the test to simulate the real fire process. Two fire temperature (500℃ and 700℃), and two load ratios (0.25 and 0.5) were tested to study the influence of fire condition to the post fire tensile behavior of TOB connected T-stub connection. The T-stubs might fail directly at firing stage at high temperature and high load ratio circumstance. The failure mode of the T-stubs also might be changed with the increase of load ratio and temperature. The post fire tensile performance of the TOB connected T-stub could be significantly increased by the BP. The residual yielding load of the T-stub strengthened by BP with 6 mm flange thickness could reach 333% to 377% to that of the un-strengthened ones with same flange thickness, and the residual ultimate load could reach 257% to 292%, depending on the fire temperature and the load ratio. T-stubs connected by Standard High Strength Bolt (SHSB) were also tested at same conditions to calibrate the behavior of TOB. Results showed that the BP strengthened TOB connections could achieve similar post fire performance compared to the SHSB connections with flange thickness. The BP strengthened TOB connections could regain at least 88.4% of their yielding load and 88.3% of their ultimate load at ambient temperature after cooling from fire, and the residual ultimate resistance could still satisfy the design requirement, which showed the good post fire performance of TOB.