Fire behavior of novel Thread-anchored One-side bolted connection with internal component

Abstract

Anchorage of the novel Thread-anchored One-side Bolt (TOB) is provided by the threads inside the bolt hole and the TOB could be installed from one side only, which provides an alternative way to install the connection of the Square Hollow Section (SHS) column. But the TOB might be pulled out from the threaded bolt hole when the SHS column wall is deformed, especially in fire conditions. The strengthening component could be installed inside the SHS column to restrict the deformation of the column wall and increase the depth of the threaded bolt hole. The tensile behavior of the TOB bolted SHS column connection and the influence of the internal strengthening component on the connection at fire scenario were studied and compared with Standard High-strength Bolted (SHB) connections by experimental method. Both steady-state fire test method and transient-state fire test method were used in the test. The TOB bolted SHS column connection had two typical failure modes, which were the yielding of the column wall (mode 1) and the yielding of the T-stub flange accompanied with the bolt failure (mode2), depending on the thickness of column wall. The internal strengthening component could change the failure mode from mode 1 to mode 2 and enhance the fire behavior of the SHS column connection when the thickness of the column wall was small. In the steady-state test, the resistance of the connection decreased obviously with the increase of the fire temperature. In transient-state test, the ductility and the failure temperature decreased obviously with the increase in load ratio. The internal component is an effective way to improve the fire behavior of the TOB bolted SHS column connection. The strengthened TOB bolted SHS column connection could replace SHB bolted connection with the same SHS column wall thickness under the same circumstance. Equations to calculate the yielding resistance of the TOB bolted SHS column connections at different temperatures were given. Comparison with test results showed the proposed equations could predict the failure mode of the TOB bolted connections precisely and predict the yielding load of the connections with acceptable accuracy.