Application of Headed Bars in Precast Concrete Wet Joints Under Accidental Loads: Experimental and Numerical Investigations

This study presents experimental and numerical investigations on behaviour of interior precast concrete (PC) joints under progressive collapse. Two types of joints, namely Type H and Type A, were studied, with Type H with a narrow wet connection utilising headed bars instead of hooked bars and Type A with a wide wet connection incorporating an additional headed bar layer (ABL) in the beam-joint region. The experimental results revealed that interior PC joints exhibited effective resistance against progressive collapse, characterised by four distinct stages: flexural, compressive arch action, transition, and catenary action stages. The usage of headed bars effectively prevented premature pull-out failure compared to conventional joints with hooked bars. Furthermore, including ABL in Type A joint yielded significant improvements in progressive collapse resistance and enhanced the integrity of the wet connections. It effectively prevented zero-applied load occurrence during the transition stage, as observed in Type H joint. A component-based joint model was developed and validated against the experimental results with satisfactory accuracy. Parametric studies using the validated model revealed positive impacts of horizontal restraint and the ABL ratio on enhancing the collapse resistance of PC joints. Designing PC structures with the strong-column-weak-beam concept and a proper balance between column and beam stiffness is recommended. These measures help facilitate the desired load transfer mechanisms and mitigate the risk of progressive collapse in PC joints.