Blast and Impact Loading and Response of Structures
Full Session with Abstracts
Testing of multi-panel flat-plate structures has indicated that the post-punching load-carrying capacity of slab-column connections plays an critical role in preventing progressive collapse of flat-plate buildings subjected to abnormal loading events such as the loss of a supporting column. The post-punching strength of slab-column connections following the current design practice depends predominantly on the slab bottom bars continuous through the columns functioning as structural integrity reinforcement. One approach for improving the post-punching strength of slab-column connections, and thus the progressive collapse resistance of flat-plates, is engaging the slab top reinforcement at the columns in providing additional post-punching load resistance. To explore this approach and identify the residual punching strength of slab-column connections that have previously suffered high temperature induced by uncontrolled fires, experiments were carried out on six 2/3-scale isolated slab-column specimens. The test variables included slab tensile reinforcement ratio, amount of cross ties that hooking slab top and bottom bars together, and the maximum temperature applied at the compressive side of slab surface. The slab tensile reinforcement ratios were 0.6% and 1.2%. The number of cross ties deployed outside punching core ranged from one to three at each side of the column. The high temperature up to 800 Celsius was applied by ceramic heating panels covering the potential punching regions of the slab. Each slab was subjected to concentric gravity loading applied beyond the initial punching failure and until an obvious strength degradation during the post-punching stage. The experiments indicated that the high temperature caused negligible effects on the two-way shear strength of slab-column connections. Moreover, the use of cross ties promoted the participation of slab tensile bars in carrying gravity loads after punching failure; it was found that using three cross ties would enable the slab-column connection to obtain a post-punching strength comparable to the punching resistance and maintain this capacity up to a large slab deformation.