New regulations for hollow core slabs after premature partial collapse

In October 2007, a floor made up of pre-cast prestressed hollow core floor elements suffered early partial collapse during a fire in a carpark of a moderately high new building in Rotterdam, predominantly in use for housing and for limited enterprise. The damage pattern revealed horizontal cracks through the webs of the hollow core slabs, causing collapse of the underflanges which contain the prestressing strands. As a consequence, the structural integrity of the floor and the entire building was jeopardized. In 2007, the municipal authorities of Rotterdam commissioned Efectis Nederland to investigate the damage that occurred during the fire. The results of the study strongly recommended further investigation and addressing the observed damage pattern in the assessment and design rules for hollow core slabs. Based on this conclusion, TNO was commissioned in 2008 by BFBN (Dutch precast industry) to further investigate the incident and whether or not this early partial collapse concerns an omission in the current regulations. TNO concluded that the structure did meet the requirements stated by the authorities, the fire development did not significantly deviate from the standard fire curve, the damage pattern has been observed more often, and the fire resistance of hollow core slabs in fire tests is often lower than the expected fire resistance based on current regulations. Therefore, TNO concluded that the current regulations contain an omission. Therefore, additional detailing and design rules for hollow core slabs were advised by BFBN, which are partially based on new rules for hollow core slabs developed by CEN. This paper addresses the research commissioned by the municipal authorities of Rotterdam, the research commissioned by BFBN and the additional rules advised by BFBN. This includes the fire development and damage to the hollow core slabs in the carpark in Rotterdam, the relevant collapse mechanisms for hollow core slabs in case of fire, their relative importance and respective uncertainties, and the measures taken in the new rules.