CONNECTION FAILURE and a lack of temporary support triggered the collapse of a multistorey car park in Atlantic City, US, last November, investigators said last month.
'Reinforcing steel and welded wire mesh were not properly installed to allow floors to be secured to outer columns and the shear wall, ' said the official report published by the US Office of Safety & Health Administration (OSHA).
Four workers died when five floors of the Tropicana Casino car park collapsed during construction on 30 October last year (NCEI December).
Fines totalling $119,000 were imposed by OSHA on four contractors involved in the construction project. The highest - $70,000 - was made against concrete sub-contractor Fabi Construction The car park was part of a $230M project to build a new hotel wing.
Fabi Construction was conducting the final stage of the concrete pour of the 11th storey deck of the building when the accident occurred.
OSHA's report concluded that inadequate shear wall connection and the lack of sufficient temporary support for the floors left them unable to support their own weight.
As a result, failure of one of the intermediate floors caused the progressive collapse of the entire structure, said the report. The OSHA report does not reveal which floor failed first.
Each floor was formed by pouring a 150mm thick layer of concrete onto steel reinforcement resting on 70mm precast concrete slabs, which acted as permanent formwork.