Progressive collapse of concrete structures during construction phase: analysis and measures for risk reduction

Shoring systems are used as temporary support for structures under construction and their primary function is to support and transmit various types of loads. To optimize this phase it has been developed a technique known as Clearing or partial Striking; it consists in removing a percentage of shores few days after the casting such that the load is redistributed between the slab and the remaining shores. In this way the shores removed in one floor can be used to start building the upper one. It is thus really important to conceive the process in a proper way assuring that the whole system is able to support the loads acting on it. This is the reason for which there is a prudent need to understand which conditions lead to the collapse of shoring systems and what measures can impounded in the design process to mitigate the risk of failure. The aim of this thesis is to perform a progressive collapse analysis, during the construction phase of the building, by instantly removing one or several primary load bearing elements and analyzing the structure’s remaining capability to absorb the damage. The analysis have been performed varying load conditions and slab thicknesses and, once the results from standard shores cases have been obtained, calculations with load limiters have been performed. The entire study has been developed with finite elements by means of ANSYS APDL starting from a FE model developed by Alvarado (2010). The important aspect of this investigation has been the risk reduction of progressive collapse, in particular it has been analyzed the behavior performed by the structure when enhanced support systems are used. Along with the finite element study it has been taken part in a experimental study aimed at analyze the load transmission in enhanced shoring system.