Progressive Collapse Retrofit of a RC Hospital Building Using Steel Braces

The progressive collapse retrofit of a RC hospital building making use of steel braces is described in the paper. The vulnerability of the construction when subjected to specific threat scenarios is preliminary analysed by removing critical column and applying the alternate load path method to evaluate the capability of the damaged structure to bridge across the removed column. A detailed three-dimensional model of the building has been created to carry out both nonlinear static and nonlinear dynamic analyses. Both geometrical and material nonlinearities have been considered in the analysis in order to account for the inelastic behaviour following the sudden column removal and the possible subsequent catenary effects. In order to retrofit the building against progressive collapse the use of steel braces in some bays has been proposed, designed on the basis on simple equilibrium conditions under vertical loads. The retrofitting bracing system proved to be effective in improving the global building behaviour under several accidental scenarios.