Seismic strengthening of existing structures by means of fibre reinforced concrete floor diaphragms

The seismic vulnerability of existing masonry structures is often associated to the perimeter wall overturning. In order to enhance the seismic performance of masonry buildings, in-plane shear resistant floor and roof diaphragms, confining the wall toppling forces and transferring the seismic actions to the shear resisting walls, can be referenced as a viable and effective strengthening solution. The same technique can be as well applied in the seismic rehabilitation of existing R/C structures, where in-plane shear diaphragms must be coupled to the vertical seismic resistant structures (either shear walls or R/C retrofitted frames). Floor and pitch diaphragms obtained by overlaying very thin fiber reinforced concrete slabs are proposed and discussed in this paper. Aim of the proposed technique is to attain the required diaphragm stiffness and strength by minimizing the dead load increase and by simplifying the construction process. In this scenario, the adoption of steel fiber reinforced concrete slabs stems as an improving alternative to the ordinary concrete slab solution, provided that in the case of FRC the slab thickness can be reduced since the steel mesh can be replaced by the smeared reinforcing fibers and the minimum concrete cover is no longer required. Parametric nonlinear finite element analyses are carried out to verify the efficiency of the proposed technique