Dissipative cross lam roof structure for seismic restoration of historical churches

In order to improve the nave transversal response of historical churches, a strategy basing on wooden roof strengthening aimed to obtain the global “box” building's behaviour should be pursued. For this strategy the wooden roof has to work as a dissipative diaphragm able to contain the out-of plane lateral walls mechanisms by allowing controlled rocking of the walls. Therefore, the roof has to reduce the in-plane shear transferred to the resistant transversal frames (or walls) by the dissipative behaviour of the steel connections. In this paper, the improvements due to the cross lam roof structure in the transversal nave response are pointed out with respect to several different solutions in terms of conservative restoration criteria. Moreover, the effects of the controlled lateral walls rocking obtained by cross lam panels are investigated for representative church configurations. The effects of the cross lam roof-diaphragm in terms of controlled rocking are shown by performing nonlinear analyses on equivalent finite element models simulating the nave transversal response. Once evaluated the target seismic performance of the church, in terms of maximum drift allowed by the masonry walls, the in-plane shear acting on the cross lam panels are evaluated too.