Equivalent damping ratio evaluation for historical church reinforced by cross lam roof structure for improving the seismic response

The paper is focused on the evaluation of the Equivalent Damping Ratio (EDR) obtained by different cross lam roof structures for an historical church for improving the seismic response. The church has one nave configuration, masonry walls and original wooden roof-structures. The seismic response of this kind of construction is afflicted by the nave transversal response, therefore structural improvements inspired to the global box behavior must be pursued for avoiding the out-of-plane mechanisms of the perimetral walls. The dissipative roof-diaphragm able to contain the lateral displacements and to permit a controlled rocking is studied by choosing pithed panel cross lam timber (CLT) panels. The wooden based solutions permit to use materials compatible to the original ones as requested by Cultural Heritage Office. By this way the dissipative effect due to the CLT roof structure must be calibrated by a careful choice of the steel connections, in terms of stiffness and strength. The optimization of connections dissipative effects is here carried out by the estimation of EDR with three methods: FEMA 440, ATC-40 and time histories (TH). Each method is applied to equivalent finite elements models in which the nonlinear properties of the masonry walls and wooden roof with steel connections are considered by inelastic rotational springs (for the walls) and inelastic shear springs (for the roof). A comparison of the EDR values is shown and discussed.