Interaction of multi-sloping timber roofs braced through sheathing panels with masonry walls in historical industrial buildings subjected to lateral loads.

The paper deals with the reduction of the seismic vulnerability of historical industrial buildings with traditional multi-sloping timber roofs laid on masonry walls along the perimeter and, internally, on wooden studs supports. These structures performed low resistance to lateral loads, behaving as a series of independent frames, which are not able to effectively distribute the actions among the lateral-resisting elements. An effective strengthening intervention has to provide, first of all, an in-plane stiffening of the timber roof; furthermore, it is necessary to adequately connect this diaphragm with the masonry, so that the roof be able to constrain the out-of-plane deformation of the longitudinal walls and to transfer the lateral loads to the seismic-resistant vertical elements. The stiffening of the roof by means of wooden based panels nailed to the main frame and the connection of the roof to the masonry walls by means of mechanical joints are discussed in the paper. Detailed and simplified numerical modeling strategies, aimed to investigate on these technique, by means of non-linear static analysis, are described and compared. The detailed modelling is based on elastic mono-dimensional and bi-dimensional elements, representing the timber and masonry components. The nonlinear behavior of the structure is lumped in correspondence of the connections between the wooden-based sheets and the main frame of the timber roof and between the roof and the masonry walls. They are schematized through non-linear springs, whose behavior is derived analytically or from experimental results available in literature. The detailed modelling results permitted to calibrate the simplified modelling strategy, based on equivalent diagonal springs arranged between adjacent rafters of the roof. A few case studies are presented; the effectiveness of the intervention is evaluated, at the varying of the different parameters concerning both the bracing system and the roof connection with the masonry structure, providing useful design indications.