Connections of Roof-Diaphragm to Perimeter Walls in Historic Masonry Buildings

Traditional seismic retrofit of historical masonry buildings is mainly aimed at inhibiting local mechanisms and at engaging the whole building into a box-like structural behavior through either perimeter ties, or floor and roof diaphragms. When the adoption of “minimally impairing” perimeter ties is unviable, floor and roof diaphragms are usually adopted. The effectiveness of such interventions requires careful design and detailing of their connections to the perimeter walls, which enable shear flow transfer from the out-of-plane loaded masonry walls to the diaphragms and from the diaphragms to the seismic resistant walls. Focus is made on the assessment of the structural performance of the connections of roof diaphragms to the perimeter walls. Stud connectors are investigated and a possible technical solution improving the connection capacity is presented. In the case of historic masonries, theoretical and numerical prediction of the connection capacity may be unviable because of the substantial heterogeneity of the masonry at local level. Accordingly, experimental in-situ tests may be the only viable solution to assess the connection capacity, thereby providing evidence of the feasibility of the intervention and providing useful reference design values to be used by design professionals. A specific experimental test is presented for the in-field measurement of the connection capacity, and experimental results are critically illustrated. A purpose designed testing frame is proposed, which allows mimicking the actual load and restrain conditions of the connections in a real application.