Chiara Passoni

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.

Prefabricated responsive diagrids for holistic renovation of existing mid-rise rc buildings

The holistic renovation of existing buildings is nowadays acknowledged as an essen- tial and urgent action to reduce the environmental impact and increase the resilience of the existing building stock. Such holistic interventions envision the adoption of an exoskeleton, en- tirely built from outside. In this paper, the exoskeleton is designed as an external diagrid, con- sisting in a lattice structure. Among possible structural typologies, diagrids are particularly interesting for their remarkable architectural potential and for the possible standardization of the components, which highly increases replicability of the retrofit solution. Furthermore, pre- fabrication of components speeds up the assembly process and reduces the construction time. In the paper, focus is made on the dynamic behaviour of a retrofitted building featuring a re- sponsive diagrid. The responsive behaviour is attained by changing boundary conditions at the diagrid’ s base supports as a function of the earthquake intensity, while the diagrid lattice struc- ture remains elastic. At the Operational Limit State, the diagrid is designed as hinged at the base, whereas at Life Safety Limit State, beyond a target base shear, hinges are conceived to downgrade into non-linear supports allowing for the controlled sliding of the diagrid’s base. Non-linear restraints limit the maximum base shear force, while avoiding excessive horizontal displacements and second order effects. Non-linear time history analyses are carried out to study the responsive behaviour of a reference 3 storey building strengthened with an external responsive diagrid. Results show that responsive diagrids require preliminary interventions at the existing building ground floor to reduce the damage following the onset of the diagrid slid- ing. Such interventions are for instance the disengagement of the infills from the RC frame and the local increase of the column ends ductility.