Stiffness requirements for floor diaphragms of in-plane regular buildings

This work presents a preliminary theoretical study dealing with the in-plane flexural stiffness of diaphragms in plan-regular structures. To this scope, a simplified mechanical model is adopted to evaluate the diaphragm stiffness, accounting for the geometrical configuration and mechanical properties of its components and highlighting the interaction between the in-plane diaphragm flexural stiffness and the lateral stiffness of vertical seismic resisting systems (MR-Frames, shear walls, etc.). In addition, the influence of the number of seismic resisting systems and the number of storeys on the infinitely rigid diaphragm assumption has been evaluated. To assess the accuracy of the proposed formulations, the theoretical predictions are compared with the results of numerical models developed using SAP2000. Finally, for typical structural configurations encountered in engineering practice, simplified relationships are provided to verify the rigid diaphragm assumption commonly adopted in the structural analysis of buildings in accordance with the deformability limits prescribed by Eurocode 8. The proposed methodology offers useful information both for the seismic design of new buildings and the assessment of existing structures.