Displacement-based seismic design procedure for framed buildings with dissipative braces - Part I: Theoretical formulation

The insertion of steel braces equipped with dissipative devices proves to be very effective in order to enhance the performance of a framed building under horizontal seismic loads. Multi-level design criteria were proposed according to the Performance-Based Design, in order to get, for a specific level of the seismic intensity, a designated performance objective of the building (e.g., an assigned damage level of either the framed structure or non-structural elements). In this paper a design procedure aiming to proportion braces with hysteretic dampers in order to attain, for a specific level of the seismic intensity, a designated performance level of the building is proposed. Exactly, a proportional stiffness criterion, which assumes the elastic lateral storey-stiffness due to the braces proportional to that of the unbraced frame, is combined with the Direct Displacement-Based Design, in which the design starts from target deformations. A computer code has been prepared for the nonlinear static and dynamic analyses, using a step-by-step procedure. Frame members and hysteretic dampers are idealized by bilinear models.