RECOMMENDATIONS FOR THE DESIGN OF CBFS TAILORED TO LOW-TO-MODERATE SEISMICITY

Abstract

The strict application of the high-seismicity code provisions for designing steel structures in the regions of low-to-moderate seismicity is leading to solutions that are on one hand rather difficult to implement and on the other hand often resulting in a significant increase of the building costs. As consequence, for economy reasons, it is often decided to design on the base of q=1,5 only (DCL design) and to neglect any further provisions aiming at enhancing the seismic performance, a practice which, from a safety point of view, cannot always lead to satisfactory structural solutions. EU-RFCS project MEAKADO studied design options that are optimised for the actual seismic action, providing the necessary safety level without imposing excessive requirements, and thus limiting the incremental complexity and costs associated with anti-seismic design. The research Meakado has chosen to focus essentially on concentrically braced frames (CBF) and moment resisting frames (MRF), as being the most common typologies in the European construction market, specifically in regions where earthquake action is not the parameter governing the design. This paper presents the findings related to the CBF systems, based on the exploitation of phenomena that are known to contribute to energy dissipation in steel structures subjected to earthquake, but whose knowledge is often considered as not sufficient to quantify them as sources of controlled energy dissipation in the definition of the q-factors. Main focus is given to slip in bolted connections, plastic ovalization of bolt holes, post-buckling strength of diagonals in compression, and moment resisting contribution in concentrically braced frames.