Overstrength factors for the strategic use of austenitic stainless steel in eccentrically braced frames

Abstract

Among many other characteristics, stainless steel has been shown to have higher level of ductility and considerable strain hardening. These properties are very attractive for seismic structural designers. Considering these features, the interest to use stainless steel for dissipative zones of frames located in seismic areas has gained attraction in recent years. Experimental tests show that strain hardening in austenitic stainless steel EN 1.4307 increases when loads are applied in cycles for different strain ranges. For particular strain levels, strain hardening can be up to 50% higher to those measured in a monotonic test. This paper shows the effect of these seemingly beneficial increment of strain hardening on the overall behaviour of seismic-resistant structures. In particular, Eccentrically Braced Frames (EBF) are chosen as exemplary cases. Both advantages and disadvantages of the use of stainless steel in dissipative zones of EBF are pointed out. In particular, this paper presents an analysis of the effect of strain hardening of links on the overstrength parameters, which are crucial for design. Different structural types as well as different link characteristics are studied numerically with geometrically hybrid beam-shell simulations with previously validated material models.