Experimental qualification of replaceable bolted links in dual eccentrically braced frames

The performance of structures under severe seismic action is ensured by properly calibrated ductility, stiffness, and strength. The “plastic” members of ductile mild carbon steel (S235 to S355) dissipate the seismic energy, acting as “structural fuses”, while the “elastic” members must be provided with adequate overstrength, to have the capacity to carry the stresses corresponding to yielded and strain hardened plastic hinges. High strength steels, such as S460 to S690, might be used for these elastic members, providing them with the necessary overstrength, without enhancing the stiffness, as that could unbalance the structural system. Dual structural systems, as moment resisting frames (MRFs) combined with eccentrically braced frames (EBFs), can be equipped with replaceable mild carbon steel dissipative links acting as seismic fuses. The MRFs, possibly fabricated from high strength steel, remain elastic, being able to recover the initial position. The key problem in such systems is the design and calibration of the fuses, i.e. the replaceable bolted links, which should be carefully qualified by tests. The present paper reviews past research on bolted replaceable links and discusses the experimental qualification requirements.