Seismic capacity of steel frames braced with cross-concentric rectangular plates: Non-linear analyses

The use of cross-concentric braced steel frames is still an effective way to realize earthquake-resistant buildings, thanks to the simplicity in the design and realization, assuring good strength, stiffness and ductility, provided that capacity design be fulfilled. Results from non-linear static and dynamic analyses of steel frames braced with cross-concentric rectangular plates are presented to discuss some significant design aspects that play a key-role in the definition of the hysteretic dissipative response of such structures. Parametric cyclic analyses were performed to assess the peak- and post-buckling lateral strength and the dissipative capacity of a small- and a full-scale frame, varying the non-dimensional slenderness of the bracing plates. Then, results of incremental dynamic analyses of a one-, three-, six- and ten-storey building are discussed to evaluate the behaviour factor for this structural typology, as function of inter-storey drift. Results from the parametric and incremental analyses give the optimal range of non-dimensional slenderness of the bracing plates as a compromise between limited overstrength and good dissipative capacity and confirm the behaviour factor currently provided by Eurocode, relating it with an expected inter-storey lateral drift.