SEISMIC PERFORMANCE OF HIGH-RISE STEEL MRFS WITH OUTRIGGER AND BELT TRUSSES THROUGH NONLINEAR DYNAMIC FE SIMULATIONS

Abstract eng:
The work reported herein summarizes the results of a series of nonlinear dynamic FE analyses devoted to assess the main criticalities in the seismic response of high-rise steel MRFs with outrigger and belt trusses. Thirty- and sixty-storey planar frames, extracted from reference three-dimensional structures composed of an internal one-way braced core, are designed in accordance with European rules. The core consists of a CBF system, while outriggers are placed every fifteen stories to limit inter-storey drifts and second order effects. FE models able to account for material and geometric nonlinearities have been developed within an open source FE code, using inelastic force-based fiber elements to model structural members and equivalent nonlinear links to reproduce the behaviour of bolted beam-column joints and welded gusset-plate connections. Out-of-plane imperfections are explicitly included in the braces to allow for potential buckling mechanisms in both braces and gusset plates. NLTHAs have been performed, in comparison with response spectrum analysis, aiming to quantify the potential of such systems, when included in the lateral-force resisting system of modern highrise steel MRFs. Global and local performance have been investigated in terms of inter-storey drift and acceleration peak profiles and axial force-displacement curves and static-to-seismic load ratios in critical braces at different floor levels. Sensitivity to the structure height has been explored by comparing the response of the two prototype MRFs. Trends are discussed to show that, if accurately designed and detailed, these structural systems provide an optimum combination of stiffness and strength.

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