Seismic performances and behaviour factor of wide-beam and deep-beam RC frames

Reinforced Concrete Wide-Beam Frames (WBF) are a common architectural solution in Mediterranean countries. On this structural typology there is not yet a uniform approach among European codes: while Eurocode 8, as other relevant seismic codes in USA and New Zealand, considers WBF capable of high ductility performances, still in recent versions of Spanish and Italian seismic codes there is cap to the maximum behaviour factor (q) for this structural system. In order to verify the appropriateness of such provisions, seismic performances of WBF and conventional deep beam frames (DBF) are comparatively assessed through nonlinear static analyses. The same architectural layout of a typical European 5-storey RC housing unit is designed as WBF and DBF according to Eurocode 8, adopting different stiffness assumptions, and according to the Spanish seismic code NCSE-02. Based on detailed assessment results, a simplified parametric assessment of 72 frames designed according to Eurocode 8, Italian seismic code NTC and NCSE-02 is then considered assuming similar q for WBF and DBF. Results suggest that any reduction of behaviour factor prescribed for wide-beam frames is at least obsolete. In fact, even if wide beams show lower local ductility than deep beams, generally WBF provide at least similar global seismic capacities than DBF, especially in frames whose design is ruled by serviceability limit state (i.e., damage limitation).