Influence of strain rate on the seismic response of RC structures

At the strain rate levels induced by seismic excitations, dynamic properties of concrete and reinforcing steel exhibit non-negligible increases if compared with the values exhibited under quasi-static properties. This is expected to change the mechanical behavior of structural systems, under seismic loading conditions. The work here presented aims to appreciate the influence of strain rate sensitivity of concrete and reinforcing steel on the global seismic response of reinforced concrete (RC) structures. In order to assess the influence of the strain-rate, first (a) the modified material properties are used to derive moment–curvature relationships of a generic RC cross section, then (b) the seismic fragility of a 2D RC frame structure is derived accounting for seismic strain rate modified material properties, and (c) the seismic assessment of a real 3D RC frame structure at the significant damage (SD) limit state is conducted in both cases of quasi-static material properties and strain rate modified material properties. The results shows that considering updated material properties, to account for earthquake induced strain rate, a strength reserve of the structural system is experienced when only ductile failure mechanisms are accounted for; on the other hand, a reduction of the structural capacity is obtained when brittle failure mechanisms are included.