Ultimate chord rotation of rc columns with smooth bars: some considerations about EC8 prescriptions

Current code prescriptions allow to evaluate the ultimate rotational capacity from hybrid (mechanical-empirical) or empirical formulations, for reinforced concrete (RC) members with ribbed bars and seismically detailed. These formulations can be extended to non-conforming elements, including members with smooth bars, by means of correction coefficients calibrated on experimental data. These coefficients imply a reduction in the deformation capacity, which increases if lapping of longitudinal bars is present. The reliability of empirically calibrated coefficients directly depends on the extension of the experimental database, that is, on the number of available tests. The experimental campaign carried out at the University of Naples on 16 real-scale columns with smooth bars allows to extend the experimental database for this typology. Experimental results highlight that rotational capacity of columns with smooth bars is rather large, even higher than the capacity of similar columns reinforced with ribbed bars. This is basically due to the increase in deformability caused by the fixed-end rotation mechanism, particularly exalted when bond capacities are low. Therefore, also based on these results, new correction coefficients are proposed.