Preliminary comparison between different software modeling of confined concrete

The aim of the work is, on the one hand, the presentation of a theoretical fiber model able to predict the moment-curvature behaviour of confined RC columns and, on the other hand, the comparison between the moment-curvature provided by common structural programs. The theoretical fiber model presented in the paper is implemented in a visual basic software and it is able provide moment-curvature (M-χ) diagrams for sections with or without axial load. The software considered in this work are Sap2000, Seismostruct and Opensees. The moment-curvature curves provided by these softwares, given the same modeling have been compared to those provided by the theoretical fiber model. In particular, the modeling has been carried out by subdividing the sections in three category of fibers: unconfined concrete fibers, confined concrete fibers and rebar fibers. The constitutive model adopted for concrete is the one proposed by Mander et al. (1988) [1] for both the confined and unconfined concrete. The constitutive model adopted for the steel rebars is an elastic perfectly plastic law. The parametric analysis has been led on rectangular column sections with different level of axial load. The accuracy of the modelling of the considered structural programs has been investigated by comparing the results belonging to them with those obtained by applying the theoretical fiber model. Besides the calculation of the moment-curvature it is possible to observe that the curves representative of SAP2000 are more in accord with the curve representative of the theoretical software, on average. Form the Seismostruct side, it is possible to observe that the resistance is well captured by the software but for increasing levels of the axial load the Seismostruct overestimate the resistance. Results become more different from the theoretical model when the axial load level increases.