In this paper, the ultimate limit state resistance of RC sections subjected to axial force and uniaxial bending moment is evaluated, both by means of non linear analyses, which take into account the effect of the confining reinforcement and the degradation of the concrete in the post-elastic range, and according to the Italian code, i.e. considering a stress-strain curve for the concrete with an ultimate compressive strain of 3,5‰ and a design value of compressive strength equal to the characteristic value reduced by means of two factors: the partial safety factor and a coefficient taking account of long term effects and of unfavourable effects resulting from the way the load is applied.
The partial factor values adopted for the fundamental combination (gc = 1,6 for concrete and gs = 1,15 for steel) must be applied also for the seismic design so as to take into account the possible strength degradation of the materials due to the cyclic deformations. The adoption of these values and of the factor for long term effects, equal to 0,85, affects the evaluation of the bending resistance and, consequently, the cross section design. To evaluate the influence of these factors on the resistances, the latter are also calculated varying the design value of the concrete compressive strength.
A comparison between the resistances computed in the aforementioned ways is performed, evaluating also the influence of different parameters, such as the cross sectional dimension, the ratio between bending moment and axial force, the amount of longitudinal and transversal reinforcement.
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