Comparison between refined and simplified models about the mean curvature of r.c. beams in service conditions

For the serviceability of r.c. structures the international standards require the verification of the deflections. A general method is based on the integration of the mean curvatures along the beam. To this end the determination of the moment-mean curvature relationship is necessary. This relationship can be obtained by a refined method that takes into account the various involved phenomena and their interaction. The calculation of stresses and strains in the section is carried out in time considering the variation of the stresses due to creep and shrinkage for uncracked and cracked elements. For cracked elements any superposition of effects is not valid because of the cracking of the section. This makes the calculation more complex. As an alternative, the international standards (Model Code 1990, Eurocode 2, ACI 435) propose simplified formulations with the purpose to reduce the difficulties of calculation. In this context the present paper analyses the basic assumptions and the critical aspects of the simplified models. The results of the refined and simplified models are here compared considering the presence of bending with or without axial force for short-term and sustained loading