Shear strain in -regions of beams in service

The effect of shear deformation is not negligible in particular for r.c. beams with thin webs and low span-to-depth ratios. In order to calculate the contribution of shear on the deflection of a r.c. beam, a theoretical model, called the mixed model, was carried out which considers the web as a smeared model subjected to tensile and compressive principal stresses and its interaction with the tensile and compressed chords. The principal direction of compressive stresses acting on the web is calculated as a function of the acting load effects and assuming, as far as the mean strains are concerned, that the sections remain plane. The constitutive laws of the cracked web are obtained from the Modified Compressive Field Theory proposed by Collins, and are supported by an experimental campaign conducted on 24 zones of 6 r.c. beams with thin webs. The difficulties in the calculations, due to the necessity of performing two iterative procedures to obtain the solution, led the authors to prepare a simplified model. In the paper the simplified model is performed and the results are compared with that obtained with the mixed method and the experimental data.