This study presents a theory of Ultimate limit state of shear failure, is based on several previous studies, particularly in communications presented to the JPEE LNEC organized in November 1982. Through the study on cracking, it was possible to conclude that all embedded steel in the concrete leads to a variation of the parcel associated with the concrete resistance according to REBAP , Vcd, which is not constant in reinforced elements, this value is inversely proportional with the amount of reinforcement. This assumption as well as the possibility of variation of the inclination of the struts and the proof of the existence of a concrete riser by assuming the compatibility of the deformations in a beam allowed to develop the theory outlined here.
In order to try to resolve this problem REBAP proposes a modified theory MĂ¶rsh through a variable Vcd . The Eurocode proposes a structural model quite different based on strut and tie model in which neglects the influence of concrete strength in the global resistance.
In summary the theory exposed here is based on the possibility that the variable Vcd results of the existence of transversal ties that are mobilized by concrete or the compatibility of the vertical deflection of the diagonals of the truss of MĂ¶rsh, or by forming a arch model through the horizontal tie.
The recent study of failure allows easy interpretations of the empirical criteria adopted in the current regulations and imposed as a consequence of laboratory tests, despite the apparent theoretical contradictions that sometimes originate and provides identical results to those obtained experimentally. Respecting the usual criteria of safety, allows the complete use of the resistance of the concrete