This paper proposes a method to calculate the torsional stiffness of reinforced concrete beams with section of any shape, in a cracked state due to bending, subjected to small torque (shape stability problems). The simultaneous influence of the various parameters (shape of the section, state of cracking, longitudinal reinforcement) is taken into account. A series of laboratory tests on beams with hollow, massive, or double-tee thin cross sections gives data to determine semi-empirically some parameters. Calculated and experimental stiffnesses are in rather good agreement. The proposed method fills in a gap in the nonlinear calculation of reinforced concrete. Key words: reinforced concrete, flexural cracking, torsional stiffness, calculation method, nonlinear elasticity, stability.

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This contribution is addressing the investigation on the effect of axial tension on the shear strength of reinforced concrete beam elements without stirrups.The paper presents the results of a test program of 15 beams without stirrups that differed from each other mainly by the intensity of the axial tensile force N. During the tests, cracking was measured by Digital Image Correlation technique to identify the crack evolution mechanisms. After some consideration on the resisting mechanisms, the experimental results are compared with several code formulas to predict the shear strength V Rc . Then an empirical formula is proposed for the variation of V Rc between its two limits: the values for N = 0 and for V Rc = 0 at the ultimate limit state of axial tension. This formula makes it possible to easily design for shear and tension.