Influence of axial tension on the shear strength of RC beams without stirrups

Abstract

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.

Influence of axial tension on the shear strength of transversally reinforced concrete beams

“…A general state of the art of the subject dealing with beams with or without stirrups was exposed in Pham et al 8 Among the numerous experimental references, the results for beams with stirrups subjected to tension are somewhat scarce. In this context, a few references will be retained.…”

“…The test setup and the loading path were the same as for beams without shear reinforcement presented in Pham et al 8 The specimens equipped with stirrups in this experimental campaign were subjected to a three-point bending loading with a maximum positive moment M + and a shear force V, and a "torque loading" that generated a uniform negative moment M − combined with an axial tension N and without shear force (Figure 1). A fully detailed description of the testing protocol, test setup and measurement devices may be found in Pham et al 8,18 F I G U R E 1 Test setup…”

“…Like beams without shear reinforcement presented in Pham et al, 8 two main cracking phases of specimens equipped with stirrups could also be defined. Figure 2 shows the first phase which corresponds to the appearance of the vertical cracks crossing the beam depth during the application of the tensile force N from 100 to 200 kN while Figure 3 shows the second phase which was related to the detection of the diagonal cracks when applying the vertical force F. These diagonal cracks were generally generated from the preexisting vertical cracks of the first phase and formed an angle (with respect to the beam axis) near the mid-height of the section.…”

“…Due to the aggregate interlocking across the cracks and to the dowel effect of the flexural bars (see Cavagnis et al, 19 Pham et al 8 ), the direction of the principal compression becomes less inclined than the cracks. This was first taken into account in a "concrete" resisting term V Rc , in addition to the truss term V Rs calculated with the angle θ assumed equal to that of the cracks.…”

“…On the contrary Walraven, 7 referring mainly to highly longitudinally reinforced members, reported that the shear strength is hardly reduced by tension. It shows that the amount of longitudinal reinforcements is the major parameter; a study previously presented (Pham et al 8 ) concluded more precisely that the capacity to develop the shear strength V Rc is tightly related to an overconservative design of the reinforcement with respect to bending and axial tension. The other important problem is the shear strength provided by the transverse reinforcement V Rs for beams with stirrups.…”