Solution for bond distribution in asymmetric R.C. structural members

Abstract

The bond problem regarding bottom reinforcing longitudinal continuous bars or anchorages or lapped splices of RC beams is analyzed. This is an asymmetric problem both for the geometry and the mechanics. The geometrical asymmetry is due to the difference in the extension of the concrete areas surrounding the bars: the concrete area below the horizontal plane crossing the bars’ axes, and the concrete area over this plane up to the plane connecting the tips of the cracks. The mechanical asymmetry is due to the loading asymmetry with respect both to the above mentioned horizontal plane and to the vertical plane crossing the beam at the midspan of two consecutive cracks. Whenever a moment gradient exists, the equilibrium of the beam bottom portion bounded by two consecutive transversal cracks needs that the horizontal components of shear stress, acting on the plane connecting the tips of the cracks, balance the forces gradient acting along the bar. However, these components of shear stress have never been considered until now. The analytical solution to bond problems under asymmetrical conditions is worked out. Long and short anchorages are considered. Comparisons between 132 experimental results and values calculated by means of the proposed asymmetrical solution and an available symmetrical one are performed. The proposed solution provides more accurate and consistent predictions than the symmetrical unreliable one, and it is useful for studying serviceability behavior of reinforced concrete members.