TENSION STIFFENING IN REINFORCED CONCRETE BEAMS AND SLABS UNDER SHORT-TERM LOAD

Abstract

The trend in the recent past for economy in the use of materials has led to a requirement for long spans of minimum depth, with the consequence that deflections are now ofter the governing design criterion. In a cracked member, the contribution to the stiffness made by the concrete between the cracks in the tension zone has long been recognized, and various empirical approaches have been incorporated in design recommendations to allow for this effect. The tests described in this report were designed to provide information on the tension stiffening phenomenon. Fourteen beams with various depths and steel areas and nine slabs with various steel areas and bar arrangements were tested. It is concluded that the tension stiffening can be calculated on the basis of an average tensile stress equal to a fraction of the tensile strength of the concrete acting over an effective area of concrete surrounding the bars in the tension zone. Recommendations are made for the value of the average tensile stress and the effective areas appropriate to beams and slabs. /Author/