THE EFFECT OF TENSION STIFFENING ON THE BEHAVIOUR OF R/C BEAMS

Tension stiffening, is attributed to the fact that concrete does not crack suddenly and completely but undergoes progressive microcracking(strain softening). Immediately after first cracking, the intact concrete between adjucent primary cracks carries considerable tensile force due to the bond between the steel and the concrete. The bending stiffness of the member is considerably greater than that based on a fully cracked section, where concrete in tension is assumed to carry zero stress. This tension stiffening effect may be significant in the service load performance of beams and slabs. This phenomenon is also effective in long- term behaviour of concrete members due to the creep and shrinkage of the concrete. Various methods have been proposed to account for tension stiffening in the analysis of concrete structures. An approach for modelling tension stiffening is to assume that an area of concrete located at the tensile steel level is effective in providing stiffening. In this paper a simple formulation is proposed for study of short-term and long-term behaviour of reinforced concrete beams and one-way slabs considering tension stiffening effect. The proposed formula is validated with experimental results and some numerical examples are worked out.