Moment curvature relationship of reinforced concrete sections under combined bending and normal force

Abstract

The modelling of tension stiffening effects is important for the verification of serviceability limit states of reinforced or prestressed concrete structures or even for the computation of the stability limit state of particular classes of slender concrete structures (bridge piles, towers, masts, etc.). The case of pure bending has received extensive analytical and experimental consideration, but little attention has been paid, up to now, to the case of combined bending and normal force. A series of tests on rectangular reinforced concrete beams submitted to bending and constant compressive normal force is reported in this paper. The moment-curvature relationships are evaluated and compared with the prediction of two theoretical models. The first model is the CEB model proposed by Favre and Koprna. It is a simplified model which refers to the uncracked and fully cracked stiffnesses in pure bending only. The second model is a proposition made by the authors which takes into account the tension stiffening effects, the variation in position of the neutral axis as a function of the eccentricity of the normal force, and the non-linear behaviour of concrete in compression.