Many of the existing tension stress–strain relations for concrete used in smeared shear models consider the contribution of concrete in tension even after steel yielding. Although the contribution of concrete in tension is less significant than its contribution in compression, the use of these existing models often leads to overestimating the shear response of reinforced concrete (RC) panels. An improved concrete tension stiffening model incorporating the effect of biaxial stresses is proposed in this study. The effect of tension stiffening on the behaviour of shear panels under normal and shear stresses is investigated by incorporating tension stiffening in the softened membrane model (SMM). The existing SMM algorithm can be used to estimate the behaviour of RC panels subjected only to pure shear. In the proposed analysis using SMM, a new secant-based algorithm is used to estimate the behaviour of RC panels under combined normal and shear loads. Estimates from the proposed model are compared with estimates from original SMM and experimental results. The comparison shows that the proposed model provides better estimates of shear response for RC panels that undergo high shear strains than the original SMM. Furthermore, the proposed secant-based algorithm estimates panel behaviour under combined loading in reduced computational time. © 2022 Elsevier Ltd