Lateral Strain Model for Concrete under Compression

The relationship between the lateral and axial strain is important when predicting the confinement stresses within reinforced concrete or fiber-reinforced polymer confined columns. Difficulties in measuring reliable lateral strains in triaxial compressive experiments mean that there is a scarcity of lateral strain experimental results. Two recent lateral strain models will be compared with available experimental results. Discussed in this paper is the transition point in the lateral and axial strain relationship at which the volumetric strain changes sign, and how this transition point is related to the peak stress. A lateral strain-versus-axial strain model is proposed based on the supposition that the concrete behaves linear elastically in the early stages of loading. Once microcracks form, nonlinear hardening occurs up to the peak stress. After the peak stress, the inelastic lateral strain varies linearly with the inelastic axial strain. The lateral-to-axial inelastic strain ratio is shown to be a function of the lateral confinement level and the failure mechanism. Moreover, the shear band and tensile cracking induced size effect is also discussed from the lateral strain versus axial strain perspective.