What do you understand from the following text?
2.3.4. Damage evolution and residual shear strength
When hardening states reach the ultimate strength of the concrete on the failure surface Y_fail damage is accumulated during further inelastic loading controlled by plastic strain. The model by NAME_1 and NAME_2 [19] is taken as basis for the evolution law. Eqs. (19) and (20) specify how the plastic increments are normalized over the effective strain to failure E_eqpl_fail. The effective strain to failure is depending on the hydrostatic pressure p with the shape parameters D_1, D_2 and a lower limit efmin. Contrary to the original paper only deviatoric plastic increments contribute to the damage evolution. Volumetric plastic increments only affect the equation of state and the elastic cap function, a detail not described by NAME_1. The effect of damage is modeled as a loss in deviatoric strength by interpolating as Eq. (21b) between the failure surface Yfail and residual friction resistance surface Yfric (Eq. (21a)). This surface can so far not be measured; this is one aim of the described work. Until this is achieved the same pressure dependence as for the intact limit surface is assumed (B=A, m=n). Respond with more than 250 words.
user