## Fixed Crack Model With Variable Shear Resistance Factor Fcmvsrf

In this model, the local reference axis system is first aligned with the principal strain directions at the instance of softening initiation, and kept nonro-tational for the rest of an analysis. The shear resistance factor, p, is derived using the strain components £n and ^corresponding to the fixed local axis directions (which are not necessarily coaxial with the principal stress directions). The definition of a variable shear resistance factor according to equation 5.27, that takes account of deformations in both lateral and normal directions to a fracture plane, is different from the usual formulations where only the crack normal strain is often considered as the damage index.

The total stress-strain relationship matrix, defined in equation 5.26, is similar to the formulation presented by BaZant and Oh (1983), except that they have not considered shear deformations in the constitutive relationship. The present formulation, with the degraded shear modulus term, maintains a backward compatibility with the presoftening isotropic elastic formulation when n = 1 and 2. The local constitutive relationship matrix, [D]np, can be transformed to the global coordinate directions as follows:

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