This paper introduces a new approach for the seismic performance evaluation of planar RC walls. Compared to existing assessment guidelines, such as those in ASCE/SEI 41-17, where performance limits are described by plastic rotation or lateral drift, the proposed method uses local (strain) quantities, obtained from computational models. The analyses rely on a user-friendly implementation of the nonlinear truss model for RC structures, which eliminates the need to manually create a line-element representation of a wall and includes a material law for steel accounting for buckling and rupture of reinforcement. The capability of the models to capture common failure patterns for planar walls is validated for a set of six previously tested wall components which experienced a variety of damage modes (bar rupture, boundary element failure, diagonal compression and tension failures). The analytical models accurately predict the lateral strength, deformation capacity and failure modes observed in the tests. A set of acceptance criteria, based on the analytically obtained concrete and steel strains, is then established for the immediate occupancy, life safety and collapse prevention levels, consistent with different levels and types of damage. An initial calibration of the limit values associated with these criteria is proposed and verified using the analytical results for the six walls considered. The results of the proposed assessment methodology applied to the six walls are compared to those obtained using the nonlinear procedures in ASCE/SEI 41-17. The results indicate that ASCE/SEI 41-17 may not accurately describe the deformability of walls exhibiting mixed flexure-shear inelastic deformations.