Civil defense shelters are often constructed beneath the ground to provide protection against blast loadings. Concrete is widely used as the material for the defense layer of the shelters. This paper adopts a continuum damage model of brittle media to numerically investigate the dynamic fracture and attenuation effect of perforated concrete defense layer on stress waves from planar charge. The model includes damage accumulation and loading rate-dependence, and has been succinctly implemented into the dynamic finite element code, LS-DYNA, via its user defined subroutine. The numerical results reveal that the adopted model can well predict the tensile damage owing to the reflection of pressure waves from cavities and free boundaries. Again, the elastoplastic properties of concrete play significant roles in the stress-wave attenuation and the peak values of hydrostatic pressure beneath a circular cavity are largely reduced. One empirical formula is finally proposed to relate the decay factor of peak hydrostatic pressure to the cavity dimensions and relative position. (C) 2006 Elsevier Ltd. All rights reserved.