This study investigates the effect of infill masonry on damage to reinforced concrete frames subjected to underground explosion induced ground motion. A two-storey reinforced concrete bare frame and frames with different masonry infill patterns are analysed. A continuum material model is applied to the masonry panels. The orthotropic elastic properties, strength envelope and damage threshold of the masonry are homogenised by analysing a representative volume element. A fracture indicator and a plastic indicator are defined respectively for monitoring concrete damage and plastic flow of reinforcement of the frame. Numerical results based on the cur-rent study show that the infill masonry affects not only the damage level but also the damage pattern of the frames. Empirical regulations for inhabited building distance (IBD) in underground ammunition storage design are examined, It is found that the empirical damage criterion for surface structures on an underground explosion site is rather conservative for modem reinforced concrete structures, but it appears to be reasonable for the masonry infill in the frame. (C) 2002 Elsevier Science Ltd. All rights reserved.