The out-of-plane performance of masonry infills in RC frame structures has been addressed in several previous analytical and experimental studies, but a significant number of problems related to the prevention of out-of-plane failure still seem to remain unsolved. Field observations from recent earthquakes in Italy have shown numerous examples of unsatisfactory out-of-plane performance of masonry infills and façade veneers. Extensive damage in some cases has occurred also in recently constructed buildings designed following modern seismic code regulations, indicating the need for improved detailing and a more effective design procedure.

The design recommendations related to the verification of the out-of-plane resistance in currently adopted code regulations are rather general, providing a simplified approach for the evaluation of seismic actions to be verified. However, no recommendations related to the evaluation of the infill resistance are given. In principle, resistance models based on full vertical arching action can be used, but they may be considered appropriate only for undamaged infills. Due to the interaction of the in-plane and out-of-plane infill degradation during seismic actions, the out-of-plane safety verification for infills, previously damaged to a certain extent, appears to be governing the design. In this work, the application of the current design procedure for out-of-plane verifications is studied, and the possibility to account for previous in-plane damage is considered, starting from existing experimental results on unreinforced and lightly reinforced thin clay masonry infills. As a result, design recommendations for a simplified approach to the out-of-plane resistance verification, accounting for possible previous in-plane damage, are provided.