INTERLOCKING EFFECTS OF MASONRY WALLS ON THEIR OUT-OF-PLANE FAILURE USING RIGID MACRO-BLOCK MODEL

Out-of-plane failure mechanisms of walls are among the most serious life-safety hazard for existing masonry buildings undergoing seismic actions. Limit analysis-based approaches are commonly used to evaluate their seismic assessment, since requiring simplified assumptions for the structural model. However, the use of models not involving the effective interlocking between walls often yields too conservative results in seismic assessment, which may not be realistic and lead to expensive repairs. Seismic codes, such as the Commentary to the Italian technical standard issued in 2019, do highlight the importance of such modelling aspects, though limited only to the simple rocking failure, but structural analysis software have not yet incorporated them properly. In this paper, an advanced macro-block model accounting for frictional resistances, very competitive for high computational efficiency, is adopted to calculate the activation load multipliers for rocking-sliding compound mechanisms and the related crack patterns in masonry buildings, as well as to evaluate the influence of the interlocking effects on the actual performance of masonry walls. The solutions adopted for the implementation of this advanced model in the 3Muri Project software are then presented and discussed with reference to the application of the proposed force-based approach to experimental benchmarks existing in the literature. This software allows high flexibility of structural configurations and masonry patterns, able to import the geometric model from CAD tools and to define material properties, boundary and loading conditions. Three possible numerical methods for the optimization routines required by the adopted solution procedure are explored with the indication of the most suitable one. Results of the analyses indicate that, especially when thrusting elements, e.g., the static thrust of vaulted structures or thrusting roofs, are present on the unreinforced front wall, the implemented approach involving the stabilizing effects of interlocked walls provides more realistic and reliable performances compared to popular methods. This paper also sets the stage for an extension of implementation to all the possible local mechanisms in masonry buildings, the modelling and design of strengthening interventions with traditional and innovative systems, according to the minimum intervention principle, and to displacement-based analyses.