Macro-Modelling of Quasi-Brittle Constructions Under Lateral In-Plane Loads

Abstract eng:
In the paper one addresses the problem of the evaluation of contribution of the masonry infill embedded into structural elastic rc or steel frames to the overall lateral resistance of the structure to lateral loads. Actually the infill may contribute to the resistance of the primary structure even significantly ([1]-[7]), and the evaluation of its static operation requires to abandon purely elastic models, which, although they result easier to be handled and implemented into commercial software, may give results very far from the real situation. The approach proposed in the paper involves the proper modeling of the infill, which is usually made of masonry or brick elements, and it thus requires an ad hoc set up for getting reliable forecasts on its influence on the main structure’s behavior. To this aim in the paper, one first synthetically introduces the procedure required by the proper implementation of the problem for infill made of masonry and thus modelled through a non-linear mechanical hypothesis about the constituent material. In order to get a proper modelling of the masonry infill embedded in the contouring structural frame, and then a suitable analysis of the coupled frame/infill system, one considers to model the infill under the No Tension assumption ([8][16]), instead of the linear elastic hypothesis usually adopted in current structural analyses. Since this approach requires an ad-hoc numerical implementation in calculus codes which is able to provide more reliable results with respect to available commercial software, one develops and compiles some specific codes able to reproduce the behaviour of the infill and of the complete frame/infill system. The developed calculus codes are more complete, and they also allow to forecast the stress distribution within the infill and the fractures developed in the masonry infill panel. In the second part of the paper, the results from the numerical investigation are then reported in Sect. 3, for varying horizontal loads. Focus is addressed as well on the effects of the detachment of the infill from the structural frame and the consequent loss of overall lateral resistance of the structure, allowing to further emphasize the influence of the presence of the infill on the overall response of the structure; the case of minimum anchoring between the infill and the structural frame, which is closer to the case when the presence of the infill is completely ignored in calculations, essentially shows a much lower performance of the structure against horizontal loads. Although this result is to be expected, the reported subsequent comparison with results from modelling provided in commercial software under varying horizontal loads allows to figure out how usual analyses that do not make recourse to appropriate modelling of masonry may largely underestimate the action of the infill, and push towards misleading conclusions.

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