Numeric research on the mechanical properties of different masonry units during and after fire

The paper is part of a research aimed at investigating the relationship between fire and post-fire (i.e. residual) mechanical behaviour of masonry walls, accounting for numerical tools to establish simplified approaches. In the paper, a FE modelling approach is applied to the problem of residual mechanical performance of load-bearing fire-separating masonry walls after insulation failure. Research on this subject has been recently done by the authors, focusing on the wall thickness as the main parameter of investigation; the present paper focus-es on the influence of different masonry units and their void percentage. The applied procedure was previous-ly calibrated with some available experimental data and has already been used in previous works. The features of the model are oriented to capture the cracking behaviour both under thermal and mechanical stress; this is performed by means of FEM analysis with DIANA 9.6 software, simulating a standard ISO 834 fire re-sistance test followed by a mechanical compressive failure test on each investigated type of wall. First, a pre-liminary transient heat flow analysis gives a numerical prediction of fire resistance after violation of I (Insula-tion) criterion; the results of fire resistance ratings are compared to currently available data. Then, a nonlinear transient heat flow - stress analysis repeats the heating of the wall up to insulation failure and calculates the thermal strain accounting for cracking. Finally, a ‘cold’ structural analysis in compression is performed on the model after cooling. The results of the FEM simulation are potentially useful for mechanical performance pre-diction of masonry walls which have withstood the action of fire maintaining structural adequacy; this is of relevance since the currently available information from fire resistance tests do not cover the post-fire perfor-mance. As well, the influence of different units on the residual properties of the wall can be mutually com-pared