Verification of second-order effects in slender reinforced masonry walls

Previous experimental and numerical works have demonstrated the effectiveness of reinforced masonry (RM) walls in tall single-storey wide-span buildings. Nevertheless, to date, EN1996 does not have a consistent approach to checking the second-order effects due to out-of-plane loads in such structures, and requirements for RM walls are too restrictive. New fibre models have been calibrated on the basis of the above tests and used to carry out parametric pushover analyses to study the influence of wall slenderness, roof vertical load and the percentage of vertical reinforcement on the out-of-plane behaviour of tall RM walls. In this numerical study, new slenderness limits for the safe use of this construction technology are defined, above which second-order moments must be calculated or failures due to instability become predominant, overcoming the shortcomings of current standards. This work also proposes and calibrates some rational approaches for evaluating second-order effects in tall RM walls, based on model column (MC) and nominal curvature (NC) methods. The reliability of the two simplified design methods is checked against the results of the above numerical models. MC method provides the best results, without limitations on the type of failure of the section (i.e. ‘balanced’, as for NC method), with errors usually lower than 25% and always conservative.