The buckling behavior of slender unreinforced masonry (URM) walls subjected to axial compression and out-of-plane lateral loads is investigated through an experimental program, where no such test data has been available prior to this study. Using the experimental data, two mathematical models, a finite element model and a linear, elastic buckling solution, are verified and, in turn, are used to validate the experimental results. The finite element model, applicable under various load and restraint conditions, incorporates material and geometric nonlinear analysis of slender URM walls and has the capability of capturing post-cracking and post-buckling behavior of the URM walls. Buckling solutions, proposed by other researchers, validate the highly nonlinear interaction between critical load and out-of-plane bending observed in the experiments. Using the experimental data and the mathematical models, the influence of bending buckling strength is illustrated and axial load eccentricity on buckling strength is illustrated.

The stability behavior of slender unreinforced masonry members (URM) under out-of-plane lateral loads in proportion to the axial load is investigated, using a finite element model developed previously [Lu M, Schultz AE, Stolarski HK. Analysis of the influence of tensile strength on the stability of eccentrically compressed slender unreinforced masonry walls under lateral loads. Journal of Structural Engineering (ASCE) 2004;130(6):921–33]. However, significant changes are made to the solution procedure, the most important of which is application of the arc-length method. A very slender wall with a height–thickness ratio of 30 is used as an example for systematic analysis. The influence of tensile strength and slenderness parameter on the buckling capacity is also investigated. It is found that tensile strength, though very low, may produce peculiar phenomena in the post-buckling equilibrium paths. Lateral loads are shown to have a similar effect on the buckling behavior to vertical load eccentricity.

A comprehensive finite element model is presented for the combined material and geometric nonlinear analysis of slender unreinforced masonry walls, with the capability of capturing postcracking and postbuckling behavior. Material tensile strength is taken into consideration; an exponential stress-strain relationship is adopted for the compressive region and its smooth linear extension is used for the tensile region. This model is applicable under different load combinations (concentrated and distributed lateral loads, vertical load with eccentricity, as well as self-weight) and different restraint conditions. Numerical results of the model show good agreement with experimental results, as well as with analytical results in published technical papers.