Strength of masonry subjected to in-plane loading: A contribution

The present paper discusses the strength of unreinforced masonry subjected to in-plane loading. Applying the methods of the theory of plasticity, the state of stresses under investigation and compatible failure mechanisms are discussed and an extension (new regime) to an existing failure criterion for in-plane loaded masonry without tensile strength is given. This new regime takes into account slip failure along the head joints line which could be observed in compression tests and which could compromise the safety of the design based on the existing criterion. In addition, a novel proposal for the simplified variation of uniaxial masonry strength as a function of the angle of inclination of the principal compressive stress relative to the head joints direction is derived and proposed for practical applications. Further, the present paper gives an overview of an experimental program comprising the author’s own compression tests on wall elements made of concrete and calcium-silicate blocks as well as of clay brick masonry that was carried out at ETH Zurich. The results of these tests, together with those from further tests carried out by other researchers, have been used for the verification of the abovementioned proposal for the simplified variation of uniaxial masonry strength. A satisfactory agreement between the proposed simplification and test data has been found.