Eccentrically loaded brickwork: Theoretical and experimental results

The assessment procedures for masonry arches and columns usually assume homogeneous constitutive models for which strength and stiffness parameters are described in terms of a uni-axial constitutive law. The limits of such an approach are seldom discussed and related to the brickwork inhomogeneity, i.e. to the brick size and to the masonry bond. In this paper, a first theoretical and experimental approach to concentric and eccentric loading of solid clay brickwork are developed and discussed, investigating the failure modes and the compressive strength of masonry and their dependence on the strength, on the geometry of the constituents and on the loading conditions. A mechanical model for the load carrying capacity of eccentrically compressed brickwork prisms, based on the Static Theorem of Limit Analysis, is proposed allowing: (i) the compressive strength to be related to the size of bricks and mortar joints, showing that edge effects at the free edges do not significantly affect the global behaviour of the material; (ii) the limit domains in the axial force-bending moment space to be derived. Moreover, a series of brickwork prisms have been tested with different load eccentricities; the comparison with the theoretical approach provides upper and lower bounds to the load carrying capacity of the material and shows that: (i) brickwork exhibits limited inelastic strains that need to be taken into account to explain the experimental data; (ii) plastic models for masonry overestimate the actual load carrying capacity. On the basis of these results, one-dimensional homogenized constitutive models, suitable for applications, are formulated and their effectiveness supported by the experimental results.