Material properties for the shear design of earth masonry under the influence of relative humidity

As sustainable development gains momentum in the construction industry, earth masonry is increasingly favoured. Recently, several standards were introduced in Germany, permitting earth masonry to be applied for load-bearing walls up to four storeys height. However, reliable data on the shear capacity of these walls and the required material parameters are hardly available. As the height of buildings increases, the verification of shear load capacity becomes increasingly important. This paper provides a detailed experimental basis for the material parameters of earth masonry that have implications on the shear design. These parameters include the initial shear strength, the coefficient of friction and the block tensile strength. An extensive test programme was conducted including 700 specimens and wallets, in which unstabilised earth mortars and earth blocks from three different manufacturers were examined. For the first time the impact of relative humidity on the initial shear strength, the coefficient of friction and the tensile strength of earth masonry is investigated. An increase of the relative humidity from 50 to 90 % during the conditioning of the test specimen resulted in a reduction of the initial shear strength of 7–21 %, a reduction of the coefficient of friction of 6–19 % and a reduction of the direct block tensile strength of 48–50 %. Furthermore, the linearity of the shear line of earth masonry is analysed in detail. In addition, a novel conversion factor for the direct, splitting and bending tensile strength of earth blocks is derived by conducting the corresponding experimental tensile tests and analysing the results. All results are analysed based on previous research findings found in the literature and are compared with other masonry materials. With regard to the transferability of the existing design concepts in accordance to Eurocode 6, the material-side partial safety factor of γ m = 1.5 can be validated for the verification of the shear strength of earth masonry. • Influence of relative humidity on shear strength properties of earth masonry (EM). • Evaluation of linearity of Mohr-Coulomb criterion for EM frictional shear strength. • Comparison of direct, splitting and bending tensile strength of earth blocks. • Statistical analysis for transferability of shear design acc. to Eurocode 6 for EM.