Masonry elements with multi-layer bed joints: Behaviour under monotonic and static-cyclic shear

• Monotonic and static-cyclic shear tests on masonry with multi-layer bed joints are presented.
• Five different types of core layer, protected by two thin elastomer layers, were considered.
• The shear strength was highly influenced by the pre-compression level and loading speed.
• The Mohr–Coulomb criterion is recommended for predicting of the shear strength.
• Large deformation capacity can be expected in URM walls with multi-layer bed joints.

The goal of the research project presented here is to investigate the effect of multi-layer bed joints on the shear behaviour of unreinforced masonry elements subjected to cyclic actions, and to assess the shear mechanical characteristics of multi-layer bed joints. Such joints consist of a core soft layer protected with two thin extruded elastomer membranes, which in turn are placed in a bed mortar joint. The extruded elastomer membranes are employed to prevent and/or limit the deterioration of the core soft layer during the cycling action, which has been observed in previous investigations. Five different core soft layer materials, namely rubber granulate, cork-rubber granulate, cork, bitumen and polyvinylchloride were employed. A total of 57 clay block masonry triplets were subjected to both monotonic and static-cyclic loading under varying levels of pre-compression.The shear behaviour of the specimens was greatly influenced by the applied pre-compression level and by the loading speed. Increasing the level of pre-compression leads to the higher values of shear strength. The same is true for increasing loading speed. Further, for the prediction of the failure shear force a Mohr–Coulomb failure criterion with zero cohesion can be applied. Finally, experimental findings showed that extruded elastomer layers largely fulfilled the intended protective role.The results indicate that multi-layer bed joints with adequate material properties have the potential to change the typical brittle shear response of unreinforced masonry walls to a more desirable quasi-ductile behaviour. Moreover, based on the observed hysteretic behaviour, considerable energy dissipation could be expected in masonry structures with multi-layer bed joints. Such behaviour would be desirable for enhanced seismic performance.