The influence of mortar head joints on the in-plane and out-of-plane seismic strength of brick masonry walls

A sound assessment of the in-plane shear and out-of-plane bending capacities of the load-bearing walls is imperative when conducting seismic assessment or seismic design of masonry buildings. The bulk of work on the subject so far has assumed uniform construction with the brick units connected to each other by mortar bed joints as well as head joints. However, in many construction practices, either for architectural purposes or for speeding up the construction process, the head joints are omitted. This omission may have a profound effect on the response and the strength capacities of the wall. In this paper, the results of a number of tests carried out on half-scale brick wall panels, having different material properties, with head joints and without head joints, are presented. The walls are subjected to in-plane shear, as well as out-of-plane bending pushover loads to failure and their load-displacement curves are established. Representing numerical models for the in-plane shear case are also analyzed and results are compared with those of the experiments. It is found that, depending on the material properties and the modes of failure of the wall, the head joints contribute 35% to 50% to the in-plane shear capacity of the wall. The contribution of the head joints to the out-of-plane flexural strength of the wall is also found to be substantial