Double brick walls with partial-height steel mullions under one-way vertical bending

To improve the out-of-plane (OOP) bending capacity of slender double brick (DB) walls and meet the design OOP load resulting from wind pressure, steel mullions (SMs) are used as reinforcement placed into the cavity between the external and internal masonry leaves of the wall. The literature presents limited data on the performance of DB walls with SMs under OOP loading. There is no guidance available to optimise the SMs within the DB walls. As such, structural engineers design these walls solely relying on the capacity of the SMs and ignoring the contribution of the DB walls in the load-resisting mechanism. Such a practice not only results in expensive design but also raises concern over the safety of such systems. This paper presents the OOP bending capacity of DB walls with partial-height SMs. A series of 04 full-scale DB walls of dimensions 2656 mm height × 935 mm width were tested under airbag surface pressure loading. The walls were constructed with partial-height SMs of heights of 0.5 m, 1.0 m and 1.5 m alongside a DB wall without any SM. The load-displacement behaviour, failure mode and structural performance parameters, i.e., stiffness and ductility of the tested walls have been analysed in detail. It is found that the presence of the partial-height SM increases the OOP bending capacity up to 149 % at the point of the first crack in addition to improvements in maximum OOP bending capacity, failure mode, stiffness, ductility and post-peak strength degradation of the DB walls.