Optimisation of Reinforcement in Double Brick Walls for Improved Vertical Bending Capacity

The economic climate of Western Australia in the year 2020 has forced residential construction companies to provide superior products at competitive prices. There is an increasing demand for houses with open-plan living spaces and high ceilings, which makes the structures, especially the external slender double brick (DB) walls, vulnerable to wind loading. The out-of-plane (OP) loads, resulting from the wind pressure on the slender DB walls have forced engineers to rely on steel mullions as reinforcement placed into the cavity between the external and internal masonry leaves, to improve the OP bending capacity. However, reviews of the literature at present have limited data on the combined effects of DB walls with steel mullions on the OP bending capacity. Furthermore, the literature does not provide any guidance on the optimisation of the steel mullions within the DB walls. As a result, engineers rely on the capacity of the steel rectangular hollow section alone, ignoring the contribution of the DB walls in the load-resisting mechanism, often resulting in a complicated and expensive design. This thesis aims to investigate the OP bending performance of DB walls with steel mullions of varying heights. For this purpose, a series of full-scale tests were performed on a total of 12 DB walls of dimensions 2657 mm height × 935 mm width. Of them, 10 DB walls were reinforced with steel mullions made using 100 mm x 50 mm x 3.0 mm rectangular hollow sections, where the height of the steel mullions was varied. A systematic material-based investigation was also carried out to ascertain the material properties of the constituent materials. The load-displacement behaviour, failure mode and displacement profile of the tested walls have been analysed in detail and revealed that the presence of the steel mullion increases the OP bending capacity of DB walls up to 167% at the point of the first crack. Based on the experimental findings, a design method has been proposed, which will assist structural design engineers to quickly design slender DB walls reinforced with steel mullions of varying heights, ensuring both safety and economy in the building construction industry. This design methodology was found to produce a design load that had a correlation of 80% the experimental first crack load result.