Brickwork - Three Devices For Structural Stability

Three Devices For Structural Stability

A wall is subject to stresses acting vertically and from the side. The design and construction of the wall must take account of the need to withstand these forces, and incorporate the means to do so. If the wall is made of bricks, these considerations may affect — or even determine — the layout of bricks in the wall.

The first of three common strengthening devices is the simple practice of ensuring that perpends do not vertically align in any two successive courses. If this rule is observed, then the weight acting on any brick is distributed across an area that widens with each downwardly successive course.

The second device is the practice of constructing brickwork that is thicker than the width of any of its individual bricks, and of tying together some or all of these bricks into the depth of the wall. If — for example — a wall describing an east-west line is under construction, then bricks oriented to point north-south may be built into the width of the wall, their length spanning two widths of brick and tying the brickwork on the transverse plane. Historically, this was the dominant method for consolidating the transverse strength of walls.

The third of three common strengthening devices has become almost ubiquitous in brickwork since the advent of the cavity wall during the mid nineteenth century. A cavity wall comprises two totally discrete walls — each one of which is called a leaf. A cavity separates the two leaves so that there is no masonry connection between them at all. Typically the main loads taken by the foundations are carried there by the inner leaf, and the major functions of the external leaf are to protect the whole from weather, and to provide a fitting aesthetic finish. Although the two leaves may not share the structural load, their transverse rigidity still needs to be guaranteed, and must come from some source other than interlocking bricks. The device used to satisfy this need is the insertion at regular intervals of wall ties into the cavity wall’s mortar beds.

There is a variety of arrangements for the cutting and layout of bricks utilising one or more of these methods for stabilising brickwork. These arrangements may generate anything from a wall of a single leaf with staggered perpends, to more substantial brickwork combining the vertical staggering of perpends with a transverse reinforcement through the wall. Any such arrangement is called a bond.