Masonry Magazine June 1988 Page. 17
NCMA-TEK
An Information series from National Concrete Masonry Association
Concrete Masonry
Radial Walls
Introduction
The development of customized architectural units over the years has completely revolutionized the concrete masonry industry. Once relegated almost entirely to fulfilling a structural role based upon its physical attributes: Strength, durability and fire resistance, concrete masonry is now in demand for its ability to impart distinctive aesthetically pleasing architectural features to buildings and other structures. The almost limitless variety of sizes, shapes, textures, colors and surface treatments has made concrete masonry one of the most versatile and sought after building materials today.
Recently, renewed interest in curved or circular wall sections has added yet a new dimension to modern masonry wall construction. No longer is the architect limited to the rectilinear design to which we have become accustomed and which permeates our cities today.
The use of concrete masonry in the design and construction of radial walls presents a unique challenge to the design professional. Where curved walls once were formed from hand hewn stone carved to fit a predetermined radius, radial walls of concrete masonry are usually formed from rectangular units of fixed shape and dimension. The end result is a series of short chords rather than a smooth arc. The greater the radius, the more closely the surface formed by the chords approaches that of a true arc.
The curvature of walls so constructed is dependent upon, such variables as length of unit, thickness of unit, width of the vertical head joints at the interior and exterior faces of the wall and whether the units will be used as is, beveled at the ends, or cut to conform to the desired radius.
The bond pattern employed also has a distinct effect on the overall appearance of a circular or curved wall section. Curved walls laid up in a stack bond possess the geometric properties of a regular polygon (Figure 1). Walls laid up in running bond, on the other hand, exhibit a similar geometric configuration at the individual courses with the exception that the ends of units in alternating courses project out beyond the faces of the units immediately above and below (Figure 2). These projections create a basket-weave effect which may or may not contribute to the aesthetic value of the wall.
Figure 1. Regular Polygon
Figure 2. Projections in Running Bond
Minimum Radii
The minimum radii for curved or circular walls constructed of concrete masonry units is determined through iterations of the plane rectilinear geometric formulae for regular polygons. These equations are: