Some residential designers and builders have failed to recognize that all brick arches are structural masonry and must be designed according to structural principals.
Arch Types and Terms
The types of arches most commonly used in residential construction are: jack, segmental, semicircular, and parabolic. Arches typically are classified as "minor" or "major." Minor arches are used to span openings of up to 6 feet and support vertical loads of less than 1,000 pounds per lineal foot. Major arches are those that span more than 6 feet and can support vertical loads greater than 1,000 pounds per lineal foot.
Although they carry loads in compression, masonry arches impart horizontal thrust loads at each end or "skewback." The abutments at each side of an arch must be strong enough to resist these loads. Most problems occur in arches that frame into columns. In residential construction arches frame into a column that often consists of a 4x4-inch wood member. Brick are laid merely to enclose the wood column. Such hollow brick columns offer little or no resistance to thrust loads. Various methods can be used to resist thrust loads. When feasible, avoid framing arches into columns and instead place arched openings in walls. Alternatively, increase the strength of columns by increasing their cross section and adding reinforcing steel and grout.