Masonry Magazine September 2002 Page. 21
Camp, a lecture on arches is often the highlight of the week, and an inspiration to participants as they build one element of their design/build challenge.
What do you want to build?
AFTER ASKING a brick what it wants to be, the logical next question is, "What does a mason want to build?" It's likely the answer will be the same. Getting to that answer, however, lies in establishing a comfort level with the craftworker.
IMI addresses craftworker preparation in terms of arch construction through its apprenticeship and training programs, assuring designers that their masonry arches will be constructed with the best craftsmanship in mind.
Both construction principles and practical application are taught through the IMI apprenticeship and training system. An ongoing Arches class at the National Training Center and regional centers is offered to all levels of craftworker, from pre-apprentices to seasoned journeymen and women, as well as to all IMI and BAC (The International Union of Bricklayers and Allied Craftworkers) instructors through the annual Instructor Certification Program.
Arches take a variety of forms that range from the jack arch to circular and elliptical arches to Gothic. Typically, a designer will select jack, segmental, semicircular and multi-centered arches for building elements. Semicircular arches are often used for very long spans, due to their structural efficiency.
Like any other building element, arches must meet the performance criteria for a building. In addition to structural performance, an arch should address weather issues and general building performance issues. Resistance to water penetration, for example, is a major concern when designing arches.
Historically the mass used in the design and construction of a masonry arch served to provide water penetration resistance. Over time, as wall sections have become thinner, water penetration has become more critical. When provisions against water penetration are required, such as in arches that become an integral part of the building envelope, water resistance can be addressed through the use of a barrier wall or drainage wall system. Regardless of the system selected, the arch should be flashed and include weep holes to best direct water away from the building's interior.
Designers should give thought to the various options available in arch designs. Issues include material selection-including brick sizes, shapes, bonding patterns and material tolerances. It is important to understand the material being used for the masonry arch to better arrive at a solution that can be easily and effectively constructed.
Additional issues include arch size and arch depths, keystones, soffits, skewbacks and the configuration of abutments. The arch designer should resist out-of-plane loads and address building and thermal movement issues while giving careful consideration to the location of expansion joints.
Proper masonry arch performance ultimately depends on workmanship and the mason's ability to understand industry guidelines, layout and construction processes.
Finally, it is important to recognize the relationship between workmanship and building performance. Proper masonry arch performance ultimately depends on workmanship and the mason's ability to understand industry guidelines, layout and construction processes.
Assistance with all these considerations and more is available from The International Masonry Institute to participating contractors, as well as to designers. IMI provides technical assistance and education on a per-project basis that assists designers with incorporating arches in their design solution. Additionally, the Brick Industries Association, Reston, Va., publishes technical notes related to the structural design of masonry arches and addresses unreinforced and reinforced solutions.
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The Voice of the Mason Contractor
September 2002
Masonry 19