Fall 2009: Minimizing Masonry Litigation
Words: Bronzella Cleveland
Avoiding Lawsuits, Part 9: Arches and Lintels
Norm Cooper, P.E., has served the justice system as a forensic engineer in more than 700 cases. He is included in Who’s Who in American Law and national and international editions of Who’s Who in Engineering. Cooper’s web address is www.realtyengineering.com.by Norm Cooper, P.E.
Code Requirements
The International Residential Code (IRC) for one- and two-family residences, and the International Building Code (IBC) for most other construction, usually is the adopted and applicable law governing design and construction. But it is essential to verify what code applies by reading the state law or local ordinance that adopts the code, which applies to the specific construction and that may contain amendments to the adopted code.
After the applicable building codes, the next ranking authority is usually manufacturer’s instructions, such as Technical Notes on Brick Construction by the Brick Industry Association (BIA), Recommended Practices by the Building Stone Institute, and TEK by the National Concrete Manufacturer’s Association (NCMA). Briefs of 2006 sections of said codes and manufacturer’s instructions relevant to arches and lintels follow:
Case #1. Masonry arch had: inadequate abutment (column) strength to resist the horizontal arch thrust; missing metal ties from arch to wood framing; and reported rebar in arch inadequate to resolve the inadequate rise-to-span ratio. Risking failure, these code violations were causes of the symptoms: cracks up from mid arch and horizontal cracks in left and right abutments.For arches and lintels, IBC (2101.2) requires masonry to comply with the allowable stress or strength design methods prescribed therein, and IRC (R301.1) requires “Buildings and structures, and all parts thereof, shall be constructed to safely support all loads, including dead loads, live loads, roof loads, flood loads, snow loads, wind loads and seismic loads as prescribed by this code. The construction of buildings and structures in accordance with the provisions of this code shall result in a system that provides a complete load path that meets all requirements for the transfer of all loads from their point of origin through the load-resisting elements to the foundation.” Masonry arches and veneer usually are required (IBC 2104.1.6, IRC R703.7.3) to be supported on non-combustible materials (e.g. no wood).
For arches, BIA Technical Notes 31 of 1995 and 1986, and NCMA TEK 14 of 1994 and TEK 7 of 1978, provide arch design principles and useful graphs and tables for design and for inspecting arch compliance.
Case #2. Mortar cracks were symptoms caused by abutting column inadequate to resist horizontal arch thrust and by inadequate rise-to-span ratio to carry vertical loads.
Case #3. Masonry arch had inadequate rise-to-span ratio, and inadequate abutment (column) to resist horizontal thrust, which caused cracks and risked collapse. Also, missing lintels under the gabled masonry over interior room spans caused cracks and risked hazardous failure.
Case #4. Masonry sag and cracks were symptoms caused by inadequate strength of garage entrance steel lintel.The abutment (often a masonry wall or column at each end of the arch) must also comply with strength requirements. BIA 31 states, “Lateral movement of the abutment is due to the horizontal thrust of the arch. … The thrust should be resisted so that lateral movement of the abutment does not cause failure in the arch.”
For lintels, IRC (R606.10) requires “Masonry over openings shall be supported by steel lintels, reinforced concrete or masonry lintels or masonry arches, designed to support load imposed” and prescribes (R703.7.3) allowable steel angle spans and minimum 4-inch bearing length.
Most states require masonry arch design, lintel design not code prescribed, and inspection of same to be performed solely by state licensed professional engineers who are qualified in arch and lintel design.
Case#5: Masonry arch supported by wood studs in wall violated code.
Case Summaries
The photos and their captions in this column are from scores of the author’s expert witness cases where compliance with the above codes, or lack thereof, determined the case outcome.