Masonry Magazine August 1983 Page. 20
Masonry Foundation Announces Additional
Proposal to Perform Masonry Research
Request for Proposal
The Masonry Research Foundation is seeking proposals from qualified researchers to undertake comprehensive testing programs to evaluate the performance of masonry veneer/metal stud wall systems for buildings.
The research will involve: 1) structural performance; 2) water penetration, and 3) corrosion of metal components.
The wide range of expertise necessary to carry out the investigation may require a joint venture arrangement, which will be acceptable. Proposals may address only one or two of the areas listed above.
Proposals must be received by September 20, 1983. Send to: Masonry Research Foundation, 815 Fifteenth St., N.W., Washington, D.C. 2005, att: Mrs. Doris Lackey.
MASONRY: Masonry Veneer/Metal
Stud System for Buildings
# 1.0 INTRODUCTION
The Advisory Council to the Masonry Research Foundation has identified this specific subject as a high priority research area.
The Advisory Council is a group of outstanding researchers, practicing professionals and academicians who are eminently familiar with the design, construction and research needs of the masonry industry as well as the needs of masonry's clients. Advisory Council members were selected by the Foundation and empowered to identify research needs, evaluate proposals and review the results of research projects.
# 2.0 BACKGROUND
Over the past dozen years, a wall system consisting of masonry veneer over metal stud backup has become a significant presence in building markets. (The system has the exterior wythe of masonry designed to be separated from the backup by a minimum one-inch-wide air space and attached to the backup with metal ties.) The system is an adaptation of the traditional masonry veneer/wood frame wall system common in housing, but the adaptation is not a simple one since the metal stud backup cannot be assumed to perform in the same manner as a wood frame backup.
The extension of masonry veneer/metal stud exterior wall systems from low-rise to mid- and high-rise buildings has accentuated the awareness that this system is particularly sensitive to design, construction details and workmanship. It is apparent, from field experience and from rational examination of the system, that problems including cracking, water penetration and corrosion, can and do occur unless proper consideration is given to the performance characteristics of the system.
Some of the areas requiring careful consideration are:
1. Deflection characteristics of the wall system and components under lateral wind loads.
2. Understanding and providing for the thermal and other movements that may be expected because of the different materials used.
3. Careful and proper detailing of flashing and weepholes.
4. Selection of suitable materials for strength and durability.
5. Use of proper ties and their adequate spacing.
6. The climatic conditions and exposure.
7. Understanding the manner in which the masonry veneers behaves.
8. Good construction techniques.
Of these problem areas, the most controversial relates to design philosophy used for determining the walls' resistance to lateral wind loading. The approaches that have been used by three concerned groups can be summarized as follows:
1. The Metal Lath/Steel Framing Association structural design criteria addresses only the steel stud backup system. Their design requires that the maximum deflection of the stud not exceed the span length divided by 360, provided that the flexural stress in the steel stud is not greater than the allowable.
2. The Brick Institute of America, while recognizing that lateral loads are distributed to veneer and backup in accordance with their relative rigidities, suggests that lateral loads be governed by limiting the deflection of the backup system to span length divided by 600. This is an empirical recommendation made in the absence of "established data on the question of relative rigidities of brick veneer and metal stud backup."
3. The National Concrete Masonry Association recommends criteria to ensure that masonry elements remain uncracked. To satisfy this criteria NCMA promulgates design procedures based on limiting flexural stresses to values not exceeding code allowables. Load distribution is based on elastic analysis in which lateral loads are distributed to the facing and backing wythes in proportion to their relative stiffness, taking into account materials properties. (E. I). span lengths of veneer and backup, and end support conditions.
# 3.0 MASONRY INDUSTRY CONCERN
The masonry industry's concern with the performance of this wall system, and with the recommendation of the metal framing industry that the stud backup be designed for a deflection limit of L/360 of the stud span, has been manifested in a number of ways and on numerous occasions:
1. The National Concrete Masonry Association conducted its own research of the system's performance in 1981, the result of which was to show that the flexibility of the backup caused flexural cracking in the masonry veneer.
2. The Brick Institute of America published Technical Note 28B, "Brick Veneer-Panel and Curtain Walls," in January, 1979 (and revised the publication a year later), which suggested design, detailing and construction procedures for the system.
3. In 1981 the National Concrete Masonry Association issued TEK Note 114A to provide designers with a method of rationally estimating the stiffness properties of the masonry veneer and metal stud backup to ensure compatibility under lateral loading.
4. BIA and the Metal Lath/Steel Framing Association jointly sponsored research conducted in 1981 at Clemson University, which BIA viewed as being aimed at testing the performance of the wall system as it was being recommended and built in the field over a typical height and with typical details, and using typical materials.
5. NCMA announced at the end of 1982 that it was initiating additional research that will examine and test the performance of the wall system when designed and built in accordance with steel framing industry recommendations and specifications.
The research performed at Clemson was undertaken by BIA and ML/SFA in an effort to resolve the question of stiffness compatability which had become a serious point of contention between the masonry industry, on the one hand, and the steel framing industry on the other. The research was conducted under the direction of Dr. Russell H. Brown, P.E.