Masonry Magazine August 1983 Page. 21
Technical representatives of BIA and ML/SFA agreed in principle on the test procedure and on the configuration of the wall system to be tested. It was hoped that the testing program would use a "typical" wall specimen, and that the study would lead to a rational design procedure for this and other masonry/metal stud wall systems of different dimensions and configurations.
The research investigation consisted of two phases. The first phase involved the testing of flat, corrugated ties and adjustable wire ties. Based on test performance, DW 10. 14 ga, two-piece, adjustable wire ties were used in the construction of the test assemblies.
In the second phase, six (6) brick veneer/steel stud wall assemblies were constructed by commercial contractors under simulated field conditions. Three (3) were subjected to positive pressure, and three (3) to negative. These same specimens underwent water permeance tests before loading and after removal of loading. Construction of the test wall assemblies followed current recommended practice as set forth by the Brick Institute of America and the Metal Lath/Steel Framing Association.
Conclusions of this research project are limited to the parameters of the test assemblies. In addition, they contain several very important qualifications which should not be overlooked or ignored. Among these are:
1. The average "structural" factor of safety of the typical wall tested is approximately 2. Normal masonry design uses a factor of safety ranging from 3 to 5.
2. The test specimens were built of standard brick, using Type S portland cement-lime mortar with excellent workmanship.
3. The vertical span of the brick wythe is about 19% longer than the vertical span of the steel studs. The L 360 limitation on deflection is applied to the steel stud span.
4. A soft joint at the top of the brick wythe, under the shelf angle, permitted lateral movement of the brickwork at that location. This movement apparently relieved some of the stresses and permitted the brick veneer to accept a higher load.
The tests described, together with the limiting qualifications stated, clearly demonstrate that the Clemson research results apply only within a narrow set of boundary conditions. Unfortunately, the promotional efforts of the steel framing industry utilizing the Clemson research report have gone far beyond such limitations and have inferred and stated conclusions that, in the view of the Masonry Research Foundation, are not appropriately restricted.
In addition, a comparison of laboratory research results points out significant discrepancies between NCMA and Clemson data. Some of the discrepancies can be attributed to the following differences:
1. NCMA tests were made on walls where veneer and backup are of the same length; Clemson data used metal studs 18 inches shorter than the veneer.
2. NCMA-tested walls were supported at the top and bottom whereas Clemson walls permitted lateral movement at the top.
3. NCMA walls were built with Type N mortar; Clemson walls used Type S mortar.
4. NCMA walls were tested with positive pressure applied to the veneer, Clemson walls were tested with positive pressure applied to three specimens, and negative pressure applied to three specimens.
Available research has left many questions about the masonry/metal stud wall system unanswered, and the use of the Clemson study report by the steel framing industry has created a need to clarify, for the benefit of designers, builders and owners, the performance characteristics of the wall system. If the unanswered questions are not addressed, and if designers, builders and owners are not given clear-cut guides to the performance of this wall system and its design and construction requirements, the masonry industry foresees far-reaching consequences.
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MASONRY-JULY/AUGUST, 1983 21