Masonry Magazine August 1967 Page. 11
mens ranged in height from 16 in. to over 15 ft., and in net thickness from 4-in. to 8-in., thus providing valuable data on the effect of the slenderness (ratio of height to thickness) of the wall on its compressive strength. Loads were applied at the centroid of the wall and at distances of 1/6 and 1/3 the wall thickness from the centerline, thus giving us data on the effect of load eccentricity on ultimate strength. The effect of "boundary conditions" was investigated by varying the loading conditions at the top and bottom of the walls in the testing machine-either by producing a degree of "fixity", a pure hinge or a combination of the two. In addition to the above three, the effect of such other variables as type of mortar, strength of masonry unit, thickness of mortar joints, bonding arrangement, and workmanship have been and are continuing to be thoroughly investigated.
While the compressive strength of the clay masonry wall is, perhaps, the most important structural property in load-bearing design, there is another property that assumes importance when it is used as an exterior wall. This is the transverse strength of the wall, or its ability to resist wind pressures or other so-called "dynamic" loadings as produced by earthquakes, etc. During the past few years, over 300 masonry test specimens have been built in the Geneva, Illinois laboratories of SCPRF and tested to determine their ultimate transverse or flexural strength. Here, again, a variety of wall types and sizes were tested, and the effect of mortar, joint size, bonding, etc. were investigated.
Another physical property of a wall that can often be of importance in the structural design of a bearing wall building is its racking or shear strength. Again, well over 300 masonry wall specimens, ranging in size from 16 in. by 16 in. to 8 ft. by 8 ft. have been built in our laboratories and subjected to a number of different test methods in order to determine the shear or racking strength of the masonry. Unlike the compressive and transverse strength test methods, there is no acceptable standard method of test for determining the ultimate shear strength of masonry. Consequently, much of our work in the investigation of the racking or shear strength of clay masonry has involved the development of a test method that, we hope, will eventually be accepted as standard. In the course of such development work, much valuable insight into the true shear strength of masonry has been obtained.
The results of this most extensive structural investigation and testing program to date, supplemented by a wealth of test data from earlier tests at such institutions as the National Bureau of Standards and numerous universities, for the backbone of SCPI's recommendations for the rational design of engineered brick masonry. These are exemplified by the SCPI Recommended Building Code Requirements for Engineered Brick Masonry and numerous Technical Notes and other technical literature yet to be published on the subject. As reference material, the test results themselves are published in our series of Research Reports of which there are now a total of 15 that have been published, are in the process of being published, or are in the final stages of being written.
While this massive structural investigative program has provided the basic data required to establish the ability of clay masonry to perform as an engineered structural material, the technology of engineered brick masonry cannot remain static. Therefore, it is envisioned that such structural investigations, experimentations and testing will continue to be important activities of the SCPI Research Division for many years. For example, little or no work has been devoted to reinforced brick masonry in the program just described it has been almost exclusively concerned with unreinforced masonry. Much of the test data on which present day requirements for the design and construction of reinforced brick masonry are based, are some 30 or more years old. Our knowledge in this area should be updated and expanded.
"All-Weather Construction" is a subject of great interest and importance to the construction industry today. One aspect of this that is of great importance, particularly in bearing wall construction, is the effect of freezing of freshly laid masonry on its structural properties. Some exploratory investigative work in this area was started this past winter in SCPRF's Geneva laboratories and will be continued and expanded after we are established in our new facilities in Virginia this fall.
Some of the more basic aspects of our structural research are being carried on under the SCPI Research (Please turn page)