INTRODUCTION In Progress Report No.1, it was reported that the initial conception of the problem was that diaphragms act almost exclusively in shear when called upon to brace compression members, and that it had been decided to test single columns with finite widths of diaphragm attached, with width of the sheet being varied to provide a range of lateral support up to that which permitted full column strength, based on strong axis to be developed. However, the first test of this kind, Test CB-l, clearly indicated that the diaphragm acted essentially in flexure only and thus had the same effect as if it were regarded as a weak cover plate. It was already quite clear at the time of the First Progress Report that the shear contribution of the diaphragm was practically nil, based on observation of combined beam-sheet tests (refer to figure 1, First Progress Report). It was thought at that time that prevention of rotation of the ends of the diaphragm would produce shear-predominant action. While the sheet, thus restrained, provided far more support to the beam than in the previous tests and could be exactly calculated, the behavior was essentially flexural and not in shear. A series of tests were proposed in Progress Report No. 1 to confirm the initial conclusion that supporting diaphragms act in flexure and function essentially as corrugated cover plates. As mentioned, this was exactly confirmed by the first test, making further tests of this character pointless. It was recognized furthermore, that any purely flexural contribution of the sheet was so small that nothing was to be gained in design, in terms of increased column strength, by counting on it. On the other hand, by experience and intuition, it seemed that the supporting ability of the sheet should be far greater than observed. In rethinking the problem, it was concluded that the sheet could act in pure shear and provide the anticipated support only if all crosssections were prevented from roaating. The simplest situation producing this condition is that of a diaphragm attached to two identical, (in all respects, including loading), columns or beams, as in figure 27. In fact, this is a rather realistic situation in that corrugated building siding is or could be attached continuously across two or more columns that are more or less identical. Accordingly, it was decided that tests should be performed on pairs of columns, each loaded and supported separately and identically, but connected by a diaphragm, as in figure 14. To the inrestigators' knowledge, tests of this kind had never been performed, and were regarded as exceedingly difficult because of the necessity of centering with absolute certainty two interconnected and interacting columns. As a simpler and less tedious way of checking the notion that the diaphragm would act primarily in shear, beam sheet tests as in figure 4 were devised. These tests, performed with a variety of diaphragms, gave substantial assurance that the idea was correct and permitted the experimental determination of the effective shear rigidities. With the information thus obtained, several double column tests were performed.
Civil, Architectural and Environmental Engineering
American Institute of Steel Construction
Wei-Wen Yu Center for Cold-Formed Steel Structures
01 Feb 1963
Pincus, George and Fisher, Gordon P., "The performance of beams and columns continuously braced with diaphragms" (1963). CCFSS Library (1939 - present). 119.