The performance of the closed joist chord to achieve a bending compression flange failure is dependent upon the structural performance of the clinch connection. For this investigation, tests were performed on joists fabricated by using two different clinch geometries, Type A and Type R. The clinches were spaced at six inches on center. Figure 3 illustrates the clinch location within the cross section.
Two joist thicknesses were considered in this study, 0.046 in and 0.035 in. Table 1 summarizes the mechanical properties of the sheet steels used to fabricate the joists profile. Table 2 summarizes the test results.
Test specimen Nos. 1 and 2, had clinches spaced at six inches on center. For Test No. 1, failure was initiated by release of the clinch at an applied load of 90.6 lb/ft and subsequent failure of the compression web at a load of 129 lb/ft. For Test No. 2 the failure was sudden with simultaneous failure of the clinch and buckling of the compression web. Figure 5 shows a typical clinch failure.
To evaluate the performance of the joist with a closer spaced clinch pattern, self-drilling screws were added between the clinches. Thus, the connectors were spaced at three inches on center. Test Nos. 3 and 4 achieved an increase in strength which is indicative of the enhanced performance to be achieved by a closer spaced clinch connector. The failure mode for both tests was a buckling of the compression web, not a failure of the clinch connection.
Based on the test results, to achieve an adequate connection, a connector spacing of three inches is required. Although the closed joist chord did not achieve a bending compression flange failure, the tests demonstrated that clinch type A was superior to clinch type R when the connector spacing was reduced to three inches.