Transactions . am, per cent. THE EFFICIENCY OF BUILT-UP WuODEN BEAMS. 765 No. 19. Beam composed of one piece of white pine thick on top, another piece of white pine inchesthick in center, and a piece of oak inches thick on bottom,or tension-side. All pieces inches wide. Secured by 12pipes and 8 bolts, as in Fig. 24. Span, 6Q inches. Weight ofbeam, 50 pounds. Broke at 9140 pounds. Check-piece: Dweighed 16 pounds, failed at 2350 pounds. Efficiency (referredto D), per cent. Fig. 23. > A, T-37 3 9 I I Piped Beam. The results of the first four show that too m
Transactions . am, per cent. THE EFFICIENCY OF BUILT-UP WuODEN BEAMS. 765 No. 19. Beam composed of one piece of white pine thick on top, another piece of white pine inchesthick in center, and a piece of oak inches thick on bottom,or tension-side. All pieces inches wide. Secured by 12pipes and 8 bolts, as in Fig. 24. Span, 6Q inches. Weight ofbeam, 50 pounds. Broke at 9140 pounds. Check-piece: Dweighed 16 pounds, failed at 2350 pounds. Efficiency (referredto D), per cent. Fig. 23. > A, T-37 3 9 I I Piped Beam. The results of the first four show that too many pipes wereused. Even with this defect the efficiency exceeds that ofClarks beam of the same size by 10 per cent. But the deflec-tion is about the same—double that of a solid beam. It wasnoted during the tests that the pine would split opposite thepipes and tend to open, thereby permitting sufficient slippageto cause the large deflection. The fact that in a solid beam the shearing-stress decreases Fig. Piped Beam. (though not in direct proportion) with the distance from theneutral plane suggested the form of beam used in ISTos. 16 and17, the idea being to supply solid timber in the neutral axis,and make the joints where the shearing-stresses would besmaller. The resultant efficiencies do not show any advan-tage gained by this method. It was apparent, in all the testsmade on beams consisting of more than two pieces, that theslight yielding of the wood around the fastenings allowed suffi- 766 THE EFFICIENCY OF BUILT-UP WOODEN BEAMS. Summary and Conclusions Regarding Piped Beams. Number of Beam. 10111213 1415 1617 16 17 1819 Number of Pieces Used. Number Ratioof Pipes Span toUsed. Depth. 18181818 1212 1212 121212 12 Breaking 1212 Efficie ncies by alter- fna te meth od. \ 1212 1212 6?50 7600334080U0 83205450 73107960 7340 7960 60009140 Cent. Flaw. 81
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
