Transactions . ches deep, inches wide,and 66 inches span. These were subjected to deflection-tests,and the results are plotted in Diagram 1. The line in thecenter has been drawn to represent about the average of thefour curves. This line gives the modulus of elasticity, E =931,000. Test on check-piece for beam No. 0 (Diagram 2)gives E = 967,000. Since the Association of Railway Superintendents of Bridgesand Buildings has recommended (Fifth Annual Convention)*that 1,000,000 be used as the modulus of elasticity of whitepine, and the results of the tests are so nearly equal to thisvalue, it
Transactions . ches deep, inches wide,and 66 inches span. These were subjected to deflection-tests,and the results are plotted in Diagram 1. The line in thecenter has been drawn to represent about the average of thefour curves. This line gives the modulus of elasticity, E =931,000. Test on check-piece for beam No. 0 (Diagram 2)gives E = 967,000. Since the Association of Railway Superintendents of Bridgesand Buildings has recommended (Fifth Annual Convention)*that 1,000,000 be used as the modulus of elasticity of whitepine, and the results of the tests are so nearly equal to thisvalue, it has been thought best to use it here in plotting thetheoretical characteristics for solid beams. No correction has been made for the deflection of the steelI-beams. The moment of inertia of each beam is As-suming a span of 66 inches, and a center-load of 4000 pounds,the girder composed of three I-beams will deflect only * Proceedings for 1895. THE EFFICIENCY OF BUILT-UP WOODEN BEAMS. 745 Diagram Indented BeamEach horizontal space=J& inch deflection. inch. The actual deflection was less than this, since, owing tothe width of the machine-platform, the weight was distributed 746 THE EFFICIENCY OF BUILT-UP WOODEN BEAMS. over a distance of 27 inches. It is therefore evident thatthe deflection of the steel beams was too trifling to be takeninto account. II. Forms of Beam not Considered Worth Testing. As the experiments proceeded it became evident that certainforms of built beam more or less recommended by some writersare devoid of merit. It is well known to engineers that manyof the complicated joints used in carpentry, even at the presentday, are of no value, and are merely the survival of methodsemployed in ancient times, when bolts and screws were un-known or too expensive to use, while timber was cheap, andjoints were made mostly with hard-wood tree-nails. Fig. 7 represents a form much advocated. When straps areused^as shown on the left, the beam is tapered sligh
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Keywords: ., bo, bookcentury1800, bookdecade1870, booksubjectmineralindustries
