. Practical structural design; a text and reference work for engineers, architects, builders, draftsmen and technical schools;. ints in timber are sometimes made with a large pin on whicha timber rests. The pieces are joined at an angle less than 90degrees and the bearing per square inch on the fibers will be some-thing less than the allowable safe bearing with the grain and con-siderably greater than the allowable safe bearing across the grainfor broad surfaces. 140 PRACTICAL STRUCTURAL DESIGN Let n = the bearing per sq. in. on the diametrical area of thepin, having a driving = the allo
. Practical structural design; a text and reference work for engineers, architects, builders, draftsmen and technical schools;. ints in timber are sometimes made with a large pin on whicha timber rests. The pieces are joined at an angle less than 90degrees and the bearing per square inch on the fibers will be some-thing less than the allowable safe bearing with the grain and con-siderably greater than the allowable safe bearing across the grainfor broad surfaces. 140 PRACTICAL STRUCTURAL DESIGN Let n = the bearing per sq. in. on the diametrical area of thepin, having a driving = the allowable bearing per sq. in. on the ends of the fibers,q = the allowable bearing per sq. in. perpendicular to the direction of the fibers,n = |p + f g. (Dewell formula) Example. — A brace rests against a2-inch pipe driven through the bottomchord of a truss to act as a pin allowable bearing on the ends ofthe fibers is 1200 lbs. per square inchand the allowable cross bearing is 300lbs. per square inch. What bearing- can be used on thediametral area of the pin? Answer. —(I x 1200) + (f X 300) =600 lbs. per sq. $o>;\> ^ I =0=* Fig. 86—Pin Connection inWood Truss Mr. H. D. Dewell was Chief Structural Engmeer, Panama-Pacific International Exposition, San Francisco, 1915. Thepossibihties of timber construction were probably never bettertreated than in the work under his charge, and a great manyexperiments and detailed studies were made in order to designproperly. The results were given by him in a series of articlesin the June to December issues (inclusive), 1916, of Western Engi-neering, San Francisco, Cal. The author has made free use of thearticles by Mr. Dewell and discarded much material prepared forthis chapter, based on older writings,some of Avhich were speculative andsome of which were founded on experi-mental work conducted by men not soskilled as are the modern experimenters. Standards are well enough in theirplaces, but men should not blindly usesta
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