36 



Division. A formula for large timber columns, the correctness of which 

 can not be questioned, is a great desideratum, and would be a boon to 

 engineers, architects, and in fact all designers of structural work.* 



Table VII is indicative of the importance attributed by the author 

 of the paper to the proper proportioning of timber structures for bear- 

 ing of timber on timber across grain. The point at which an indenta- 

 tion due to the bearing of timber on timber across grain becomes 

 dangerous or objectionable depends upon individual views and local 

 conditions. The units for crushing strength across the grain are 

 assumed by the author of the paper as being the stresses at which an 

 indentation of 3 per cent of the height of the stick would take place. 



In regard to inspection of timber, the author of the paper outlines 

 the principal points affecting the strength of timber, which points 

 form the basis of the investigations and tests now being conducted by 

 the Forestry Division. There is no doubt that, with additional system- 

 atic and reliable information furnished on these different questions, 

 the proper inspection of timber will be greatly assisted and benefited, 

 but, as the author of the paper states, the present time is premature 

 for the formulation of rules for scientific inspection of timber. 



Referring now to the second division of the paper, in which the 

 present practice of trestle construction is compared with designs pro- 

 posed by the author of the paper, it should be said, in a general way, 

 that it is to be regretted that, in selecting a structure from everyday 

 practice to illustrate the actual practical economies that can be intro- 

 duced, owing to our present better information on the subject of 

 strength of timber, the author did not select some other timber struc- 

 ture in place of a trestle. The different parts of a railroad trestle can 

 not always be designed so as to be subject to or to correspond to 

 mathematical calculations, as there are certain conditions in the actual 

 construction or erection work and subsequent use of the structure 

 which predominate in establishing the design and the dimensions far 

 more than theoretical calculations of the strength of individual parts. 



The principal features of the proposed new designs, as compared with 

 the present practice, consist in the recommendation for the introduction 

 of corbels, in which case the caps are reduced to 9 inches; the scaling 

 down of the posts to correspond to the new formula for wooden col- 

 umns; the proper designing of stringers, not only to be safe for cross 

 breaking and deflection under load, but especially for bearing value at 

 end of stringer, and a corresponding general scaling down of all other 

 parts, such as sills, braces, etc., although no attempt is made to warrant 

 these last reductions of sizes by calculations, f 



*The data for the development of such a formula are being collected, but are not 

 yet sufficient to warrant ((inclusion?. — B. E. F. 



t Not true as far as caps and sills are concerned. (See p. 28. ) The braces have not 

 been computed in the paper; in fact, they are not mentioned. There is a radical 

 change in them, however, and I computed them before putting them in. 



On the design in fig. 2, present practice, it will be noticed that there is one brace 

 in each panel, while in the new designs there are two braces in every other panel. 



