APPENDIX IV. 



REPORT OF A COMMITTEE OF THE AMERICAN INTERNATIONAL 

 ASSOCIATION OF RAILWAY SUPERINTENDENTS OF BRIDGES 

 AND BUILDINGS ON "STRENGTH OF BRIDGE AND TRESTLE 

 TIMBERS."* 



Your committee appointed to report on "Strength of bridge and trestle timbers, 

 with special reference to Southern yellow pine, white pine, fir, and oak," desire to 

 present herewith, as part of their report, the very valuable data, compiled by the 

 chairman of the committee, relative to tests of the principal American bridge and 

 trestle timbers and the recommendations of the leading authorities on the subject 

 of strength of timber during the last twenty-five years, embodied in the appendix 

 to this report and tabulated for easy reference in the accompanying tallies (I to IV). 



The uncertainty of our knowledge relative to the strength of timber is clearly 

 demonstrated after a perusal of this information, and emphasizes, better than long 

 dissertations on the subject, the necessity for more extensive, thorough, ami reliable 

 scries of tests, conducted on a truly scientific basis, approximating as nearly as pos- 

 sible actual conditions encountered in practice. 



The wide range of values recommended by the various recognized authorities is to 

 be regretted, especially so when undue influence has been attributed by them in 

 their deductions to isolated tests of small-size specimens, not only limited in num- 

 ber, but especially defective in not having noted and recorded properly the exact 

 species of each specimen tested, its origin, condition, quality, degree of seasoning, 

 method of testing, etc. 



The fact has been proved beyond dispute that small-size specimen tests give much 

 larger average results than full-size tests, owing to the greater freedom of small 

 selected test pieces from blemishes and imperfections and their being, as a rule, 

 comparatively drier and better seasoned than full-sized sticks. The exact increase, 

 as shown by tests and by statements of different authorities, is from 10 to over 100 

 per cent. 



Great credit is due to such investigators and experimenters as Profs. G. Lanza, 

 J. B. Johnson, H. T. Bovey, C. B. Wing, and .Messrs. Onward Bates, W. H. Finley, 

 C. B. Talbot, and others, for their experimental work and agitation in favor of full- 

 size tests. Profs. G. Lanza, R. H. Thurston, and William II. Burr have contributed 

 valuable treatises on the subject of strength of timber. The extensive series of 

 small and full size United States Government tests, conducted in 1880 to 1882 at the 

 Watertown Arsenal, under Col. T. T. S. Laidley, and more recently the very elabo- 

 rate and thorough timber tests being conducted by the United States Forestry 

 Division under Dr. B. E. Fernow, chief, and Prof. J. B. Johnson, of Washington 



*Mr. Berg also kindly supplied in time for insertion in this publication the above 

 report on "Strength of bridge and trestle timbers," to be read before the convention 

 at New Orleans on October 16, 1895. As this comes in the shape of a recommenda- 

 tion from an international body regarding the future practice, it was considered 

 desirable to make it a part of this bulletin. — B. E. F. 



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