3GO 



FORESTRY INVESTIGATIONS U. S. DEPARTMENT OF AGRICULTURE. 



Results discordant from these may be explained by differences in the degree of seasoning of tlic ontor layers 

 and also by the fact that especially in the northern pineries timbers are often cut from the top logs, which aru 

 weaker and more defective. 



Test of large and nnta/1 columns Compression strength . 



The square columns were mostly 8 by 8 inches, some 10 by 10 inches, a few of larger and also some of smaller dimen- 

 sions. The ratio of length to width varied from 12 to27, about one-half being under and the other half over 18 to 1. The 

 compression pieces of the regular series, and those cut from the broken columns, were in general about 4 by 4 by 6 inches. 



It will appear from this statement of average results that columns develop only from 62 per cent (in CnbaiO to 

 78 per cent (longleaf) of the compression strength of ordinary short pieces. The explanation may be due to several 

 reasons, natural and mechanical. In a column, unlike a beam, all the fibers are under great strain; heuce all the 

 defects, which are by necessity found in every column, influence the results; the flexure of a column under strain is 

 an element of weakness, to which the short compression piece is not subject. In addition the difficulty of determin- 

 ing the average moisture condition of the large timber throughout the cross section and that of the small pieces cut 

 from them afterwards would render this method for columns less satisfactory; a larger number of tests will still bo 

 required to establish comparable average conditions in the two kinds of tests. It would, therefore, be unsafe to 

 generalize too hastily from these average figures, at least as to the numerical difference, for there are remarkable 

 individual exceptions. Not only do individual columns show differences in strength 50 per cent and more lower 

 than the compression pieces from the same log, but sometimes they show practically the same or even a higher value 

 of strength, as will appear from the following selected cases, in which the data for the columns are placed in com- 

 parison with those obtained on compression pieces from the same tree. 



ADDITIONAL SERIES ON BEAMS AND COLUMNS. 



A series more extended as regards beams, involving 68 largo and 777 small beams, besides over 1;000 compression 

 tests on the same material on which the beam tests were made, and tests on 6 large columns, has fully confirmed the 

 indications of the previous experiments. 



TESTS ON COLUMNS. 



The columns were 12 by 12 inches and 8 by 12 inches in cross section, with a length of 132 to 168 inches. From 

 these were ciit, as near as possible from the place of failure, two blocks 2-1 inches long, and these blocks were tested 

 on the same large testing machine (described in Bulletin 6), so that inaccuracies of machinery do not enter into 

 consideration. The results, tabulated as follows, prove conclusively the statement made upon the former more 

 extensive series (see Circular 12), that wooden columns in which the diameter and length are to each other as 1 to 

 18 or less behave like short blocks and fail in simple compression. The four columns of long-leaf pine exhibit 

 practically the same strength as the short blocks i. e., within 10 per cent which, as has been shown above, it 

 within the limits of maximum uniformity. 



Strength of large columns and iltort (34-inch) blocks cut from these columns. 



BEAM TESTS. 



The experiments, of which the following tables contain the principal results, were performed on beams 

 generally 8 by 12 by 192 inches. After breaking the large beam 12 small beams were cut from the uninjured portion 

 of the large beam 1 in such a way that the entire cross section of the large piece was represented by two sets of 6 

 small beams each, liesides these tests ou small beams, the compression strength of part of the material was tested 

 on small blocks, part of which was sawed and part split from portions of the large beam. (See diagram at head of 



1 The legitimacy of using such material for such purpose has been fully established by a long series of experi- 

 ments. (See Circular 12, Division of Forestry, p. 11.) 



