TIMBER 



285 



with its ends as nearly parallel as possible, and the compression is 

 measured by an ordinary compressometer, or similar instrument for 

 measuring the lowering of the moving head. To provide for the non- 

 parallelism of the ends, it is well to use a spherical bearing for one 

 of the bearing ends. Tins will insure the proper "lining up" of the 

 specimen so that the compression will be along the grain 



^train diagram may be drawn by plotting loads in lb./in. 2 as 

 ordinates and the corresponding relative compressions as abscissas. 

 The elastic limit, modulus of elasticity, modulus of resilience, and 

 maximum strength may then 

 be obtained from the diagram 

 in the usual manner. Failure is 

 either due to a splitting of the 

 specimen or to a shearing off at 

 an angle of about 30 to the 

 h >i izontal (Fig. 1 63). The latter 

 is the characteristic failure for 

 green timber. 



tests on long columns are 



made in much the same way as 



the tests on short blocks. Provision is made for fixing the ends of 



the columns so as to give the standard end conditions, namely, square 



round ends, pin and square ends, etc. In either case sufficient 



data is taken to get a load-deflection curve by measuring the deflec- 



- at the center corresponding to selected load increments. These 



tions are usually measured in two directions at right angles to 



each other.* 



FIG. 163 



Problem 187. Fi.ir. 104 represents the results of compression tests of pine, 



poplar, and oak, plotted with loads in pounds as ordinates and compression in 



as abscissas. The blocks were all 7 in. high, with an area of cross section as 



follows: pine, 2 in. x 1.48 in.; poplar, 2 in. x 1.48 in.; oak, 2 in. x 1.47 in. Redraw 



irves, plotting the loads in lb./in. 2 as ordinates and the corresponding unit 



impressions in inches as abscissas. Determine for each material the elastic limit, 



flu- tin Mluliis of elasticity, and the modulus of elastic resilience. Also compare the 



t| obtained with the results reported for these materials in compression in 



the following tables. 



r a report of the tests that have been made on full-sized timber columns the 

 student is n-fcrn-cl to Lan/.a's .\i>i>l''<l 



