HEAVY TIMBER 



the load on the girder is uniformly distributed, the reaction 

 will be one-half of the load. If the result obtained by dividing 

 the area thus found by the width of the girder is less than 5 

 inches, this distance should be taken as the minimum length 

 of support. Table F gives values for compressive strength 

 across the grain for timber. 



The unit bending stress (f) may be taken from Table F, 

 according to the kind of timber used. This table gives working 

 unit stresses for structural timbers used in dry locations, and is 

 compiled in the main from material furnished by the Forest 

 Products Laboratory, Madison, Wis. Other values of unit 

 stresses for use in the various formulas will be found in this 

 same table. Where definite unit stresses are stated in the build- 

 ing code of a city, such values should be used in all calculations, 

 but Table F may be used with safety when no scheduled values 

 are demanded. 



Table F. Working Unit Stresses for Structural Timbers Used in 



Dry Locations. 



Species of Timber 



BENDING 



Stress in Horizon- 

 Extreme tal Shear 

 Fiber Stress 



COMPRESSION 



*Fir, Douglas Lbs.Sq.In. Lbs.Sq.In. 



Dense Grade 1600 100 



Sound " 1300 85 



Hemlock, Eastern 1000 70 



Hemlock, Western 1300 75 



Oak 1400 125 



Tine, Eastern White 900 80 



Pine, Norway 1100 85 



*Pine, Southern Yellow 



Dense Grade 1600 125 



Sound " 1300 85 



Spruce 900 70 



Tamarack 1200 95 



Parallel 



to Grain 



1 < Short 



Columns ' ' 



Lbs.Sq.In. 



1200 



900 



700 



900 



900 



700 



800 



1200 

 900 

 600 

 900 



Perpen- 

 dicular 

 to Grain 



Lbs.Sq.In. 

 350 

 300 

 300 

 300 

 400 

 250 

 300 



350 

 300 

 200 

 350 



*NOTE: "The safe working stresses given in this table are for timbers with 

 defects limited according to the sections on defects in the rules of the Southern 

 Pine Association for Select Structural Material. 'Dense' southern yellow pine 

 and 'dense' Douglas fir should also conform to the other requirements of this 

 rule. ' Sound ' southern yellow pine and ' sound ' Douglas fir require no additional 

 qualifications, whereas the other species should, in addition to being graded for 

 defects, have all pieces of exceptionally low density for the species excluded. ' ' 



For reference to "dense" and "sound" classes, see footnote page 48. 



Page sixty-two 



