RECTANGULAR BEAMS 



103 



The following table gives the values of 4^ for different working 



values of tension and bond, as developed by Messrs. Taylor and 

 Thompson in " Concrete, Plain and Reinforced." 1 



Allowable unit bond 



stress in pounds per 



square inch (u) 



Allowable unit tension in inclined bar, 

 in pounds per square inch (/ s ) 



The length of embedment may be obtained by multiplying 

 the value selected from this table by the diameter of the bar. 



The bond of deformed bars may be figured the same. as the 

 bond of plain bars except using for their diameter, the diameter 

 of a cylinder based on the longest projections that is, of a 

 cylinder which would be sheared out by the deformed bar. 

 For smooth metal of the nature of tool steel not over 40 Ib. per 

 square inch should be permitted for allowable bond strength. 

 Flat steel should be given a similarly low value per square inch. 



If the allowable f s = 16,000 Ib. per square inch and the allow- 

 able u = SO Ib. per square inch, then V (as shown at No. 4 bars in 

 Fig. 48) should equal 50 diameters by the above table. Suppose 

 a deformed bar is used with u =150 Ib. per square inch. The 

 length V should then equal 27 diameters, or 1 ft. 81/4 in. for a 

 3/4 in. rod. Hooks should be provided at the ends of the bars 

 to provide additional safety. 



44. Vertical Stirrups and Bent Rods Combined. Usually the 

 diagonal tension in a simply supported beam of rectangular 

 section can all be provided for by bent up rods and the theoretical 

 combination of stirrups with bent up rods need not be con- 

 sidered. This combination, however, is a common one in 

 T-beam design and may just as well be treated at this time. 



Consider uniform loading and, in Fig. 49, let ABC be the 

 diagonal tension triangle. Assume that four rods may be bent 

 near the end of beam, but not so that they can take any diagonal 



1 From Taylor and Thompson's "Concrete, Plain and Reinforced," 2nd edition, page 454. 

 Copyright, 1905, 1909, by Frederick W. Taylor. 



