78 REINFORCED CONCRETE CONSTRUCTION 



same as those which cause diagonal tension failure in a beam 

 without web reinforcement. The beam, however, is found to 

 withstand a great deal more shear, confirming the theoretical 

 deductions. 



Tests by Talbot in which curved and inclined rods were used, 

 but in which no rods continued straight for the entire length of the 

 beam, showed results very little better than for straight rods. 



Vertical stirrups and bent rods combined are found by tests to 

 give the very best results. Tests also seem to indicate that too 

 much reliance should not be placed upon one or two bent rods. 

 For this reason, even if one or two rods are bent up properly to 

 take the diagonal tension, it would be good design to consider 

 this rod as not taking any diagonal tensile stress and to provide 

 a thorough web reinforcement by means of stirrups. 



Fig. 43 represents the conditions which developed in the 

 test of a beam. The cracks are numbered in the order of their 



1 I 



I 1 



FIG. 43. 



appearance, final failure occurring at crack No. 4 and being due 

 to inadequate web reinforcement. The stirrups were stressed 

 beyond their yield point. 



It appears from tests of beams in which bent rods were em- 

 ployed with a good anchorage at their ends, that considerable arch 

 action is developed, and that the anchorage is quite advantageous 

 in increasing web resistance. This form of construction is also 

 found to be an insurance against failure at low loads through de- 

 fective concrete or insufficient bond. 



The results of experiments show that the ultimate compressive 

 strength of concrete in a beam is at least equal to its crushing 

 strength as determined by tests on cubes hardened under similar 

 conditions; also, that the yield-point of the steel should be 

 regarded as ultimate strength as far as reinforced beams are con- 

 cerned. When the steel reaches its yield point, the beam de- 



