INS 



WROUGHT IRON AND STEEL BEAMS. 



to attempt to foretell the strength of a cast-iron beam 

 simply from a knowledge of the tensile strength of the 

 metal. 



On Fig. 90 is shown a complete load-strain diagram* 

 plotted from the figures obtained in the above bending 

 test. The actual plotted points are indicated as before by 



-0-30V 



0-2b 



0-20 



0-05 



500 









1 000 1500 2000 2500 3000 POUNDS 

 LOADS. 



FIG. 90. Deflection Diagram for a Cast-iron Beam. 



the centres of small circles. It will be noticed that, up to 

 a load of about l,5001b., the points lie on a sensibly 

 straight line, but, beyond this point the diagram curves 

 upwards, as shown by its deviation from the dotted 

 line. This upward curvature may be taken as indicating 

 a departure from the truly elastic conditions. As a matter 

 of fact, very careful experiments have shown that even at 

 the lowest loads cast iron is not elastic in the strict mean- 

 ing of the word. 



106. Testing of Wrought Iron and Steel Beams. Beams 

 of these metals may be tested in all sizes, so long as the 

 necessary loads do not go beyond the capacity of the 

 machine which is to be used for the purpose. Generally 

 speaking, plain rectangular bars are not often tested as 

 beams, the most usual forms being rolled joists, built-up 

 beams, girders, and rails of various forms. The example 

 that will be taken for the purpose of illustrating this part 



