30 



REINFORCED CONCRETE CONSTRUCTION 



Thus, if an external load, of P Ib. be applied to a steel bar 

 whose length is I in, and whose cross-section is A sq. in., and if 

 the compression under this load be d in., we should have 



F _f_P/A_Pl 

 ~ d~ d/l ~ Ad 



Suppose an external force of 30,000 Ib. be applied to a bar 

 whose length is 10 in. and whose cross-section is 1 sq. in., and 

 suppose the extension under this force is 0.01 in. We should 

 have 



PZ = (30,000) (10) 

 Ad~ 



30,000,000 



If the external force, or load, in pounds per square inch be 

 represented by ordinates and the corresponding elongations or 



Deformation 

 ( Unit Elongations, Inches per inch ) 



FIG. 9. 



compressions be represented by abscissae, then the action of the 

 specimen under test may be indicated by what is known as a 

 stress-deformation diagram. In Fig. 9 a typical stress-deforma- 

 tion diagram is shown for medium steel in tension. There are 

 three significant points which need to be noted. These are: 

 the elastic limit, the ultimate strength, and the breaking-point. 

 These three points are indicated by the letters A, B, and C, 

 respectively. 



