114 F. M. GUMMOW. 



fracture in plain concrete bodies, did not fracture and must 

 therefore have taken part in the resistance of the stress. 

 (2) That if the loadings and unloadings be repeated with 

 the same load time after time, the coefficient of form-alter- 

 ation becomes greater and greater until a certain limit is 

 reached, whence the concrete-iron body acts as a perfectly 

 elastic body, that is, its length alterations become strictly 

 proportionate to the loads, a phenomenon which we are 

 only accustomed to find in such bodies as wrought iron and 

 steel. 



Subjecting thereafter the concrete-iron body to greater 

 loads than were applied in the reloading and unloading 

 (above mentioned) then the line of form-alteration will 

 continue in the direction of O" G E exactly as if the same 

 had been subjected to the greater load from the first. In 

 other words the construction, within its elastic limit, 

 regains by the application of a greater load entirely its 

 former ability of resistance. 



The character of the line of form-alteration in tension 

 suggests three distinct stages or periods during testing to 

 destruction. In the earlier stages of loading called the 

 first period, lying between O and B. During that period 

 the elongations in the tension fibres increase slowly until 

 the point B is reached, by which time the concrete has 

 undergone such elongations w T hich would in an unarmoured 

 or plain concrete body have caused fracture. 



The stresses in the iron are comparatively small, indicating 

 that the concrete takes up the bulk of the loading, and 

 this is more especially the case where initial stresses are 

 already affecting the two materials, in which case the iron 

 does not take up any tension until such elongations are 

 reached as overcome the initial compressive stresses. The 

 lines of form-alteration indicate that the two materials 

 during this period behave as if they were independent of 



