Ferro-Concrete. 



389 



by the above-mentioned tests will doubtless exist in ferro-concrete 

 structures under a bending or compression load. Supposing we had 

 to investigate a column or a concrete wall, I am sure you will agree 

 with me that the assumption of the immutability of the cross-sec- 

 tions cannot be correct, at least not at the point where the external 

 force strains the structure, as the load is always distributed over 

 a more or less extensive area of the surface of the structure. But 

 the impossibility to estimate the manner of load distribution in 

 structures makes every investigation in that direction dubious. 



If we take the case of a body under a bending load, we will 

 also find that the assumption in question does not possess a scientific 

 basis. The law of bending, as taught to-day, shows us that the 

 assumption of the immutability of the cross-sections was originated 

 for the purpose of simplifying our calculations. In certain limits, 

 however, it was possible to prove this assumption through tests which 

 were made with bodies of rectangular cross-sections, but nothing 

 has confirmed it with bodies of irregular shape, but on the other 

 hand it is known that the immutability is incompatible with the 

 existence of shearing stresses, because these cause the section to curve 

 into an S-shaped form. 



Law of the Elastic Power. 



Through the two above-mentioned assumptions, the manner in 

 which a body of ferro-concrete changes its form is defined, and it only 

 remains to determine the law, which will define in the equilibrium 

 actions the elastic power of the concrete in connection with the 

 corresponding changes of form. 



This question has troubled theorists very much, and has been 

 the cause of long disputes. 



To make the point in question as clear as possible, we will 

 only consider the condition of prismatic bodies subjected to bending. 



I 



o a 

 Figure I. 



