388 Report S.A.A. Advancement of Science. 



bodies. It is, tlierefore, conformable for the purpose and in accord- 

 ance with the usual stability calculations, to disregard the elastic 

 change of form resulting from the shearing forces. One must there- 

 fore be satisfied to admit an eventual elastic sliding of the iron in 

 the concrete without being able to take the change of form into 

 consideration. All practical tests have proved that the iron takes 

 an actual part in the elongations of the concrete. 



Uniformity of Ferro-Concrete. 



Uniformity in the ferro-concrete is the chief factor, and upon 

 this the complete co-operation of the iron and the concrete entirely 

 depends. There is, for instance, the Monier system ; in this system 

 a reinforcement of iron rods of small cross-sections are used, which 

 are divided in the concrete in regular and short distances, and thereby 

 both materials are as closely as possible connected with one another. 

 For such a system it must be admitted that the smallest particles, 

 of the enveloping concrete take an active part in the bearing of the 

 stresses, to which the reinforcement may be subjected. If, however, 

 the reinforcement is limited to only a few iron bars of larger dia- 

 meter, or if it consists of profilated iron embedded in greater 

 distances from one another, the co-operation of both materials will 

 not be the same as in the former system, and the actual bearing 

 power will be less if these reinforcements are not interlocked by 

 cross-connections. 



This has been fully recognised by practical men, and most of 

 our constructional systems are based upon the principle that it is 

 better to divide the reinforcement uniformly, and to distribute iron 

 rods of smaller cross-sections at shorter distances. A construction 

 disregarding this principle cannot be acknowledged as a ferro-con- 

 crete building system, as the assumption of the co-operation of both 

 materials is not applicable with such a form of construction, and 

 economy cannot be effected as they require a greater factor of safety. 

 This will be especially proved with ferro-concrete constructions under 

 a bending load, which naturally causes shearing stresses. The dis- 

 advantage of a reinforcement of greater cross-sections will not be 

 so apparent with parts under compression or with bridge arches, 

 where shearing stresses of importance seldom appear. 



Immutability of the Cross-Sections. 



The common law of the strength of the building materials is 

 based upon the following assumption : — - 



Each cross-section of a prismatic body, which is subjected to 

 stresses caused by external forces remains even during its change 

 of form, and all scientists engaged in the investigation of ferro-con- 

 crete have accepted this law as a basis for their researches. It may, 

 however, be possible that this assumption is not correct. I may 

 mention that it has been proved through extensive tests, that in: 

 concrete bodies under tension, the tensile strains are not equally 

 distributed over the cross-sections of the body. This fact proved 



