INGENUITY AND LUXURY 



support a load of four tons was loaded with thirty-four 

 tons of iron rails as an experiment by a French engineer. 

 Under this load four cracks appeared, and there was a 

 slight sagging at the center. As the beam did not break, 

 the load of rails was left in place. At the end of eight 

 years no more cracks had appeared ; and at last accounts 

 the beam was still supporting its load. 



THE REINFORCING SKELETON OF METAL 



When it comes to determining the exact form of 

 metal reinforcement best calculated to strengthen con- 

 crete, it is evident, from the numerous systems which 

 have been evolved, that no single one is preeminently 

 superior, but that there are a great number which are 

 perfectly practical. Almost every engineer seems to 

 have evolved a system of his own, more or less care- 

 fully studied out along practical, scientific lines. Some 

 of these are simply longitudinal and transverse rods of 

 the simplest arrangement, while others are complicated 

 networks of steel bars and wires. It is the aim of 

 every system to use the smallest possible amount of 

 metal to obtain a given strength; and the amazing 

 thing to the layman is how little metal is required for 

 this purpose, where every strain, even of the smallest 

 wires, is accurately calculated, and placed to the best 

 advantage. Since the greatest strength of concrete 

 lies in resisting compression, it is obvious that the re- 

 inforcement of upright columns require less metal 

 strengthening than horizontal ones, and must have 

 this reinforcement differently placed. Everything 



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