254 STEEL REINFORCEMENT 



There are to be had on the market twisted bars of square 

 and hexagonal section. Such bars are from 8 to 25% 

 stronger than the bars in their original form. The per- 

 centage of increase of strength is greatest with the bars of 

 small section and least with those of large section. 



Rerolled Bars. Bars made from old steel rails can be 

 obtained for reinforcing concrete. In making such bars, 

 the flange, web, and bulb of the rails are cut apart, and 

 rerolled into square and round sections. The square sections 

 may be had twisted, the twisting being performed while the 

 material is hot. 



Much of this material has a high elastic limit and tensile 

 strength, but it is inclined to be brittle and variable in 

 strength and ductility. Besides, any lapping or folding of 

 the original material when passed through the rolls is liable to 

 develop laminations throughout the bar, tending to diminish 

 its strength. 



TYPES OF STEEL REINFORCEMENT 

 Plain Bar Iron. The cheapest form of metallic reinforce- 

 ment for concrete is the plain, round, rolled bar. Bars of 

 this kind can be obtained in 

 any part of the United States. 

 The pound price of round, 

 rolled bars is lower than that 

 of any other form of rolled 

 steel, so they offer the cheapest 

 and most available material. 

 For slabs, f- to -in. round 

 bars are used, while for beam, 

 girder, and column reinforce- 

 ment, from |- to l|-in. bars 

 are ordinarily employed. 



<*> The principal objection to 



FIG. 1 the use of plain, round bars in 



reinforced-concrete work is that they are not gripped, or held, 

 well by the concrete. 



Plain square and flat bars are sometimes used for the 

 reinforcement of concrete, though, generally, both of these 

 sections, when so used, are deformed by twisting. 





