250 STEEL REINFORCEMENT 



The principle of hooped columns is best explained as follows : 

 It is well known that a column of sand will not resist com- 

 pression, because it will spread, and it is likewise certain 

 that a cylinder of,- say, very thin metal will sustain only 

 a small load. However, if the cylinder is filled with sand, 

 the combination, in which the tensile strength of the cylinder 

 is realized with the compressive resistance of the sand, will 

 result in a strong column, or post, capable of resisting con- 

 siderable compression. This principle is applied to the rein- 

 forcement of concrete columns by binding, or tying, together 

 the concrete with cylindrical hoops, or helical, or spiral, 

 windings of steel. 



Parts of Steel Reinforcement Defined. In Fig. 2 (a) is 

 shown a perspective view of a complete bay of a reinforced- 

 concrete floor system, and in (6), a diagrammatic representa- 

 tion of a typical system of reinforcement for a concrete 

 girder and column. In (a), the heavy members A running 

 between columns are commonly known as girders, and the 

 lighter members B running between girders, as beams. In 

 both (a) and (b), the rods, or bars, a are the main reinforcing 

 bars, or rods, of the girders. The beams, of course, have 

 similar main reinforcing bars. Of these main reinforcing 

 bars, several are bent up, as at b, to form trussed bars. The 

 web reinforcement of the girders is shown at c, and consists 

 of U-shaped pieces of iron or steel, called stirrups. ( The rods 

 that reinforce the slab of the reinforced-concrete floor system, 

 called slab rods, are shown at d. This slab reinforcement 

 may consist of straight rods, expanded metal, woven- wire 

 lath, or any other metallic reinforcement. The rods of the 

 columns, shown at e, are called longitudinal column rods, and 

 the hooped separators, or ties, shown at f, column ties. 



Any rod, or bar, used to resist shearing stresses is desig- 

 nated as a shear bar. A rod, or bar, used to resist the shrink- 

 age of the concrete in setting, or to provide against cracks 

 due to thermal changes, is called a shrinkage rod. Shrinkage 

 rods are shown at g in view (a). A rod used to connect 

 abutting beams or girders is called a tension bar or a tie- 

 bar' The short rods used at the splice when longitudinal 

 column rods are butted are called splice rods, or bars. 





