248 STEEL REINFORCEMENT 



cutting away, the old surface, saturating it with water, and 

 working into it thin coats of a 1-1 Portland-cement mortar, 

 and, then, while the coating is still fresh, placing against it 

 the new concrete. 



There are some high-grade, imported cements that, in the 

 form of cement mortar, more readily adhere to old concrete 

 work than the usual Portland cements. These cements are 

 frequently used for patching and piecing out work already 

 in place. 



ELEMENTS OF STEEL REINFORCEMENT 



THEORY OF STEEL REINFORCEMENT 



Principles of Construction. When a beam is subjected 

 to transverse stress, the portion of the beam section above 

 the neutral axis is in compression, while in that portion 

 below the neutral axis, tensile stresses are created. Ordi- 

 narily, concrete is about ten times as strong in compression 

 as it is in tension. Thus, it can readily be seen that a beam 

 of plain concrete without steel reinforcement would fail 

 primarily from lack of tensile resistance, without realizing 



its full compressive 

 strength. In order, 

 therefore, to make 

 concrete an eco- 

 nomical material to 

 use in construction, 

 its deficiency in 

 FIG. 1 tensile resistance 



must be made up by embedding steel rods, bars, or some 

 other form of metallic reinforcement in that portion of the 

 beam section subjected to tensile stress. 



In order to explain more fully this primary principle of 

 reinforced concrete, reference is made to the reinforced, 

 rectangular concrete beam shown in Fig. 1. The neutral line 

 of the section is shown at y\ y\ in the side view (a), while the 

 neutral axis is represented by y y in the end view (fc). When 

 the concrete beam is under transverse stress, there is neither 



