lengthen the bottom portion of the beam. Thispart is said to be in tension, and that is where thesteel reinforcing bars are needed. As a result ofthe combination of the concrete and steel, thetensile strength in the beam resists the force ofthe load and keeps the beam from breaking apart.At the exact center of the beam, between thecompressive stress and the tensile stress, there isno stress at all—it is neutral.In the case of a continuous beam, it is a littledifferent. The top of the beam may be incompression along part of its length and intension along another part. This is because acontinuous beam rests on more than two supports.Thus, the bending of the beam is NOT all in onedirection but is reversed as it goes overintermediate supports.To help the concrete resist these stresses,engineers design the bends of reinforcing steel sothat the steel will set into the concrete just wherethe tensile stresses take place. That is why somereinforcing rods are bent in almost a zigzagpattern. The joining of each bar with the next,the anchoring of the bar ends with concrete, andthe anchoring by overlapping two bar endstogether are some of the important ways toincrease and keep bond strength. Some of thebends you will encounter are shown in figure 7-11.Figure 7-11.-Typical reinforcement bar bends.7-8
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