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(t1,t2,t3)=(7,14,365)

(ti,t2,t3)=(28,90,365)

As/bd=0.5%

-2%

+2%

As/bd=1.5%

-3%

+3%

Table 7.5. Influence of load history on the slenderness limit. ((L/d)(10,60,365)- (L/d)(t1,t2,t3))/(L/d)(10,60,365)

Table 7.5. Influence of load history on the slenderness limit. ((L/d)(10,60,365)- (L/d)(t1,t2,t3))/(L/d)(10,60,365)

7.4.3.6 Influence of additional reinforcement

The slenderness ratio is referred to the deflection occurring in case the strict reinforcement is placed in the beam. However, it is normal for structures to have extra reinforcement due to rounding off, on the safe side, of the required values.

The influence of this factor has been studied by comparing the deflection of a beam with different required reinforcement ratios in case an extra 5% or 10% reinforcement is provided in tension. The

Figure 7.19. Influence of round-off extra reinforcement in the deflection of a simply supported beam

7.4.3.7 Influence of distribution of reinforcement

Distribution of reinforcement in beams is not constant in practice.

Normally, minimum reinforcement is placed near the points of zero bending moment (base reinforcement) and a supplementary reinforcement is placed in the areas near the maximum bending moment. The influence of the length of the additional reinforcement has been studied for two reinforcement ratios (0.5% and 1.5%) and assuming a length (ls) of the supplementary reinforcement of 60, 80, 90 and 100% of the span. Outside this length minimum reinforcement was considered. The results are given in Table 7.6 by comparing the deflection for ls_100% to the deflection for the different values of ls. It can be seen that for low values of the reinforcement ratio and no influence is detected. The difference becomes significant only for high reinforcement ratios and small length of additional reinforcement.

100%

Ratio \JL

0 0

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