[10] 1. A 25 ft. reinforced concrete beam is being designed to support a uniformly distributed load. This

load has an average value of 1.4 kip/ft with a standard deviation of 0.3 kip/ft. The average flexural

resistance of the beam is 230 ft-kip with a standard deviation of 15 ft-kip, and the average shear

resistance of the beam is 45 kip with a standard deviation of 7 kip.

1) [1] Find the global safety factor in both flexure and shear (note: safety factor = resistance/load

effect)

2) [2] Find the safety index in both flexure and shear

3) [3] If the average flexural resistance is increased to 270 ft-kip with the same standard deviation

of 15 ft-kip, find the new safety index in flexure

4) [3] If the standard deviation of the shear resistance is decreased to 5 kip with the same shear

resistance, find the new safety index in shear

5) [1] Comment on your results

25 ft.

Fig. 1. Reinforced concrete beam

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