12 in 15 in 410 bars 3 in f 60000 psi 124000 psi 18 i n Figu

12 in. 15 in. 4#10 bars 3 in. f,- 60.000 psi 1:24,000 psi 18 i n.--- Figure 2 Problem V- Questions 27 and 28 refer to the beam section shown in Figure 2 27) The depth of the neutral axis (c) for the cracked inelastic range at ultimate conditions is: A. 5 in B. 5.9 in C. 7.5 in D. 10.5 in 28) Which of the following statements is NOT true about this section: A. The tension steel is yielding B. The minimum amount of steel for this section per ACI is 0.72 in2 C. The section may be used as per ACI Section 9.3.3.1 (ie..a 20.004) D. The section shown is in the transition-zone

Solution

Soultion:-

(1) Answer (b) 5.9 inch

Depth of neutral axis (x_u) = 0.87f_yA_st/(0.36f_ckb)

                                             = 0.87*60000*4*/4*(1.25)²/(.36*4000*18)

                                             = 9.88 inch

X_ulim/d =0.48

X_ulim = 0.48 *d = 0.48 *12 =5.9 inch

X_ulim less than x_u

So section is over reinforced.

So exact neutral axis of section is 5.9 inch

(2) Answer:- (a) the tension steel is yielding

Reason:- Section is over reinforced section. So section will not fail due to steel.