Question

A rectangular concrete beam measures 12 inches wide and has a depth of 26 inches. The centroid of the tension rebars is located 4 inches from the tension surface of the beam. Use fy = 60 ksi f’c = 3 ksi, compressive failure strain of concrete = 0.003.

(A) Find the required tension rebars As to carry Mu = 5,700 kips-in. Show that the steel ratio does not meet the ACI requirements.

(B) What can you do to meet ACI requiremen for this moment if you are not allowed to change the dimensions of the concrete beam?

(C) Now use 4 No. 9 and 2 No. 8 bars in two layers (each layer with 2 No.9 and 1 No.8) for tension rebars and 2 No. 9 and 1 No. 8 bars (in one layer) for compression steel. The centroid of the compression rebars is located 2.5 inches from the compression surface of the beam and the location of the centroid of the tension rebars is the same as part (A). Check if this beam can carry the above moment (Mu = 5,700 kips-in.) and check if the steel ratio meets the ACI requirements. Use Table A.2 to obtain the steel area.

(D) Show the exact location of suggested rebars in part (C) and the concrete cover. Check all the ACI requirements. It is not necessary to show stirrups.

Answer 1