Question

How to determine the right structural steel section from the provided information?

1. Moment of inertia (Iz) = 640 inches^4, Area (A) = 17.9 inches^2

2. Moment of inertia (Iz) = 800 inches^4, Area (A) = 11.8 inches^2

E = 29000 ksi

If you can show the procedure to find the right answer, that would be great.

Answer 1

From the steel tables, start from the lowest depth and move up such that the Ix value (in the table) is greater than or equal to Iz value provided.

1) W10x112 (Ix = 716) and A = 32.9 in²

  W12x79 (Ix = 662) and A = 23.2 in²

W14x61 (Ix = 640) and A = 17.9 in²

Thus, W14x61 exactly matches with the required values of Iz and A values.

2) W12x96 (Ix = 833) and A = 28.2 in²

  W14x82 (Ix = 881) and A = 24in²

W16x67 (Ix = 954) and A = 19.6 in²

W18x50 (Ix = 800) and A = 14.7 in²

W21x44 (Ix = 843) and A = 13 in²

Thus, the lightest among the above sizes which satisfy the required Iz and A values is : W21x44.