You are viewing this question as it will appear in the manual grading interface. Return to the normal view when you are done.

Compute the normal stress

Consider the I-beam cross-section:

The table below has the geometric properties for different specifications for a steel beam:

Designation	h (in)	w (in)	Ix (in^4)	Iy (in^4)
S24 x 80	24	7	2,100	42.2
S20 x 96	20.3	7.2	1,670	50.2
S20 x 86	20.3	7.06	1,580	46.8
S20 x 75	20	6.385	1,280	29.8
S20 x 66	20	6.255	1,190	27.7
S18 x 70	18	6.251	926	24.1
S18 x 54.7	18	6.001	804	20.8
S15 x 50	15	5.64	486	15.7
S15 x 42.9	15	5.501	447	14.4
S12 x 50	12	5.477	305	15.7

For the beam designations indicated below, determine the maximum normal stress $\sigma_x$ assuming that the maximum moment is equal to $M_{max} = 4 \times 10^5 \rm\ lb \cdot in$.

Designation	$\sigma_x$
S15 x 42.9
S12 x 50
S20 x 75
S18 x 70

Note: this is an example of repeated variant question. Read more here.

Correct answer

Designation	$\sigma_x$
S15 x 42.9	`6.71140939597`
S12 x 50	`7.86885245902`
S20 x 75	`3.125`
S18 x 70	`3.88768898488`

Student view placeholder

In student views this area is used for assessment and score info.

Tools

Staff information

Question

QID:

demo/annotated/engBeamStress

Title:

Compute the normal stress

Variant

Started at:

2026-09-19 07:59:46 (CDT)

Duration:

Show/Hide answer

{
  "sigma1": 6.7114093959731544,
  "sigma2": 7.868852459016394,
  "sigma3": 3.125,
  "sigma4": 3.8876889848812093
}

This box is not visible to students.