Steel Beams

Question 1

For a typical simple span steel W-section, what part buckles in flexure?

Answer 1

the top flange

Question 2

When the stress at a section in a beam reaches a level of Fy across the entire depth, what is formed?

Answer 2

a plastic hinge

Question 3

In LRFD steel beam design, what tabulated sectional property is usually used to choose the beam size?

Answer 3

The strong axis Plastic Modulus, Zx

Question 4

Except for unusual conditions of loading, what type of stress generally governs the design of a steel beam?

Answer 4

bending stress

Question 5

What two methods of analysis are used by the AISC steel manual?

Answer 5

Allowable Stress Design (ASD) and Load & Resistance Factor Design (LRFD)

Question 6

What do the two numbers used to designate a wide flange steel section describe?

Answer 6

nominal depth in IN and weight in PLF

Question 7

The beam shown weighs 135 PLF. What is its designation (name)?

W Beam
h = 35.55”

Answer 7

W35x135

Question 8

Assuming the areas of the two sections shown are equal, which would make a more efficient beam?

A. square wide flange beam
B. Rectangular wide flange beam where h > b

Answer 8

B

Question 9

A column is usually more square than a beam, a beam has deeper section than a column. (T/F)

Answer 9

True, evenly braced columns have rx proportional ry, but beams have a strong axis in bending, x-x.

Question 10

The flange of a beam is usually thinner than its web. (T/F)

Answer 10

false, it is thicker because it carries more of the flexural stress.

Question 11

For steel sections, what do the section descriptors W, S, C, and L stand for?

Answer 11

W = Wide flange
S = American standard beam
C = American standard channel
L = angle

Question 12

What is the weight in pounds per linear foot (PLF) of a W36x300 steel section?

Answer 12

300 plf

Question 13

For a W18X76 with A-36 steel, which orientation would carry the greater load?

A. Vertically oriented W beam
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B. Horizontally oriented W beam
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Answer 13

A, since x is greater than y

Question 14

Which steel section will carry the highest strong axis moment?
A) W18X60
B) W24X62
C) W30X108
D) W21X68

Answer 14

C (see section modulus table)

Question 15

What is the total weight in kips of a 30’ long W16X100 beam?

Answer 15

3 kips, 30’ x 100 plf = 3000 lbs = 3 k.

Question 16

What is the plastic section modulus?

Answer 16

The plastic section modulus is one of the classifications of a section modulus, a geometric property for a given cross section.
The plastic section modulus is used for materials such as steel where elastic yielding is acceptable and plastic behavior is acceptable within limit