PE Problem #9

6/14/2019

A 4-inch schedule 40 main is routed parallel in-between two beams and requires a trapeze hanger. The main is 2 ft. from one beam and 8.5 ft from the other for a total span of 10.5 ft. What is the smallest schedule 10 pipe capable of supporting this main as a trapeze hanger?
     a. 2 inch
     b. 2-1/2 inch
     c. 3 inch
     d. 3-1/2 inch

Solution | Posted 06/17/19

3 Comments

Ryan

6/14/2019 06:47:56 am

C) 3"

Section 9.1.1.7.1 of NFPA 13 (2016) states that the section modulus required in Table 9.1.1.7.1(a) shall not exceed the available section modulus in Table 9.1.1.7.1(b) or (c).

From Table 9.1.1.7.1(a), the required section modulus for a 10.5' schedule 40 span is 1.04.

From Table 9.1.1.7.1(b), a 3" schedule 10 pipe has a modulus of 1.04 as well, which does not exceed the required section modulus.

Ryan

6/14/2019 06:52:02 am

Correction: since the applied load is not at the midpoint, the equivalent length from A.9.1.1.7 should be used. The equivalent length is 6.5', with a required section modulus of 0.64. A 2.5" schedule 10 pipe has a section modulus of 0.69, so B) 2.5"

Amr

6/14/2019 10:46:03 am

I do agree with the last one, B) 2.5"

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