In roof trusses, the most frequently used section is
- Atwo-angle sections placed back to backCorrect
- Btwo channel sections placed back to back
- Ctwo channel sections placed at a distance apart
- Dfour angle section
Solution
Concept
Common structural sections for roof trusses
Formula
NONE
Step-by-step solution
1. Roof truss members carry light to moderate axial forces. 2. Two angle sections placed back to back are easily connected to gusset plates using rivets or welds. 3. This configuration provides symmetry, prevents eccentric loading, and is cost-effective, making it the most frequently used section in roof trusses. Answer: A
Explanation
In roof trusses, members are commonly constructed using two angle sections placed back to back separated by gusset plates. This arrangement provides symmetrical cross-sectional properties about the plane of the truss, eliminating eccentric bending moments. Therefore, option A is the most frequently used section in standard roof truss design.
Why the other options are wrong
A) Two-angle sections placed back-to-back are the standard choice for light roof truss members due to structural efficiency and ease of connection. B) Two channel sections placed back to back are heavier and economically unsuited for light roof trusses. C) Spaced channel sections are typically reserved for heavy built-up columns rather than light truss members. D) Four-angle box sections entail higher fabrication costs and are utilized in heavy towers or columns.
Shortcut
Roof trusses commonly use two angle sections placed back-to-back.
Common mistake
Selecting channel sections or single angles rather than two angles placed back to back.
Correct answer: A) two-angle sections placed back to back