Commercial Building Inspector B2Structural SystemsMedium
A commercial building inspector is reviewing the plans for a new single-story warehouse with a large open floor area. The structural system utilizes long-span steel trusses for the roof. What is the primary purpose of cambering these long-span steel trusses?
- ATo offset anticipated deflection and appear level under dead load.
- BTo reduce the required amount of steel in the truss.
- CTo improve the seismic performance of the truss system.
- DTo increase the ultimate strength of the truss members.
Show answer & explanationAnswer & explanation
Correct answer: A. To offset anticipated deflection and appear level under dead load.
Cambering involves pre-stressing or curving a structural member in the opposite direction of its anticipated deflection. For long-span trusses, this is primarily done so that under dead load, the truss appears level or nearly level, preventing a visually undesirable sag and ensuring proper drainage for roof systems.
Why the other options are wrong
- B. Cambering does not inherently reduce the required amount of steel; it's a shaping technique for deflection control.
- C. While deflection control can indirectly affect seismic performance, cambering's direct purpose is not primarily for seismic resistance but for serviceability.
- D. Cambering does not increase the ultimate strength of individual members; it's a serviceability consideration.
Cambering (Steel Trusses)
The intentional upward curvature or pre-setting of a structural member, such as a long-span steel truss, to counteract the anticipated downward deflection under gravity loads.
- Primarily for aesthetic and serviceability reasons.
- Offsets deflection, making the member appear level.
- Common for long-span beams, girders, and trusses.
Memory trick: Trusses need strength, stability, and straightness.