CSLB General Building (B)Framing and CarpentryHard
A window opening is 6 feet wide and supports a roof-only tributary width of 12 feet, with a combined dead and live roof load of 40 pounds per square foot. What is the reaction force at each end of the header supporting this opening?
- A2,880 pounds
- B480 pounds
- C960 pounds
- D1,440 pounds
Show answer & explanationAnswer & explanation
Correct answer: D. 1,440 pounds
First calculate the uniform load per linear foot on the header: 40 psf × 12 ft tributary width = 480 lbs/ft. Total load on the 6-foot header = 480 lbs/ft × 6 ft = 2,880 lbs. For a simply supported header with uniform load, each end reaction equals half the total load: 2,880 ÷ 2 = 1,440 lbs.
Why the other options are wrong
- A. This is the total load on the header, not the reaction at a single end.
- B. This is only the load per linear foot, not the actual end reaction force.
- C. This is 480 × 2, an incorrect intermediate calculation, not the final reaction.
Header Load & Reaction Calculation
Header design requires converting tributary roof area load into a uniform load per foot, then calculating total load and dividing by two for simply supported end reactions.
- Uniform load (plf) = psf × tributary width
- Total load = uniform load × span
- Each end reaction = total load ÷ 2
Memory trick: psf times width gives plf; plf times span gives total; total divided by two gives each end's share.