CSLB General Building (B)Framing and CarpentryHard
A header spanning 16 feet over a garage door opening supports a uniform load of 400 pounds per linear foot from the roof structure above. Treating the header as a simply supported beam, what reaction load is transferred to each of the jack studs at the ends of the header?
- A6,400 pounds
- B8,000 pounds
- C3,200 pounds
- D1,600 pounds
Show answer & explanationAnswer & explanation
Correct answer: C. 3,200 pounds
Total load on the header = 400 plf × 16 ft = 6,400 lbs. For a simply supported beam with a uniform load, each end reaction equals half the total load: 6,400 ÷ 2 = 3,200 lbs, which each set of jack studs must be sized to bear.
Why the other options are wrong
- A. 6,400 lbs is the total load on the header, not the individual end reaction.
- B. 8,000 lbs does not correspond to any correct step in this beam reaction calculation.
- D. 1,600 lbs is a quarter of the total load, not the correct half-share reaction.
Simple Beam End Reactions
For a simply supported beam carrying a uniform load, each end reaction equals half the total load (total load = w × L, reaction = total load ÷ 2).
- Total load = uniform load (plf) × span length (ft)
- Each end reaction = total load ÷ 2 for a simple span
- Jack studs must be sized/counted to bear the calculated end reaction
Memory trick: 'Multiply load by length, then split the strength.'