CSLB General Building (B)Framing and CarpentryHard
A jack truss transfers a concentrated point load of 900 pounds to the exact midspan of a girder truss that spans 20 feet and is simply supported at each end. Assuming the girder truss carries no other loads, what is the reaction force at each end support?
- A450 pounds
- B1,800 pounds
- C225 pounds
- D900 pounds
Show answer & explanationAnswer & explanation
Correct answer: A. 450 pounds
For a simply supported beam or truss with a single point load applied exactly at midspan, the load is shared equally between the two end supports. Therefore, each reaction equals half of the applied point load: 900 lbs ÷ 2 = 450 lbs.
Why the other options are wrong
- B. This doubles the load instead of splitting it between supports.
- C. This incorrectly divides the load by four instead of two.
- D. This is the full applied load, not divided between the two supports.
Midspan Point Load Reaction
For a simply supported beam or truss with a single concentrated load at midspan, each end reaction equals half of the applied load.
- Midspan point load splits equally between both supports
- Reaction = point load ÷ 2 for center-span loads
- Off-center loads require proportional distribution based on distance
Memory trick: A load dropped dead center splits evenly, half to each side.