A 2x10 Southern Pine joist spans 14 feet and supports a live load of 40 psf plus dead load of 15 psf. The joists are spaced 16 inches on center. What is the total load per linear foot on each joist?
Correct Answer
B) 73.3 pounds per linear foot
Total load = (40 psf + 15 psf) × (16 inches ÷ 12 inches) = 55 psf × 1.33 ft = 73.3 pounds per linear foot. The joist spacing determines the tributary width for load calculation.
Why This Is the Correct Answer
Option B is correct because it properly accounts for the tributary width of the joist. Each joist supports the load from a strip of floor equal to its spacing (16 inches = 1.33 feet). The total load per square foot (55 psf) must be multiplied by this tributary width to get the load per linear foot on each joist. This gives us 55 psf × 1.33 ft = 73.3 pounds per linear foot.
Why the Other Options Are Wrong
Option A: 55 pounds per linear foot
Option A only gives the total load per square foot (40 + 15 = 55 psf) but fails to account for the tributary width. This would be the answer if joists were spaced 12 inches on center, but at 16 inches spacing, each joist carries more load.
Option C: 88 pounds per linear foot
Option C appears to multiply the total load by an incorrect factor, possibly confusing the calculation method or using wrong spacing assumptions.
Option D: 110 pounds per linear foot
Option D doubles the correct answer, possibly from incorrectly applying the tributary width concept or making an error in unit conversion.
Memory Technique
Remember 'TLC': Total load × Length (tributary width) = Concentrated load per linear foot. The joist spacing becomes the tributary width that each joist must support.
Reference Hint
Look up structural load calculations in Chapter 16 (Structural Design) of the Florida Building Code, or beam/joist loading tables in structural engineering references.
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