A contractor is installing hurricane straps rated at 1,500 pounds each. If the calculated uplift force on a rafter is 3,200 pounds, how many straps are required with a 2.0 safety factor?
Correct Answer
B) 5 straps
Required capacity = 3,200 lbs × 2.0 = 6,400 lbs. Number of straps = 6,400 ÷ 1,500 = 4.27, round up to 5 straps minimum.
Why This Is the Correct Answer
Option B is correct because the total required capacity is 3,200 lbs × 2.0 safety factor = 6,400 lbs. Dividing by each strap's 1,500 lb capacity gives 6,400 ÷ 1,500 = 4.27 straps. Since you cannot install a partial strap, this must be rounded up to 5 complete straps to meet the safety requirements. This ensures adequate structural protection against hurricane uplift forces.
Why the Other Options Are Wrong
Option A: 6 straps
6 straps would provide 9,000 lbs capacity (6 × 1,500), which exceeds the required 6,400 lbs. While this would be safe, it's unnecessarily conservative and wasteful of materials and labor costs.
Option C: 3 straps
3 straps would only provide 4,500 lbs capacity (3 × 1,500), which is significantly less than the required 6,400 lbs with safety factor. This would create a dangerous structural deficiency.
Option D: 4 straps
4 straps would provide 6,000 lbs capacity (4 × 1,500), which falls short of the required 6,400 lbs with the 2.0 safety factor. This creates an unsafe condition that doesn't meet code requirements.
Memory Technique
Remember 'Safety First, Round Up': Always multiply by safety factor FIRST, then divide by strap capacity, and always round UP to the next whole number of straps.
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