What is the maximum allowable deflection for a 20-foot roof beam under Hawaii's high wind load conditions?
Correct Answer
A) L/360 (0.67 inches)
Hawaii building code requires L/360 deflection limits for roof beams under wind loads: 20 feet × 12 inches/foot ÷ 360 = 0.67 inches maximum.
Why This Is the Correct Answer
The L/360 deflection limit is the standard for structural members under live loads (including wind) in Hawaii's building code. For a 20-foot (240-inch) span: 240 ÷ 360 = 0.667 inches, which rounds to 0.67 inches. L/360 is the most restrictive common deflection limit and is required for roof beams under wind loads in Hawaii, which experiences significant wind events including hurricane-force conditions.
Why the Other Options Are Wrong
Option B: L/240 (1.0 inch)
L/240 (1.0 inch for a 20-foot span) is a less restrictive deflection limit, typically used for floor beams supporting non-brittle finishes or for roof members not subject to high wind loads. Using L/240 under Hawaii's high wind conditions would allow excessive deflection that could compromise roofing system integrity.
Option C: L/300 (0.8 inches)
L/300 (0.8 inches for a 20-foot span) is an intermediate value that falls between standard code limits. It is not a standard code-prescribed limit for roof beams under wind loads and does not appear in Hawaii's building code tables for this application.
Option D: L/180 (1.33 inches)
L/180 (1.33 inches for a 20-foot span) is the least restrictive option and is typically reserved for roof members in limited applications where deflection is less critical. Using L/180 under Hawaii's high wind conditions would be dangerously permissive and is not acceptable for standard roof beam design.
Memory Technique
Remember the hierarchy: 360 > 300 > 240 > 180 in the denominator = increasingly permissive (more deflection allowed). For Hawaii roof beams under wind: think '360 degrees in a full circle = maximum protection.' High winds demand the highest (most restrictive) standard.
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