Factored Moment for Girder Strength
Mediumload factorsstrength combination
At one bridge girder section, concurrent same-sense moments are MDC = 300 kN·m (structural dead load), MDW = 80 kN·m (wearing surface and utilities), and Mlive = 420 kN·m (live load already including dynamic allowance). Evaluate the supplied combination Mu = 1.25MDC + 1.50MDW + 1.75Mlive. What is Mu?
- A1,472.55 kN·m
- B800 kN·m
- C1,230 kN·m
- D1,400 kN·m
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Answer: C. 1,230 kN·m
Factor each effect and add: 1.25(300) = 375; 1.50(80) = 120; 1.75(420) = 735. Mu = 375 + 120 + 735 = 1,230 kN·m. Dynamic allowance is already in Mlive. 1,472.55 kN·m applies another 1.33 impact to the live term (375 + 120 + 1.33·735). 800 kN·m is the unfactored sum. 1,400 kN·m applies the single largest factor, 1.75, to every effect.
kN·m
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