Bridge Load Rating Factor
Mediumratingload factors
Use the simplified rating expression RF = (C − γD·MD)/(γL·Mlive). Adjusted resistance C = 1,000 kN·m already includes resistance, condition and system adjustments. Dead-load effect MD = 200 kN·m. Live-load effect Mlive = 300 kN·m already includes dynamic allowance. γD = 1.25 and γL = 1.75. What is RF?
- A1.43
- B1.07
- C1.05
- D2.67
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Answer: A. 1.43
Factored dead demand γD·MD = 1.25(200) = 250 kN·m. Remaining capacity = 1,000 − 250 = 750 kN·m. Factored live effect γL·Mlive = 1.75(300) = 525 kN·m. RF = 750/525 = 1.43. 1.07 adds a second dynamic allowance (1.33) to a live effect that already includes it: 750/(525·1.33). 1.05 factors capacity again (dividing C by 1.25 before subtracting): 550/525. 2.67 uses no load factors at all: (1,000 − 200)/300.
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