Given: DC = 1000 kip-ft, LL = 1500 kip-ft, ( \phi = 0.90 ) (flexure). Demand: ( Q_u = 1.25(1000) + 1.75(1500) = 1250 + 2625 = 3875 ) kip-ft. Required Resistance: ( M_n \geq 3875 / 0.90 = 4305 ) kip-ft.
Compared to ASD: ASD (FS=1.67) would require ( M_n \geq 1.67 \times (1000+1500) = 4175 ) kip-ft. LRFD requires 3.1% more capacity due to higher live load variability. aashto lrfd bridge design specifications 10th edition
[ \sum \eta_i \gamma_i Q_i \leq \phi R_n = R_r ] Given: DC = 1000 kip-ft, LL = 1500 kip-ft, ( \phi = 0