IMPACT ANALYSIS OF CONTINUOUS MULTIGIRDER BRIDGES DUE TO MOVING VEHICLES

The impact of six continuous multigirder steel bridges, with overall span lengths ranged from 130 ft to 260 ft (39.62 m to 70.25 m), due to vehicles moving across rough bridge decks is analyzed. Bridges are modeled as grillage beam systems. The vehicle is simulated as a nonlinear vehicle model with 12 degrees of freedom according to the HS20-44 truck design loading included in the American Association of State Highway and Transportation Officials (AASHTO) specifications. Based on International Standards Organization specifications, the road-surface roughness of the approach roadways and bridge decks is generated from the power spectral density function for very good, good, average, and poor roads. Maximum dynamic responses of the longitudinal girders are evaluated for two trucks (side by side) through changing their transverse positions, with different speeds and road-surface roughnesses. A comparison between the impact factors calculated by the presented theory and AASHTO impact formula is given. Furthermore, the effect of span length, transverse stiffness, spacing of girders, damping ratio, and others are discussed. The results can be used for the design of continuous multigirder steel bridges and the further study of impact formula proposed by AASHTO specifications.