Dynamic Amplification Factor of Continuous versus Simply Supported Bridges Due to the Action of a Moving Load

Abstract

This paper extends the research on dynamic amplification factors (DAFs) caused by traffic loading from simply supported to continuous (highway and railway) bridges. DAF is defined here as the ratio of maximum total load effect to maximum static load effect at a given section (mid-span). Another dynamic amplification factor FDAF can be defined as the ratio of the maximum total load effect throughout the entire bridge length to the maximum static load effect at a given section (mid-span). For continuous beam DAF/FDAF can be determined for both sagging and hogging bending moments. Noticeable differences appear among DAF/FDAF of mid-span bending moment in a simply supported beam, DAF/FDAF of the mid-span bending moment in a continuous beam and the DAF/FDAF of the bending moment over the internal support in a continuous beam. Three span lengths are tested in the simply supported beam models as well as three continuous beams made of two equal spans. Each model is subjected to a moving constant point load that travels at different velocities. The location of the maximum total moment varies depending on the speed. FDAF and DAF are plotted versus frequency ratio. The results showed that FDAF is often greater than DAF in simply supported and continuous beams. Also, FDAF of sagging bending moment in continuous beam is about 12 % greater than that the simply supported case. Moreover, the results showed that FDAF of hogging bending moments is about 3 % greater than those of sagging bending moments in continuous beam. Consequently, all values were larger than those of simply supported case.