Dynamic Amplification Factor in Culverts: a Parametric Study using Three-Dimensional Finite Element Analysis

Load rating is a common practice used to evaluate the condition and strength of bridges and culverts. When load ratings result in rating factor values of less than one, bridges and culverts must often be posted to limit the speed and weight of vehicles traveling over them. In many cases, such restrictions could significantly limit or prevent traffic flow and are costly. To evaluate the dynamic response of a structure, a dynamic amplification factor (DAF) is applied to the response of the structure subjected to an equivalent static load. American Association of State Highway and Transportation Officials (AASHTO) guidelines specify the DAF for culverts as a function of only fill depth. Studies have shown that AASHTO-calculated DAFs can be overly conservative in many cases, thus resulting in the unnecessary posting of culverts. Though this issue is relatively widely recognized, a better alternative for determining DAFs has yet to be proposed and accepted. In the results reported in this paper, DAFs were calculated from the static and dynamic response of 83 unique pavement-soil-culvert models using three-dimensional (3D) finite element analyses (FEAs). Four parameters were chosen and varied across three values to assess their effect on the DAF. The parameters included the span length, the asphalt pavement thicknesses, the soil fill depth, and the elastic modulus used to characterize the soil. Two additional models, with intermediate fill depths, were also analyzed. The results of this study indicate that, compared with the other parameters, DAFs are most affected by changes in the fill depth. However, contrary to AASHTO’s guidelines, the DAF increases with increasing fill depth.