Investigation of Dynamic Impact Factor of Metal Multipipe Culvert under Shallow Cover

The design of buried culverts and other buried components is typically carried out by static analysis assuming static truck loads. In reality, the culvert is subjected to a combination of static and dynamic loads. The total design load capacity depends on several parameters such as load modifier, load factor, and dynamic load allowance depends on the depth of earth cover above the culverts. However, there is limited information for minimum soil cover (less than or equal to three feet at the crown) to assess a pipe’s dynamic load allowance. The objective of this study is to investigate the performance and dynamic response of a triple circular culvert instrumented and tested under dynamic truckloads with different truck speeds. For the dynamic loading, the truck was driven over the driving lane at four different speeds: 5, 10, 20, and 25 mph. The strains at the five locations of the outside Pipe-1 and the center Pipe 2 and the displacements were recorded at a 1,200 Hz frequency. Due to the symmetry of the pipe construction, only two pipes were instrumented; Pipe-3 might react in a manner similar to Pipe 1. Response to dynamic loads was measured by driving the loaded truck over the culvert at various speeds ranging from 5 mph to 25 mph. Maximum longitudinal and transverse strains were observed in Pipe 2. The maximum longitudinal strain of 1,112 με was observed at sensor 2-3AL during the run at 20 mph run; the maximum transverse strain of 713 με was observed at sensor 2-2AT during the run at 20 mph run. These dynamic results were then used with previously published static experimental results by the authors to calculate the dynamic load allowance. It has been found that the dynamic load allowance obtained was higher than the magnitude recommended by AASHTO LRFD Bridge Design Specification for buried culverts. However, it is recommended that the dynamic load allowance value be investigated further in the buried culverts under shallow cover since these results yielded a higher amplification factor than the one recommended by the AASHTO LRFD.