Field Investigation of Metal Multi-Pipe Culvert under Shallow Cover

Across the United States (U.S.), a large number of corrugated steel pipes, installed three or four decades ago, are approaching the end of their useful service life. However, information for minimum soil cover (less than or equal to three feet at the crown) and the applicability of previous methods to assess a pipe’s load rating factor is limited. To obtain such a load rating factor, measuring structural responses of several metal culvert structures in the field under in-service live loads during controlled load tests are required because neither Federal Highway Administration (FHWA) nor American Association of State Highway and Transportation Officials (AASHTO) has a comprehensive procedure on load rating of large-span culverts and multi-pipe system. In this study, a triple circular culvert was instrumented and tested under in-service live loads during controlled load tests to investigate the culver performance and calculated the pipes’ load rating factor. Because of the symmetry of the construction, only two pipes were instrumented with strain gauges and string potentiometers, the outside Pipe-1 and the center Pipe-2; Pipe-3 might react in a manner similar to Pipe-1. Eleven positions for static loading, where the positions indicated the location of the load from the tandem axle, which was heavier than the other axle, were applied to measure the strains and deflections and calculate the stresses, thrusts, and bending moments. For Pipe-1, the highest longitudinal strain recorded was 919 με located at gauge 1-3AL when the load was in Position 5. The maximum deflection was 0.395 in. recorded at location 4 when the load was in Position 3 (on the crown). The Pipe-2 of the culvert responded to the load with fewer strains, deflections, and thrusts/moments than Pipe-1 results except for transverse strain with 472 με located at gauge 2-2AT. The anecdotal field evidence of a load rating factor for cover less than minimum suggests a guide to stability design criteria for metal structures method proposed by ODOT is too conservative.