Load Rating Corrugated Metal Culverts with Shallow Soil Cover

Eight low-profile arch corrugated metal culverts were recently annexed by the city of Anniston, Alabama. These structures are nearly 80 years old and have never been load rated. To satisfy federal requirements, load rating of the culverts was required. Attempts to rate these structures using methods developed by the corrugated steel pipe industry implied that the culverts require posting due to low soil cover, without any consideration for structural integrity. Guidance for load rating of steel and concrete bridges and cast-in-place concrete culverts is well established, while the guidance for corrugated metal culvert structures is limited. The objective of this study was to examine the contemporary practice of load rating corrugated metal culverts with shallow cover and use diagnostic load testing to demonstrate the capacity and overcome the shortfall of the current rating methods. To verify the load-carrying capacity of these structures and improve the load rating, diagnostic load tests were therefore carried out to assess the load response of two of the culverts using a $381.3\text{-}\mathrm{kN}$ ($85.7\text{-}\mathrm{kip}$) test truck. The load testing program featured a very simple instrumentation package that was easy to install, recover, and reuse. The instrumentation plan consisted of displacement transducers and electrical resistance strain gauges. Load, displacement, and strain data collected in the field load tests were analyzed, which showed satisfactory performance with a maximum deflection of less than 0.1% of the span length and a maximum strain that corresponds to approximately 24% of the estimated yield stress. Following standard procedures, the test response data were used to improve the analytically derived rating factors, and challenges associated with the approach are discussed.