Flexural Capacity Criteria for Load And Resistance Factor Rating of Shallow Covered Corrugated Metal Culverts

Departments of transportation are required to inspect and rate bridges that span more than 20 ft (6.1 m). One frequent challenge is rating shallow-buried corrugated metal culverts, since there are no standard methodologies deemed applicable to all sections and depths for defining the resistance when moment or combined moment and thrust controls. The commonly used Culvert ANalysis and DEsign (CANDE) finite element software was developed specifically for culvert design; its companion program, CANDE Tool Box, enables computing of load rating factors. However, owing to nonlinearities associated with soil–structure interaction and yielding of the corrugated cross-section, extracting accurate representations of available resistance for shallow-buried corrugated metal culverts may require a cumbersome iterative procedure. Furthermore, the resulting rating factor from not properly implementing nonlinear procedures may indicate an available resistance that is unconservative from a safety perspective. Recent improvements adopted by AASHTO and incorporated into CANDE include combined thrust–moment criterion, but are deemed suitable only for culverts with deep corrugation cross-sections. The objective of this research was therefore to assess flexure criteria for load rating shallow-buried corrugated metal pipe and arch structures, including standard corrugation cross-sections, to simplify the process without significantly sacrificing accuracy. Challenges with available methods and recently implemented combined criterion for the shallow-buried culvert scenario are first discussed. A modified flexural capacity criterion based on load and resistance factor rating is then developed and presented. Finally, the accuracy and applicability of the methodologies are assessed using a range of practical corrugated metal culvert dimensions and parameters.