Laboratory Study on the Behavior of a Horizontal-Ellipse Culvert during Service and Ultimate Load Testing

Horizontal-ellipse culverts have been used for many years as a substitute for more conventional short-span bridges; however, their performance has never been evaluated experimentally. This paper describes an experimental program to understand the behavior of a horizontal-ellipse culvert during backfilling, when subjected to simulated service loading at the ground surface, and during an ultimate limit states test. The backfill response of the specimen was similar to circular culverts except that, as expected, the specimen exhibited lower vertical stiffness than horizontal stiffness due to its shape. Contrary to current design conventions, the response of the culvert to surface loading was influenced by the cover depth. At 0.9 m of cover, the load-carrying mechanism was ring compression, whereas at 0.45 m, significant bending stresses developed in the top of the pipe. At 0.45 m of cover, the ultimate capacity of the culvert was measured as a tandem axle load of 1,324 kN. Although this is approximately twice the fully factored design load, the culvert failed after the development of a plastic hinge mechanism instead of the wall compression considered in American and Canadian design codes, although the structure still had reserve capacity.