Soil-Steel Structures and the Canadian Highway Bridge Design Code

The Canadian Highway Bridge Design Code (CHBDC) is the new Canadian design standard for bridge structures over three metres in span. Soil-steel structures fall into the category of buried structures, which is the subject of Section 7 of the Code. Soil-steel structures have been in existence for over 100 years. A variety of design methods were developed during that period, each improving on the one before. Most of the soil-steel structure design methods used prior to the CHBDC were based on working stress, while the new CHBDC is based on the limit states design method developed for the Ontario Highway Bridge Design Code (OHBDC). The CHBDC also includes a specific check of strength requirements during construction which was not in the OHBDC. This part of the design method replaces the flexibility factor check of the previous design methods. The purpose of this paper is to: review the historic design methods used for soil-steel structures, provide a detailed description of the philosophies used in the CHBDC and AISI (American Iron and Steel Institute) methods, including a description of the critical differences between the methods, and report on a comparison of design results using the two methods. In order to compare design results from the two methods, a range of structure shapes and sizes were evaluated for numerous depths of cover. The study was limited to the 152 mm x 51 mm corrugation profile. Assumptions were required such that the comparison of methods using different design philosophies (working stress, limit states) are realistic. In general, the CHBDC results in more liberal designs for shallow depths of cover and more conservative designs for large depths of cover. However, the differences between the methods compared are relatively small for the shorter span structures under mid-range depths of cover combined with normal highway loading.