Estimation of live load deflections for soil-steel composite bridges

The design of soil-steel composite bridges (SSCB) does not generally require verifying live load deflections (LLD) in the design process, because these are normally considered very small compared to the span of the structure. Typically, the emphasis is more put on the shape control during the backfilling process. However, the advances in production techniques and the development of new corrugations have allowed for bigger spans and shallower soil covers. Spans of more than 30 m are being built. This has led to that similar to conventional bridges - bridge owners may occasionally require proofs of the serviceability limit state (SLS) regarding LLD for SSCB. In these cases, and due to the complexity of the structure, ordinary beam theories cannot be used. Designers are compelled to utilize advanced analytical methods such as finite element method (i.e. modelling) for the calculation of the LLD, which can be impractical for daily design works. The paper attempts to find expressions for the estimation of LLD for SSCB. Three-dimensional finite element modeling is used to analyze LLD under a predefined live load for different profile shapes under different soil covers. The considered cases cover open and closed profiles including box culverts. The finite element results are analyzed to find valid mathematical expressions for the different analyzed cases. In addition, the proposed calculation method is compared to different field tests from the literature.