3-DIMENSIONAL ANALYSIS OF SOIL - STEEL BRIDGES

The present design of soil-steel bridges is based on plane-strain anal ysis by considering a slice of a unit width of the conduit wall and th e surrounding soil. This two-dimensional analysis neglects the third-d imensional effect of the steel shell and the soil continuum which coul d be significant especially when the load varies in the longitudinal d irection, as in the case of live load acting over a shallow cover. The structure is also subjected to a varying dead load due to the variati on in the depth of cover from maximum at the middle part of the condui t to zero at the conduit edges. A three-dimensional finite element ana lysis is presented in this paper to examine the actual three-dimension al behaviour of soil-steel bridges. The thrust and bending moment arou nd the conduit walls as well as the stability of a single conduit are presented and compared with the results obtained from plane-strain ana lysis. Also, the live load dispersion in the soil above the conduit is examined and compared with some present codes. The study leads to eva luation of the degree of approximation inherited with the practical ap proaches of the two-dimensional analysis.