Chapter 7: Substructures

‘Substructure’ is a collective term comprising all elements below the deck, which transfer loads to the ground below. No two bridge sites share the same ground conditions, so by definition substructure design must be bespoke for each structure. In the substructure, structural and geotechnical engineering come together, with the nature of the ground influencing not just the selection of piles or footings, but the stiffness and behaviour of the supported elements and, ultimately, the bridge in its entirety. One cannot divorce the supports from the deck or vice versa; a successful bridge design must consider sub- and superstructure holistically. In a single chapter, it is not possible to do justice to all aspects of substructure design, or to cover the myriad of variations of abutments, piers, towers and pylons in use around the globe. The aim in this chapter is to describe the overarching principles governing selection of bridge substructures, provide an introduction to the parameters to be considered during design, and direct the reader to sources of further guidance.