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Why must arch bridge foundations resist both settling and sliding?
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bridge
The multiple-span Seto Great Bridge over the Inland Sea, linking Kojima, Honshu, with Sakaide, Shikoku, Japan.
An arch bridge carries loads primarily through compression, which exerts both vertical and horizontal forces on the bridge's foundation.12
Because the arch structure generates a diagonal force known as thrust, the foundation must be robust enough to manage these complex stresses. Specifically, the foundation must prevent vertical settling caused by the downward load and horizontal sliding caused by the outward thrust of the arch. If the foundation is not properly designed to buttress this thrust and conduct it safely into the ground, the arch may collapse.12