Since a gravity abutment is subject to compressive loads only, it can be constructed of masonry or unreinforced concrete. The cantilever abutment requires the use of reinforced concrete to withstand the stress caused by bending. If we disregard all forces except the vertical loads from the superstructure, the pier can be considered a compression member and can be built of masonry or unreinforced concrete. Should a crack develop due to settlement or temperature stresses, the mesh will keep the faces of the crack in contact. Maintenance Maintenance of substructure units is normally minimal, consisting of patching of spalled concrete or masonry.
Major maintenance occurs only if erosion undermines abutments or piers.
In this case filling in the eroded area and placing rock protection to prevent further erosion are required. As prevention, substructure units should be inspected yearly for erosion damage or immediately after unusual run-off.