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<br />E. Bridge Foundations. <br /> <br />1, The foundation is the bridge component most vulnerable to attack <br />by floods. <br /> <br />2. Foundation types include spread footings, piles with pile caps, <br />drilled shafts, and caissons. <br /> <br />3, Spread footings are used where sound rock is relativE~ly shallow; <br />however, it is important to note that failures have occurred where <br />spread footing~> were placed 011 erodible rock, <br /> <br />4. Friction pilings are dependent on the surrounding material for skin <br />friction and lateral stability, End bearin!~ piles depend on the <br />surrounding material for lateral stability, Tip elevation should be <br />based on estimates of scour depths as well as bearing capacity to <br />avoid failure during flooding. <br /> <br />5, Caissons are typically used in large rivers. FOlmding depths are <br />such that scour is usually not a problem after construction, <br /> <br />F. Superstructures, <br /> <br />1, Hydraulic forces that should be considered in the design of a bridge <br />superstructure include buoyancy, drag and impact from ice and <br />floating debris. <br /> <br />2, The configuration of the superstructure should be influenced by the <br />highway profile, the probability of submergEmce, expected problems <br />with ice and debris and flow velocities, as well as the usual <br />economic, structural and geometric considerations, <br /> <br />3, Superstructures need to have alternate load paths (redundancy) to <br />minimize the risk of total failure from failure of a single element. <br /> <br />3.25 <br />