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<br />Bridge Factors <br /> <br />Bridge length--This factor refers to the total distance across the stream <br /> <br />between abutments. <br /> <br />Foundation type--The bridge foundation is one of two basic types, either <br /> <br /> <br />spread-supported or piling-supported. At some bridges, both types of <br /> <br /> <br />foundations are used. Spread footings may rest of alluvium or bedrock. <br /> <br /> <br />Pilings are either driven piles or bored caissons and provide support by end <br /> <br />bearing or perimeter friction. <br /> <br />Skewness--The definition of bridge skew angle requires clarification, because <br /> <br />the effect of the bridge crossing angularity may be insignificant as compared <br /> <br />with the effect of piers skewed to flow. The skewness, or angularity of a <br /> <br />bridge is the acute angle subtended by a line normal to the main axis of a <br /> <br />bridge and a line parallel to the main axis of streamflow (Brice and Blodgett, <br /> <br />1978, Fig. 38). <br /> <br />The skewness of a bridge pier is also referenced to the main axis of <br /> <br />streamflow, but the pier skewness may not be equivalent to the bridge skew. <br /> <br />If the piers are aligned with the flow, the pier skew is zero, but if the <br /> <br />piers are normal to the main axis of the bridge, the skewness of the bridge <br /> <br />and piers will be the same. To obtain the normal waterway opening, the angle <br /> <br />of bridge skew should be considered separately from pier skew. <br /> <br />k <br />