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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />3.5.1 Pretensioned Concrete Cylinder Pipe <br /> <br />Concrete cylinder pipe has been in use for almost 50 years with an excellent <br />performance record. It is a custom-designed pipe made by lining a steel <br />cylinder with cement mortar; the cylinder is then wrapped with helically wound <br />steel rods in tension. A cement mortar coating is then placed around the <br />cylinder covering the rods. <br /> <br />The pi pe is desi gned to resi st the expected internal pressures by varvi ng the <br />cyl i nder thickness antI the area of rod rei nforcement. The external <br />load-carrying capacity is determined by the Spangler equation with the <br />deflection limited to 0.00025 D2 based on a Marston equation for fill heiqht. <br /> <br />The smooth surface of the cement mortar lining, which is continued through the <br />joint by field monitoring, provides excellent flow characteristics that will <br />not decrease significantly with age. The cement-mortar encasement also <br />maintains the steel elements in a highly alkaline environment and thus <br />inhibits galvanic corrosion. Supplemental cathodic protection can be provided <br />for unusually hostile environmental conditions. <br /> <br />The combi nati on of a self-centeri ng bell and spi got coupl i ng seal ed with a <br />confined rubber gasket, and long laying length (usually 30 to 40 feet) permit <br />the pipe to be laid rapidly and economically. Installation rates of 1000 feet <br />per day, per crew, can be attained where excavation is not restrictive. <br /> <br />The pi pe is consi dered to be semi ri gi din the 10- to 1 B-i nch di ameter range <br />and requires pipe zone backfill material in the excavated trench to a height <br />of 0.37 times the outside pipe diameter. <br /> <br />Bends up to five degrees per joint may be made bv usinq beveled-end pipe. <br />Extremely short or promi nent bends are made by fabri cated mi tered secti ons. <br />Thrust restraint is easily obtained by field welding the steel bell and spigot. <br /> <br />Fitti ngs are manufactured in the <br />configuration, and quite often are <br />delivery. <br /> <br />pl ant, furni shed <br />incorporated into <br /> <br />in any size and <br />the pipe prior to <br /> <br />3-18 <br /> <br />l060c <br />