[anbarasan]

A comprehensive direct structural design method for buried concrete pipe is presented that has been included in a new section (1.15.4–Reinforced Concrete Pipe, Precast) of the bridge specifications of the American Association of State Highway and Transportation Officials. The method is based on the ultimate-strength and crack control behavior of reinforced-concrete pipe and other structures observed in various tests of pipe, box sections, slabs, and beams under known loading conditions that encompass both concentrated and distributed test loads. The new design method includes criteria for ultimate flexural strength based on both tensile yield of reinforcement and compressive strength of concrete, ultimate shear (diagonal tension) strength, and ultimate flexural strength as limited by radial tension in pipe without radial ties. Also included is a crack-control criterion. Additional design equations are provided for radial ties when radial tension or shear strength is inadequate without such reinforcement. In order to adequately predict the ultimate shear and radial tension strengths of buried concrete pipe, it was necessary to develop new relations between significant variables that go beyond or extensively modify existing design methods. These are based on an extensive evaluation of new and existing tests of pipe, box sections, slabs, beams, and frames without web reinforcement that failed in shear by tests of curved slabs that failed in radial tension without simultaneous application of shear and by pipe industry design practices derived from accumulated test data. Design relations proposed for crack control also differ significantly from crack-control criteria available in existing standards. They also have been based on extensive tests of pipe, box sections, and slabs. The design method may also be applied to pipe for three-edge bearing strength and for buried box sections. (Author)

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