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134 Cha pte r F o u r
FIGURE 4.9 Flexural failure in rigid pipe resulting in quarter point cracking.
Ring flexure refers to cross-sectional bending of a pipe where
the vertical diameter tends to decrease and horizontal diameter
tends to increase. Owing to the high stiffness of rigid pipes, crack-
ing at quarter points occurs before the pipe is able to deform (see
Fig. 4.9). Longitudinal flexure is caused when a pipe is forced to
behave as a beam resulting in axial bending stresses (see Fig. 4.13).
Major causes for bending action include nonuniform bedding sup-
port, differential settlement, and ground movement due to external
forces such as earthquake, frost, expansive soils, and so on (Moser
and Folkman, 2008).
Circumferential crack
FIGURE 4.10 Circumferential failure of rigid cast-iron pipe. (Makar, 2000.)
