6.13.1 Structural Requirements
Structurally, closed conduits must resist a number of different forces or in combination.
- (a) Internal pressure equal to the full head of water to which the conduict can be subjected, vide Appendix 6.4.
- (b) Unbalanced pressures at bends, constructions and closures which has been cussed in 6.16.18.
- (c) Water hammer or increased pressure caused by sudden reduction in the velocity of the water; by the rapid clsing of a gate or shut down of a pump, for example which has been discussed in 6.17.
- (d) External loads in the form of backfill, traffic, and their own weight between external supports (piers or hangers) A reference may be made to the Manual on Sewarage Sewage Treatment.
- (e) Temperature-induced expension and contraction, which is discussed in 6.13.2
Internal pressure, including water hammer, creates transverse stress or hoop tension Bends and closures at dead ends or gates produce unbalanced pressures and longitudinal stress. When conduits are not permitted to change length, variations in temperture likewise create longitudinal stress. External loads and foundation reactions (manner of support including the weight of the full conduit and atmospheric pressure (when the conduits is under vacuum) produce flexural stress.