Load factor for fluid loads seems too high for some structures 4

[Mawaca]

Regarding the load factor for fluid loads

Ref. ACI 318-11 9.2.4 and 9.2.1 Eq. (9-1)

U = 1.4F

This factor seems too high for deeply submerged structures or for retaining structures whose walls are too short to keep out 40% higher water.

For example, if I am designing a concrete immersed tube tunnel with 100 feet of water above it (plus something for high tide, wave crests, and sea level rise), this factor implies that I am planning for a case where the water level increases by 40 feet (or that undefined dynamic effects, 100 feet underwater, are equivalent to 40 feet of additional head).

Does anyone know of phenomena that justify 1.4 or a code, standard, or reference that allows a lower factor?

 

[CELinOttawa]

Mawaca: Now I disagree with you about the retained/held in issue, but whatever; Professional judgement is well tempered by Code requirements these days... I can see some logic to having different load factors for retaining structures and tanks, and in fact that's what the Canadian code DOES have!

If you apply the NBCC live load factor for TANKS to a retaining structure, I believe all of Jed's concerns are going to come true.

Also, if you apply this NBCC factor without applying the rest of the NBCC, I believe all of Jed's concerns may come true.

The NBCC is a different code, with different requirements. You can't go picking our part factors from different codes and mixing them. It just doesn't work that way.