AWWA D-115 Prestressed Tank Question 1

[waytsh]

AWWA D-115 states "The maximum center-to-center spacing of circumferential tendons shall not exceed three times the wall thickness, unless an elastic analysis is made for the effects of the greater spacing". I have a situation where I will need to exceed three times the wall thickness (somewhere around 4.5). What exactly does the code mean by elastic analysis. Do I simply need to check the deflection and design flexural steel for the concrete spanning vertically between the tendons or is there something more involved that needs to be considered?

Also, is it sufficient to perform the check with static fluid pressures or do impulsive and dynamic seismic forces need to be considered as well?

One more thing, if any one knows of some good reference material on this topic I would appreciate some recommendations.

Thanks,

 

[JStephen]

It sounds like they want you to use shell theory to confirm proper prestress in between the tendons. The shell would tend to bulge out slightly there. I believe this would normally be based on static pressures, not seismic loads.

"Formulas for Stress and Strain" has various cylindrical shell formulas that would probably cover the case.

 

[JedClampett]

I'm confused. There are a very limited number of companies that install prestressed tanks. They mostly do there own designs. If you don't work for a prestressed tank company why are you doing the design? And besides that, why exceed the spacing recommended by the code?

 

[JStephen]

Jed, maybe he does work for a tank company. Anyway, it's a reasonable question, figured we'd see some other answers.

 

[waytsh]

Yes, JStephen is right. I do work for a young prestressed company. Up until now we have always met this criteria but now we have a situation where a large penetration will force our strand spacing past this limit and sweeping will only get us so far.
Anyway, good idea JStephen, I will check my Roarks.