Temperature and Shrinkage Horizontal and Vertical Reinforcement

[EngrJosh]

I am designing a ring wall foundation for an above ground crude oil storage tank and i am using PIP STE03350 as a guide. I clearly understand Hoop Tension (and have been able to find that) and from example 2 in PIP, i do not necessarily have to design for Twist moment since my tank has the same specifications and environmental factors as that example. My challenge is: PIP does not exactly state the formula for vertical and horizontal minimum steel for temperature and shrinkage and API 650 does not state it precisely too... can anyone pls give me a detailed formula and steps of how to determine the minimum horizontal and vertical reinforcement for this? Urgent answers would be appreciated..

 

[TXStructural]

To the extent that a normal code like ACI 318 applies to a foundation like this, temperature and shrinkage steel is the area of steel placed in perpendicular directions in order to restrain crack growth and crack width under these T&S strains. It is only required in a direction where there is no flexural reinforcement. The minimum reinforcement ratio under ACI 318 (for the common 60 ksi reinforcement) is 0.0018, which represents 0.26 sq. in. of steel for every square foot of concrete in a section.

These are only T&S for buildings, and NOT directly applicable to API, which may require higher minimums. If you are reinforcing for hoop tension, then you should already have vertical reinforcement to tie the "hoops" together, so unless a specific minimum reinforcement ratio is identified, you should be above the minimum. Is there a pad under the tank, or will the tank be built/installed on fill inside your wall? (I've seen them both ways)

 

[msquared48]

Even the .0018 is not a hard and fast rule for grade 60 steel - see ACI 10.5.3.

Mike McCann
MMC Engineering

 

[EngrJosh]

Tanx TX and Mike! Thanks for ur explanation on T&S reinforcement. Let me add some more information so we can get a better picture of the situation:

1) The tank is to be built directly on the fill (crushed stone - sharp sand + an asphaltic coating for water resistance) in the ring wall. No pads would be used.
2) The location where the tank is to be installed is south-south Nigeria. The soil in the site is primarily clayey.

3) The tank is a 10000Metric tonne tank with R:9250mm, H:7500mm, b: 450mm, h:1500mm, drw: 1000mm, L: 150mm. fOr reinforcement is 60Ksi.

Tx,from ur 2nd paragraph, r u implying that there are cases where you dont need to design for T&S because your As(hoops) already covers for it? Pls clarify.

Thanks

 

[TXStructural]

Good practice is to have AT LEAST the 0.0018 minimum, and if there is already at least that amount in both directions, you do not need to add more. Closely-spaced reinforcement results in better crack control. If you want excellent crack control, consider using a layer of welded wire reinforcement just inside the concrete cover.

 

[EngrJosh]

Thanks Tx...i've been able to crack it, ur input was really helpful. The next issue is: we are also doing a concrete slab foundation for another tank. What are the detailed steps to take to design a concrete slab foundation (20 ft by 10 ft by 300mm thickness) with three supporting beams below it (each 20ft * 225mm by 900mm thickness - i.e: length spans across the slab). Our clients say they need T16 as reinforcements for the beams and T12 as reinforcement(doubly) for the beams...I also need a link to any electronic material i can read online that explains such designs well.

Thanks

 

[hokie66]

You can't learn reinforced concrete design by asking questions on this site. The site is for exchange of information between engineers informed in their own discipline, not for plug and play designs. You need to engage a structural engineer.