Concrete Tank - Concrete Lid poured on site and craned onto tank

[BigswedeCO]

I have a little spin to add to a standard concrete tank design. With the underground concrete tank I am working on, the contractor/timeline requires to form and pour the lid on the ground while working on the floor and walls. When the walls are complete with adequate cure time, the lid(s) would be craned on to the tank.
Can anyone recommend information on specifying lift loops and guidance on spacing and associated reinforcing details required for the lift?
The lid(s) also have openings of various sizes and arrangements to allow future mechanical replacement, ie pumps, etc.
Thanks.

 

[JedClampett]

Tilt up contractors do this all the time. Require that the manufacturer of the lifting devices do calculations to qualify them and their locations. I think if any additional reinforcing is required, they'll call that out too.

 

[SteveMort]

I created a finite-element model in RISA of a tank lid with pin supports at the lifting lug locations and ran an analysis with selfweight-only to determine the bending and shear stresses at the lifting locataions and between the lifting locations. Then I designed the reinforcing steel accordingly. Keep in mind that the reinforcing steel will have to work for the lifting load case and then for the in-place load case. You may need steel for one load case that is not necessary for the other, but since the lid will experience both, it all has to be installed. The lifting lugs can be bent re-bar but should be checked for the reaction in double shear and tension failure modes and should be hooked around the reinforcing grid.

 

[oneintheeye]

you can get detaiks from manufacturers of lifting sockets. ill try and dig some out tomorrow but basically you can either link under reinforcing bars or not (dependent on load). you will need to design your slab to take the stresses from being lifted to as earlier poster said. FEA is easiest.

 

[BigswedeCO]

Thanks to all.

Stevemort: How much training does the RISA program require and approximate cost for program/training?

herewegothen: That would be great if you can send the details on lifting sockets.
What is FEA?

Here is secondary problem associated with adding top on after walls are poured, what would be the best way to connect the lid to the walls to give walls stability to resist deflection from backfill loads?

 

[BarryEng]

My comment does not address your original question, however it may give you another method - I don't know if this would suit your installation.

I have designed some tanks recently (about 40 m dia & 3 m deep with up to 4 m of soil over the roof & 3 m into the ground water). These have been for wastewater pump station emergency overflow situations. I design the roof using precast beams on top of columns & hollow planks (conc slabs with longitudinal holes) on top. I check the design three times - for transfer (they are pretensioned), loading from a concrete topping (eventually will become a composite slab), then loading from the soil after composite action can be established.

This method is used so that no roof formwork is required (that would have to be extracted out of the tank later) & the only opening is the final access hole.

The principle of 'lost formwork' has proved to be quick & economical for the very high loads from the soil loading. Tank floor is constructed, walls & columns next, then all the rest of the construction will be from above the tank (outside the tank wall perimeter).

I can't see that this method would be economical for a lightly loaded roof.

 

[oneintheeye]

Hi do a search for halfen. they produce various items one is lifting sysytems. The data sheets have design information, angle of lifts, load ratio applied etc. Only copy here is hard copy. May be a company closer to you but principle is same. FEA is finite element analyis. If you haven't access to a package you will need to calculate it by hand. Shouldn't be to difficult. Any more info let me know.

 

[SteveMort]

Go to

http://www.risatech.com

and you can download a demo for free. I use RISA-3D. You can also request current pricing via e-mail through their Web site. It shouldn't take very long to create a rectangular finite element model of your tank lid. Then familiarize yourself with the meaning of the output to obtain the maximum bending moments and shears in the lid model. I like to run the animation of the exaggerated deflected shape to be sure that the model is behaving as expected

 

[ajbstructural]

I once let a contractor pour a lid on the ground and then lift it on to the tank. Only I though he was going to pour it right next to the tank. However, he poured it about a quarter mile away and used a backhoe to drive it to the site. Then he wondered why it had cracked.

You might want to think about adding some extra reinforcement for impact loading.

 

[BigswedeCO]

Thanks again everyone,

What would be the best way to connect the lid (either cast on the ground and craned on top or pre-stressed craned on top) to the walls to give walls stability to resist deflection from backfill loads?
I was thinking of dowelling and epoxy into the top of the walls thru holes in the lid and epoxy to seal - what do you think?

Regarding contraction joints; 60 feet is maximum length of wall recommended without joints with 30 to 50 feet being more common, would you consider that length measured along each wall or measured along the tank length?
For example: sanitary tank 60 feet long x 15 feet wide with 4 compartments of various sizes.
Do you add the perimeter dimensions to determine the need for joints in this case 150' or just go by the tank length of 60' and that would not require any joints?