External roof structure erection

[MANS1987]

Dear Experts,

I'm designing a storage tank with the following conditions:
DI: 33 m
H: 12 m
Roof type: cone
structure type: External Rafters

My question is about the erection procedure of roof plates (rectangular shape) and the roof structure. what's the method of erection??

Thanks in advance for any help you can provide.

 

[Duwe6]

They pick them up, they put them into position, they weld them in. Requires a fair ammount of preplanning and a LOT of experience. Or a LOT of preplanning and a fair ammount of experience. This is why experienced engineers* and good project managers hire a first-rate tank erection firm. It is an order of magnitude, or more, harder than it looks to erect an API tank. They are VERY thin for their internal volume, making them very delicate until each ring of the shell and the entire roof are completed.

*REALLY smart engineers consult with the chosen tank erection company on design details and erection sequence [ mostly crane location(s) ]. Really smart project managers determine where and how fast the full quantity of water to hydro the finished tank can be obtained - not a trivial excersise.

 

[MANS1987]

thank uou Duwe6, but how they can erect plate and rafters on the shell. the plate will be under the rafters ( i have external roof structure). which method will be applied?

 

[Duwe6]

My guesses are
1 - Install several rafters and start adding plates to the underside of these rafters
2 - Pre-fab panels with the rafters & roof plates already welded up.

Hopefully, somebody will talk you out of having the roof rafters on the exterior. "When everybody does something one way, there usually is a good reason" Very poor practice to attach roof plates to the rafters. Tanks work best with the rafters holding up the plates, without the plates being welded to the rafters. Makes the roof a membrane that cha flex, makes the rafters a 'structural' item only.

 

[MANS1987]

concerning the option 2, pre-fab panel can be rectangular shape?

 

[Duwe6]

With good engineering, some could be. But the rafters are radial, out from the center of the tank.

 

[JStephen]

Erection procedures and details would vary depending on who was doing the work. Suggest you contact some of the contractors that will actually be building the tank and check on feasibility of different options and recommended details.

 

[MANS1987]

Thanks for all your prompt responses

 

[valleytank]

Better make that a Revision 1 and change to INTERNAL rafters. Is there a specific reason why these would be located externally? This is a field fabricating nightmare and your best option would be shop pre-fabbed if you did go with this. The problem with pre-fab is the extra QC work that needs to be covered with shop wor. The extra field checks, the re-checks. Then it gets on site and guess what there are still dimensional issues. Never mind all the seal welding you will have to do on the topside..

The tank is a pretty flexible structure. Typically your roof plates are simply laying on the beams and are welded to the outer angle and center post. The beams themselves are typically bolted together via structural bolts to attachment brackets. Having the structural ironwork completed makes it easy for the contractor to simply order pre-cut roof plates and work their way out plate by plate. Any dimensional issues can be fixed on the fly and you will be left with a proven design that works.

 

[MANS1987]

We have proposed to our client to change the structure from external to internal, but he have a corrosion problem and he want an external structure. I couldn't find the right way to erect this tank
Really is a nightmare