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Rafter fin plate to shell connection

Rafter fin plate to shell connection

Rafter fin plate to shell connection

(OP)
In steel oil storage tanks I have cone roof with diameter of 24 m supported on rafter the rafter effect the shell by large horizontal force and vertical force how to check that the shell will withstand the loads

RE: Rafter fin plate to shell connection

There is no center column?
You will need to calculate the tha axial forces in the rafters and use that to determine the hoop stress in the top portion of the shell. A free body diagram will help and otherwise basic statics. You may have uplift from wind or internal pressure causing compression in the top of the shell, dead and live loads that are resisted by tension in the same area. Unbalanced loads may control. There will also be shear (up / down) and possibly moments at the rafter to shell connection, all should be looked at.

RE: Rafter fin plate to shell connection

(OP)
There is no center column I am considering only a center ring on the center of the 24 D tanks should I put a center column I modeld this roof in sap 2000 and considerd the ring as pined joint .the rafter will be 25 rafter and the section will be IPE 300 the hight of tanks is 12 meter and it stored Do the hight of cone is 2 meter

RE: Rafter fin plate to shell connection

I think you will need a center column, and several layers of rings around to utilized two way action of the roof plate. Are you using shell element?

RE: Rafter fin plate to shell connection

(OP)
Is it required to lhave a center of column and if yes is my assupmtion about the the crown ring is rong and cannot haben in prcaticev 'Yes, I modeled roof plate as shell element and released the moment in the joints between the ring and the rafter and between the rafter and the shell,also I put several layera of ring every 1.2 m

RE: Rafter fin plate to shell connection

(OP)
IFRs
How a concetrated load will effect tye shell and how can I check that the shell withstand it is pr/2t valid for this condition

RE: Rafter fin plate to shell connection

A center column is not required by tank standards and there are many built without, using the same or similar construction as yours. Attaching the roof plate to the rafters is also not needed, typical or particularly useful. One benefit to a column is that API 650 relaxes wind uplift for structurally supported cone roof tanks that meat a specific section of the standard.

RE: Rafter fin plate to shell connection

Once you have all the forces in the tank shell from all load combinations (see API 650 section 5.2.2 and 5.11.2 for load combinations), pick a roof-to-shell configuration (using API 650 5.9.5 as a starting point) then review section 5.10 for reference. Note that your roof does not match any of the designs noted in section 5.10.1 but falls under 5.10.2.8. Section 5.10.3 covers allowable stresses for roof components and refers you to ANSI/AISC 360, using ASD only (not LRFD). Note that 5.11 requires that you consider wind uplift loading if the roof does not meet 5.10.4, which yours does not. Add material to the roof-to-shell junction using one of the details in figure F.2 until the hoop stress is within allowables. Your critical load case may be uplift since that induces compression into the upper shell area. There is typically very little stress in this upper section of tank shell from liquid loading so you are usually just designing the roof-to-shell area as a separate structure. The vertical force can be assumed to follow 45 degree lnes downwards, make the vertical attachement tall enough to create a tall enough triangle such that at the bottom of the triangle the compressive stress is within allowables. Typically combining vertical loading from the fixed roof with hoop stress is not considered in API 650 tanks. As a possible guide see E.6.2.2 to see how vertical loads from seismic conditions are treated.

Remember - you read this on the wild wild web and is not a complete nor necessarily reilable response to your question, and although I most likely left out something important I can't think of it right now as I dash off this quick reply to your question.

RE: Rafter fin plate to shell connection

You need to do more research on large diameter tank to find out which roof system is desirable. There are many threads on this subject. Here is one. Link

RE: Rafter fin plate to shell connection

This is a relatively small tank, self supported roofs are certainly an option but fall outside the cookbook designs in API 650. There must be a good reason to not use a center column and spend so much more money, but that's up to the owner.

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