Rectangular tank & notch in stiffener rings. 1

[TheMehanic08]

Need some help guys,

I am currently designing a rectangular tank. 5 m ht x 4 m wide x 7 m long placed on a structure 20 m high.

We have designed the tank using staad and provided it with vertical channel stiffeners and horizontal stiffeners. We designed the stiffeners considering vertical stiffeners as primary stffeners for the entire height of the tank and the horizontal stiffeners as intermediate stiffeners. Now we need to notch the stiffeners both horizontal and vertical stiffeners to accomodate the nozzles at some intervals. I wish to know if this local notching is acceptable????

 

[EnergyMix]

What Code are you building this to? How deep are your notches (a detail you didn't mention)? What is the interval that the notches need to be cut (another unmentioned detail)?

Last question ... have you checked the Code to see if it's acceptable to notch the stiffeners to the depth and at the intervals that you know and that we don't?

Want to know the do's and don'ts of Eng-Tips? Read FAQ731-376.
English not your native language? Looking for some help in getting your question across to others or understanding their answers? Go to forum1529.

 

[TheMehanic08]

The design code is "Good Engineering practice" so we are reffering many handbooks like Megessy, Dennis Moss & Roark's. Well the notches in the primary vertical members are big enough to clear the pad of nozzles, we have around 10 primary stiffeners out of which 2 have 2 notches to clear the nozzle pads. simlar is the case for each side of the wall of the tank.
Tank thk of wall is 14 mm with ISMC 250 as vertical stiffeners.

 

[racookpe1978]

Come on!

What pressure?
What temperature?
What fluid - or is it a fluid at all?
What are the penalties if (when ????) it fails?
How many could get hurt, what is the financial, civil, and technical penalties when it fails?
Open top? Closed? vented?
What steel, wood, or plastic are you using? Why? What reinforcement size width length weld method are you using?

Re-read your question and figure out if you can figure out just how somebody else can be expected to give you any useful advice and feedback?

A rectangular tank 20 feet on stands could be anything from Petticoat Junctions RR water tank - complete with the liability of 3x girls swimming 20 feet off the ground, to Bhopal's vat of poison surrounded by a slum with12,000 potential victims ....

 

[fegenbush]

If the stiffeners are tension controlled on the unnotched face, it may be possible to use the shear lag values from the AISC Steel Construction Manual. If they are compression controlled on the notch face, that is a more complex issue. I would recommend reinforcing to create the same section modulus at the notched portion as the unnotched portion. I would not thicken the entire member to compensate, since there will still be a reduction instiffness at the notch.

That being said, racookpe1978 is correct. You must take into account all design factors that he mentioned plus all of the ones that you cannot think of (unknown unknowns) and take the conservative approach.

 

[jtseng123]

Good engineering practice ? Here is one: build a square or round box around the nozzle, and weld the existing stiffeners to it. Guarantee it will work fine.