Bracing Rectangular Steel Vac Lid, -psi

[projectmanagereng]

Hello,

Since gradation of Architectural Eng. and Civil I have been a Project Manager, getting further and further from my engineering background...

at any rate... i have problem i would like to ask the pros here...

We have a vacuum tank at our facility. I have been asked to redesign the lid as it is failing. This lid will see pressure for 4-6 days... pressure will be broke (removal of lid) and reapplied...

The six sided rectangular lid are made of solid A36 sheets, 1/2" thick. Vacuum (negative pressure) is approx. 17 psi.

Largest piece that would see the most deflection is the roof, 146"X98". My thought would be to create a "roll cage" of either I beams or WT. I beam for example would run vertical, connect to horizontal "beam" on top and connect back down vertically, all welded.

I need a good formula for finding my max deflection and what size and distance of structural support I need. Overall box size is 145"x61.5", 97"x61.5" ends, top as stated, 146"x98".

Any help would very much be appreciated.

 

[civilperson]

Weld stiffeners to the lid. Use either angles or WT 5x16.5 sections. Span the short direction, (98"), and space at 12" centers.

 

[projectmanagereng]

... i planned on welding stiffeners to the lid... WT, i would think the stem would be welded to the lid, because the plate would want to buckle in on itself. I thought of using channel in between to prevent any twisting affect and to give more welding surface.

Also, I beam I found is cheaper... and I wouldn't need the Channel sub-bracing.

Comments?

 

[civilperson]

Calculate the two section modulus for the beam welded to the lid and for the WT with the stem welded to the lid, (tension section modulus and compression section modulus). I bet the WT has less cost per unit section modulus in the controlling case! (This is because the added area at the lid does little while the area far away from the lid does a lot.)

 

[projectmanagereng]

I'll agree with that...

Using that WT, or with a WT6, I wanted to go with 4" Channel on end between the WT's for more welding area and better stability for any torsion that may happen.

I have attached the drawing...

... Comments?

Thanks for taking the time...

 

[civilperson]

Vacuum load is probably less than 15 psi, (2.2 KSF), and the compact criteria for the flange of the WT is sufficient to prevent buckling. The channels suggested seem unneeded except maybe at the perimeter to brace the ends of the stiffeners.