Internal Floating Roof Sheeting Design

[reesecc66]

I have a question about IFR sheeting design. We recently had a tank out of service and had a part of the roof fail while people were working on it. I am trying to back calculate to check the stresses and loads in the sheeting that caused the failure. I really want to see how bad the strength had degraded over time versus new.

I've reached out to the original manufacturer for calculations but I'm having a hard time following exactly what they are doing. All calculations that I've run don't even support original API 650 Ann. H design. (Roark's, simple beam)

Any help would be appreciated. I've attached the manufacturer's calcs for review.

 

[IFRs]

The original manufacturer should be able to help - do they have an engineer on staff you can contact?

The calculation you posted uses several simplifying assumptions. First, it assumes that surface sheeting deforms to a simple triangular shape under load ( not a catenary ). The force is then calculated based on vector geometry. Then it is assumed that this force is distributed along the supporting beams on both sides for a distance limited by 45 degree angles both ways. Then the tension in the sheeting is calculated based on the force, length of connection and sheet thickness. Finally this stress is compared to allowable tensile stress for the material.

Guessing that workers fell through the sheeting, I'd take a close look at the boundary conditions - where the sheet joins the beams, corrosion, how much sag there is in the sheeting, the load applied. If corrosion and excessive load are not the culprits, my guesses are that the sheet was not fully clamped because the fasteners in the beams were loose or the sheet was not fully overlapped when installed.

I hope no one got injured !!

 

[JStephen]

It looks to me like that's calculating stress at the beam, but calculating out away from the beam would lead to correspondingly higher stresses?