Structural Deck Load Capacity

[SubseaDeep]

Hi All,

I am designing a steel deck for a client for a structure which will go on a offshore vessel. Attached is a model of the structure. I am using Roark's 7th edition to look for formulas to calculate the deck capacity (uniform thick steel plate, with beams and angles running underneath the plate, see attached file). But I am not being able find literature/formulas to calculate the deck capacity from Roark's or anywhere else. Can anybody here help in advising a good practical method to calculate the deck capacity? Given are: deck plate is 1/2" steel plate, 5" angle and W10 beam. The deck will stand on 4 columns (with truss), but I am not looking into that right now. Just need some advice on the deck load rating calculation first. Thanks for your help in advance.

Regards,

SubseaDeep

 

[BAretired]

The ultimate capacity of the deck spanning between angles is simply Fy*Z, or yield times the plastic modulus.

The ultimate capacity of the deck, reinforced with steel angles and spanning between beams is also Fy*Z, where Z is the plastic modulus of the angle plus plate. The problem is that the section is not symmetrical. It would be better if you used a 'T' section with flange down and web welded to the plate. Then you could have absolute certainty that the resisting moment would be Fy*Z.

If you insist on using angles, the theory is not exact and you may wish to modify your calculations by an "ignorance" factor.

BA

 

[weab]

I have never seen this type of deck for an offshore application. Usually I would see wide flange or at least channels beneath the deck plate.

I would think that you could analyze this similarly to stiffened panels in a bin. The blue book by Blodgett (I forget the name, but many older engineers would have it) has a section on stiffened panels. The combined section of the angle stiffener plus the deck plate of about 30xthickness wide (but maximum of angle spacing) is the section to consider. Use about 0.6Fy for allowable stress.

Be careful. If the owner ever needs to apply a point load in this area, the maximum load would be whatever the angle web (vertical section) can handle. Unless you have discussed this with the owner, I'd be inclined to use perhaps a 6" or 8" channel. I guess going from a 5" angle to a 6" channel may not be much of an increase, but do consider point loads.

 

[msquared48]

I have done this type of design before for ferry vessels. Check in the design codes for vessels under Naval Architecture. I think you will find the equations you are seeking there.

Mike McCann
MMC Engineering