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Effective Flange for Stiffened Plate

Effective Flange for Stiffened Plate

Effective Flange for Stiffened Plate

(OP)
Very often in ship or oil rig construction, the most efficient way to design a deck is to weld tees or angles to the plating. The plating then acts as the top flange of the beam. The question is ... what width of plating is effective as a top flange. I have seen numerous formulations from the simple 2*sqrt(E/Fy) to others that require loading info and a lot of details. API RP-2A, Norsok, Roarke all give formulations.

I wanted to get a consensus of what others have used in this situation to see if there is one formulation that stands out as popular choice. If anyone has a copy of or knows where to obtain the paper "Thin Walled Structures. Theoretical Solutions and Test Results" by G. Winters 1968 you can let me know.

Thanks

RE: Effective Flange for Stiffened Plate

According to M.S. Troitsky "Tubular Steel Structures - Theory and Design" published by James F.Lincoln Arc Welding Foundation (P.O.Box 17035, Cleveland, Ohio 44117-0035, Fax 216-361-5901) page 7-28:
"the width of the plate should not exceed:
a. When L/t<40, the actual width center-to-center of stiffeners should be used.
b. When L/t>40, no more then 40t.
In any event, the distance center-to-center of stiffeners should not exceed 80t."
Where L - stiffener spacing,
      t - thickness of plate.

Good luck.

RE: Effective Flange for Stiffened Plate

The US Navy publishes a document MIL-HDBK-264 Properties of Steel Shapes and Plate-Beam Combination Used in Ship Building.  This provides guidance on the effective breadth of plate when used in conjunction with tees, angles, etc welded to plate. This can be ordered through the Department of Defense Single Stock Point www.DODSSP.daps.mil

In general for mild steel the effective breadth of plate is half the distance to the next stiffener each side or 60*thickness whichever is less.  If you have other materials the effective breadth comes from the equation

b= 2*(E/Fy)^.5 *t       Fy=yield  t=plate thickness

RE: Effective Flange for Stiffened Plate

A great reference for effective width issues is Design of Aircraft Structures by Bruhn.  

If I remember correctly, you often find

b(eff) = 1.7 * t * sqrt(E/Fcy) where Fcy is the compressive yield stress (applies to stainless  steel)

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