Allowable material used for composite member

[thiswontfall]

Engineers,

I am trying to determine stiffener size for a steel hopper for lignite. How much of the plate can I count on to help me carry the moment. I have found everything from 40 x thickness of the plate to 16 x thickness of the plate. I am using 1/2" plate and wide flange stiffeners. I have attached a sketch to try to clarify.

 

[dhengr]

You are talking about an effective plate width problem; a shear lag problem which is dependant upon how the load is put into the member and over what length of member it acts. On a longer stiffener span, you will bring more of hopper pl. into play at the max. stiffener moment, assuming uniform loading. Since your hopper plate is already .5" thick, you might consider WT’s for the stiffeners and just weld them to the hopper pl. Drill a few drain holes in the WT webs, down near radius btwn. the flange and web of the WT. You can vary the hopper pl. thickness as the span length of the stiffener increases or you can vary the stiffener spacing over some width of the same thickness of the hopper pl. as the span length increases. You should most likely consider some loss of hopper pl. thickness over time for corrosion and abrasion.

The Lincoln Arc Welding Foundation has a pretty good book on this general topic: “Tubular Steel Structures, Theory and Design,” by M.S. Troitsky. Several of the Structural Engineering Handbooks and Texts cover the general topic. For effective width and shear lag, take a look at some of the good Strength of Materials and Theory of Elasticity text books.