Effective width of Steel Plate

[StrP88]

Anybody knows when you have a steel plate (3/8" thick) and is stiffened with a 3/8" thich bar with depth of 3" what will be the effective width of whole thing when plate is due to bending load and NOT IN COMPRESSION?

Thank you

 

[TLHS]

Depends. It'll vary heavily based on the span to width ratio of everything, restraint conditions, and other fun things.

I'd start by treating it as a T-Section and assume that the effective width is a width that meets the flange width to thickness requirements for bending for a W-Section flange.

If you need more capacity, you might start looking at other options.

 

[canwesteng]

If the plate is in tension during bending, it won't buckle locally, and you could take as much tributary as you like without worrying about the width to thickness requirement. Then you might want to take an amount of plate tributary such that the netural axis is on the interface between the stiffener and the plate.

 

[JStephen]

In some of our calculations, we assume 16t either side, based more on easy of calculation than any firm theoretical basis, I believe.
Making the plate wider gives very modest increases in section modulus at the tip of the bar, where the highest stress is, and where buckling is the limiting factor.

 

[bootlegend]

I use the AISC equations for the effective width of slender stiffened elements in compression. Equation E7-17 or E7-18 in the 14th edition.

 

[KootK]

Using 36 ksi steel, you width to thickness ration on the bar should be such that you won't have to worry about it buckling.

Without a sketch of the situation, it's tough to give meaningful advice regarding the effective width of the section. For purposes of general illustration, lets assume that you've got a single bar centered over a 12" wide plate and your section is a cantilevered beam with a point load at the end.

At a given location (x) away from the concentrated load, I would assume that your effective tension flange (the plate) is 2*x*tan(30 degrees). You'd have the full section available to you at a location 10.4" away from the point load.

I'm basing my load spread estimate on two precedents:

1) The Whitmore section used in connection design (30 deg spread).
2) The 2.5k stuff used in web crippling checks (22 degree spread)/



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[SAIL3]

I use a usually conservative value of 12t on each side of stiff and move on....