Stiffening a W-beam with a T of different strength
Stiffening a W-beam with a T of different strength
(OP)
When welding a WT stiffener to the bottom of a W beam you get two different elastic section modulus: one for the top flange and one for the very bottom flange.
I am trying to stiffen a simply supported W beam with a yield strength of 240MPa with a WT with a yield strength of 350MPa.
Is it too conservative to use the lower 240MPa strength for the top flange or should I use a ratio of the yield strengths?
I am trying to stiffen a simply supported W beam with a yield strength of 240MPa with a WT with a yield strength of 350MPa.
Is it too conservative to use the lower 240MPa strength for the top flange or should I use a ratio of the yield strengths?






RE: Stiffening a W-beam with a T of different strength
RE: Stiffening a W-beam with a T of different strength
The bottom with the welded T needs to be checked against the new stress in the new section and the old stress in the bottom of the old section.
If the T is of greater stiffness than the original then this can sometimes make a difference, if not then the highest stress will be in the original section and this wont really make any difference.
RE: Stiffening a W-beam with a T of different strength
RE: Stiffening a W-beam with a T of different strength
RE: Stiffening a W-beam with a T of different strength
The Tee section is nearly as deep as the original member. But the flange thickness of the Tee is thicker and hence I am calculating different elastic section modulus for the top and bottom regions.
When I am selecting a Tee I am calculating the moment resistance from the elastic section modulus of the compression zone (i.e. top) with the grade of steel of the top member (i.e. 240MPa).
Am I correct in using the elastic section modulus of the compression zone?
RE: Stiffening a W-beam with a T of different strength
Use the distance from the NA to the bottom to calculate the stress in the bottom of the section and compare this stress to the allowable stress of the grade 350 steel.
Depending on the location of the NA you may also have a maximum stress in the bottom of the grade 240 steel that also needs to be checked.
Is it a simply supported beam or do you have moment reversal?
RE: Stiffening a W-beam with a T of different strength
The value of E is the same for both steels, so there is no "transformed" section.
BA
RE: Stiffening a W-beam with a T of different strength
RE: Stiffening a W-beam with a T of different strength
RE: Stiffening a W-beam with a T of different strength
(ht
RE: Stiffening a W-beam with a T of different strength
What I've found to be true is that for unsymmetrical sections Z/S can get very high. I remember being shocked at the difference in capacity for a composite beam comparing the 9th ed. to the 13th ed.. This is all because "Z" (if you want to call it that for a composit beam, please don't let the point of my post be lost in the detail of using the term "Z" for a composite section). If Z/S is greater than your combined load factor you will get yielding under service loads. This is especially true when the least critically stressed portion of the section (the bottom in this case) has a higher yield strength or when you consider superposition of elastic stresses.
I'm not saying the ultimate moment is affected, because it isn't, but it is possible that the section experiences yielding under service loads and I think it's a check worth doing.
RE: Stiffening a W-beam with a T of different strength
Note that it is possible, though not likely, to yield even a regular rolled W-shape composite beams with high dead to live load ratios as some shape factors are as high as 1.3, and as far as I am aware no "canned" software will perform this check for LRFD design.
RE: Stiffening a W-beam with a T of different strength
RE: Stiffening a W-beam with a T of different strength
Brad