Partial Depth Stiffeners for Compression Force 1

Partial depth stiffener are allowed. Stiffener buckling would not apply since the plate is not restrained at the bottom. Design the plate for bearing at the flange connection and shear at the column web. The weld at the column web is eccentric from the center of the bearing width. Check bending in the plate for the same eccentricity.

connectegr, do you consider all of the moment to be resisted at the beam web? or do you share it with the flange weld? If the web weld fails in bending, the flange weld must fail in shear.

Michael.
Timing has a lot to do with the outcome of a rain dance.

I am assuming the flange is loaded on both sides, with stiffeners near side and far side. The weld of the stiffener to the flange should develop the compression load, unless the plate is finished to bear.

Connect-
If I remember correctly, there are applications where partial height stiffeners must be used...as in fatigue applications.

KootenayKid said:

Also, does the last sentence of AISC J10.5 preclude the use of partial height stiffeners for addressing the limit state of web compression buckling? I can't tell for certain from the language and punctuation used.

Click to expand...

The text reads as follows:

When required, a single transverse stiffener, a pair of transverse stiffeners, or a doubler plate extending the full depth of the web shall be provided.

I interpret that as saying that if stiffeners are required, that they must be full depth. The last line in J10.8 seems to support this.

Transverse stiffeners shall extend a minimum of one-half the depth of the member except as required in J10.5 and J10.7.

It makes sense that the stiffener would be full depth. This limit state occurs when you have compressive loads on both sides of the member. If you needed a stiffener, and you were going to use half-depth stiffeners, you'd have one half-depth stiffener at each flange, making a full-depth stiffener anyway.

A full depth stiffener is necessary if the force is continuous. For example a beam bearing on a column, with a post on the top flange on the same workline. If the stiffener is provided as flange reinforcement for a one-sided application, full depth is not required.

It depends on whether they are web stiffeners or flange stiffeners. Web stiffeners go full depth. Flange stiffeners are to distribute a load on the flange that is greater than the root capacity to carry into the web.

Michael.
Timing has a lot to do with the outcome of a rain dance.

Looking at AISE (now AIST) Tech report 13, intermediate stiffeners on crane runway girders should be stopped short of the bottom flange. End bearing stiffeners are to be full depth.
It escapes me right now why this is the case.
Also, I do believe there are provisions in AISC for stopping welds short of the fillet radius on wideflanges ...again the reason escapes me other than welding in the "K" regions can cause problems in heavy wideflange shapes.

Thanks everybody.

@Connectegr: The flange/stiffener is welded for the difference between the capacity required and the critical, non-stiffened, limit state correct? Also, shear buckling is a possibility for partial height stiffeners isn't it?

@Toad: You're absolutely right. Welding into the k region near the tension flange does cause fatigue problems.

@Nutte: I agree with your interpretation. Thanks.

@Connectegr: Let's say, hypothetically that you designed a partial depth stiffener loaded from one side. However, to make the numbers work, the stiffener had to extend exactly full depth. Since the shear in the stiffener dies off to zero at the far end, would you then NOT have to design it as a compression member?

@Paddington: I'm not so sure about your statement regarding web stiffeners. From my reading of the code, and my understanding of the failure mechanisms I think that partial height stiffeners can be used to address both web crippling and web yielding.

A couple more things:

1) When AISC mandates a full depth stiffener for situations where only one flange is loaded, does that mean:

a) A truly full depth (flange to flange) stiffener or;
b) A stiffener that extends to NEARLY full depth but not into the k region as discussed above.

I have seen many girders with end bearing stiffeners that were detailed as described in "b".

2) For the three web stiffening limit states (crippling, yielding, and buckling), how do you know that your partial height stiffener has successfully resolved the issue? Couldn't you have just moved your crippling, yielding, or buckling failure to the end of the stiffener rather than at the web/flange intersection? This goes back to paddington's comments above.

I suppose that b/t ratios take care of shear buckling...

I suppose the critical factor here is the reason for the stiffener.
Is it to...
Transfer a continuous force thru the beam?
or
To stiffen the web?
Then apply limit states of chapter K in your check.

In the case of crane runways and probably highway bridge girders, I do know that, do to fatigue cracking, intermediate stiffeners should not be full depth and should not be welded to the bottom flange.

KootenayKid

In your hypothetical case, I think you have to check the plates for buckling. You can stop the plate at the "k" (nearly full depth) without buckling.

KootenayKid

In most cases your plate thickness will be controlled by the tensile or compressive capacity of bearing area at the flange. Buckling will not control unless the beam is very deep. Bending will not control unless the flanges are very wide. Also the welds at the flanges are often larger than the weld at the web.