Intermediate Stiffeners Welding to top flange or tight fit? 2

[WayneRuin10]

Hello All,

I have a question about intermediate stiffeners in plate girders. Is there a benefit of welding of the stiffeners to the compression Flange? Tight fit vs welding? which is better design and why?

Please see attached snip for your reference.

Looking forward to hearing your thoughts!
Thanks!

 

[driftLimiter]

Depends on the application for the stiffeners. If your using the stiffeners as part of the load path for lateral or torsional restraint you may want full depth. If used as bearing stiffeners, it is very common to use partial height.

In general it is simpler to build if you hold one side away from the flange. In both of the options in your image, they hold one side away from the flange.

AISC 360 15th edition Section G2.3 Provides more requirements and information on when stiffeners are used to increase shear strength.

 

[dik]

I'm not sure about plate girders; I don't get these often... but with regular beams, I usually cut the web stiffener about 1" to the underside of the flange (attached to the compression favourably) to make it easier to fit and fabricate. I suspect the same could be said for plate girders. I nearly always add them to both sides.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[MotorCity]

Stiffeners are usually (always?) welded to the compression flange. This helps to reduce compression flange buckling in addition to strengthening the web. Note in your diagram that the stiffeners are fit tight to the compression flange in both cases (the compression flange is the top flange in one case and the bottom flange in the other case)

 

[dik]

Thanks Motor... I had the wrong side inferenced...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[WayneRuin10]

All, Thank you for you response. I do realize now that the snip shows tight fit at compression flange. However I have noticed that standard practice is to weld comp flange to stiffener, and just wanted to see what the reason behind that standard practice is? If you have any literature to refer, please let me know

Thanks!

 

[BridgeSmith]

It depends on the purpose of the 'stiffeners'. What many details and bridge designers call "stiffeners" are actually connection plates for bracing (crosframes or diaphragms). The AASHTO design specifications have finally corrected the terminology to distinguish between connection plates and actual stiffeners.

Connection plates are typically welded to both flanges, to prevent out-of-plane bending of the web that can lead to fatigue cracks, but are sometimes "fit" to the tension flange to avoid the reduction in the fatigue stress limit for locations with transverse welds. If fatigue stress limits dictate, a full-penetration groove weld may be used. Otherwise, they can be fillet welded.

Transverse stiffeners not used as connection plates, but only for stiffening the web against shear buckling (which is rarely done anymore) do not need to be welded to the flanges.

Bearing stiffeners at supports have to be either "finished to bear" or welded. Since support locations in continuous girders are the highest stress location for the girder, those welds are typically full-pen groove welds, also.