Horizontal Shear Failure?

[Once20036]

To start, I think I've got a solid understand of VQ/I as it relates to horizontal shear in steel beams. I woke up feeling well versed on the subject and spent a couple hours reading some amazing discussions here on this forum.

So here's the question: Has anybody ever witnessed a horizontal shear failure of a steel beam web?

It's easy to imagine a shear failure of the welds connecting a web and flange (typical application for the equation) but let's say that you have a custom built plate girder with sufficient welds connecting the web and flanges and some vertical stiffeners to prevent web buckling,. Max horizontal shear stress occurs at the neutral axis near the ends of the beam. Is there some other failure mode that typically precedes a horizontal web shear failure? Has anybody ever seen this happen?

 

[MiketheEngineer]

Nope - usually the beam rolls over (lack of lateral bracing) and dies!!

 

[Teguci]

Define sufficient welds (smile)!

 

[JAE]

Shear doesn't usually control in steel shapes.

In wood though, it does sometimes become the main limit state.

 

[SteelPE]

Well, I haven't personally witnesses a horizontal shear failure but I had a conversation with an engineer last week who had. I don't know how we got on the subject but he had said that the failure occurred on a crane girder. In this project, the client had provided the design team with the wrong wheel loads.

Kind of like I know a guy who knows a guy who has a friend.... but there you go.

 

[Teguci]

Yeah, crane girders are a special animal. I have witnessed cracks in crane girder webs, but those cracks are due more to fatigue than shear flow stresses (ie small amount of shear flow stress but many cycles) . If you follow Appendix 3 (AISC) you don't even get the chance to design the flange to web weld. You are instructed to go right to full pens unless you're OK with 1/10th the number of cycles and 1/4 the threshold stress.

 

[Lion06]

I think a horizontal shear failure of a steel beam is near impossible (provided it's not castellated or something similar).

This is for the same reason that composite studs can be spaced evenly along the length. It's ductile (assuming no web buckling), and there is a half beam length of web to resist the total horizontal shear. Once you get away from the immediate end, the shear is dropping off quickly, thus the horizontal shear is dropping quickly.

Additionally, remember that the vertical shear stress is equal to the horizontal shear stress, so you're probably more likely to fail the section in vertial shear before you ever fail it in horizontal shear.