Can anyone explain why these steel highway girders have this uniform deformed-like appearance?

[Mylzie]

I drive under this on my way to work every day and have always been curious about it. My boss told me, at the time this bridge was built, these were the deepest wide-flange girders in the world (or maybe it was just the U.S.?). At first, I thought it was just the bridge above me casting a wavy shadow, but all 4 girders appear like this.

The lighter portions look like a uniform \/\/\/\/\/\/\/\/\/\/\/\/ strain. My guess is the darker and lighter portions of the flange are deflecting outward opposite of one another. Is this a defect from the fabrication process? Flange local-buckling E: web buckling? Just spit balling at this point.

Located in NH by the way.

 

[bridgebuster]

Here's a thought, could the V's be a cast shadow from the adjacent bridge rail?

I've also seen something similar on plate girders, not V's but straight lines, where diaphragm connection plates are welded to the opposite side.

The below photo is the Quinnipiac River Bridge (I-95) in New Haven CT. When it opened in 1958 it had the deepest plate girders in the US.

 

[3DDave]

Does this bridge appear on Google maps?

 

[BridgeSmith]

This is probably not due to shear buckling. The out of plane displacements from shear buckling are not very visible until you get near the ultimate strength.

Shear buckling sounds more severe than it actually is, the way bridge designers understand the term. Perhaps referring to the phenomenon as elastic deformation due to truss action would better convey what I and others think we are seeing. I am by no means sure that is what is going on here, but it's my best guess.

 

[Eng16080]

I live in NH and somehow recognized the location. This is at the intersection of Routes 108 and 101 in Exeter. Looking up from below, there are stiffeners at a spacing somewhere around 2-3 times the girder depth. From other pictures on google streetview, it almost looks like the shadow lines match what you would expect to be the web members of a truss. The lines seem to be mirrored about the middle. The pictures on streetview aren't great though, and perhaps I'm imagining this.

 

[271828]

Shear buckling sounds more severe than it actually is, the way bridge designers understand the term. Perhaps referring to the phenomenon as elastic deformation due to truss action would better convey what I and others think we are seeing. I am by no means sure that is what is going on here, but it's my best guess.

I guess we'll never know for sure, but I'll place my bet on the other theory. LOL!

Looking at test specimens in the lab, it's hard to see out-of-plane displacements until pretty late in a test. The load vs vertical displacement curve will soften and when the test is pushed further, out-of-plane displacements become more clear. In some of the pictures in research papers, the specimen has reached its ultimate strength and then is pushed much farther to make the buckled shape more visible.

The displacements in the picture aren't just in the high shear regions.

The truss action approach comes from Basler's tension field action model of post-buckling strength. That behavior doesn't kick in until after shear buckling. At anything resembling a normal shear, the web is just in in-plane shear and isn't noticeably deflecting out-of-plane.

 

[bridgebuster]

3DDave[/b] Does this bridge appear on Google maps?]

Not anymore. The original "Q' Bridge was demolished about 12 years ago.

 

[dauwerda]

From google maps:

https://www.google.com/maps/@42.992...0dz53Ijg!2e0!5s20170901T000000!7i13312!8i6656

https://www.google.com/maps/@42.992...Z4cluU0w!2e0!5s20190901T000000!7i16384!8i8192

 

[JoshPlumSE]

The next time you get a chance, look on the inside face of the web and see if there are transverse stiffeners like in the following.

https://www.bgstructuralengineering.com/BGSCM13/BG...

That's exactly what I was thinking.... That they left the stiffeners on the inside of the bridge so that the exterior looked better. But, that the fabrication caused some minor warping visible from this side.

 

[rb1957]

I think they're shear deformations ... incredibly small amplitude, completely elastic, highly visible (due to light distorsions).

I would if they change if a heavy truck goes over ?

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[skewl]

I believe this issue came up on a thin web girder bridge in Ontario. The attached report has some interesting discussions on weld distortion and tension field theory. I haven't read the report in its entirety but it seems relevant to this discussion.

Due to file size (34MB) I can only share via OneDrive. This report was released in an RFP so no confidential information here.

https://1drv.ms/b/s!As8lKkwt3K1VhIZq0ytQ7dHh4kJ8SA?e=dwLOB9

 

[Tomfh]

It’s not a buckle, it’s an elastic shear deformation.

 

[jorton]

I use the term "oil-canning". I've seen it in a number of bridges with slender webs. The paint and lighting probably make it more noticeable here than on other structures. There is some discussion of the issue in

https://onlinepubs.trb.org/Onlinepubs/NCHRP/docs/NCHRP20-07-415-Final_Report.pdf

"11. “Aesthetics and the visibility of distortions and deflections,” cited by Respondents 9 and 20. This issue
is often referred to as “oil canning” within the broader literature related to metal roofing and metal wall
panels in building construction (Metal Construction Association 2013). This issue can be related to
Items 1, 2, 5 and 6 of Table 1. It is generally accepted that the thicker the plate, the less likely it is to
“oil can.” In addition, it is well known that oil canning is commonly more visible on higher gloss
surfaces. However, no clear correlation is available between plate thickness or b/t and acceptable lack
of visibility of distortions and deflections."