Full Penetration Weld at Bearing Stiffeners?

[OSUCivlEng]

The client wants to do full pen welds for bearing stiffeners on a plate girder instead of mill to bear with fillet welds. My understanding is fabricators don't like it because it causes distortion to the flanges. It also adds NDT testing cost and is a more expensive weld. I would tend to agree since there are 40 stiffeners times 2 welds (top and bottom) for a total of 80 full pen welds.

The client says full pen welding provides better bearing and there shouldn't be any distortion with 1" thick flanges. I am not sure how he arrives at his conclusions.

This would seem to confirm my thoughts as well.

http://www.highsteel.com/technical_resources/faqs/FAQ3.cfm

I am curious what other engineer's experiences are?

Thanks

 

[msquared48]

Full Pen is OK, but I never weld the bottom of a bearing stiffener where it bears on the bottom flange, only where it touches the web and top flange. Intermediate stiffeners, yes, all around, but not bearing stiffeners.

Mike McCann
MMC Engineering

 

[TomDOT]

So, how do you deal with the crevice corrosion at the stiffener/bottom flange interface? Bearing stiffeners are typically under joints, which leak water and debris, which in turn tend to collect at the bottom of the stiffener and accelerate corrosion.

 

[msquared48]

Well, in buildings, I do not usually have that problem, but I can definitely see the issue in bridges.

Maybe this would be the case where the lesser of two weevils would govern the detaining. Or hire an Architect to provide a better cladding detail...

Mike McCann
MMC Engineering

 

[TomDOT]

Whoops, I always think bridges first.

 

[bridgebuster]

NYSDOT allows full pen welds or MTB with fillet welds.

Don't worry about the cost, the client is willing to pay.

 

[graybeach]

I always weld both the bottom and top of bearing stiffener on bridges to transfer lateral loads.

 

[OSUCivlEng]

Yes the top and bottom of the stiffener should be welded because they are transferring some lateral loads through the cross frames. Especially these cross frames since the bridge is skewed. A lot of people think you shouldn't weld the stiffeners to the tension flange because that's how they used to do it. AASHTO allows welding to the tension flange as long as you don't exceed the allowable stress which I think would be around 12 ksi in this case.

Bridgebuster I assume you mean don't worry about cost IF the client is willing to pay? I don't like wasting taxpayer dollars on stuff like this. I just don't see the reasoning for full pen welds. I always think of full pen welds for moment connections or where you need that kind of a strength in a weld. That kind of strength simply isn't needed and I don't see the reason to take the risk of screwing up 900,000 lbs of plate girders.

Oh well screw it. It's their bridge they can take the blame for their decisions.

 

[bridgebuster]

OSU - If that's their preference/policy don't worry about it. Look, it's not going to bankrupt the state or screw up 900,000 lbs of steel. Bridge fabricators make full pen welds all the time. What's the difference between a full pen weld between the stiffener and flange or between two butting flange plates?

 

[ukbridge]

Have a read of SCI Steel Bridge Group: Guidance Notes on Best Practice in Steel Bridge Construction. It is a well-respected publication in the UK which deals with questions like these in excellent detail

http://www.steelconstruction.info/index.php?title=Special:ImagePage&t=SCI+P185.pdf

 

[OSUCivlEng]

Page 83 of that document says "Full penetration butt welds are unlikely to be necessary and are undesirable; the cruciform detail (stiffeners on either side of the web) creates restraint during welding and can result in lamellar tearing." It also states "Where the stiffener is fitted, the majority of the load is transmitted in direct bearing, so a full penetration butt weld is unlikely to be necessary for ULS loads."


Additionally it states "However, it is advantageous to avoid a full penetration butt weld, because shrinkage strains (vertically) will distort the transverse profile of the flange and cause misfit of the bearing." This is also the recommendation of AISC's National Steel Bridge Alliance.

Like I said previously, it's an invitation to warp the flange and hence an unnecessary risk and adds fabrication cost. We are spending other people's money here, why waste it?

Bridgebuster - The full pen weld between to flange plates is necessary to develop the full strength of the steel on either side of the weld. There is no such requirement for a bearing stiffener in compression.

Every full pen weld has to be inspected. Why add an additional 80 weld inspections when there is simply no justifiable engineering reason to do so? The decision is being made out of ignorance. As engineers we should be able to justify every decision we make with a better reason than "because I say so".

However, I have no choice but to obey the client's decision.

 

[bridgebuster]

OSU - I've been around a long time. Over the years I've learned there are things that are not worth agonizing over. Just move on.

BTW - Don't try to justify every decision by citing a code or theory. There will be times when all you have to go on is your gut feeling.

 

[OSUCivlEng]

Personal experience by bridge fabricators is hardly citing codes or theory. It's a real world experience that is documented by people who actually get dirty and do the work. Which is more than a lot of engineers ever do, most prefer to sit in their office rather than get insight from the people who actually build what we put on paper.

There have/will be plenty of times in my career where citing my gut as a reason for doing something will never cut it when asked by a superior to justify my reasoning. The lack of curiosity by some engineers is frankly disturbing.

You are correct though, I'm going to comply with their desires.

 

[bridgebuster]

OSU - you missed the point. You got bent out of shape because the client changed your detail. Nothing wrong with M&B with fillet welds or CP welds.

Fabricators have their preferences. DOTs have theirs and they usually consult industry people so as not to create undue burdens. Why not ask your client the reason for the change in policy? The guys at High Steel are smart but you're also implying your client is stupid, no less smart.

I've worked both sides of the fence - design & construction - no one knows everything. And sometimes we just have to wing it - gut instinct.

 

[BridgeEI]

How much is the cost of the welds in comparison to the entire project? I'm sure it's almost negligible.

You probably can squeeze more material out of the girders to offset the cost of the welds. Like bridge buster said, one fabricator won't mind doing it while others will.

 

[OSUCivlEng]

It's physically impossible to do mill to bear with CJP welds. Everyone seems to not care about the flange distortion at the bearing locations. Seems like a big deal to me.

The client's justification was that this is how it's shown on their bridge standards for rolled beams and you get better bearing with CJP welds. I have no idea if this is a change in policy as they have no written policy, no design manual or anything. They change things frequently, but those emails are not circulated to the consultants. Generally the only way you know of changes is after a plan review.

So yes I get bent out of shape because things change arbitrarily. Then I ask questions and I get responses like that's why we have the AASHTO bridge code. However, they don't always follow the code. Now do you understand my frustration?

The owner at my first job out of school taught me something I'll never forget. When being deposed by a lawyer it's best to have a reason why you did something.

 

[bridgebuster]

Why mill to bear with CP welds? Anyway, we get frustrated with clients, and guess what? they get frustrated with us. There are things that you have to argue for and things you have to let go. IMO, bearing stiffeners aren't worth fighting over. What state are you working in?

Here's something to think about....

"Structural engineering is the art of molding materials we don't wholly understand, into shapes we can't fully analyze, so as to withstand forces we can't really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." ...Jim Amrhein