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Concrete Encased Vierendeel Truss Girder

Concrete Encased Vierendeel Truss Girder

Concrete Encased Vierendeel Truss Girder

(OP)
I am working on a project where another Engineer has designed a bridge girder (140ft span) as a structural steel vierendeel truss. Top and bottom chord are W12x252's. 5'-0" deep truss. The vertical webs are intermittently spaced lighter W12 members. The whole girder is then encased in concrete. 6ft deep by 2ft wide rectangle. There are no shear studs of any type so it's uncertain what kind of composite action their getting, if any out of the design. IMO the design is terrible and I have a whole list of items of why but what I need is third party documentation of why it's bad. I want to say it's an antiquated design but I'm not really sure if concrete encased structural steel was ever a thing in bridge or building design. It's just a really weird and inefficient design that is going to be a maintenance nightmare. I can't find anything in AASHTO that addresses this type of design which is an indicator that no one does this. Have you guys heard of anything like this? Any articles, documents, publications that would cover anything like this? I'll take anything at all. Even if it covers just concrete encased wide flange beam flexural elements.

RE: Concrete Encased Vierendeel Truss Girder

What is the point of the concrete?

RE: Concrete Encased Vierendeel Truss Girder

(OP)
Most likely corrosion protection. Less than 5% of the bridges in my state are steel bridges.

RE: Concrete Encased Vierendeel Truss Girder

Are you sure there is no wire mesh wrapped around? Otherwise the concrete wouldn't stay long, as it would be cracks all over the places.

RE: Concrete Encased Vierendeel Truss Girder

(OP)
There are 2 piece stirrups that envelope the entire truss @12" o.c.

RE: Concrete Encased Vierendeel Truss Girder

Would it be for fire protection consideration?

RE: Concrete Encased Vierendeel Truss Girder

(OP)
If it were for a building... yes. Not a bridge over a stream.

RE: Concrete Encased Vierendeel Truss Girder

Is this project in Canada? It is make sense for location with stream can be iced up during winter, steel structure is not desirable under such condition. But I don't understand why not simply use concrete girder instead.

RE: Concrete Encased Vierendeel Truss Girder

Why not a triangulated truss since the steel isn't exposed. It's not precisely a reason the original is bad but it's a pointer to better IMO.

I agree though that the concrete engagement is odd. No longitudinal reinforcement at all?

It appears that encasing girders was done more than a few times. You've probably seen the same docs I just found. No great criticism was given.

RE: Concrete Encased Vierendeel Truss Girder

IMO , concrete for two purposes: corrosion protection and triangulating the vierendeel truss . Very bad idea since the water will ingress between the concrete and the steel members . Eventually severe corrosion of the steel members (which will not be visible) may cause the collapse of the bridge.

RE: Concrete Encased Vierendeel Truss Girder

I have 3 words for you: prestressed bulb tee. 'Nuff said.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Concrete Encased Vierendeel Truss Girder

Did you post about this a few months ago? Seems familiar but can't find an earlier topic.

Can you request the designer justify the choice against alternatives? Let them do the leg work.

RE: Concrete Encased Vierendeel Truss Girder

Rod,

Are you providing solution/alternative?

STructPOno,

Quote:

I am working on a project where another Engineer has designed ...

What is status of this project, and your role?

RE: Concrete Encased Vierendeel Truss Girder

Quote:

Rod,

Are you providing solution/alternative?

Indeed, that was meant to be a suggested alternative. Bulb tees are available that will span up to 210' for typical highway bridges.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Concrete Encased Vierendeel Truss Girder

(OP)
steveh,

Nominal longitudinal reinforcement. Just enough for T&S. I did post about this a while back and it's still ongoing but that previous post was directed at the bearings that they were using.

Rod,

I couldn't agree more!

retired,

Currently, I am just looking for design specs, technical articles, addressing the deficiencies for a design like this. Or even why a prestressed precompressed zero tension design is more modern and better. This is obvious to a bridge engineer but not so much to others. Need supporting evidence.

RE: Concrete Encased Vierendeel Truss Girder

If you know any bridge been constructed using this design, it will be beneficial to visit and take notes on it. The age, the defects, or lack of defect. All worth to think about, and add values to your works.

RE: Concrete Encased Vierendeel Truss Girder

Quote:

If you know any bridge been constructed using this design, it will be beneficial to visit and take notes on it.

That's a good idea, assuming you can find one. If you don't have it already, ask the engineer for a cost estimate for these girders, then get a quote from a prestressed girder manufacturer and show the owner. That should put and end to this foolishness.

Rod Smith, P.E., The artist formerly known as HotRod10

RE: Concrete Encased Vierendeel Truss Girder

(OP)
Thanks. I wish I knew of another design like this. Unfortunately, I don't as it is rather unusual.

RE: Concrete Encased Vierendeel Truss Girder

I feel like I've seen this detail on an older bridge structure but I can't place it. It's not uncommon to see concrete encased girders on older bridges.

They are a maintenance nightmare as the concrete usually spalls off over time.

RE: Concrete Encased Vierendeel Truss Girder

If the purpose is to fend off the idea, I think HTURKAK has provided the most valuable reasoning for why it is a bad idea, so as the "maintenance nightmare" mentioned by MIKE 311. Also, the lack of design standard and available literatures should put the idea to rest.

RE: Concrete Encased Vierendeel Truss Girder

Maintenance will be problematic, but it sounds like a major PITA to build as well. Building formwork around all those truss members so they can be encased in concrete? That's gonna cost the owner a bunch of money.

How can you inspect the truss connections?

Not to mention the cost of fabricating and erecting a truss. A 140 foot span isn't that big. Plate girders or bulb tees would would work much better.

Is there an architect involved in this project?

RE: Concrete Encased Vierendeel Truss Girder

It sounds like a fun experimental project for an engineer to me. If it's for a paying customer I wouldn't touch it with a 10' pole. Unless you know where it's been done before successfully, then who knows what will happen, as many posters have speculated. Five feet is very shallow (inefficient) especially for a vierendeel (more inefficient) 140' span so deflections will be significant. I would be doing some serious analysis to prove shear connectors aren't warranted. If it's pedestrian, it might work. (Might also means might not). If there's highway loads, I can envision the concrete popping right off, but who knows?

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