Concrete Encased Vierendeel Truss Girder

[STrctPono]

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.

 

[MIKE_311]

What is the point of the concrete?

 

[STrctPono]

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

 

[r13]

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.

 

[STrctPono]

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

 

[r13]

Would it be for fire protection consideration?

 

[STrctPono]

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

 

[r13]

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.

 

[Settingsun]

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.

 

[HTURKAK]

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.

 

[BridgeSmith]

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

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

 

[Settingsun]

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.

 

[r13]

Rod,

Are you providing solution/alternative?

STructPOno,

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

What is status of this project, and your role?

 

[BridgeSmith]

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

 

[STrctPono]

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.

 

[r13]

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.

 

[BridgeSmith]

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

 

[STrctPono]

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

 

[MIKE_311]

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.

 

[r13]

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.