Curved Girder Analysis

[NS4U]

Hi All,

I'm looking for some references on curved girder stress analysis, like something out of a grad class strength of materials text.

I know AASHTO puts out the V-load method, but I am interested in doing some more exact analysis by hand.

Any thoughts?

 

[Qshake]

mikehughes819 -

There are no texts with complete worked out examples for curved girder stress analysis more refined than the v-load.

The reason is simple, it is too computationally intensive.

There are, however, texts on curved girder analysis deriving the equations from advanced mechanics of materials or elasticity.

Nakai and Yoo have a nice text but it is likely out of print by now. Once again, it would be up to you to take the equations and move them into practicality.

While V-load is mentioned in AASHTO and guide specs, I pretty sure that V-load was developed by AISC to promote the use of curved steel girders over concrete and dealing with the issue of thin, slender members subject to torsion.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[bridgebuster]

Here's a link for two design examples by AASHTO; not much theory but if you want to see how it's done:

http://bridges.transportation.org/?siteid=34&pageid=339

 

[NS4U]

Thanks for the replies!

I am a bit concerned that the text's don't really carry out any examples, makes me think I'm missing something.

For a simple, say cantilevered, curved beam, the only real complexity is the added torsional component. Which if we assume linear elastic behavior those stress can be superimposed.

Am I thinking about this correctly?

 

[Qshake]

I don't disagree with you for a simple cantilever curved beam.

However, unless the cantilever beam is oriented transverse to the centerline of roadway, bridge engineers don't normally design single, cantilever, prismatic beams for bridges. When such members are oriented normal to the centerline of roadway their analysis is different than what we're discussing.

The complexity for curved bridge members comes from the following:

1. Continuous or indeterminate structures,
2. Non-prismatic members,
3. several stringers are used and are coupled by way of crossframes or diaphragms,
4. Loading involves multiple vehicle loading over the width of the bridge deck such that the loading differs from girder to girder.
5. There are other loading concerns also resulting from the curvature such as centrifugal force, wind on superstructure, etc.

All of the above, and probably a few I've not written, make for a very computationally intensive problem.

I suspect by way of your handle (petroleum) that you're not designing a bridge girder but rather some other type of curved structure. In this case, perhaps Roark's stress and strain may be more appropriate. They should hav a case for a simple curved beam and if teh loading is simple, you can do it with a spreadsheet.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.

 

[NS4U]

Actually, I accidentally selected the wrong field when I signed up, I am in structures, but my background is in buildings.

The reason I ask is because I read the paper "Historical Perspective on Horizontally Curved I Girder Bridge
Design in the United States" in it the author states curved girders are more efficient than similar straight ones.

This is just a preliminary investigation, hence the cantilevered structure, as I often spec. straight girders, when I am not brave enough to use curved. Even if it may not be so efficient, I am very interested getting a better understanding of this.

I agree, adding indeterminacy, just to name one thing, gets complicated quickly especially when you have open sections, such as I girders, and warping is a concern.

Could you offer some insight on warping and how it affects this formulation?