Relative deflection of girders on horizontally cruved bridge 1

[Noopur]

I have a question regarding the deflection of curved girders. The bridge I am working on:

Has skewed supports (not radial)

Supports are not parallel to each other

Span is a simple span (167’ longest girder, 158’ shortest girder)

The supports are skewed such that the outer girder is actually the shortest. And the girder on the inside of the curve is the longest.

Radius of all girders is 605.22’

I am getting larger deflection (8.6”) for the outside girder and about 5” less (3.7”) for the inside girder.

For a normal curved girder bridge with radial support, it is understandable that the outside girder (longest) would deflect more. But for this bridge, with the outside girder being shortest, is this still true?

Does anybody of you had a similar situation like this. I am designing a curved girder bridge for first time and really do not know where to look for answers.

Your valuable input from experience is much appreciated.

thanks.
Njain





Noopur Jain
Bridge/Structural Engineer

 

[Noopur]

Qshake

So if I use tapered diaphragm...that means having a variable spacing of the exterior and first interior girder all along the length of the bridge?

Noopur Jain
Bridge/Structural Engineer

 

[Qshake]

You need to visualize your model. As explained to me, you are going to join the center of gravity for the slan to the center of gravity to the girder. That is not at all like the system you intend to model. The difference is the eccentricity I mentioned earlier.

I don't think you'd have a variable spacing, should be paralell.

As to staad, I don't favor the program from past years of experience. However it is under new management and perhaps they've improved it. Generally it is not good for large DOF structures.

Regards,
Qshake

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

 

[LobstaEata]

Unfortunately the only thing Bentley has changed with Staad is the method of licensing. The software is still the Staad we all know and love to hate. Staad still operates on a traditional stiffness matrix analysis engine, similar to most other general structural analysis packages, so the results should be within reason. I do like that Staad's moving load generator is completely transparent and easily verified as compared with other software...not sure about the improvements to SAP, since I haven't used it since 1998.

I also wonder if MDX is able to model a curved girder bridge with non-radial supports. I think they still have a 30 day trial, so it couldn't hurt to check it out.

 

[MichSt]

This comment is off topic to the OP's question and the discussion above. But, the curve shown in the attached plan view seems so slight, why would you not just design the bridge using straight girders and varying width deck overhangs?? I'm sure this was addressed in the structure study, but it seems like a much simpler design and construction than going with a curved girder structure.