Continuous Bridge LiveLoad with Varying I

[PeteIL]

Has anyone found good software or a method of calculating live load moment envelopes on a continuous bridge? I have a structure length that is beyond AISC Moment Shears and Reactions tables, and I would like to verify my Visual Analysis results against something. The key is that the section properties vary along the span lengths.

 

[swine]

Moment distribution and a #2 pencil? But you haven't really described the structure...

 

[PeteIL]

The structure is a 3 span N = 1.27 built up plate girder with cover plates over the piers.

Is there a method of moment distribution using variable section properties?

 

[bridgebuster]

I thought I was the only one left who used those tables.

You can interpolate between between the 1.2 and 1.3 tables. If the variation in the moment of inertia is not drastic, the tables are a good approximation.

Yes, moment distribution can be used for members with a variable section; just look in a book on structural analysis.

 

[PeteIL]

Unfortunately the bridge I am working on has a total length of 412' which is beyond the AISC charts of 360'.

I'm am familiar with the methods of moment distribution using different section properties for each span or frame unit including sway, from the analysis books I have. Are you aware of a reference that would have nodes mid-span where section properties change?

 

[atomicman]

You could try the influence line spreadsheet on

http://www.yakpol.net.

Not exactly what you're looking for, but it's a start.

Other than that, I use the moving load generator in GT-STRUDL or RISA for this, but those are a bit costly I think for just checking your analysis.

 

[swine]

I wish that was my project--oh well. I only work on little teeny projects and my advice is free--about what it's worth. I would break each member into finite elements (using a spreadsheet). I could get my carry-over factors, stiffnesses and FEMs from that. Then use moment distribution. Then go back to the spreadsheet apply the boundary conditions and draw the moment envelopes.

 

[bridgebuster]

You could do it the old-fashioned way: Turn to the second half of the book and use the influence coefficients.

 

[wiktor]

Any structural software could be used to create influence lines and calculate moment and shear envelopes. The major difference is the amount of work to be done by hand.
Try the software from Washington State DOT:

http://www.wsdot.wa.gov/eesc/bridge/software/index.cfm?fuseaction=download&software_id=48

This package should be capable of creating the envelopes you are trying to verify.