Program for Designing Multi-Span Steel Beam Bridges (Simple for Dead Load, Continuous for Live Load)

[CalebA]

I'm looking for a program that will allow me to make the live load continuous, but the dead loads simply supported. So for I have tried LEAP Steel, MDX, & MIDAS. I also have access to LUSAS, but haven't used this program much. If I can't get one of these programs to work I may just end up using LEAP Steel to get my loads for each support condition and designing the beam from there, but for prelim design it would be nice if one of these programs could do it. Thanks.

 

[brTCP]

For this specific task I would consider building my own tool (I normally do this kind of thing in python). I don't know all the software you mentioned, but I don't think any of them can do this kind of analysis.

 

[CalebA]

Unfortunately, I don't think we have the budget to build a tool like this for a one off project, but I think I figured out a solution with LEAP Steel. I'm going to make my model continuous for live load and then I'm going to calculate all of my other loads separately and enter them in the program manually. I'd still be interested to hear what others would do though.

 

[bugbus]

We would normally use Midas Civil for anything involving construction staging like that. For preliminary design though, I think you could create two separate models, one simply supported for dead loads, the other continuous for live loads, and just superimpose the results. Should give something pretty close to the real thing.

 

[Lomarandil]

Agreed that MIDAS can handle it using construction staging.

 

[CalebA]

Can anyone elaborate a bit on how MIDAS construction staging works to accomplish this?

 

[BridgeSmith]

Well, I consulted with another engineer here concerning BRASS, and it's not set up to handle that scenario, either.

It seems the reason most software doesn't do steel girders simple for dead and continuous for live is that there's no demand for it. We've never considered designing steel girders that way. All of our steel girder bridges are continuous spans. I'm curious as to why you need a program to analyze that loading. Are you rating a bridge that was designed that way or are you designing a new bridge?

 

[CalebA]

This is the design of a replacement bridge requested by the DOT since they had success with it during a design build project, so it's a matter of accelerated construction. The spans are relatively short at 23'-40'-23', so the idea is that the negative moment is completely taken by the deck reinforcing.

 

[Lomarandil]

Caleb, when setting up the MIDAS construction staging, the wet concrete load will be applied in one stage as a uniform load, then in the next stage the concrete deck elements will be activated. In your case, I would also activate an element representing your deck reinforcement (probably at eac girder top flange to simplify meshing).

 

[CalebA]

Do I need to model my girders as simple or continuous?

 

[BridgeSmith]

the idea is that the negative moment is completely taken by the deck reinforcing.

I don't understand how that saves time during construction, but if that's what they want...

Seems like there would be a significant increase in the reinforcing steel in the deck, and alot more shear studs.

In that case, you should be able to design it in pretty much any program by coding in a short section at the piers with a tiny top flange and web (assuming you're just blocking between the bottom flanges of the pieces, which is the only way I would recommend doing it), and then make it composite in the 2nd stage. I know that is fairly straightforward in BRASS. You'll obviously have to ignore the 'failure' of the top flange and web at the piers.

 

[CalebA]

The problem with defining a short section at the piers is that the beam & deck self-weight would also be modeled as continuous instead of simple.

 

[Lomarandil]

Not if it's staged. Look up some of the MIDAS walkthroughs, they're not great but they all seem to cover the implementation of this general idea

 

[BridgeSmith]

If you model the top flange and web with a tiny area for a few inches of the length, it will also have a tiny stiffness. While it would technically be continuous, it would be a very close approximation of putting a hinge in the model.