Haunched Steel Girder End? 1

[OSUCivlEng]

I am looking at a bridge rehab where I might consider replacing the old girders with shallower depth girders. The end spans are simple spans and I don't want to have to modify the abutments. I was thinking of just putting a haunch at the ends of the girders to make up for the lack of depth. Is haunch the correct term to use? Basically the girder would transition to be deeper at the ends. Does anyone know where I can find more information about something like this? I am struggling to find any information and I don't wont to cause some kind of fatigue or fabrication problem.

 

[bridgebuster]

Haunch or bolster, which ever you like. If you're a purist go with bolster as haunch is an extension of the web plate. Anyway, down load the NYSDOT Bridge Manual, Chapter 8 has the information you need.

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If you'd like to see some plan details go to this link, download the PDF named D263288_Plans_Vol3of3


Link

That's from a bridge rehab project I was involved with. One bridge is going to be raised 19". Steel bolsters were more practical than trying to build up the pedestals. If you need another example let me; I have another set of plans somewhere.

 

[bridgebuster]

Oops, I misspoke. Bolsters are usually put on existing beams. Since you're replacing the superstructure you would be creating a haunched girder. If you go to Chapter 23 of the NYSDOT bridge Manual there is some guidance on proportioning the haunch. There's nothing complicated about haunches. AASHTO LRFD specs also has some guidance. If you're new superstructure is going to be rolled beams a bolster may be a viable option from a cost perspective.

 

[OSUCivlEng]

Thanks. That is exactly what I was looking for.

The center two spans are continuous. I think using the same depth for all spans would be more pleasing to the eye by keeping the depth constant, and the haunched girder at each end would help it "flow" into the abutment. As a bridge engineer, I think that's about as artistic as I want to be...

 

[bridgebuster]

You're welcome; glad it was helpful. In pre-war NYC, haunched girders (and concrete rigid frames) were a standard on what we call parkways (roads without commercial traffic). I attached a plan sheet from one of them.

 

[EQguys]

OSU: I have a question on what you are trying to do. Considering the end spans are simple spans, why would a haunched girder make sense structurally where the moments are the least ? If you are replacing the superstructure girders, then you will have access to the abutments and piers and can elevate the girder pedestals to make up the elevation difference. Depending on how deep the girders are, a haunched girder will add to the fabrication cost of the plates (variable cuts in web plates, complete penetration welds at the flange elevation change point, welding geometry etc.)

 

[OSUCivlEng]

EQ: the owner does not like to rebuild pedestals to make up elevation differences. They have had trouble with those type of modifications in the past. Bolsters may be the better solution, but a haunched girder end is also worth considering.