1960s concrete bridge girder

[WesternJeb]

Hello all. I have ran into a project where we are determining the capacity of a 1960's pedestrian bridge. The bridge is cast-in-place concrete, approximately 58' long, and ties into concrete beams at each support end. See the attachment for the rather odd cross section.

I know that it is similar to a box-style bridge girder but it is not exactly that either. Does anyone have a reference to this style of design that I could use to determine capacities?

Thank you!

 

[Lomarandil]

Looks unusual enough to me that I'd expect to derive capacity from basic concrete theory. There are also a number of tools (IES Concrete Bending, the Python ConcreteSection library) which would simplify the unusual geometry exercise.

 

[bridgebuster]

Is this a prestressed or post-tension bridge? 4" slabs are pretty thin for reinforced concrete spanning 58'. Reminds me a little of a ped bridge that was constructed between the old World Trade Center and the old Bankers Trust Building in lower Manhattan. In the early 70's as a student I worked in the BT building during the summer. The bank news letter had an article on the bridge being constructed, it was CIP/PT. The bridge got wiped out on 9/11. Anyway, enough reminiscing.

Attached are two pages from the 65 AASHO on CIP box girders, not much there, and 2 pages from the 63 ACI 318, not much there. The ACI doesn't mention box beams. However, it did cite Section 1503 for design assumptions for beams with non-standard cross sections.

 

[bugbus]

Are you able to share where this bridge is? I'm just really curious to see how it looks.

 

[WesternJeb]

It is a cast-in-place pedestrian bridge in KY. It is in the inner area of a hospital, so unfortunately not available to see through google earth.

Thanks Bridgebuster for the references.

Yes, concrete principles will govern and will ultimately be what I do. I just find it hard to imagine the original designer did this without any reference of design. After more research, I guess this bridge would be classified as a "folded plate bridge."

 

[bridgebuster]

@WesternJeb - you're welcome; good luck