Composite section design - effective flange width

Question

Composite section design - effective flange width

bbagar (Structural)

(OP)

11 Aug 01 00:26

Hello

I am trying to design a composite girder for a bridge using AASHTO.  I have a situation where I need to determine the effective flange width for the following situation:

The fascia girder of the bridge is the girder in question, which is supporting the beams under the turn lanes for a diamond type interchange, so the configuration kind of looks something like:

=============  Main girders

=============  Main girder (fascia)
------/
-----/ <-----Wing beam supporting wing stub beams (-)
----/

Anyway the fascia beam has a 1'-6" overhang of deck slab on the outside.  The other side is like a regular bridge deck.

What would you do if you wanted to determine the effective slab width for composite girder design?  All AASHTO considers is if the beam is an interior or exterior beam. and if it is exterior, it is considered that the deck slab ends at the end of the flange on one side and keeps going on the other side.  how do you consider that 1'6" overhang?

Thanks

LPPE (Structural) · Answer 1 · 2001-08-11 10:21:49

Reading AASHTO sometimes is like trying to read Nitchze. Some design procedures allow you to use your overhang for strength. However, if you have to design using AASHTO, and they say do not use the overhang (just to the edge of flange), then I would just use what AASHTO has put forth.

Also, if the 1'6 overhang is only on part of the girder, I dont think you would be allowed to use it.

bbagar (Structural) · Answer 2 · 2001-08-13 09:36:17

pylko:Thanks for your reply. The overhang is only on one side of the girder. You are right about AASHTO, it is sometimes fuzzy about things, especially on this one. It does not say anything about not using the overhang. I guess they only assume two conditions: a.The deck is continuous on both sides or b.The deck is continuous on one side and ends at the end of the girder flange on the other. No provisions for an overhang type of situation was is considered.

LPPE (Structural) · Answer 3 · 2001-08-14 07:24:34

Yes, I think you're right about AASHTO and their 2 conditions. What if you analyze the girder without the overhang to see if it works, and if you then come up short in what you need, include the overhang.

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Composite section design - effective flange width