AASHTO effective span length definition = clr + 1/2 flange width

[hippo11]

Can anyone explain to me what the reasoning is behind using an effective span length (not width) of clr span + 1/2 flange width? Or where I could read about it? It just seems kind of an arbitrary definition of effective span length for AASHTO...

I'm studying AASHTO for the first time for my PE exam...

Thanks

 

[strainman]

AASHTO assumption is that the flange will bend slightly under load increasing the bending in the slab. This is for steel beams only. For stiff supports such as concrete I-beams and boxes the effective span length is the clear span. Hope this helps and good luck on the exam.

 

[minorchord2000]

The largest AASHTO concrete girders where the top flange is 3'-6" wide, the design span is the clear span between the tops of the flanges + 17 inches. This increase is due to the flexibility and propensity for flange tip bending under load. This distance is the design span for the concrete deck which spans between the girders.

For the smaller girder, the design span is simply the clear distance between flange tips.