Prestress I-Beam Girder w/raised concrete median load
Prestress I-Beam Girder w/raised concrete median load
(OP)
I am looking at the AASHTO Standard Specs Section 3.23.2.3.1.3 for design of a Prestress I beam girder type IV. I am looking at an interior beam carrying some of the load of a raised concrete median. I have always thought of a raised median and a sidewalk as being similar (concrete load on the composite section), except for the sidewalk LL provisions. My question is why is an exterior beam carrying a sidewalk LL designed as per AASHTO standard Specs 3.23.2.3.1.3,overstress allowed at 125%. But no similar criteria for interior beams? Any guidance would be appreciated.





RE: Prestress I-Beam Girder w/raised concrete median load
1. All composite dead loads (railing, sidewalks, wearing surfaces, raised medians, etc.) get evenly distributed among al of the beams per AASHTO 3.23.2.3.1.1.
2. Sidewalk live load assumed to be carried by the exterior girders. This is the part I'm not exactly sure of. I have sometimes also distributed sidewalk live load among all of the beams and ignored the 25% allowable stress increase.
3. If you assume that the sidewalk live load is carried by the exterior girders only, you can increase the allowable stress by 25% for the condition of sidewalk live load and traffic live load acting on this beam.
4. If for some reason the sidewalk was down the center of the bridge, I think this provision could be applied to an interior girder.
Hope this helps.
RE: Prestress I-Beam Girder w/raised concrete median load
RE: Prestress I-Beam Girder w/raised concrete median load
Regards,

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