Concrete T-Beam

[spats]

Section 8.12.4 of the ACI 318-08 code seems to be saying that a T-beam flange can't be less than one-half the width of the beam. This seems awfully restrictive, and unreasonable. I'm not sure what the significance is of being "isolated beams in which the T-shape is used to provide a flange for additional compression area". What other reason would you have for treating it as a T-beam? What is the significance of "isolated"... what does it mean? Does anybody understand the thinking on this provision?

 

[slickdeals]

I think an isolated T beam is one where the slab is not poured monolithically with the beam. A case where you physically only have a certain width, not arbitrary code required eff. flange width.

 

[hokie66]

That's not correct, slick. An isolated T beam is generally a precast beam, and the provisions are just to prevent the use of very thin flanges. The exact same provision has been in the code since at least the 1963 version.

 

[spats]

Thanks for the replies, but I'm still a little confused. I guess the precast is made composite with the slab using shear connectors cast into the precast... is that the idea?

 

[Teguci]

To the best of my knowledge, precast single tees went the way of the dodo. Double tees are made composite with a roughened surface - no steel. I'd have another look at this for high seismic, but for mild areas, this is standard.