Inverse T beam design and L beam design 1

[altecdesigns]

Hello Engineers,
i was wondering if any of you had ever design inverse T beams or L shape beams. If you have, what is the standards for design process.

 

[altecdesigns]

I mean concrete reinforced concrete beams.

 

[JAE]

Well, you basically treat it the same as a rectangular or T beam - same principles apply. For simple span cases, in fact, the inverted beams compression area is simply the top portion of the beam as in a rectangular beam. The lower area, with the "L" or the "T" flanges, are in tension so this really doesn't enter into your calculations for a simply supported beam. You can spread out your tensile reinforcing in the full width of the flange.

For a continuous beam of this type, at the support the lower portions of the beam are in compression and you treat it just like a normal "T" beam (its just upside down). But all the same design principles for designing "T" beams apply.

 

[altecdesigns]

what if the the inverted T is used to carry loads from a 8" hollowcore +2" toping. The flange is carring the load of the 8" hollowcore +2" top.

 

[JAE]

Two issues:

1. The flexural design of the beam is as I stated above.

2. The flanges carrying the HC must be checked for shear across the flange, bending of the flange itself, and web tension failure.

The shear and flexure are resisted by the concrete and horizontal reinforcing ties running just under the hollowcore in the flange. This is a lot like corbel design covered by ACI in 318 - chapter 11.

The web tension is resisted by vertical stirrups running up the side of the main beam body and resist the tension in the web from the downward pull of the hollowcore.

These calculations are outlined in the PCI Design Handbook as you use a lot of inverted T beams in the precast industry.