8" x 84" x 40' Concrete Beam/Wall Top Restraint

[north85]

I am completing the structural design of the precast concrete components for a building. In one area I have two 40' long beams that support a lower roof at the bottom of the beam and an upper roof at the top of the beam. The problem I am having is the Engineer of Record has indicated that the roof between the top of these beams is to be comprised of conventional wood truss without any sheathing (1x4 strapping only). I am concerned about this and I am looking for opinions. The factored bending moment in the beam is around 390k*ft.

Thanks

 

[msquared48]

Ask the EOR if the concrete beam has been designed for no top restraint for a starter. If he says yes, log it in in writing, sending him a copy, and proceed with your design.

If he says no, then ask why not. See what he says.



Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[north85]

I dont have a lot of faith in his engineering skills. I know his answer to that question will be that the roof diaphragm is fine, but even with that, I am not all that pleased about this design item.

Brad

 

[JAE]

Are you worried about lateral buckling of the concrete beam?

Usually this isn't a concern for concrete beams if the width of the beam is > Span/50 which in your case is 9.6 inches of width. (see ACI section 10.4)

 

[vandede427]

8"x84" probably classifies as a deep beam in ACI which requires lateral buckling to be considered. i assume that includes lateral buckling of the top "flange" (thinking steel) and web buckling.