Roof PT Beam cast to fall 1

[struggle66]

Hi Post again

I have a simple 3 span PT Beams on the roof as shown in fig 1.

But contractor wants to do in a way shown in fig 2. The slope is 1:100 for the rain water to runoff to the drain.

It is gonna push up my low tendon profile. Any other thing to take into account?

Any benefits I can get out of this situation?

(1) Pre-camber that will help my deflection?
(2) Lesser vertical gravity load? Horizontal lateral force to column?
These two are all I can think of now.

Thanks

 

[KootK]

1) At 1:100, most impacts will be small.

2) I'd detail your mid span mild bottom steel as a slight opening joint with the bars lapping generously at the pitch break.

3) I'd like it better with a flat soffit if that doesn't interfere with formwork plans.

4) The relative vertical positions of the tendons and section centriod is important to member behaviour. Ensure that you've got any changes to that modelled appropriately. It shouldn't be a big deal but, since your tendons probably won't have the same slope discontinuity at the apex that the member does, there will be some impacts to design.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[struggle66]

Thanks KootK

Any benefits I can get out of this situation?

(1) Pre-camber that will help my deflection?
(2) Lesser vertical gravity load? Horizontal lateral force to column?
These two are all I can think of now.

Any comment on this?

 

[KootK]

Pre-camber that will help my deflection?

I agree that it will be like extra precamber. And like precamber, it would not affect deflection but, rather, only final vertical position.

Lesser vertical gravity load?

Lesser gravity load in the sense that some of the load formerly resisted by flexure would now be resisted by axial/arching action.

Horizontal lateral force to column?

Agreed.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.