Pitch Roof Slab 1

[strawhats2000]

Hi, I am looking for anyone with experience with Reinforced Concrete Pitch Roof Slab (Hip Roof) who can help/advise on the right pitch and principles involved in this type of construction. Many thanks in advance for your input.

 

[Ron]

Your design will have some complicated issues with which to deal...you need a LOCAL structural engineer. You cannot get adequate advice from a forum and certainly not a proper design from these forums either. That's not our purpose.

 

[ztengguy]

Im gonna pass on this job.

 

[XR250]

No kidding!

 

[JAE]

Just throw some #4 bars in there - should be good to go!

 

[EngineeringEric]

I always gotten by with WWF in my past projects and have never had any problems.

 

[Archie264]

Fyi, JAE is being facetious. Hopefully that's obvious but sometimes people take such comments seriously.

 

[ztengguy]

Why does it need to be concrete?

Maybe contact a precaster and have them make roof panels.

 

[msquared48]

Really Archie?

Mike McCann
MMC Engineering

 

[Archie264]

msquared, while it's obvious to you, I've seen such comments on this board be taken seriously. I thought I would cut this one off at the pass.

 

[JAE]

Archie - I do appreciate you mopping up behind me. Thank you.

 

[Archie264]

No problem. It was a funny one, for sure. I just thought I'd make sure no one took it and ran with it.

 

[msquared48]

Actually, if you put enough steel in the slab, the wet concrete will not move.

Mike McCann
MMC Engineering

 

[BAretired]

Was EngineeringEric being facetious too?

BA

 

[BAretired]

If the project is located in Mauritania, what kind of loading would it get?

BA

 

[strawhats2000]

Hi,

The roof needs to be in Reinforced Concrete to grade 30. I am not looking for information about wind loading and steel reinforcement and so on. I am looking for advices, hints on optimum and practical design for a safer structural stabiity, for drainage of rain water. Here the ridge is at the very center of the building with the disadvantage that it is not aligned to the vertical supporting unit in the form of hollow concrete blocks, beam and columns which extend from one end to the other end of the building. I am also looking for information regarding pitch. I have seen many time people using an angle of 27 degree which they get with a rise of 50 for every run of 100. In my case and which is quite the norm here, the angle is usually 22.5 or 30 degree. This is a hip roof on 200 mm. wall/beam/column support.

Thanks in advance for your help.

 

[BAretired]

Structural stability can be attained using any pitch you wish, including no pitch at all, or a perfectly flat slab.

Pitch required for drainage depends on the type of roofing materials you intend to use. The minimum recommended slope for drainage is about 1:50 or about 1.15^o when the surface is smooth.

For asphalt shingles, the recommended minimum slope is 1:3 or about 18^o but this can be reduced with other types of shingle or other types of roofing material.

Sometimes a steeper pitch is used to reduce snow load in areas where snowfall is known to be very high. Sometimes it is chosen by the architect in order to achieve a particular appearance, but roof pitch is rarely dictated by structural or drainage requirements.

BA

 

[TDIengineer]

I'll make a stab at answering your question. I'll make some assumptions first. It appears there are no interior columns? I would approach this design very similarly if it was of wood construction. Treat the concrete as a 1-way slab that spans from bearing wall to ridge. The 2 sets of slabs act as your top chord of your triangular truss element. Check the concrete slab for compression plus bending considering the axial loads from your truss action. Provide some type of tensile element for the bottom chord that spans wall to wall (similar to a wood ceiling joist) but use steel or concrete. You should be able to really cut down on the slab thickness by taking advantage of the truss formed and the depth from the ridge to your bottom chord.

Hope this make sense. Looks like a nice little bomb shelter to me!
As far as roof slope, it appears this is purely driven by the architect and the appearance of a gabled roof system. As far as drainage, BA nailed it.. 1/4" / foot is the norm ... or 1:48.