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Long Term Deflection Criteria - Wood Frame Building

Long Term Deflection Criteria - Wood Frame Building

Long Term Deflection Criteria - Wood Frame Building

I am working on a project with a concrete transfer slab that is supporting the load bearing walls of a conventional wood framed five storey building. It is a residential building with gypsum walls, hardwood floors, ceramic tiles, etc.

I am trying to get some advice on the deflection criteria to be used to design the concrete slab.

In my opinion the concrete slab deflection criteria for long term total deflection should fall under L/480.
(i.e. Roof or floor construction supporting or attached to non-structural elements likely to be damaged by large deflections.)

However, I believe that some engineers use L/240 for this type of construction.

I'd just like to get some prospective on this. Is L/480 too stringent?


RE: Long Term Deflection Criteria - Wood Frame Building

Is it post tensioned? I don't think you will have a problem with L/480 if it is. All my podium slabs are PT and deflection almost never controls.

RE: Long Term Deflection Criteria - Wood Frame Building

No its not post-tensioned. That's why I do have a problem....

RE: Long Term Deflection Criteria - Wood Frame Building

I believe that the Australian code has provisions for this. L/500 if you've considered the deflection in the framing above and L/1000 if you haven't. I don't know of anyone in North America being so stringent with these types of structures however.

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.

RE: Long Term Deflection Criteria - Wood Frame Building

It has been my experience that the long-term creep characteristics of dimensional and engineered lumber are underestimated. i.e. the stuff sags more than it should
I would not skimp at all - especially with a heavy, sustained load. L/600 min.

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