Post Tension Slab on Grade Deflection Criteria Question

[Aesur]

I am curious if someone could explain to me why with PT slabs on grade the deflection limits for "Prefab Roof Trusses spanning the full length or width of the foundation" are limited to L/1000 for Center Lift and L/2000 for Edge Lift. Wouldn't this apply to most residential structures? In my experience it is common for most engineers in the Southwest US to design the PT slabs for L/240 and L/480 (Wood Frame), even when the structures typically have Stucco or Plaster walls (L/360 and L/720).

 

[Aesur]

Here is the table showing the deflection limits:

Source: Link

 

[r13]

You need to read section 4.5.6 (whatever it references) to see the discussion on the stiffness coefficient for the prefab roof truss. Note, it is always help/necessary to read guidelines/reports with the original source document to have a full understanding of the subject.

 

[Aesur]

@retired13, maybe I am missing where in that document the reference to that standard is, but I cannot find it. I know it says see 4.5.6, however I cannot find a reference standard that would have that section (4.5.6) to review. This is why I posted the question in hopes someone could point me in the right direction.

However based on the lack of responses/help I kept looking elsewhere and found that it has to do with non-bearing partition walls being rigidly attached to trusses causing the more stringent deflection requirements. You are allowed to reduce the deflection requirements if the non-bearing walls are designed, detailed and built such that the interior walls allow movement between the trusses and non-bearing partition walls.

 

[r13]

A list of references is at the end of this paper. Try everything by PTI (the last one, and one above), including "Design Slabs-on-Ground", if there is such publication/manual.