Deflection Limits (IBC) for roof framing system
Deflection Limits (IBC) for roof framing system
(OP)
I know the deflection limits for each member are L/360, 240, 180...for each member.
But if the rafter deflects 2" at midspan and purlin deflects 1.5" at midspan. Then the total deflection is 3.5"
Is there any part in the code (or any code) about the combined effect of deflections?
Adam
But if the rafter deflects 2" at midspan and purlin deflects 1.5" at midspan. Then the total deflection is 3.5"
Is there any part in the code (or any code) about the combined effect of deflections?
Adam






RE: Deflection Limits (IBC) for roof framing system
RE: Deflection Limits (IBC) for roof framing system
RE: Deflection Limits (IBC) for roof framing system
If the rafter deflects 2" and purlin 1.5" does necessarily mean it is 3.5" deflection. Just draw it. It is like simply supported beam (draw it with little deflection), then drop one support a little and keep the same curvature of the beam. How low is the mid point of the beam? I dont think it changes that much. I hope I am making any sense. I wouldnt worry about it if I were you.
RE: Deflection Limits (IBC) for roof framing system
The purlins also sag the same amount at the eaves, so it is usually not an issue. If you really wanted to check the combined deflection then you would check the 3.5" over the diagonal.
There are a few situations where I probably would check this:
1. A 2 way flat slab with fragile finishes or sensitive equipment.
2. A very flat roof that may pond (as noted above).
3. Where partitions or similar are attached to the roof and the actual maximum deflection is important.
RE: Deflection Limits (IBC) for roof framing system