Parapet deflection
Parapet deflection
(OP)
What does everyone use as the minimum deflection limit for parapets? Footnote i in Table 1604.3 of the IBC allows cantilever members to have twice the deflection of the wall. In an application where the wall deflection limit is L/180, that would allow a parapet deflection of L/90. Does that seem a bit excessive assuming it isn't affected by other factors such as siding, stucco, etc.






RE: Parapet deflection
RE: Parapet deflection
For a simple span:
M = wL2/8; Δ = 5wL4/384EI
So Δspan = 5ML2/48EI
For a cantilever:
M = wL2/2; Δ = wL4/8EI
So Δcant = ML2/4EI
The main reason to limit deflection is to limit curvature which would cause cracking in brittle finishes. Curvature = M/EI, so to maintain the same curvature in a cantilever or a simple span:
Another reason to limit deflection is to limit P*δ, a moment magnifier. In the case of a parapet, P is very small and δ is about Δ/3 so that does not seem to be a concern.
This would suggest that if a simple span is permitted L/180 deflection, a cantilever should be permitted L/90.
BA
RE: Parapet deflection
RE: Parapet deflection
BA