Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: Plywood shear wall, nailing, deflection

[Subject Prev][Subject Next][Thread Prev][Thread Next]
In a message dated 98-07-15 11:26:05 EDT, you write:

<< Assuming the shear to the wall is 2.79 kips.Uplift does not exceed 4.5
 kips and so I am planning to use one Simpson Strong-tie's  PHD5 holddown
 at each end.  The header is a  5-1/8"x12 glulam beam.  To minimize the
 drift I am planning to using with 8d at 3" BN o.c.
 
 Here are the values I used to calculated the deflectoin:
  max shear = 443 plf
  height = 8 ft
  width wall = 6.4 ft
  chord member area = 19.25 in^2
  da = 0.047 in
  en = 0.023 in
  effective thickness of plywood = 0.535 in
  E, chord member = 1700000  psi
  G, plywood = 90000 psi
 
 Here is the result:
  deflection = 8*v*h^3/E*A*b + v*h/G*t + 0.75*h*en + h/b*da
  deflection from bending = 0.00866 in.   1.46%
  deflection from shear = 0.0736 in.   12.4%
  deflection from nail slip = 0.453 in.   76.2%   <<-------
  deflection from holddown slip = 0.0587 in.   9.9%
  sum of deflections = 0.594 inches
 
 This deflection is still exceeding the drift limit.  But I used Rw=6 not
 8 to calculate the base shear.
 
 I have two questions:
 
 1) Why is the nail slip accounts about 3/4 of the total deflection?
 2) Do I need to require pre-drill the nail holes (4xs) to prevent the
 nail splitting the 4xs?
 
 Thanks
 
 Sam Chang, SE
 Cupertino, CA
  >>

Sam,

Double check your math;  I get 0.75*h*en = 0.75 (8)(.023) = 0.138  <<< 0.453
Revised drift = 0.2789" << than .005h = .005*8*12 = 0.48 inches.

You may want to use 10d commons since they have less slip than the 8d and I
would not worry to much about splitting the 4x6 posts.

In your drift calculation, remember that the the equation is for a statically
applied load.  Some sources recommend that you use a 1.25 multiplier to
account for the approximate cyclic deflection.

Michael Cochran