CIVIL ENGINEERING FORMULAS

238 CHAPTER NINE

However, the wall material and its attachments to the studs must comply with
the following:

1.Wall sheathing is attached to both faces or flanges of the studs.

2.The spacing in inches of attachments of wall material to each face or flange
of the stud does not exceed ain either:

(9.99)

(9.100)

whereLlength of stud, in
Afull cross-sectional area of stud, sq in
r 1 radius of gyration of full cross section of stud about its axis parallel
to wall, in
r 2 radius of gyration of full cross section of stud about its axis perpen-
dicular to wall, in
kcombined modulus of elastic support, or spring constant, of one
attachment of wall material to stud and of wall material tributary to
that attachment, lb per in (kPa)

For any steel other than Grade C, having a yield point fy,acomputed from
Eq. (9.99) should be multiplied by (33,000/fy)^2.
For continuous attachment—by an adhesive, for example—ashould be
taken as unity in solving Eq. (9.99) for k.
One attachment and the wall material tributary to it should be able to exert
on the stud a force in the plane of the wall at least equal to

(9.101)

whereI 2 moment of inertia of full cross section of stud about its axis perpen-
dicular to wall
Pload on stud

For continuous attachment, a1.
Values of kandFfor any particular combination of stud, wall material, and
attaching means can only be determined by test.
A satisfactory value of kcan be determined from the expression

(9.102)

wherePultultimate load
P 0 initial or zero load
nnumber of attachments
yaverage change in length between attachments of each of the stud
pieces from initial load P 0 to 0.75 Pult

k

0.75PultP 0

0.5ny

Fmin

kLP

2,600,000I 2 (k/a) 240 P

amax

L

2

r 2

r 1

amax0.22

r 22

A

k