Page 280 - Civil Engineering Formulas

214 CHAPTER NINE

For shapes to which Eq. (9.24) applies,

EI y GJ I y C w 2

E
L b B L b
M cr C b (9.25)
For solid rectangular bars and symmetrical box sections,
57,000C b JA
M cr (9.26)
L b / r y
For determination of the flexural strength of noncompact plate girders and
other shapes not covered by the preceding requirements, see the AISC manual
on LRFD.

ALLOWABLE-STRESS DESIGN FOR SHEAR IN BUILDINGS

The AISC specification for ASD specifies the following allowable shear
stresses F , ksi (ksi 6.894 MPa):
v
F v 0.40F y h 380 (9.27)

t w F y
C v F y 0.40F y h 380
F v (9.28)
289 t w F y
where C 45,000k /F (h/t ) 2 for C 0.8
v
w
v
y
v
2 36,000k v /F y (h/t w ) 2 for C 0.8
v
k 4.00 5.34/(a/h) 2 for a/h 1.0
v
5.34 4.00/(a/h) 2 for a/h 1.0
a clear distance between transverse stiffeners
The allowable shear stress with tension-field action is
F y 1 C v 2
F v C v 0.40F y (9.29)
289 1.15√1 (a/h)
where C v 1,
When the shear in the web exceeds F , stiffeners are required.
v
Within the boundaries of a rigid connection of two or more members with
webs lying in a common plane, shear stresses in the webs generally are high.
The commentary on the AISC specification for buildings states that such webs
should be reinforced when the calculated shear stresses, such as those along