CIVIL ENGINEERING FORMULAS

BUILDING AND STRUCTURES FORMULAS 221

Units used in these equations are those commonly applied in United States
Customary System(USCS) and the System International(SI) measurements,
that is, kip (kN), lb /in^2 (MPa), ft (m), and in (mm).
Where shear walls contain openings, such as those for doors, corridors, or win-
dows, computations for deflection and rigidity are more complicated. Approxi-
mate methods, however, may be used.

COMBINED AXIAL COMPRESSION
OR TENSION AND BENDING

The AISC specification for allowable stress design for buildings includes three
interaction formulas for combined axial compression and bending.
When the ratio of computed axial stress to allowable axial stress fu/Fa
exceeds 0.15, both of the following equations must be satisfied:

(9.52)

(9.53)

fa

0.60Fy



fbx

Fbx



fby

Fby

 1

fa

Fa



Cmxfbx

(1fa/Fex)Fbx



Cmyfby

(1fa / Fey)Fby

 1

Wind bent

Shear

walls

Spandrel

beam

Columns

(a)

(c) (d) (e) (f)

(b)

(g)

FIGURE 9.3 Building frame resists lateral forces with (a) wind bents or (b) shear

walls or a combination of the two. Bents may be braced in any of several ways,

including (c) X bracing, (d) K bracing, (e) inverted V bracing, (f) knee bracing, and

(g) rigid connections.