CIVIL ENGINEERING FORMULAS

BUILDING AND STRUCTURES FORMULAS 223

To prevent web crippling, the AISC specification requires that bearing stiff-
eners be provided on webs where concentrated loads occur when the compres-
sive force exceeds R, kip (kN), computed from the following:

For a concentrated load applied at a distance from the beam end of at least d/2,
wheredis the depth of beam,

(9.57)

wheretfflange thickness, in (mm).

For a concentrated load applied closer than d/2 from the beam end,

(9.58)

If stiffeners are provided and extend at least one-half of the web, Rneed not be
computed.
Another consideration is prevention of sidesway web buckling. The AISC
specification requires bearing stiffeners when the compressive force from a con-
centrated load exceeds limits that depend on the relative slenderness of web and
flangerwfand whether or not the loaded flange is restrained against rotation:

(9.59)

wherellargest unbraced length, in (mm), along either top or bottom flange at
point of application of load
bfflange width, in (mm)
dcweb depth clear of fillets d 2 k

rwf

dc/tw

l / bf

R 34 t^2 w 1  (^3) 

N

d

tw

tf

1.5

^2 Fywtf/tw

R67.5t^2 w 1  (^3) 

N

d

tw

tf

1.5

^2 Fywtf/tw

N

N+ 2.5k

N+ 5k

N

k

k

Toe of fillet

FIGURE 9.4 For investigating web yielding, stresses are assumed to be distributed

over lengths of web indicated at the bearings, where Nis the length of bearing plates,

andkis the distance from outer surface of beam to the toe of the fillet.