CIVIL ENGINEERING FORMULAS

258 CHAPTER TEN

BEARING ON MILLED SURFACES

For highway design, AASHTO limits the allowable bearing stress on milled
stiffeners and other steel parts in contact to Fp0.80Fu. Allowable bearing
stresses on pins are given in Table 10.4.
The allowable bearing stress for expansion rollers and rockers used in
bridges depends on the yield point in tension Fyof the steel in the roller or the
base, whichever is smaller. For diameters up to 25 in (635 mm) the allowable
stress, kip/linear in (kN/mm), is

(10.40)

For diameters from 25 to 125 in (635 to 3175 mm),

(10.41)

whereddiameter of roller or rocker, in (mm).

BRIDGE FASTENERS

For bridges, AASHTO specifies the working stresses for bolts. Bearing-type
connections with high-strength bolts are limited to members in compression
and secondary members. The allowable bearing stress is

(10.42)

whereFpallowable bearing stress, ksi (MPa); and Futensile strength of
the connected part, ksi (MPa) (or as limited by allowable bearing on the fas-
teners). The allowable bearing stress on A307 bolts is 20 ksi (137.8 MPa) and
on structural-steel rivets is 40 ksi (275.6 MPa).

Fp1.35Fu

p

Fy 13

20

3 d

p

Fy 13

20

0.6d

TABLE 10.4 Allowable Bearing Stresses on Pins*

Bridges

Pins subject Pins not subject

Buildings to rotation to rotation

Fy Fp0.90Fy Fp0.40Fy Fp0.80Fy

36 (248) 33 (227) 14 (96) 29 (199)

50 (344) 45 (310) 20 (137) 40 (225)

*Units in ksi (MPa).