Page 325 - Civil Engineering Formulas

258 CHAPTER TEN

TABLE 10.4 Allowable Bearing Stresses on Pins*
Bridges
Pins subject Pins not subject
Buildings to rotation to rotation
F y F p 0.90F y F p 0.40F y F p 0.80F y
36 (248) 33 (227) 14 (96) 29 (199)
50 (344) 45 (310) 20 (137) 40 (225)
* Units in ksi (MPa).

BEARING ON MILLED SURFACES

For highway design, AASHTO limits the allowable bearing stress on milled
stiffeners and other steel parts in contact to F 0.80F . Allowable bearing
p
u
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 F of the steel in the roller or the
y
base, whichever is smaller. For diameters up to 25 in (635 mm) the allowable
stress, kip/linear in (kN/mm), is
F y 13
p 0.6d (10.40)
20
For diameters from 25 to 125 in (635 to 3175 mm),

F y 13
p 3 d (10.41)
20
where d diameter 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)
F p 1.35F u
where F allowable bearing stress, ksi (MPa); and F tensile strength of
p u
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).