256 CHAPTER TEN
Thickness of stiffener, in (mm), should be at least wherebis the stiff-
ener width, in (mm); and fbis the flange compressive bending stress, ksi (MPa).
The bending stress in the stiffener should not exceed that allowable for the material.
HYBRID BRIDGE GIRDERS
These may have flanges with larger yield strength than the web and may be
composite or noncomposite with a concrete slab, or they may utilize an
orthotropic-plate deck as the top flange.
Computation of bending stresses and allowable stresses is generally the
same as that for girders with uniform yield strength. The bending stress in the
web, however, may exceed the allowable bending stress if the computed flange
bending stress does not exceed the allowable stress multiplied by
(10.39)
whereratio of web yield strength to flange yield strength
#distance from outer edge of tension flange or bottom flange of
orthotropic deck to neutral axis divided by depth of steel section
ratio of web area to area of tension flange or bottom flange of
orthotropic-plate bridge
LOAD-FACTOR DESIGN FOR BRIDGE BEAMS
For LFD of symmetrical beams, there are three general types of members to
consider: compact, braced noncompact, and unbraced sections. The maximum
strength of each (moment, inkip) (mmkN) depends on member dimensions
and unbraced length, as well as on applied shear and axial load (Table 10.3).
The maximum strengths given by the formulas in Table 10.3 apply only
when the maximum axial stress does not exceed 0.15FyA, where Ais the
area of the member. Symbols used in Table 10.3 are defined as follows:
Fysteel yield strength, ksi (MPa)
Zplastic section modulus, in^3 (mm^3 )
Ssection modulus, in^3 (mm^3 )
bwidth of projection of flange, in (mm)
ddepth of section, in (mm)
hunsupported distance between flanges, in (mm)
M 1 smaller moment, inkip (mmkN), at ends of unbraced length of member
MuFyZ
M 1 /Muis positive for single-curvature bending.R 1
#(1)^2 (3##)
6 #(3#)
bfb/71.2,