Page 321 - Civil Engineering Formulas

BRIDGE AND SUSPENSION-CABLE FORMULAS 255

where M smaller beam end moment; and M larger beam end moment.
1
2
The algebraic sign of M /M is positive for double-curvature bending and nega-
2
1
tive for single-curvature bending.
STIFFENERS ON BRIDGE GIRDERS

4
4
The minimum moment of inertia, in (mm ), of a transverse stiffener should be
at least
3
I a 0 t J (10.36)
2
2
where J 2.5h /a 2 0.5
0
h clear distance between flanges, in (mm)
a actual stiffener spacing, in (mm)
0
t web thickness, in (mm)
For paired stiffeners, the moment of inertia should be taken about the centerline
of the web; for single stiffeners, about the face in contact with the web.
The gross cross-sectional area of intermediate stiffeners should be at least
V 18t w
2
A 0.15BDt w (1 C) " (10.37)
V u
where " is the ratio of web-plate yield strength to stiffener-plate yield strength,
B 1.0 for stiffener pairs, 1.8 for single angles, and 2.4 for single plates; and C
is defined in the earlier section, “Allowable-Stress Design for Bridge Columns.”
V should be computed from the previous section equations in “Shear Strength
u
Design for Bridges.”
The width of an intermediate transverse stiffener, plate, or outstanding leg
1
of an angle should be at least 2 in (50.8 mm), plus 30 of the depth of the girder
1
and preferably not less than 4 of the width of the flange. Minimum thickness is
1
16 of the width.
Longitudinal Stiffeners

These should be placed with the center of gravity of the fasteners h/5 from the
4
4
toe, or inner face, of the compression flange. Moment of inertia, in (mm ),
should be at least
a 0 2
I ht 3 2.4 0.13 (10.38)
h 2
where a actual distance between transverse stiffeners, in (mm); and t web
0
thickness, in (mm).