Civil Engineering Reference
In-Depth Information
The recommended compression flange width-to-thickness ratio is
0.43
E
b
2
t
f
≤
F
y
,
(7.54)
when there are no ties bearing directly on compression flanges and
0.35
E
F
y
b
2
t
f
≤
,
(7.55)
when ties bear directly on compression flanges.
7.2.6.1.2.2 CompressionFlangeSplices
Splices in girder compression flanges
are treated in a similar manner to those for tension flanges. The requirements are
outlined above in the section on girder tension flange design.
7.2.6.1.3 Girder Web Plates and Splices
7.2.6.1.3.1 Web Plates
Economical railway girders have relatively thin web
plates. Therefore, in addition to designing the web plate to carry shear forces (Equa-
tion 7.32), it is also necessary to ensure stability of the web plates in girders.
Figure 7.12 indicates the forces on the web plate that may create instability.
The stability criteria for shear, bending, and compression forces are separately
developed and appropriately combined to investigate web plate stability. Inelastic
buckling, due to residual stresses, load eccentricities, and geometric tolerances, is
modeled by a buckling strength transition parabola formulation consistent with other
structural instability criteria (e.g., axial and flexural compression).
Uniform compression stress,
σ
c
Shear stress,
τ
Bending stress,
σ
b
h
a
FIGURE 7.12
Stresses on girder web plates.
