Civil Engineering Reference
In-Depth Information
Girder #1—max (−) forces
−0.28
kip =
F
z
30
649.72
kip
−0.58
kip-ft =
M
y
18.71
kip-ft =
M
z
−9.95
kip =
F
y
1.12 ft
838
−26.84 kip
102.62 kip =
F
y
Top and bottom length =
4.0
ft
Side length =
2.234
ft
1.12 ft
ickness =
0.052
ft
Top element
h
shear =
883.38
kip
Top element
v
shear =
−129.05
kip
1.12 ft
Bottom element
h
shear =
−1009.66
kip
−78.70 kip
−117.29 kip =
F
y
Bottom element
v
shear =
−378.38
kip
898
1.12 ft
−2.45
kip =
F
z
−635.01
kip
90
−0.82
kip-ft =
M
y
−19.95
kip-ft =
M
z
10.02
kip =
F
y
Torsion =
−45.85 kip-ft
Moment = 3114.33 kip-ft
Shear = −108.28 kip
Figure 7.9
Conversion of FEM stress resultants to beam moments and shears.
M
y
(transverse moment = 0.58 kip-ft or 0.8 kN-m for the top flange),
and
M
z
(vertical moment
=
18.71 kip-ft or 25.4 kN-m). Resultants
for shell elements are shown in
F
y
(horizontal force
=
102.62 kip or
456.5 kN for the web top element) and
F
z
(vertical force
=
26.84 kip
or 119.4 kN for the web top element). By integrating all resultants
of these four elements, moment, shear, and torsion can be obtained
at the central or any location of the cross section. This process can
be a significant undertaking, particularly with regard to proper pro-
portioning of deck stresses and deck section properties to individual
girders.
When and how to use a refined 3D FEA for engineering design is
a controversial issue, and in the United States such an approach has
not been fully incorporated into the AASHTO specifications to date
(2013). The typical AASHTO methodology for design is generally
based on the assessment of nominal (average) stresses calculated by
simplified methods, such as P/A or Mc/I, and not localized peak stresses
obtained by shell- or solid-based finite element models. Refined analy-
sis can provide substantially more detailed and accurate information
about the stress state of the structure. This could allow for more cost-
effective and reliable design but often comes with increased engineer-
ing effort and increased potential for error. The results are often more
sensitive to the input parameters and the mathematical assumptions
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