Straight and curved steel box girder bridges - Computational Analysis and Design of Bridge Structures - page 251

y

z x

y

x

z

M MN

−13000 −9333 −5667 1667 9000 16333 20000

−2000 5333 12667

Figure 8.18 Stress contour of straight box shell model (insertion shows moment distribution).

support location. The plate thicknesses and the material properties are
required inputs for Shell 63. Link 8 elements were used to model the top
bracing truss and the cross frames. The stress contour of the straight box
is shown in Figure 8.18.

8.3.2 Straight box beam model (M3)
The straight box beam model is made using Beam 188. Beam 4 (with a hinge
at an end or a truss element) is used at supports to provide bearing support
and apply boundary conditions. In the beam element model, the bracing and
stiffener effects are not considered. Two cases are modeled: (1) two bearings
are provided at all supports and (2) two bearings are provided in the middle
support (at pier) and single bearing is provided at end supports. The inser-
tion in Figure 8.18 shows the bending moment throughout the span.

8.3.3 comparison results
To better understand the structural behavior, the same box girder bridge
is also analyzed with DESCUS-II, a dedicated design and analysis system
for straight or curved box girder bridges by using beam models. Tables 8.2
and 8.3 compared analysis results from these two systems. Table 8.2 com-
pares support reactions, moments, and bending stresses for 2D and 3D mod-
els. In the model, twin bearings are supplied to all supports. Not like the
curved model shown in Section 8.4, twin bearings at all supports behave
no different from twin bearings at support 2 only. Table 8.3 compares the