Civil Engineering Reference
In-Depth Information
Deck
Girder (TYP)
Steel straddle
bent cap
Column (TYP)
k
1
k
2
k
3
k
4
k
5
k
6
Figure 7.23
Straddle bent cap modeled by support stiffness. (a) Girders supported by
straddle bent cap and (b) support stiffness.
plans clearly indicate the assumed erection sequence and designers should
be ready to assess different erection sequences during shop drawing review
if the contractor chooses to erect the girders in a different way. Depending
on the complexity of the steel framing and the proposed erection sequence,
the level of analysis required can range from simple hand calculations to
3D finite element modeling. In general, for a simple framing plan such as a
simple-span bridge with no skew, hand calculations may be sufficient. On
the other hand, for a large curved steel I-girder bridge where vertical and
lateral displacements may be of concern to ensure proper fit-up or where
lateral bending stresses at certain stages of erection may be of concern, a full
3D FEA may be warranted (White et al. 2012).
The 2D or 3D model can be created for the completed steel framing and
then reconstructed stage by stage in accordance with the proposed erection
sequence. For the analysis of the steel erection sequence, dead loads and
construction loads need to be determined and applied to the appropriate
elements in the model. Dead loads typically include the self-weight of the
structural members and detail attachments. Wind loads must be considered
in the analysis of the steel erection sequence.
Increasingly, engineers are required to evaluate the stability of steel members
under partial stages of completion, for instance, the behavior of a beam sus-
pended by a crane or spreader beams during lifting or the behavior of partly
completed spans during erection with beams cantilevered or partly suspended
by holding cranes. Prior to the casting of deck concrete, uneven solar heat-
ing may cause the misalignment of girders and other construction issues.
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