Cable-stayed bridges - Computational Analysis and Design of Bridge Structures - page 347

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Figure 11.20 Submeshed cables with crossties.
stage. Again, a specialized FEA package considering the effective cable stiff-
ness calculation under multiple construction stages is preferred.
For long-span cable-stayed bridges, the geometric nonlinear effects,
including the P-Delta effect, cable sags, and large displacements, become
significant. Full geometric nonlinear analysis is required in certain detailed
design and study situations. It should be noted that the effective stiffness
approach for sag effects is suitable only for cases where each long cable
is modeled as only one element by its two anchor points. When a cable is
submeshed into small segments to investigate the large displacements in
detail or when cable crossties are considered (Figure 11.20), effective stiff-
ness calculation is no longer needed during the iteration processes. During
iteration in large displacement analysis, the stiffness of an element will be
evaluated at current geometric locations. The axial stiffness of such a cable
segment is very close to the actual stiffness as the sag between two end
points of a cable segment becomes negligible.
11.2.8 geometric nonlinearity—large
displacements
As the main span of the bridge increases, the global stiffness decreases
and the displacements (not the deformation) become significant. There
are two features that can be used to help understand what will impact a
regular linear analysis when displacement becomes large. The first one is
that the difference of stiffness at current geometry configurations and at
its original positions is no longer negligible. It will cause major errors to
evaluate the responses of an incremental load at the current configuration
when using the stiffness obtained from the original geometry configura-
tion. The second aspect is the coupling between displacements and forces,