Suspension bridges - Computational Analysis and Design of Bridge Structures - page 386

to be obtained or estimated first. In this step, all dead loads including
the structural weight of cables and stiffened girders plus all superim-
posed dead loads are assumed to be acting on the main cable. The
cable geometry can be assumed the same as the design geometry. The
elastic method mentioned in Section 12.3.2 can be used.
2. Establish the starting state of backward analysis by building a model
using the design geometry and including the estimated cables in step
(1) as the initial stress.
3. Remove superimposed dead loads at all hanger locations. This
removal may be split into several stages according to the sequence of
the imposed dead loads on deck. In addition to a full scale of geo-
metric nonlinearity, including initial stress and large displacements,
a special displacement restraint at cable ends should be applied to
consider the tangent change over saddles during the load increments
and iterations in nonlinear analysis, which will be described in
Section 12.3.5.
4. Reverse the jacking of saddles on the top of pylons if saddles are
adjusted after all girder segments are erected.
5. Remove dead loads due to stiffened girder weights at all hanger loca-
tions. This removal should truly reflect the girder erection process. If
saddles are jacked during the erection of stiffened girders, correspon-
dent reversal actions should be inserted. The analysis method is the
same as in step (3).
6. Remove cable loads due to cable weights and other additional loads
such as wrapping wires and sheathing. The analysis method is the
same as in step (3).
7. Take the current geometric state as the initial state.
8. Conduct forward analyses simulating the loading of cables, erecting
of stiffened girder segments, adjustment of saddles, and application of
superimposed loads after joints between girder segments are changed
to rigid connections. Difference will be found from the final state
obtained in this step and the design state. The bending of the stiffened
girder due to the superimposed dead loads should be considered in
backward analysis after the first round of forward analysis. Rebuild
the starting state including hangers and stiffened girder; repeat steps
(3) to (7). Superimposed dead loads should be removed directly from
the stiffened girder.
9. The initial state obtained in step (7) may be manually adjusted so as
to match the final state obtained in forward analyses and the design
state. This adjustment could be simply change of the chord height
of the cable in zero-stress state. The adjusted initial state will be the
basis of all other succeeding analyses. The total length of cable in
zero-stress state can also be calculated from the initial state.