# Final and Forward Construction Stage Analysis for a PC Cable-Stayed Bridge

• Bridge Engineering
• midas Civil
• 2012.09.14

Cable-stayed bridges are structural systems effectively composing cables,  main  girders and towers. This bridge form has a beautiful appearance and easily fits in with the surrounding environment due to

the fact that various structural systems can be  created  by changing  the  tower shapes and cable arrangements.

To determine the cable prestress forces that are introduced at the time of cable installation, the initial equilibrium state for dead load at the final stage must be determined first. Then, construction stage analysis according to the construction sequence is performed.

In general, with forward construction stage analysis, we cannot obtain cable pretension loads for each stage which satisfy the initial equilibrium state at the final stage. By using cable pretension loads resulting from backward stage analysis, we can perform forward stage analysis. However, newly added function, Lack-of-Fit Force finds cable pretension loads for each construction stage from cable pretension loads at the final stage wit hout backward stage analysis.

This tutorial explains techniques for modeling a cable-stayed bridge, calculating initial cable prestress forces, performing construction stage analysis and reviewing the output data. The model used in this tutorial is a three span continuous cable-stayed bridge composed of a 110 m center span and 40 m side

spans.

Cable- stayed bridges are structural systems effectively  composed of cables, main girders and towers.  This bridge form has a beautiful appearance and easily blends in with the surrounding environment due to the fact that various structural systems can be created by changing the tower shapes and cable arrangements.

Cable-stayed  bridge is a bridge type where inclined cables transfer member forces induced in the girder. High compression is induced in the tower and main girder due to the   structural system. Considering the above features, PC cable- stayed bridges using Prestressed  Concrete material for the main girder, have following  advantages :

High buckling resistance compared to  steel cable- stayed bridges because of the high stiffness of the tower and the main girder
High wind and earthquake resistance  compared to steel cable- stayed bridges because of  the higher weight, stiffness, and damping ratio
Concrete cable- stayed bridges  are better than steel cable- stayed bridges in terms of serviceability as the stiffness of main girder is large, and thus the deflection due to live load is small (resulting in good control of noise/vibration).
Low cost and easy maintenance compared to steel cable-stayed bridges
Efficient  constructability because it essentially  consists of cantilevers, and can be built by constructing out from the towers.
Economical because the  minimized girder depth allows large space under the bridge and  this type of bridge allows shorter  approach length.

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