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h2. How are suspension bridges and cable forces modeled and analyzed? *Answer:* Suspension bridges |
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Detailed Staged Construction Analysis
Set up a staged construction load case to reflect the actual erection sequence of the bridge as it progresses for the foundations, pylons, main cables, suspenders and finally the deck.
Finding Deformed Equilibrium Configuration
If you know the desired deformed configuration of the bridge based on the parameters such as the main cable sag, main cable span and deck profile, you can use SAP2000 to obtain the forces that correspond to this desired deformed configuration. You can start the analysis with coordinates representing the desired final deflected shape of the structure. It is important to specify cable loading that corresponds to the final deformed configuration on the "Cable Geometry" form. After running the analysis, use the "Analyze > Modify Undeformed Geometry" menu command to change the joint coordinates so that the deflected shape at the end of the staged construction case matches the originally specified geometry. Iterate a few times until the coordinates converge to the desired shape.
See Also
References
- Wei-Xin Ren, George E. Blandford,and Issam E. Harik: Roebling Suspension Bridge. I: Finite-Element Model and Free Vibration Response, J. Bridge Engrg. Volume 9, Issue 2, pp. 110-118 (March/April 2004)
FAQ
How to model suspension bridge in SAP2000? How to setup the initial geometry and cable forces?
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may be [modeled|kb:Modeling techniques] and analyzed in [SAP2000|sap2000:home] through either of the following methods:
* [Staged construction|kb:Staged construction], which simulates the construction sequence.
* Direct solution of the deformed equilibrium configuration under dead load.
Once bridge stiffness under dead load is obtained, additional analyses ([moving-load|kb:Moving-load analysis], wind, seismic, etc.) may be performed using the stiffness at the end of the dead load case.
h2. Detailed staged-construction analysis
To perform the staged-construction analysis of a suspension bridge, create a staged-construction [load case|kb:Load case] which reflects the erection sequence from foundation construction through pylon, main-cable, suspender, and deck assembly.
h2. Solve for deformed equilibrium configuration
When deformed configuration is derived through input parameters (main cable sag, main cable span, deck profile, etc.), the corresponding force values may be obtained using [SAP2000|sap2000:home]. Analysis may begin with coordinates which specify the final deflected shape. The cable load which corresponds to the final deformed configuration should be specified in the Cable Geometry menu. After analysis, [joint|kb:Joint] coordinates should be modified through Analyze > Modify Undeformed Geometry such that deflected shape at the end of staged construction matches the geometry initially specified. Several iterations may be necessary for convergence to the desired shape.
h2. See Also
* [Accounting for deformed shape in staged construction] article
h2. References
* Ren, W., Blandford, G., Harik, I. (2004, March/April). {new-tab-link:http://ascelibrary.org/beo/resource/1/jbenf2/v9/i2/p110_s1?isAuthorized=no}Roebling Suspension Bridge. I: Finite-Element Model and Free Vibration Response{new-tab-link}, _Journal of Bridge Engineering, Volume 9, Issue 2_, 110.
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