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SAP2000: seeking help in modeling of transmission line towers

tubsdua (Civil/Environmental) (OP)
18 Dec 11 7:07
Hello All,
I'm making a coupled model of transmission lines and towers. The aim is to develop the numerical model and compare results with output of the monitoring system on a test transmission line. After modelling the 4 towers, SAP2000 was able to perform the modal analysis of all the towers separately. Later the conductors (as cable element) were added and obviously due to the geometric non linearity of the the conductors, non-linear analysis was sought. SAP2000 was not able to converge the solution for this coupled model with 4 towers and conductors. I have tried the all hinge unloading options and also increased the null steps and total steps of iterations, but still no solution. I then proceeded to simplify all the towers as a single frame element using static condensation and lumped mass. Alongside, to check if I am doing something wrong in modeling the cables, I modeled random simplified towers and conductors to check. SAP2000 was not able to converge this simple model too. Hence I feel that the towers are correctly modeled and there is something wrong in modeling the insulators (on towers) and the conductors. I am attaching the simplified model. I would appreciate a brain storming to help me. Thanks.
rko2011 (Structural)
18 Dec 11 22:11
How are we suppose to open this file? Shouldn't it be an SDB file?
tubsdua (Civil/Environmental) (OP)
20 Dec 11 4:23
Hello rko2011,

since I am using SAP200 v15 to obligate version issues I have attached the SAP text file which you can import in any version of SAP2000. You will have to import the file in a model.
 
tubsdua (Civil/Environmental) (OP)
20 Dec 11 4:25
Never the less as an update this is what I found. For large models like the one I spoke about, a solution is converged if I use cable elements. In case I use the option to model the cable as frame elements a solution is not converged.
transmissiontowers (Structural)
22 Dec 11 0:48
Most utilities use PLS-CADD to model transmission lines and towers and they have a cable element for the conductors.  The towers are usually assumed to be truss structures.  ASCE 10 is the standard for tower design.

The conductors suspended on insulators are usually so flexible that the loads don't transfer along the line unless you get a broken wire case.  ASCE 74 talks about the loads and having enough slack in the line to prevent a cascade failure.

The nice thing about PLS-CADD is it handles the creep in the aluminum wire plus the increased sag when the wire heats up.  We rate some lines for 250°C which is why you don't see many birds sit on the conductors.

Conductor manufacturers have been tabulating wire creep data for about 80 years.  I'm pretty sure your SAP cable element does not consider creep and the increase in line length with temperature.

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