Stringing tables – initial or final?
The stringing table generator gives sags/tensions that are final conditions (after creep). Final condition is commonly considered to have been achieved after 10 years. The calculation method used in Poles ‘n’ Wires is shown in AS/NZS7000 appendix S.
How to derive initial (stringing) conditions
To derive initial conditions from final conditions AS7000 and other equivalent documents recommend using a temperature compensation.
a temperature compensation means the conductor will be tensioned
tighter at installation so after creep occurs the sag is at the correct
design level. Let’s say the conductor is at 25º on the day of stringing.
If the appropriate temperature compensation for the conductor type and
tension is 20º you need to tell the installers what the sag would be if
the conductor was at 25-20 = 5º (which will be a smaller sag than for
25º) to make them pull the conductor up tighter. After about 10 years
the conductor would have “crept” and the sag will be (theoretically) as
specified in the design.
You will need to generate a stringing table with that 20º offset and label it as initial (stringing) conditions. Your design (profile and tiploads) shows final conditions as usual.
Modifying the stringing table
This is how you modify the table generated by the Stringing Table module to allow for a temperature compensation.
Generate the table for the conditions you need. Here’s an example.
If the compensation is 20º you need to shift the sag results in the table right by 20º. You can cut and paste the data in Excel.
You can see for example if the temperature on the day of stringing is 35º and you have a 70m span the new table tells the crew to use a sag of 1.34m instead of 1.53m ie tighter.