Calculating mounting stresses and sag

(manually and explanations to the program)

The calculation is based on permissible tension method, according to which the calculations should be performed once again due to the fact that LineMount is a stand-alone program. Climatic conditions, maximum tension and tension at average annual temperature accepted for the project are justified by mechanical calculation in LineMech. To calculate mounting stresses and sag manually, it is also necessary to perform mechanical calculation at first.

Stresses and sag acquired as the result of mechanical calculation, except for some coincidences should not be used as the basis for mounting.

After the final spotting of the supports on the line profile, upon releasing the project, the mounters should be given the tables of stresses for each strain sector of the line and sag for particular attested spans. Based on the ambient temperature and the mounting tables, the mounters draw the wire as necessary in particular strain spans and provide the sag in particular denoted spans.

The equivalent span is defined for the strain sector

Using the equation of the wire state, see example of «manual» calculation, inserting the temperatures of -30 and +40ºС and taking only the load from own weight of the wire , define for these temperatures.

Provided we know that the tension (stress) throughout the strain sector is practically the same, which corresponds to the equivalent span at each temperature, define the sag for particular (attested) spans of the strain sector

We have the sag for each particular span of the given strain sector at 30 and +40ºС.

 

Now we can make a temperature-sag chart for each particular span of the given strain sector for the corresponding equivalent span by drawing a line between the sag at -30 and that at +40ºС.

Then, the following strain sector is taken, and the calculation is repeated.

The calculation by the program is performed for temperatures with the pitch of 10ºС between the extreme temperatures. The chart in this case will be close to a horizontal line.

 

It is customary to attest the second spans from strain supports, crossings spans, and approximately each 7th span throughout the entire strain sector, each span enclosed by strain supports.

 

Attested spans should be present in all the strain sectors of the line.

In case the permissible tension is decreased in sectors of descents to portals, spur lines form an intermediate support, and other similar cases, when the weight of strain insulator strings influences the sag considerable, the weight and length of insulator strings is taken into account, as well as the difference in heights of attachment.

Warning. The calculations should be performed for each strain sector.

 

The same length of particular spans in case of different equivalent spans does not mean the same sag.