A question arises within the O-Calc Pro application in terms of guy wires; what is the difference between the attributes ‘Over-tension (lbs)’ and ‘Pre-stretch (lbs)’ found on the “GuyBrace” object within the Data Entry panel under the filter ‘Tension’.
The ‘Pre-Stretch (lbs)’ attribute represents the pre-tensioning of the stranded guy wire to achieve a final neutral resting length. When new guy wire being installed coming off the spool may not have been under any load, therefore the practice of cycling through a pre-tensioning (or pre-stretching) process enables the guy wire to become more elastic and to remove any constructional stretch. The following link is a good description of this pre-stretching practice:
Pre-stretching | Assembly Specialty Products
The O-Calc Pro calculation engine does not consider the ‘Pre-stretch’ attribute. This attribute is part of the application for explicit labeling and reporting needs. Some Electric Utilities prefer to have this pre-stretch value listed for reporting needs.
On the other hand, the ‘Over-tension (lbs)’ is used within the O-Calc Pro calculation engine and will affect the final tension value on the guy wire.
Recall, that the guy wire tension is a reaction to the load on the pole. In the example below, the pole has a single guy wire with its ‘Over-tension’ attribute set to 0 lbs, i.e. no over-tensioning. This means that when the guy wire was installed assuming no wind, no ice, on a 60-degree day, the tension on the guy was 0 lbs. Now, as we simulate the wind in all 360-degree directions the guy tension varies as a function of wind angle. For this example, the maximum value is at a 90-degree wind angle and the minimum is at 270 degrees with a value of about 300 lbs of dynamic tension. (see example 1 below).
Now if we set the Over-tension value to 500 lbs for this guy wire, we are setting the floor of the dynamic tension of the guy wire to this value, so as the wind is simulated in all directions, whenever the calculated value the guy wire tension falls below 500 lbs, the O-Calc Pro calculation engine will use the Over-tension value and set it to this value (see example 2 below).
Example 1: Over-tension set to 0 lbs, minimal guy wire tension is at 270-degree wind angle and has a value of about 300 lbs.