Applied Lateral Tension Load Definition

[MSchisano]

I have an existing structure located at an electrical substation that currently has several transmission lines terminating on it. The local utility would like to modify the locations of the lines, requiring me to run some structure checks. My question is, would the load from the tensioned transmission lines be considered a dead load or a live load? I keep going back and forth between the two. Thank you in advance for any and all replies.

 

[centondollar]

The relevant question is not whether it is a dead or live load, but rather how it affects the functionality of the cable. The cable cannot be allowed to sag freely, and since its behavior is highly non-linear w.r.t. loading and boundary conditions (the same applies for the possibly guyed masts regularly spaced along the transmission line), the tensile force should be carefully chosen.

The design standards for utility lines probably present the calculation models. Start from there.

 

[dik]

I generally treat electrical cable loads as LL, but mechanical equipment loads as DL, thinking that there may be a variation in the electrical loads. Electrical equipment, like Xformers, etc. are DL.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[MSchisano]

centondollar, thank you for the reply. We are not concerned with the functionality of the cables as the lines that want to be moved will be designed in accordance with the relevant code (NESC). My concern is how the structure will react if the currently de-energized lines are removed. In order to run my analysis, I need to classify the tension loads as either dead or live. Personally I can see it both ways. The current tensions are always present which to me implies a dead load. That said, these tensions do vary based on weather conditions, so I could also classify them as a live load.

dik, thank you for your response as well. While I agree with you, I also have an argument as classifying them as dead loads (see above).

Some additional insight to the reason for my query is that we are looking to see if by removing some of the lines, the changes in loads due to change in load path do not exceed the code limits and require full detailed analysis and design to current standards.

 

[le99]

The linked design guide defines the design dead load for substation includes: Link

- Weight of structure.
- Weight of supporting equipment.
- Weight of accessories.

Though it was not clearly stated, all other loads are considered the "live load" in nature, including "Wire Tension Load", which is defined as:

[li]Tension loads resulting from phase conductors and shield wires under extreme weather events such as

– extreme wind​

– extreme ice and concurrent wind​

[/li]
[li]Wires attached to the station deadends and strain bus[/li]
[li]Station deadends

– Full tension deadend​

– Slack-span deadend​

[/li]

Note, the load factor for transverse load due to wire tension = 1.65.

 

[dhengr]

MSchisano:
What code are you using, and what part of that code allows you to ignore analysis and redesign when the primary loads and load paths change? Was that code provision for some small percentage increase in gravity loading, one of many different gravity loads over a large area, without a redesign and code update ever intended/contemplated for your type of structure and set of conditions? Once upon a time some engineering judgement and experience were involved in these types of decisions. It will be nice when the codes cover every possible detail and condition, on every planet in the universe, then we won’t need any engineering judgement, just follow the cookbook; never mind what the leavening does. When you have a few discrete loads which make significant changes to the structure, it is incumbent upon you to chase those loads along their load path until they do not change things much. And, I for one, would just as soon not have some tech. writer working hard to keep his job by publishing new codes, without much understanding of the codes or their intent, telling me what to do in these situations.