Tower Vibration Problem
Tower Vibration Problem
(OP)
Hi Friends, I have a strange problem to discuss...
I work for National Grid. Few days back, I got a video in which a person was applying force on the lowermost diaphragm/horizontal bracing of the latticed steel tower. He was applying force manually (which probably wouldn't be more than 50 kgf) at the centre of this horizontal bracing. Result was a great amount of vibration observed in the horizontal and diagonal bracings in the lower portion of latticed tower, which perhaps are of the magnitude of over 200 mm. This caused a great panic in the management. The tower was a new one without any conductors erected yet. I was asked to recheck the analysis. I replied that towers are not designed for such load application, but this isn't the answer my managers want to hear. They just want to stop/reduce the vibration. Now the same towers have been used in here for over 15 years. And I'm unable to satisfy my bosses with the reason for such huge vibration. Can anyone explain the probable reason of vibration.
Thanks
I work for National Grid. Few days back, I got a video in which a person was applying force on the lowermost diaphragm/horizontal bracing of the latticed steel tower. He was applying force manually (which probably wouldn't be more than 50 kgf) at the centre of this horizontal bracing. Result was a great amount of vibration observed in the horizontal and diagonal bracings in the lower portion of latticed tower, which perhaps are of the magnitude of over 200 mm. This caused a great panic in the management. The tower was a new one without any conductors erected yet. I was asked to recheck the analysis. I replied that towers are not designed for such load application, but this isn't the answer my managers want to hear. They just want to stop/reduce the vibration. Now the same towers have been used in here for over 15 years. And I'm unable to satisfy my bosses with the reason for such huge vibration. Can anyone explain the probable reason of vibration.
Thanks






RE: Tower Vibration Problem
http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."
RE: Tower Vibration Problem
RE: Tower Vibration Problem
RE: Tower Vibration Problem
Your condition is not overly concerning.
RE: Tower Vibration Problem
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Tower Vibration Problem
I also agree that this is a non-issue.
Mike McCann
MMC Engineering
RE: Tower Vibration Problem
You could add cables from the center of that accessible diaphragm going up and down to other nodes, or a strut going up, or partially sister it, or half a dozen other things to reduce the tower's sensitivity to vandals or to make it a less attractive target for them.
If management says it's a problem, then it's a problem. Simply declaring it to be a non-issue is a non-solution. ... and a career decision.
Pick something to do that will solve the specific 'problem' as cited by management, make plans, figure out what it will cost, and submit it as a response. Let management decide whether to add it to every tower, or just the ones most accessible, and whether and to what extent to retrofit something.
Does National Grid keep records of vandalism? There might be historical data to help you support a recommendation of partial execution. ... or, not.
Mike Halloran
Pembroke Pines, FL, USA
RE: Tower Vibration Problem
RE: Tower Vibration Problem
Do you know who this person is that was applying the load ?
Could it be an engineering student or young experimenting with resonace ?
Surely there must be a reason why he was doing this other than vandalism.
I remember as a young engineer I used to check structures by testing them manually and got reponses even in fairly large structures.
I got a feel for structures that way.
Any one else do this ?
RE: Tower Vibration Problem
RE: Tower Vibration Problem
Mike McCann
MMC Engineering
RE: Tower Vibration Problem
Only someone with some sort of knowledge of structures would attempt anything like this.
RE: Tower Vibration Problem
... but it could be stated in a way that makes it an engineering problem, or that allows an engineered response to what is basically a nontechnical problem.
I.e., you could state that the goal is to prevent or suppress a disproportionate response to an anomalous input.
Nontechnical solutions are possible, also. I have no problem with declaring vandals who attack the grid to be terrorists, putting a bounty on their heads, and deploying snipers to deal with them, er, pre-emptively.
Mike Halloran
Pembroke Pines, FL, USA
RE: Tower Vibration Problem
RE: Tower Vibration Problem
Where did you get the idea that this is a guyed tower?
RE: Tower Vibration Problem
Mike:
OK. I see your point. I guess I'm just tired on non-technical managers calling the shots structurally. Where I currently work, my structural opinion is taken at face value and not challenged. That is refreshing for a change.
Mike McCann
MMC Engineering
RE: Tower Vibration Problem
I just printed this page and showed the responses of you guys to my boss and everybody here was laughing. :)
That video was made by a guy who always points problems in everyone's work.
Anyhow, I modeled the towers on SAP2000 and applied 100 kg force at the same point where that guy was pushing.
Result is vibration off course, but the magnitude is very small, about 10mm but in the video it's much more. I guess there is some construction eccentricity almost always present during the tower fabrication, but can this create so much difference in the calculated and actual results?
RE: Tower Vibration Problem
RE: Tower Vibration Problem
RE: Tower Vibration Problem
RE: Tower Vibration Problem
RE: Tower Vibration Problem
RE: Tower Vibration Problem
There are a lot of dynamic phenomena which are difficult to imagine. The Galloping Gertie bridge was one...probably not a good example, as that was indeed suspended/guyed. I didn't find it beyond reason that resonance could cause the affect observed in the video described by nibbi, but neither would I accept it without further investigation.
RE: Tower Vibration Problem
I saw the video and responded immediately that we cant stop this vibration induced by applying push force on the centre/joint of horizontal and diagonal bracings, simply because the towers are not designed for this force.
But I was asked to check again, why so much vibration is being induced in the lower portion of tower (off course it's a localized vibration). I knew this whole effort was a waste of time, but I had to model the towers and check the response, which is what I've written earlier. (10mm deflection as compared to much larger one seen in the video). And That's why I published the problem here so as to get your views. Anyhow, after so much deliberation and not being able to satisfy my (Electrical Engineer) Boss, I have now distanced myself from this problem, with apologies. Some problems are better left unresolved !
RE: Tower Vibration Problem
RE: Tower Vibration Problem
Mike McCann
MMC Engineering
RE: Tower Vibration Problem
I don't know the magnitude of what this will carry, but adding gravity load should dampen this.
Load it up and have him try again
RE: Tower Vibration Problem