Angles welded in TOWER

[rubenpezu]

Hi,

I´m new in the forum. I am new working with software TOWER of powerline. I have to design a small tower, the complete head is welded. I have seen that in the examples of TOWER, in the library of tower, there are a kind of angles SAW (single angle welded) but all of them are really big. Are there any table with dimension of this size? I'm from Spain and here we don't use inches, and I want to finde the dimensional characteristics of this angles to configure the angles we use.
Thank you very much.

 

[transmissiontowers]

You might write to tech support at PLS and ask about that example Number 8 leg bracing factors. Also, take a look at example number 5 where the bracing ratios are 2.4/2.4/0.67 for the staggered braced legs. Example 12 also uses 2/1/1.

Like I said before, I don't use these staggered bracing patterns and I would have to ask the experts I know.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

Thank you very much. I will ask them why the differences.
I will be conservative to avoid problems.

 

[transmissiontowers]

I talked to PLS-TOWER tech support and they feel that Ex8 bracing ratios are probably not correct and should be 2.4/1.2/1.2 for the staggered leg bracing which makes some sense to me after reading ASCE 10 and thinking about it for a while. They said that SAE Towers used this staggered leg bracing after much full scale testing, so you may be able to contact them and ask about it. I believe they started out in Italy and operate in Brazil and Mexico. They opened an office in Houston, Texas a couple of years ago and I know their Vice President of Engineering.

The examples provided with PLS-Tower are meant to show the program functionality and some modeling concepts and are not meant to be 100% correct. I think Ex8, Ex5, and Ex12 were probably provided by clients.

If your new tower is square, I would drop the staggered leg bracing and/or add some redundants (these can be included in the PLS-Tower model now) to get the legs symmetrically braced.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

I am using 2.4/1.2/1.2 for the first option, and I will prepare a 2nd option with 1/1/1 and the redundants angles. The Tower with less weight will be the final Tower.

Thank you very much for your help.

 

[rubenpezu]

I am looking for a good book of tower design according ASCE-10. I have found this

http://www.amazon.com/dp/0784407908/ref=rdr_ext_tmb.

The author is Robert E. Nickerson who is the person who teach the trainning of PLS-TOWER. Do you know some book? Could you recomend me any book?

 

[transmissiontowers]

Yes Bob was the editor of the conference proceedings. I think he also presented a paper at that conference or the previous one in Omaha in 2002. The proceedings are a series of presentations given at the conference and cover many topics. I was there and have a copy somewhere but I believe it was also on CD. We are having another conference this year in Columbus, Ohio on November 4-8, 2012 that would be good to attend if you can get away. They are held every 3 years.

http://content.asce.org/files/pdf/E...dTechTour2&utm_medium=email&utm_source=Eloqua

As far as text books, I don't know of any out there. I have written a paper that is available on the PLS-CADD web site called Efficient Tower Design that you can read although it is getting old and was based on older versions of the program.

http://www.powline.com/contrib/EfficientTower.pdf

Maybe once I retire, I will write a book on transmission tower design. I could probably sell 100 copies because our industry is so specialized that there are not many more than 100 of us in the world.

You might also get a copy of the loading guide ASCE 74.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

I will read carefully your paper.

As you said our industry is so specialized and there are no many documentation to learn. And here in Spain there is not many documentation because of this I am looking for in USA. If you write a book I will buy a copy sure!

I have the ASCE 74 and IEC 60826 but at this moment I don't have time to study.

 

[rubenpezu]

For me the most difficult part of design a tower is define the Ecc. code and the Rest. Code.

 

[transmissiontowers]

If you can get away for the November conference in Ohio, there will be hundreds of Structural Engineers present plus the PLS-CADD developers and you can ask questions of all the experts like Bob Nickerson.

The restraint code can be tricky and you have to remember which axis controls the compression.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

For me will be very difficult be in the coference. I wish but is a long trip and here in Spain all the companies are saving money.

In PLS-TOWER is possible have in consideration an earthquake load? For example the tower have to support 0,4 in the three directions. How I use this in PLS-TOWER? I have read in a CIGRE document that is not necessary for a TOWER, but one company ask me if our towers support this earthquake load.

 

[transmissiontowers]

Since T-Lines are distributed systems connected by very flexible cables, the seismic loads are rarely if ever considered as a load case. We don't allow earthquakes into Texas so I have never done any load cases for them. I don't know how you would do a load case in Tower, but you can write to Erik J. in tech support to see how you would do it. If I had to guess, I think you would calculate an equivalent static load and apply that as a load case where the wires attach.

If you have access to some high powered FEA programs, you could model the tower in SAPS/Nastran/GTstrudl and put the mass of the conductors at the end of the insulators and find out the dynamic forcing function for an earthquake in you area and check the tower for that load. I really doubt that the earthquake load will control anything, and I would try to really discourage your client from requiring it. I think it could be done with lots of extra work, but I doubt it will be worth the extra effort.

Now you could just tell the client, "sure, our towers will withstand 0.4G in all 3 directions" and hope the big earthquake never happens. I would probably write to PLS Tech support and see how they recommend you analyze for the seismic loads.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

Thank you very much.
I was speaking with the client and I have said that in ASCE or IEC or ISO standars don't have seismic loads. I have explain what ASCE and IEC said and he said OK, they will think about it.

Tell the client, "sure, our tower will withstand 0.4G in all 3 directions" I have to defend the project in front of them. Is better try to persuade and don't ask for de 0.4G.

There is no way to do a load case in PLS-TOWER, I should calculate the LTV loads whit a standar (ASCE, ISO or IEC) but no one have formulation to do.

 

[transmissiontowers]

Take a look at ASCE 113 (if you have a copy) in section 3.1.7.1 which gives an equation for an earthquake load where you calculate an equivalent static load that is applied at the centroid. You could make a PLS-Tower load case with no wind and all factors as 1.0 and apply a joint load on a joint close to the centroid. I doubt that this load will control any members but I believe is is possible.

If you can convince the client that the earthquake performance of a tower is good, you will be better off. I have heard of only one incident where an earthquake damaged a tower. The fault line went between the tower legs and the relative foundation motion ripped the tower apart.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

Great information!
I supose my 0.4 should be Ss or S1. Is this correct?
When it speak about Structure Earthquake loads it said lateral force (Transversal). How I apply in 3 directions?
And the last doubt, in the Eq. 3-10, W that is the dead load, could I use the maintenance load for example.
Please find the attached file.

 

[transmissiontowers]

You are out of my expertise area with the seismic loads. The people from Oregon and California wrote those equations in ASCE 113. If I had to guess (and it is a pure guess), I would say that the dead load would include the tower, wire, and any ice weight. I would apply the seismic load in the transverse and longitudinal directions as 2 separate load cases and if you really wanted to, a third vertical load case with the 0.4G although I can't see the vertical case as meaningful since an additional 0.4G added to the normal 1G vertical would only be 1.4G which is like having a 1.4 factor on the vertical loads. I suppose there might be some dynamic amplification factor in a vertical subduction event.

Good luck;
George

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

Where I should be the 0.4G in consideration is in the foundation, is not? But I'm not sure how. I think I have to multiply the Support Reactions by 1.4 and later calculate the stub and the dimension and volume of foundation. Do you think this way could be correct?

 

[transmissiontowers]

If I had to guess, and like I said before I never do these dynamic loads, I would apply a 1.4 overload to all the vertical loads and check all members. This may load up the conductor arms. If F=ma and a is 1.4G, then this is the basis of my theory (which may be totally wrong). I don't think the vertical direction seismic load will do much to the tower.

I believe the simple equivalent static approach will give you something to input into PLS-Tower to check the members, and I really doubt these loads will control anything. In order to do a thorough seismic analysis, you would need to model the tower in some FEA program like ANSYS and apply the earthquake forcing function and run a dynamic analysis.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[rubenpezu]

At this moment, they don't ask for dinamic loads because they don't know the kind of terrain. Later probably we will have a meeting and discuss this issue.

 

[rubenpezu]

I have to modify an old tower (80's). The tower was modeled in PLS-TOWER before I came to this company. Now the person who design is not here. I have one doubt about the crossing- diagonals in the body. He put the Ecc. Code and Rest. Code with 2/5 and the connection is with one bolt directly to the leg. But I am not sure I think should be 3/4 with one bolt and could be 2/5 with 2 bolts. Do you think I am right? Ore the old design could be OK?

Thanks.

 

[transmissiontowers]

If the crossing diagonals do not have intermediate redundant bracing and it is connected to the leg by 2 bolts so there is rotational restraint at one end, I can see a 2,5 code because it will rotate about the center bolt where they cross. For a 1 bolt connection at the leg, I would use a 3,4. The old model you have might be a little off. The compression equations in ASCE 10 were derived from lots of testing and have some safety factor in them. Change the code and look at what difference it makes. It may be very small.

_____________________________________
I have been called "A storehouse of worthless information" many times.