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Angles welded in TOWER

Angles welded in TOWER

Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

The SAW shape type is for very large angle sections that are not rolled. In the USA 8x8x1.125 is the largest AISC shape available, so when we use something like a 12x12x1.5, we have to calculate the shape properties.

Your welded "head" is not a term I am familiar with. Do you have a truss section consisting of single angles welded to the legs? If so you just use SAE or SAU type members and do not use bolts or holes.

As far as properties in metric units, you might write to PLS support and see if they have any tables of metric shapes. If your client or company does not have the metric tables already done, you will need to derive the properties yourself. Older versions of the AISC manual have formulas for angles. I have done a spreadsheet to generate the table data required for the PLS .ANG file.

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

RE: Angles welded in TOWER

(OP)
Thank you very much.

What I have is a truss section consisting of single angles welded to the legs. I have a complete table of metric shapes. The problem with this kind of tower is that in the tower fail about 115% but in the real test the tower is OK. This tower is design in 80's but now the results in TOWER is not OK. I just model like you said without bolts or holes. I wanted to ask if there was any other way to do.

Thanks

RE: Angles welded in TOWER

OK, I see. This is the Engineer's dilemma. The computer says it fails and the testing says it was fine, so which do you believe? I would suggest that you try to put in a load case that is exactly what was tested and look at the results in PLS-TOWER to compare the computer results to the real test. If the computer says something like 112% and the real test showed the tower passed, then you may have some rationalization that the computer under-predicted the capacity. As members get close to their capacity in a lattice tower, the load path can redistribute and the tower will remain standing while the computer will predict failure.

About the only thing you can do is report your results to your management and recommend that the tower be modified or replaced and let them make the economic decision. There is a saying, "the loss of human life will be more than offset by the cost savings". If they choose to ignore the failure and risk the potential damages, you can point to your results that predicted failure in the event the towers collapse.

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

RE: Angles welded in TOWER

(OP)
Thank you very much.

I have model the tower in all possibilities. And always fail in PLS-TOWER. Reduce the RLX, RLY, RLZ but always fail.
The final decission will be modify the old tower according the result of PLS-TOWER. The most important thing is the security.

Thank you very much for your help.

RE: Angles welded in TOWER

Which group is failing? Is it the legs or the lacing? How are the lacing connected to the legs? Sometimes the toes of the lacing is welded to the leg but it is usual for the leg of the lacing to be welded to the leg of the post and if the lacings cross, they are connected with a bolt so the Lzz is cut in half.

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

RE: Angles welded in TOWER

(OP)
It is failing the leg of the head just above the connection between the head and the stretch 1º. The for legs of the head are one angle each one and they are connected with the stretch 1º with bolts. All the angles in the head are welded. I have model n PLS-CADD the tower with maximun detail.
In the attached file you can see the details of the tower.

RE: Angles welded in TOWER

If you can add the lacing to make an "X" and then add redundants from the center to the mid panel point of the leg, you can increase the compression allowable. I have attached a sketch to make it a little more clear.

If the towers already exist, you may be able to weld in the additional lacing and bolt in the redundants.

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

RE: Angles welded in TOWER

(OP)
It is failing the leg above the joint connected with bolts, where I have painted the red cloud.

RE: Angles welded in TOWER

For what it's worth, I notice notes 11 & 12 which I assume are antennas, the antennas should be attached as close to the tower nodes as possible.

RE: Angles welded in TOWER

Voyage; I think what you are seeing is the mark number of the legs enclosed in a circle.

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

RE: Angles welded in TOWER

(OP)
You are right transmissiontowers. It is a TOWER for 20 kV or less.

RE: Angles welded in TOWER

It must have some arms and suspension insulators on it to hold up the conductors for one or two distribution circuits.

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

RE: Angles welded in TOWER

(OP)
It have arms,could be use for suspension or angle. But the load test is the nominal (transversal or longitudinal) load with the vertical and other load test is the longitudinal load at 1,5 meter from the axis.

RE: Angles welded in TOWER

(OP)
One more doubt,

If I have the leg of the firs part of body like in the drawing attached. In the angle member conectivity for the RLX, RLY, RLZ, I think should be 2/1/1. The old design was made with 2.4/1.34/1.34. If I use 2/1/1 the weight of structure is less. Am I right?

Thanks

RE: Angles welded in TOWER

I don't use these staggered leg bracing much and I would probably put in a redundant from where the lacing crosses to the leg so I could use 1/1/1. Take a look at ASCE 10 Figure 3.2 and read 3.7.4.4 because your leg load is not constant. I would tend to be more conservative and use the higher values. If you have the ability to test your design in a full scale test to verify your bracing assumptions, you could justify the lower values.

To answer your question, yes the tower design will be lighter if you use the staggered bracing and 2/1/1, but I'm not sure you can justify it unless you do some testing.

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

RE: Angles welded in TOWER

This configuration has no diaphragms, how would you handle twisting and global buckling of the entire tower in this case?

RE: Angles welded in TOWER

(OP)
Thank you very much for your answer. At this moment is impossible test the design in a full scale test. I will be conservative.

RE: Angles welded in TOWER

(OP)
I was checking the examples and in the example nº8 of PLS-TOWER the RLX, RLY, RLZ is with 2/1/1 and the configuration of staggered bracing. Do you know if this example is true? if this example is reliable in its design?
Thanks for all your support.

RE: Angles welded in TOWER

Quote (This configuration has no diaphragms, how would you handle twisting and global buckling of the entire tower in this case? )

I'm not sure what you meant by no diaphragms, but his picture is the output from PLS-Tower showing his 4 sided tower with the 4 sides color coded. I look at these pictures daily so it is not too foreign to me. The tower uses a staggered bracing pattern and the KL/r is adjusted for the leg. At its compression limit, the leg may try to twist but the equations were developed with lots of full scale testing and are conservative.

The legs are continuous but are usually analyzed as truss members with pinned joints. The program takes into account some bending stiffness of the legs so that it is mathematically stable. In the strictest sense, a truss member analysis of the staggered leg bracing is unstable and a normal FEA program will never solve the stiffness matrix because of the instability that you see.

Our T-Line industry is fairly unique in that we will accept occasional failure in order to put up cost effective lines. The bridge and building engineers that have to consider human occupancy would faint if they had to deal with the factors of safety we use all the time.

I have attached a marked up screen shot with a few redundants added that would stabilize the legs and allow K=1 for them.

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

RE: Angles welded in TOWER

Quote (I was checking the examples and in the example nº8 of PLS-TOWER the RLX, RLY, RLZ is with 2/1/1 and the configuration of staggered bracing. Do you know if this example is true? if this example is reliable in its design?)


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.

RE: Angles welded in TOWER

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

RE: Angles welded in TOWER

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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

(OP)
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_tm.... 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?

RE: Angles welded in TOWER

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/ETS2012PrelPrgfo...

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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

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

RE: Angles welded in TOWER

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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

Quote (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.)


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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

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.

RE: Angles welded in TOWER

(OP)
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?

RE: Angles welded in TOWER

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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

(OP)
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.

RE: Angles welded in TOWER

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.

RE: Angles welded in TOWER

(OP)
I some crossing diagonals I have to place the next L angular. We will change the drawings. For me it is clear that for 2 bolts connection at leg it is clearly 2,5. For a 1 bolt connection at leg, could be 2,4? Or never?

RE: Angles welded in TOWER

The connection codes are tough to visualize and it depends on which segment of the angle is the one that controls the compression. Crossing diagonals are even harder. If you count on the tension member to brace the compression member, then the tension value must be greater than 20% of the compression load, so it is load case dependent.

Take a look at ASCE 10, Example 7 for a very good explanation of which code to use.

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

RE: Angles welded in TOWER

(OP)
Because I have read this example, I have asked for the possibility of use 2,4. This example is great.

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