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]

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.

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

 

[rubenpezu]

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

 

[transmissiontowers]

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.

 

[rubenpezu]

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.

 

[transmissiontowers]

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.

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

 

[rubenpezu]

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.

 

[transmissiontowers]

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.

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

 

[rubenpezu]

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

 

[VoyageofDiscovery]

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.

 

[transmissiontowers]

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.

 

[rubenpezu]

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

 

[transmissiontowers]

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.

 

[rubenpezu]

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.

 

[rubenpezu]

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

 

[transmissiontowers]

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.

 

[VoyageofDiscovery]

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

 

[rubenpezu]

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

 

[rubenpezu]

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.

 

[transmissiontowers]

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.


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