Triangular Lattice tower with Pipe Sections
Triangular Lattice tower with Pipe Sections
(OP)
I´m trying to design Triangular Lattice tower for Communications with Circular Hollow Sections or Pipe Sections. I would like to know if ASCE 10-97 is the right code to check this kind of structure. I used to design transmission tower with this code, but there´s no reference to Pipe Sections(3.7 COMPRESSION MEMBERS:ANGLES and 3.9 COMPRESSION MEMBERS NOT COVERED IN SECTIONS 3.7). Should I read the ASCE 48-05 (Design of Steel Transmission Pole Structure)?
Thanks
Thanks





RE: Triangular Lattice tower with Pipe Sections
ASCE 48 is mainly for tubular pole structures, while ASCE 10 is for angles and/or light gage shapes.
GTStrudl has a module for Comm Towers that costs extra.
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RE: Triangular Lattice tower with Pipe Sections
Thanks
RE: Triangular Lattice tower with Pipe Sections
IIRC, TIA Rev F is based on ASD while TIA Rev G is LRFD based. PLS-Tower will check for either method. You will have to remember that PLS-Tower is a truss analysis program and any moments in the members are not considered in the allowables and many warnings are given when the moments in the members become large.
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I have been called "A storehouse of worthless information" many times.
RE: Triangular Lattice tower with Pipe Sections
Today, I have been reading AISC ASD and AISC LRFD, what is the main difference between them??? Because I have heart that for Overhead Transmission Towers with Pipe Sections you have to check them by ASD code.
Thank you.
RE: Triangular Lattice tower with Pipe Sections
In ASD you apply the loads in some specified combination (I don't do ASD so forgive my errors if I make them) and the steel members are limited to some allowable stress like 0.6 x Fy for bending. The safety factor comes from reducing the allowable stress.
The NESC requires certain overload factors on the applied loads and codes like ASCE 10 give the capacity of the members from lots of testing of single angle members for compression and tension.
In LRFD, you apply overloads to the loads and design up to a Phi factor times the yield. The LRFD is more suited to 3 leg lattice towers with pipe or round legs, in my opinion.
EIA/TIA Rev F uses ASD (IIRC) and the older Fastest Mile wind. EIA/TIA Rev G uses LRFD and the more modern ASCE 7 wind maps with 3 second averaging period winds.
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I have been called "A storehouse of worthless information" many times.
RE: Triangular Lattice tower with Pipe Sections
Could you tell me why do you apply overloads to the loads, and then design up to a Phi Factors (0,85 or 0,9).
As you told me, are different wind calculations defined in 222-F and 222-G?
RE: Triangular Lattice tower with Pipe Sections
The Fastest Mile is a rather old method and the averaging period is a variable. It was used by structural engineers in the 1930's until the change was made to a 3 second wind sometime in the 1970's. If you imagine a "mile of wind" passing a fixed point and you measured the wind speeds as they fluctuate from lulls to peak gusts, the average speed for that "mile of wind" was recorded for many weather data locations and published. At 120 MPH, a "mile of wind" would pass a fixed point in 30 seconds but at 60 MPH average the "Mile of Wind" would take 60 seconds to pass, thus the variable averaging period.
A 3 second wind report gives the average wind speed for many 3 second time periods and you publish the maximum of those measurements on a wind map.
The ratio of peak gust to the "fastest mile" average speed is always much greater than the 3 second wind average to peak gust ratio because the averaging time is so much shorter. IIRC, the gust factor used to be around 1.3 for fastest mile and it was squared with the velocity to get the pressure on a stationary object.
The LRFD is just a method of doing an analysis where you apply overloads to the loads and reduce the allowable with a relatively small Phi Factor based on the material. For codes like the NESC that specify what minimum OLF's to use, the LRFD method is better.
_____________________________________
I have been called "A storehouse of worthless information" many times.