ASCE 48-11 wedge method for base plates

[Runmdc]

I am looking for information on why ASCE 48 changed to the wedge method for bendline calculations in version 11. It is a big change from ASCE 48-05 and I would like to know the history of why the change took place.

Thanks

 

[transmissiontowers]

I know a couple of people on the revision committee and will ask them the next time I see them, but FWIR there are several people on the committee from pole suppliers. They sent out a trial pole geometry to all the pole suppliers with pole base geometry and the moments and shears at the base and asked the providers what thickness base plate they would provide. They got many different answers and tried to come up with a method that would come close to the answers submitted. If you start from a clean slate and ask 20 Engineers to design a pole base plate (both inside the providers and those that design their own poles) you will get many different answers.

The old method in 48-2005 did produce thinner base plates because the effective bend line could be longer than the 48-2011 method which limits the bend line to the flat width. I assume they wanted to err on the side of the conservative and set the bend line to a known quantity. If you allow the effective bend line to go all the way to the plate edge, you may not load the entire bend line.

As an extreme example, lets say you have a 36" AF 12 sided pole with 2.25" A-Bolts on a 50" bolt circle but the base plate is 120" diameter. You might assume an effective bend line along the pole shaft flat that went all the way to the plate edge which would be 114.473". This long of a bend line would produce a thin base plate but can the a-Bolts load that entire length? We generally use 12 times the plate thickness as a limit on the effective bend line.

It's been a while since I read over ASCE 48 but I assume they have a statement that if you have the experience and have done the research on base plate thickness, you can use your own method. If you mesh up the plate in an FEA program and check the stress across the assumed bend line, you might be able to justify the thickness.

I believe PLS-POLE will use either method and if you choose ASCE 48-05, you can over ride the effective bend length and put in your own. I also think that base plates designed with the old method did not have an excessive failure rate.

Many years ago I wrote a Fortran program to design poles and base plates and we used a home brewed method similar to ASCE 48-2005. Later, we made an AI application to do pole design using ICAD but we stopped using it when we got "free" engineering done by the pole supplier. If you design your own poles and base plates, you assume the responsibility. If you accept the pole supplier's pole, then they accept the responsibility and they will probably want to be very safe.

HTH

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