The Importance of Finite Element Analysis (FEA) in Steel Pole Design

How do you, the buyer, guarantee you are getting a quality product for your EPC projects? I have heard a couple of shockers recently around quality in design and structures being fit-for-purpose. First one is 'it's the responsibility of the pole supplier' and the second is 'doesn't PLS-POLE do all the FEA we need'

Firstly, and usually contractually, it is the responsibility of the EPC contractor to the Principal to ensure that products they procure are fit-for-purpose.? Sure, commercially that is passed down the line, but it doesn’t absolve the EPC contractor from damages (or reputation damage) for that matter if they get it wrong.? Rarely do we see a spec requiring detailed FEA on critical connections such as crossarm connections to pole or pole base plate connections to foundations. Structural specs should be written by suitably qualified people, and we've seen specs recently that aren't and leave a lot to be desired.

Secondly, the answer is a hard no.? PLS-POLE is great for designing the main members like arm bodies and pole bodies and yes it does basic FEA on these components.? But that is where it ends for PLS.? It does not have the functionality to do detailed FEA on specific connection designs.? We use Strand7 to fully model up connections to see how they behave under various load cases, and the results are sometimes surprising.

Anything in the 275kV+ range by default is going to put huge loads on the arm connections, even suspension that may see large failure containment loads or construction and maintenance with fall arrest loads, sometimes string to ground loads.? If you are receiving poles without detailed FEA of critical connections in the structural certification report, it is our opinion as professional engineers that this is professionally negligent (unless of course supported by load testing of equivalent design and loads).

Below is the same design and loading in the first picture above but with the gussets moved inwards.? This is an unacceptable design and we have recently seen multiple examples of supply by others with gussets in the flats of arms of highly loaded structural members, a clear indication that FEA may not have been done to develop the final design solution.? White areas exceed the maximum allowable material stress.

If you are receiving large poles with simple unbraced vang systems to connect arms to, you need to look at the FEA on how this has been structurally certified because we'd generally be unable to certify these designs.? You will never receive large suspension poles with unbraced vangs from Gateway Energy.? On 330kV we prefer to flange all arm connections.? You should not receive 330kV suspension poles with hexagonal arms and a C-Plate connection with a top fold line centre of the C-Plate.? The fold line at the top of the arm creates a stress raiser that can lead to failure.? This is a poor design.? We always prefer octagonal arms with a good flat face top and bottom for normal loads and even load path into the pole and flat faces on the sides of the arm for failure containment load distribution.

And it is the same with base plates.? We see a concerning hangover from the days when pole bases were grouted, some had fully tensioned foundation bolts and the industry practice was to assume the base plate was infinitely stiff.? Now with the move to double-nut moment joints where the pole base plate sits on leveling nuts, it is highly erroneous to assume that the base plate is infinitely stiff.? It will flex under high loads and when the base plate flexes, gussets will create a punching stress into the wall of the pole, that is generally already highly utilised with limited excess capacity to handle additional punching stresses.? This is why you will see Gateway Energy poles with top rings on base gussets of medium-heavy poles.? No other supplier does this that we know of and cannot understand why.

For us, detailed FEA using software such as Strand7 is not only critical in structural certification, it is a critical tool in design development.? The picture below shows gussets that are too short and have a stress raiser on the lower toe.

Responsible procurement means understanding what you are specifying and purchasing. It shouldn't be a race to the bottom, and we will not compromise on excellence in engineering, nor should you.

Gateway Energy - Your Trusted Steel Pole Supplier