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Peter,
Yes you are right - the original comparisons were between ungussetted mild steel piers of a cylindrical shape.
Using higher tensile steel - eg Gas pipeline improves the bottom line.
I am not sure what effect these gussets will have, that is why I calculated it without and stated accordingly.
A structural engineer would need to model that one.
But if we assumed they were perfectly rigid (which they are not) and completely shortened the pier by their approx length becasue of this perfect rigidty - I still calculate a deflection of 0.51 arc sec, so I am guessing its somewhere between the two measurements for 2.5kg lateral load
Remember this is with only a 2.5kg load applied, the reality is that if the load is applied at the OTA (which is most likely) the increased leverage will increase the amount of deflection.
It is extremely difficult if not impossible in practical reality to properly balance eccentric loads on larger systems - which are a normal occurrence.
The imbalance is usually at the very ends of the OTA - eg a STL11000m with 8 filter wheel and cables is quite eccentric and it hangs out nearly a metre rearward from the centre of Dec rotation on a large refractor.
Focuser motors, Rotation motors and other items such as guide scopes and guide cameras hang off the sides or tops of the system in most cases.
The entire camera system is rotating about the end of the telescope too - so the eccentricity is a dynamic problem.
Thus as the telescope swings through the full movement of travel it goes in and out of ideal balance in many different directions - although this is happening slowly and guiding can take care of that, it does cause problems with Polar Alignment and pointing accuracy and its variable.
People can go to a lot of trouble with getting their Polar Alignment below 1 arc minute in RA and Alt in a pemanent observatory situation and then create a many point star model to get the pointing and tracking accurate and apply PEC correction.
A pier that deflects through its travel simply adds to your woes - I would argue unnecessarily.
Spend $100+ extra on extra steel or concrete on a system worth potentially $10,000's and this problem is for the most part nearly eliminated.
Rally
PS
If you want to get fancy - as is done in many military pier designs they use a cone shaped pier and I am aware of at least one amateur astronomer who has applied this engineering design to his pier.
It means it takes up a larger footprint but the increase in rigidity is enormous and the wall thickness can then be reduced down from 10-15mm.
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