It is nice to see some criticism on HN. The tone of the post is a bit off but apart from that the points made should be considered.
Personally I don't see the problem with a 150m slippage tolerance, but I think it might have to come before the fixed base stations. basically I could imagine the tubes transitioning into a slightly larger enclosing tube which is able fixed to the base station. surely there are other alternatives and unlike the OP I think the quotes from the report sound to me as if Musk hasn't thought of this at all.
As for the FEM analysis I would tend to agree that the value does not go far beyond being a pretty picture in its current form.
The problem with a 150m slippage tolerance is that it means the horizontal dampers on the pylons near the end have to deal with movements of up to 150m, which is significantly larger than the distance between pylons. Maybe that's feasible (seems unlikely, but I'm no engineer), but it's the kind of point that ought to be addressed explicitly.
It seems to me that expecting hundreds of miles of pipe to be pushed back and forth hundreds of feet (albeit presumably slowly) puts a heck of a lot of stress on the self-same pipe. How is this that much different from building a side-ways space elevator? Even if it's easier to push sideways than up, it still adds up to quite a bit over hundreds of miles.
I think the proposal says explicitly there are no longitudinal dampers on the pylons, only horizontal transverse, but thermal expansion shouldn't be a problem for those.
Personally I don't see the problem with a 150m slippage tolerance, but I think it might have to come before the fixed base stations. basically I could imagine the tubes transitioning into a slightly larger enclosing tube which is able fixed to the base station. surely there are other alternatives and unlike the OP I think the quotes from the report sound to me as if Musk hasn't thought of this at all.
As for the FEM analysis I would tend to agree that the value does not go far beyond being a pretty picture in its current form.