Yeah, this seemed like the biggest killer, besides inertia and politics.
My friends and I were wondering aloud if you could put a slight bow in the pipe - so instead of expanding lengthwise, the pipe might raise and lower at certain places. Of course, none of us are engineers in that sense.
1. Most of the tubes would need some bowing anyway for curves, since they can't find a perfect straight path from LA to SF
2. Tests show that tubes where L >> D, thermal expansion is linear along the length. If you restrained both ends you'd get the buckling in the interior sections that you describe. That might even be a bigger problem though because it would affect the path geometry and alter the attitude control requirements of the pods. I think the wrinkling in the tube skin would also be more dangerous than just letting it stretch.
My friends and I were wondering aloud if you could put a slight bow in the pipe - so instead of expanding lengthwise, the pipe might raise and lower at certain places. Of course, none of us are engineers in that sense.