Imagine you constructed a hiking trail across the country. It is perfectly straight and flat, the total distance is 4000 miles.
You also installed a metal handrail along the trail.
An engineer comes along and tells you that in the summer the metal rail will expand increasing its length by one inch in total.
You think one inch over 4000 miles is no big deal but the engineer says no one will be able to reach the handrail.
Assuming the rail will buckle upward at the very centre how much higher from level will the handrail deflect?