I absolutely adore the St Louis arch - technically The Gateway Arch - and have been to the top at least a half dozen times. If I had my druthers, I would get to the top every time I'm in St Louis, but my wife and mother-in-law are less interested, so I merely admire it crossing the bridge each time we're in town.
One of our campers in Boise this summer explained that she had a lesson in her science class about the final topping-out ceremony of the arch, it being interesting because one side was in more direct sun. This lead to that sun side expanding more than the other, causing the two legs not to initially line up and the gap for the keystone to be too narrow if not for the hydraulic jacks installed to spread the legs apart.
Check out the details in the above video at 0:50 and in from the Arch's wikipedia article...
It was slated to be inserted at 10:00 a.m. local time but was done 30 minutes early because thermal expansion had constricted the 8.5-foot (2.6 m) gap at the top by 5 inches (13 cm). To mitigate this, workers used fire hoses to spray water on the surface of the south leg to cool it down and make it contract. The keystone was inserted in 13 minutes with only 6 inches (15 cm) remaining. For the next section, a hydraulic jack had to pry apart the legs six feet (1.8 m). The last section was left only 2.5 feet (0.76 m). By noon, the keystone was secured.
Brilliant, man. hose down the hot side with cold water.
How cool is that?
I'm sorry...I know...it's a corny joke...but it was right there...I couldn't help myself...
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