Dear PoP – What the Helen of Troy is This?


“Dear PoP,

I live in mount vernon square and i was wondering if you know what the deal is with the metal tracks in the street/side walk around the convention center. they’re on 7th and 9th and on the sidewalks around the building.

i’ve thought of lots of different explanations (both practical and ridiculous) but i’m not really sure. any ideas?”

I am completely stumped. But first reader that gets it (and I can confirm it) gets a free PoP t-shirt. What the Helen of Troy is This?


9 Comment

  • Portions of the convention center are underground, under the sidewalk and parts of 7th and 9th Streets. These are expansion joints around the edges of the underground parts of the convention center.

  • these look like expansion joints to me….

  • mt p is exactly right.

  • what do expansion joints do? i need more details!

    • I’m no engineer, but my best guess is that they are there for essentially the same reasons they are on a bridge span. If there really is a tunnel underground, that would suggest there is air beneath it, which warms and cools faster than the ground around it. That part of the street is effectively a “span,” just with the sides enclosed and underground. Without the joints, expansion during the summer or humid weather would cause undue stress on the surface, possibly causing it to crack or buckle. The joints make spaces that allow for some wiggle room.

      Builders use a similar concept in much the same way – you never make a door completely flush with a door frame because during certain weather, you’ll never be able to shut it.

      Again, I’m no engineer, but that’s my stab at it!

  • They are expansion joints. Due to changes in weather, hot and cold, materials expand or contract. You will most commonly see these on bridges. The reason why the convention center has these is because of the sky walks over the streets. The expansion joints allow the entire building to move together and prevents cracking.

  • they are new tracks for a secret streetcar for drunk people.

  • in addition, the truck ramps and loading docks for the convention center are partially located underneath 9th street.

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