Tuesday, June 14, 2011

Tempe Town Lake's Crossed Tied-Arch Bridge



Span 3 ready to lift

A bowstring, or tied-arch bridge, handles the horizontal outward thrusts of the arches in a tie beam, or the deck itself, at the bottom of the arch. The advantages of taking the horizontal forces in tension in the tie are that the bridge can be assembled and then dropped into place, and the supports only have to handle the vertical downward forces. These rubber dam abutments or piers probably have enough to worry about without having horizontal bridge forces pushing sideways on them, too.

The arches of this one also cross, which promises to throw some graceful and interesting shadows on the bridge deck. I wonder what a time-lapse of the shadows would look like as the sun crosses the sky. Or are there going to be tensile shade structures within the arches? Some of the renderings show them. (I searched for "crossed-arch bridge" because that's what this looks like, but got a bunch of dental information back instead.)

Time flies when you're building bridges

This TCT was on the last of the moderate temperature Arizona mornings for a while, I imagine. That's good in my book, though, I'm ready for the bright heat of summer to arrive. Technically, this was an extended TCT, since I ventured up north in Scottsdale to have a look at the wall destruction along the 101 before turning back south again to check up on the bridge progress. Honestly I was just looking for, and found, any excuse to ride a little longer. When they get this bridge finished, I'll inaugurate TCT2 with some even-longer route that crosses the new bridge. Not sure if I will be able to swing the time-lapse though. Get up. Go ride.

 

2 comments:

  1. That bridge looks better as it grows - until they paint it orange!

    ReplyDelete
  2. Steve, I note that the color of those blocker-floats in the bottom photo is just about right for a tied-arch ped-bike bridge.

    ReplyDelete

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