May. 6th, 2017

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There's a new bridge under construction here in town, a floater (just like the old one) that bobs atop Lake Washington between Seattle and the north part of the East Side (as opposed to the bobber that bobs betwixt Seattle and Mercer Island, farther south). I've been driving across the newest section since the day it opened to traffic. Compared to the old bridge (still being demolished right next to the new) it's a smooth ride.

With one exception, that is.

Since this is a floating bridge, and since the level of the lake varies from day to day (sometimes from hour to hour, in a heavy downpour), the bridge requires a flexible section bridge people call an expansion joint. You feel these joints when you cross bridges, generally; they're like an old cattle crossing gate, a series of bars perpendicular to the road's direction of travel. As the bridge flexes with the movement of the water below, the bars either get closer or farther from each other. Given the number of bars involved, this allows quite a bit of movement. Think about it: put twelve bars down and an inch difference between the bars is a foot of overall travel.

There is one grumble from the neighbors, though. Since they opened the East section, peeps living nearby have noted the noise. It has increased compared to the old bridge.

There were some significant changes, of course. The new bridge is taller, for one. And I believe the expansion joint is larger. Whatever the cause, be it placement of the noise maker or the overall size of same, the state bridge builder has been scrambling to find a solution.

So, Wednesday comes along, and my friend secures me a tour of the new section, still under construction. And I see this thing.


It's called a sinusoidal plate.


Sinusoidal, like the wave form. (The construction guys giving the tour, though, kept calling it a sinus plate, which my friend and I found pretty funny. Nose jokes galore.) Look carefully, and you can see the parallel straight bars below the waveform plates; those are the standard compression joint elements with the waveform pieces simply bolted atop.


Here's another pic, but not as crisp, due to [reasons].


The theory, and it's a good one, is simply that car tires hitting that plate will not hit the plate in the same perpendicular plane at once. Rather, the leading edge of the tire footprint will hit the nearest "point" and follow the curved sinusoidal shape. Different impact points means a smoothed impact sound, just like a muffler allows the escaping exhaust gases to not bang out the pipe, or a spiral cut gear doesn't clack when it rotates.

Sadly, given the size, the other compression joint on the east side (we were touring the west side, still getting built) cannot be easily adapted. Replacement would be required, and that would cost multi-millions.

Here's a thought: could you just buy out the neighbors? Pay for the houses they cannot easily live in?

Here's another thought that should put that cash outlay in perspective: the neighborhood affected by the rumble of passing freeway traffic has as one resident Bill Gates. He's about a mile from the rumblin' joint.

It'll be interesting to see what they can do.

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