There are 614,387 bridges in the United States and 55,707 of them are thought to be structurally deficient according to the US Department of Transportation (2016). About 188 million people cross “a deficient bridge” every day in the US (also a 2016 figure).

Inspections are often infrequent and only visual, and so MIT Senseable City Lab is currently on a mission to come up with a more scientific approach. They believe that there’s a solution in crowd-sourced data and that it’s possible to create a community-driven maintenance program.

What they discovered through a recent study, called Good Vibrations, is that mobile phone sensors can actually pick up the natural vibrations and oscillations of a bridge. And, that a mobile sensor located within a traveling car is actually 120x more precise than fixed sensors located on the bridge.

Part of the problem is that fixed sensors have poor spatial coverage. They are located in specific locations. Whereas mobile sensors give you data across the entire span of the bridge as someone crosses it. And if you know how a bridge normally vibrates, you can quickly tell when something is off. 

Here’s a quick video overview of the study. And here’s what you should do if you want to get involved.

Photo by Joseph Barrientos on Unsplash

Many of you are probably aware of the 58-storey Millennium Tower in San Francisco which is estimated to have sunk about 17 inches and to have tilted about 14 inches to the west since it was built.

Well today it was announced that they may have a fix. Here is what is apparently being proposed as a retrofit (image from SFGate):

The tower was originally built on top of a 10 foot thick raft or mat foundation, which was then supported by concrete piles that went down 60-90 feet into soft clay. Notably, the piles didn’t reach bedrock.

The proposed solution involves drilling 275-300 new micropiles into the bedrock below. But here’s where things get really interesting: The plan is to stabilize the west side of the building first and allow the east side of the building to continue sinking. In theory, this will give the building an opportunity to level out before they fully stabilize it. 

According to SFGate, the entire retrofit is expected to take anywhere from 2 to 5 years, and cost somewhere in the range of $200 to $500 million. The original tower cost $350 million to build. (I’m assuming that’s just the hard cost number.)