Engineering-related News Stories

Two stories that recently came to my attention:

• Wind-powered car reaches 136 mph

This is a really amazing design for a high-speed land yacht. There are lots of details, pictures, etc at their web site and blog.

• Ann Arbor (MI) concrete bridge failing

This is a really good article, complete with pictures (some of which have links to higher-resolution versions), about the deterioration and partial failure of an important multi-lane bridge in Ann Arbor, Michigan. (Additional background information and pictures are in an earlier article about the bridge.) You might find the engineer's drawing of the problem area, designing the layout for lane closures, interesting. It shows that "beam 8" is at the centerline of the bridge, so a problem with it would require reducing this to a one-lane bridge.

The engineering part of the problem is that concrete is very strong in compression but very weak in tension. A concrete beam will break like a piece of chalk when a load is placed at its center. Steel cables (which are strong under tension but weak under compression) are placed along the bottom of the concrete beam to keep it from breaking. In this case, the effect of salt (used to deice the bridge in winter) and water has been to rust the steel cable and weaken one beam so much that it cannot even hold up its own weight without sagging.

By the way, despite the appearance of the area around the bridge, this is not in some rural area. State St is the main N-S street through Ann Arbor, sort of bisecting the University of Michigan main campus (academics to NE, athletics to the SE), and Stadium (surprise surprise) goes by the football stadium (whose main entrance is at Stadium and Main) and the basketball arean. On game day, this bridge would normally be four lanes one way to or from the stadium and a major freeway interchange! (FYI, here is a link to the Google satellite map centered on this bridge.) Because of the railroad tracks that run parallel to State St, this bridge and route provides one of only two convenient paths between parking in the residential area to the right and the stadium. (Normal game-day parking in AA includes people's front lawns.)

By the way, the current set of satellite images shows the recent reconstruction work on the UM stadium. That area of the east stands where the concrete has been torn out goes back to the 1930s, I believe.