November 12, 2009

Happy Over-and-Under Day

On this date in 1927, the Holland Tunnel, which connects New Jersey to New York City by going UNDER the Hudson River, was opened with a ceremony, and 20,000 people walked through it. The tunnel is really a double tunnel that consists of two tubes, and it runs more than 8,000 feet in length (in other words, more than 2,500 meters, more than a mile and a half). The deepest part of the tunnel is about 93 feet (28 meters) below ground (or, rather, water).

The Holland Tunnel is unusual in that it is not named for a government official nor local hero; instead, it is named after the chief engineer, Clifford Holland. Perhaps it was named for him because It's one of the earliest examples of a ventilated design, necessary because of automobile exhaust. Or perhaps it was named for him because he died before it was completed.

On this date in 1936, the Oakland Bay Bridge was opened. This bridge connects Oakland, California, to San Francisco, soaring OVER the San Francisco Bay. The governor of California, Frank Merriam, opened the bridge by using an acetylene torch to cut gold chains that stretched across the traffic lanes. According to the San Francisco Chronicle, tens of thousands of happy people walked and drove over the bridge and crammed into San Franciso, creating the largest traffic jam the city had seen thus far.

The Bay Bridge is a double-decker bridge that carries westbound traffic over eastbound traffic. It's not only double-decker, it's also a double bridge, because it is made up of two halves that are connected by a tunnel through an island in the bay. The total length of the bridge is 4.46 miles (7.18 km). According to Wikipedia, the western half is made up of  suspension bridges, and the eastern half consists of a double-tower cantilever span, truss bridges, and a causeway.

That's a lot of engineering!

Source: http://en.wikipedia.org/wiki/Oakland_Bay_Bridge

One of the worst things to happen to the Bay Bridge occurred during the 1989 Loma Prieta earthquake. A 50-foot (15 m) section of the upper deck of the eastern truss portion of the bridge collapsed onto the lower deck. Luckily, the collapse caused only one death. The bridge was closed for little more than a month. However, the earthquake damage was a wake-up call to retrofit and replace portions of the bridge that were at risk in future earthquakes. One of the repairs failed on October 27th of this year, and three pieces of steel fell onto three vehicles. Remarkably, no one was injured. The bridge reopened once more on November 2.

The Bay Bridge is really named the James “Sunny Jim” Rolph Bridge (after the California governor, who died during its construction), but people don't use the official name; many locals don't even recognize the name!

Build a Bridge, Dig a Tunnel

Make a paper bridge that can support 100 pennies!

Build a popsicle-stick bridge that can support your own weight!

How about a very pretty toothpick bridge?


Using just sand and water, how long of a tunnel can you make in a sandbox? It's hard to make a tunnel that doesn't collapse!

If you want to play with toy trucks and cars in the sand, you can make a tunnel using a plastic tube.

Building a real tunnel big enough to walk or ride through is very dangerous, but luckily PBS has put a website on the internet on which you can try your hand at virtual tunnel building! (Go to the bottom of the page to "Tunnel Challenge" for the virtual building activity.)