Concrete can last forever

Check out this photo of a concrete bridge built in 1926 that has been submerged behind a dam since 1952. (Details about the ghost town and the maintenance work being done on the earthen dam used to supply water to the Santa Clara area are in this article from the Mercury News in San Jose, California.)

My dad made two observations about this bridge:

1. It is very similar to bridges my grandfather designed when they were building the first highways in Michigan in the early 20s
2. Concrete in fresh water simply cures and gets stronger. This bridge not only looks like new (having been washed by an artificial lake every day), it is stronger than new.

Concrete is made from Portland cement, sand and gravel, and water along with various chemicals and other additions to suit a specific purpose. The water and cement form a hydrate that glues together the rocky "aggregate" material. Concrete actually gets stronger over a period of decades before slowly weakening. (There are many examples of concrete Roman structures that are 1800 years old.) It loves being in fresh water, but anything that likes to remove water (particularly salt) will attack it and weaken it prematurely. Concrete bridges along the gulf, like ones up north where salt is used to de-ice roads, have a hard life. This bridge has had an easy one.

Ran into one of my former students a year or two ago, and he was finishing up his degree in Civil Engineering with a advanced course in concrete. If civil engineering interests you, get a start by reading what Wiki has to say about concrete. That appears to be a high quality, very detailed article including information about newly developed types of concrete that are still in the research stage.

Video of fatal NC bridge collapse

The collapse starts at about 2:39 into this video. For details, read the news article from StarNews Online.


You need to be looking at the very top of the picture. The pre-stressed concrete girder that fell is the second from the left. The left-most girder was being placed by the crane at the time. It's too bad that the camera is looking down at the crane at this moment, because a change in the shadows between the girders makes it seem like the failure started at the top plate of the girder. If you look closely around 2:39 and 2:40, it would appear that some material breaks off and falls before the entire girder falls.

It would have helped a lot to see the entire girder during the failure, but forensic work will probably identify the point of failure and its cause. Did the new girder bump the previous one, or was there a manufacturing or design flaw? We will find out in a few months.

Report on Minnesota I-35 Bridge Collapse

Two links to news stories about the pending NTSB report on the collapse of the I-35 bridge in Minneapolis, MN. Check back; I plan to update this article with additional links as they become available.

News articles from 12 and 13 November:

• AP: Safety Board to release report
• Duluth: State of Minnesota improves bridge inspection process
• AP: Extra load of construction material contribute to collapse
• AP: Design errors led to collapse

NTSB Presentation and related articles:

• NTSB Official Press Release
• Synopsis of NTSB conclusions
• Presentation by Jim Wildey on conclusions of investigation (11 Mb pdf)
• Links to other presentations and flash or wmv animations

Anyone who has seen my class lecture on the static equilibrium calculation for the gusset plate (based on the January 2008 NTSB Interim report (400 kb pdf) about gusset plate design flaw) will recognize many of the details in this presentation.

• WP: article on the report
• ASCE article about the report
• and collection of ASCE info on the investigation
• CNN: Design flaw led to collapse
• AP: Design errors led to collapse (includes photo of deformed gusset plate)

The final NTSB report does not seem to be in their publication archives yet. Based on the publication dates, it might not appear there for some time.

Fourier Analysis of the Beatles

I mentioned this in class late last week:

The mathematical technique of a Fourier Transform (see pg 230 of the Wolfson physics textbook we use, but also any number of math or physics textbooks) has been used to solve the mystery of the unique opening chord of the Beatles' "Hard Days Night". The mathematical software used to do this is capable of isolating the fundamental and all harmonics of a note played by a particular instrument, which made it possible to find the missing fourth instrument (George Martin on piano) responsible for the sound.

The article in Wired includes a sample of this chord, and a link to the pdf version of the report.

Computer aided bridge inspection

News story forwarded to me by my dad:

German scientists say they have developed an image-processing software program that automatically detects irregularities in bridge materials. (United Press International)

Quite interesting. This program would probably have warned of the defect in the Minnesota I-35 bridge that was in photographs taken several years before it collapsed, but not noticed at the time.

IMPT. ENGINEERING CLUB MEETING FRI. 10/31/08 @ 2:30 SM 260

In case you are not on Vernon’s email list… Here is a
MESSAGE FROM VERNON

I hope to see all club members at SMA 260 at 2:30 this Friday. In addition we will be going over our club roster for submission to the SOC. If any members would like to email me their name and student id number in advance to the meeting for convenience, feel free to do so. The Space Grant Consortium has received our W-9 form and we should be receiving funding for the rocket competition soon. All who are interested in continuing research for our rocket team should attend the meeting. Next month we begin building and planning for testing!!!
Vernon Babich
Engineering Club Chair
850-510-2473
________________________________________

Space Station Viewing

The International Space Station (ISS) can be seen in skies over Tallahassee tonight (Friday, October 10) between 7:47 pm (rising in the NW) and 7:52 pm (setting in the SE). It will be very high in the sky (68 degrees above the horizon, just 22 degrees from overhead) to the NE at about 7:49. It should be very bright (-2.4 magnitude).

You can use this link

• The Heavens Above web site (set up for Tallahassee)

to get detailed information for the ISS and other objects orbiting the earth.