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Busy Friday

Posting has been spotty lately, as I finish up my spring class. The final is next week and then the spring is done and onto the summer!

One of the things I hate at the end of a class is the phenomena known as grade negotiation. Students who are on the bubble and try to “help” their grades along through interesting arguments……

A quick study of a TL-5 barrier rail.

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Playing around with sketchup, grading my test. One more week until the final, then summer school!

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Protecting your bridge pier

I’m sitting in a classroom giving my second test, so this post may not make sense….and I drew a pier, so naturally a pier story follows.

The AASHTO bridge design specification calls for a 400 kip (400,000 lbs or 720,00o hockey pucks for you non-Canadians) collision load be added to your calculations when designing a pier.

In section, piers located within 30 feet of the traveled way, must be able to resist a 400 kip load placed horizontally at 4 feet in any direction. This is leading to crash walls as stated in various DOT bridge manuals.

Piers Adjacent to Roadways
Piers located within 30 feet of the edge of roadway are required to have crash walls incorporated into their design unless they are protected as specified in LRFD The crash walls adjacent to roadways shall be designed for a minimum load of 400 kips. It will be assumed that the soil will provide the required resistance. The crash wall shall be a minimum height of 4 ft above the ground.

Protection is often worse than the cure. (Did that make sense?) If you do not design the pier to resist the 400k load then you have to protect it with a 42″ high TL-5 barrier between 30′ & 10′ and a 54″ high TL-5 barrier with less that 10 feet of clear zone. (Here is a TL-5 bridge rail in Texas.)

This is leading to some interesting looking piers.

From MnDOT,

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Fly Ash Looms As The ‘New Asbestos’

In an article original from the Engineering News Record (ENR), concrete groups are waiting to hear if fly ash will be designated as a hazardous material. I have to agree with this quote,

A hazardous-waste designation for fly ash would “stigmatize its use as an ingredient in concrete, even if EPA were to focus a designation only on fly ash that is disposed rather than beneficially reused,” says Andrew T. O’Hare, vice president of regulatory affairs in Portland Cement Association’s Washington, D.C., office.

I would think a ruling against fly ash would essentially ban it from concrete products.

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Engineering student pranks

When I went to the University of Calgary, engineering students were well known for pulling pranks during engineering week. Things like unbolting all the seats and turning them backwards or assembling a car in a classroom.

From some old articles it seems the University of British Columbia has a history of pulling pranks involving bridges. I have not seen this level of “enthusiasm” in America students.

Is this a British influence kind of thing?

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Got piles?

Our state is a pile state. Meaning our rock layer is very deep, so we use friction piles to hold up most of our bridges. The bridge below has 90′ long piles at the abutments due to 40′ of fill and a great deal of downdrag forces.

(Downdrag forces are the loads caused by the fill settling. In this case the bridge has to be built in a hurry instead of letting the berms consolidate and settle over time.)

The prestressed beams are 5′-3 tall and have a length of 156′-0. This particular bridge carries six lanes of traffic over a four lane highway.

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Another test

Posting has been a little sporadic lately, with design deadlines and teaching. Tonight I am giving another structural analysis test on moment distribution, the force method and the stiffness method. Should be a fun night.

One of the things that came up in class is the amount of time scheduled for the test. From what I understand, the time period for a test should be 3-4 times what it takes for me to do the test. (Last test I gave them an extra 30 minutes and they still had trouble finishing.)

So the students asked me to make sure the test could be finished in two hours. I took my test and I did it in about 41 minutes, so it should work out. The interesting thing to me was that students did not want extra time. They want me to shut down the test at the end of two hours.

When I give the final in three weeks, the test will only last two hours because that is how long I have the room…but I always felt that, if we had the choice, students would like extra time to work on an exam. I didn’t want the excuse to be “if I only had more time”.

Am I crazy?

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Temperature expansion

This may be old news but they are interesting photos…

Bridge deck replacements are becoming more frequent as our infrastucture matures. (okay its old.)

In this case, a 400′ steel girder bridge, with integral abutments, was in the process of getting a new deck. The ends of the steel girders were left encased in concrete (integral abutments) and you can see the result.

From what I understand, the temperature only reached the low 70s, resulting in the bending of the girders due to temperature expansion.

I’m not sure what the final solution was in this case? Removing fill behind the abutment to allow the abutments to move and take the pressure off the steel or wait until the sun went down….

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Arup and the Four Mile Bridge

Sorry to keep harping on the Four Mile bridge competition. (see post below) But you really should go and look at the three finalists presentations. I am struck by how many of the images are of structures/bridges that are so beyond the scope of this little bridge.

I mean, they are very impressive, but I don’t see how the design of the Sydney opera house is in the same league as the Four mile bridge, especially the final solution.

After viewing the presentations I feel let down by the actual final design….

Arup presentation material

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Websites and Cost

Go to the Four Mile Bridge Competition webpage and click on the three finalist links. Wow, some of the websites have more bling than Paris Hilton! (Wow Paris and bridge design, I know how to appeal to the youth of America. I will probably triple my site hits!)

My cheezy websites barely have a single moving part let alone FLASH-tastic images and amazing lighting. Since I can find little mention of the budget for the bridge, I will assume from the participants websites, a lot. (Man I’m bitter lately…but imagine feeding those consultants and their interns.)

But seriously, I should have entered my team,

TBG, Calatrava, Menn, ARUP (they are always there), James Cameron (Avator 3D effects) and Lucusfilms for the robots. IT must be really hard out there that a little bridge in an industrial section warrants the heavy hitters of bridge design. (nawww, I’m not bitter..)

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Four Mile Run Bridge winner

Update: Here is a screenshot form the Four mile bridge site. Really crappy images but it looks like some kind of curvy (four span!) bridge won. My initial reaction is blaah…an open contest would have been better. (One of them seems to be Calatrava-lite..)

I received a tip (thanks Nick) that Grimshaw / Arup / Scape won the competition but I still cannot find any information online.
Grimshaw recently completed this footbridge in Acton(?).

The bridge looks fine but look at this photo and see how difficult it is to incorporate pedestrian walking ramps at the ends of a bridge.

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Sketchup Homework problems

I was just playing around in Google Sketchup and I thought it might be fun to hand out homework problems in sketchup (not this semester in the future).

(Most of the students in my class have the textbook solutions for all the problems in the book. So I have been giving out custom homework.)

In the future I think it would be worthwhile to post homework in sketchup for three reasons.

1) It gives them a sense of what the structure really looks like and
2) it would “force” them to learn a 3D “cadd” program by working through sketchup.
3) they would have to look up the beam properties for different beam shapes..

This would add some visualization to the course and I think make it more valuable.