I am fairly impressed with the Washington State Department of Transportation. It is unusal to see a DOT making use of sites such as flickr and youtube. Typically DOTs are very closely managed and scared of negative public reaction.
I also like the project page idea so that residents can get a sense of what is going on with a nearby bridge.
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 18.104.22.168, 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 22.214.171.124. 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.
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.
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.
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.
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”.
Bustler.net has some interesting articles about architecture and bridges.
Take a look at the winning entry for the Four Mile Bridge. I wonder how they design it for the unbalanced loads on the single piers and how they expect their little sandbar islands will survive in a flood channel. (scour much)