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I do not know if this is the appropriate forum? We do not have a forum called civil engineering.
My question is that we have many bridges that constantly need work on their approach slabs. Of course there will always be expansion and contraction differences between our bridges and the ground they are attached to. Almost every Spring our state highway departments end up making repairs to these connections. Sometimes the potholes that open up can be formidable.
So I want to know if we have ever experimented with hinged bridge approach slabs that would move up and down with the expansion and contraction or slabs that slide as our bridges get longer and shorter from expansion and contraction? Maybe we have experimented and I am not aware? I do know that our civil engineers are aware of the problems: http://onlinepubs.trb.org/Onlinepubs...3/1113-008.pdf. Maybe I just need somebody to put all this into layman's terms why we don't do a better job?
Location: East of Seattle since 1992, 615' Elevation, Zone 8b - originally from SF Bay Area
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Our floating bridge across Lake Washington to Seattle is closed at night once a year for repairs to the expansion joints, so they do exist and are used. The expansion joints are both connecting the slabs to the bridge and within the bridge itself.
If you look at the undersides of many bridges (even highway overpasses) one side uses a pin and bracket to mount it to the abutment and the other end either has a skid plate or a roller system to allow the bridge to expand and contract. The pin and bracket (basically a hinge) transfers both vertical load and horizontal load from the bridge structure to the earth. At the other end the skid/roller support only transfers vertical load allowing the horizontal load to be transfered via the structure to the other end.
This is all covered in a basic 'Static structures' class early in an engineering curriculum (commonly called Statics). the follow on course (Dynamics) covers calculating loads as they move. Statics is real straight forward uses basic algebra and triginometry. It has been over 40 years since I took a Statics course so they may have changed the details but we did the math with slide rules!
Different problems and different strategies for maintainance...
Quote:
Originally Posted by fisheye
I do not know if this is the appropriate forum? We do not have a forum called civil engineering.
My question is that we have many bridges that constantly need work on their approach slabs. Of course there will always be expansion and contraction differences between our bridges and the ground they are attached to. Almost every Spring our state highway departments end up making repairs to these connections. Sometimes the potholes that open up can be formidable.
So I want to know if we have ever experimented with hinged bridge approach slabs that would move up and down with the expansion and contraction or slabs that slide as our bridges get longer and shorter from expansion and contraction? Maybe we have experimented and I am not aware? I do know that our civil engineers are aware of the problems: http://onlinepubs.trb.org/Onlinepubs...3/1113-008.pdf. Maybe I just need somebody to put all this into layman's terms why we don't do a better job?
Quote:
Originally Posted by MidValleyDad
If you look at the undersides of many bridges (even highway overpasses) one side uses a pin and bracket to mount it to the abutment and the other end either has a skid plate or a roller system to allow the bridge to expand and contract. The pin and bracket (basically a hinge) transfers both vertical load and horizontal load from the bridge structure to the earth. At the other end the skid/roller support only transfers vertical load allowing the horizontal load to be transfered via the structure to the other end.
This is all covered in a basic 'Static structures' class early in an engineering curriculum (commonly called Statics). the follow on course (Dynamics) covers calculating loads as they move. Statics is real straight forward uses basic algebra and triginometry. It has been over 40 years since I took a Statics course so they may have changed the details but we did the math with slide rules!
MidValleyDad is talking about the movement / deflection of the bridge -- that is what keeps the STRUCTURAL element of the bridge intact as opposed to crushing itself due to changes in temperature or load -- https://www.popularmechanics.com/sci...-made-to-move/
Most the POTHOLES that fisheye sees as being "worked on every spring" is about PAVEMENT. The thing that causes spring potholes is overwhelming winter ICE. This greatly exaggerated cartoon highlights how water the works it way into the various layers of pavement will freeze and thaw created a pocket that is fractured by traffic -- https://www.michigan.gov/mdot/0,4616...8113--,00.html Changing the specification of the pavement is not a simple task, it involves politics, scientists, and a mix of contractors who are all aware of who benefits from the current status quo - https://www.thestar.com/news/gta/tra...professor.html
There are interesting results being tested with everything from roads to facilitate "self healing" to those that include microbes capable of secreting restorative compounds -- https://www.theverge.com/2017/5/4/15...transportation Bridge abutments are especially susceptible to freeze-thaw cycles because of the well-know "bridge freeze first" cooling / evaporative effects -- https://wonderopolis.org/wonder/why-...e-before-roads That means that if there are going to be improvements in the "pothole proof roads" the real work will need to include more thought to what the benefits really are -- Asphalt Alternatives: Can We Escape Winter Potholes? | Moss Architecture
The reason road crews want to address potholes on bridges with urgency is due to the increased risk of water accelerating the corrosion and erosion effects and forcing early replacement of the structure. To help deal with this there are firms that are literally encasing the bridge structure in waterproof coatings - https://theasphaltpro.com/articles/m...rface-project/
Thank all of you for the information. Here, in PA, it is smart to hug the left side of the slow lane in Spring. Many times we have potholes form that could blow a tire or worse. So I wanted more information to go on when I holler at our Representatives. Of course I will not change anything; but it makes me feel better and I like to be informed!
PS chet Everett - thank you especially; you provided me with lots of good reading!
Pothole issues are generally caused because of funding issues. The Highway engineers know that the sooner they are fixed the better but budgets constrain them to only working on the worst. It isn't a lack of knowledge, it is a lack of money.
Pothole issues are generally caused because of funding issues. The Highway engineers know that the sooner they are fixed the better but budgets constrain them to only working on the worst. It isn't a lack of knowledge, it is a lack of money.
Years ago the National Highway Traffic Safety Administration published some articles about how our states could do a better job with the funds that were available (how they could become more proficient). Some states listened and did give their taxpayers more for their money and other states still listened to the special interest lining their pockets. I know that is a simplification and there are many twist and turns and grey areas.
Logistics kill many road projects. You have a company, that owns the stone quarry, that owns the construction company, that gets most of the state bids. It is far too costly to transport the millions of tons of highway materials any long distance. It isn't only that; but trying to get the mining permits for new companies to become competitive is very expensive and almost impossible (do you want a quarry in your back yard).
Even when you own everything (the supply, transport and construction) that does not mean you will do a great job repairing or building. First you are working to the state specifications (supposedly) and secondly everything works as one (let me explain). Concrete and asphalt paving machines are most efficient when working at their optimal speed. If they stop and start; there can be a seam in the pavement. That seam lets in water and the pavement cracks prematurely. That is especially true with asphalt paving machines because the next load could be held up in traffic. At the time it is held up it can be cooling and will go down with a different texture. Ideally the asphalt plant keeps up with the trucks which keep up with the paver and the rollers also keep up with the paver - everything runs smooth.
Taxpayers lose their money with workfare - pavement that breaks up every year and has to be redone. Many times the DOT (using contractors) is putting down a thin layer of asphalt over broken concrete - they are lucky if it last a full year. So the process is repeated year after year and the taxpayer loses. Jobs should be warrantied; if they cannot last for two years why did we do them in the first place? Personally I would like to see heads fly when these jobs don't last (but I do not have that power).
One of the problems is somewhat counterintuitive to saving money but we all do it ourselves on many things. But for some reason we taxpayers don't like when government does it. That thing is paying more for something to start with. Many government projects, in order to be fair, because big, mean, nasty, government has to be forced to be fair, is to use the lowest bidder. You know, cut out that waste by overpaying.
Well there's a reason for the lowest bidder and it's usually quality. So you get what you pay for.
One of the problems is somewhat counterintuitive to saving money but we all do it ourselves on many things. But for some reason we taxpayers don't like when government does it. That thing is paying more for something to start with. Many government projects, in order to be fair, because big, mean, nasty, government has to be forced to be fair, is to use the lowest bidder. You know, cut out that waste by overpaying.
Well there's a reason for the lowest bidder and it's usually quality. So you get what you pay for.
My feeling is that, with the contractors that also own the quarries, that it is hard to compete. It cost a lot of money to move mountains long distances. Besides the transportation cost; there is also the wear and tear on our roads that has to be taken into account. We might fix a road in one place and destroy roads leading to Rome. Just saying.
These are not easy questions or easy answers. I was a truck driver and I drove through many states. I saw highway departments that made me jealous. But, of course, I could not see the big picture (only what I saw from the road). In other words I had no idea how much, what I saw as proficiency, cost. If I saw a state that got out there, quickly got the job done, did not hold up traffic or cause accidents, then I though they did a great job. I use to send out "ATTA Boys" to DOT departments that I felt were doing great jobs - I wanted to encourage them. An example would be watching NJ put down more asphalt in one night, during the off peak hours, than PA would do in a month! PA has improved slightly since then (maybe).
Discussion of potholes reminded me of this product as a temporary fix in climates with freeze thaw cycles. (Non Newtonian fluids as temporary and reusable fix!)
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Different problems and different strategies for maintainance...
