I was having a conservation with a colleague today about whether or not an engineer is able to design a signature bridge. By design I mean, develop the artistic concept, or look, of the bridge.
Santiago Calatrava is an Architect first, with a dash of engineering thrown in. (I know he has an engineering degree but he doesn’t seem to know it, looking at his designs.)
Engineers are always developing rules for bridge design, for example, it should be true to it’s function. (meaning its a bridge, so act like one) But Architects don’t play by those rules. They know what a client really wants is something special, something unique, not a bridge with a side of Art, but a story.
The Happy Pontist ( HP, a very good writer) does a great job of discussing the state of bridge criticism concerning engineers and bridge design. I agree completely with him/her (I don’t know) that engineers need to get in the game and start talking about good and bad bridge design. We should be free to dislike a bridge and let everyone know it.
Well, I was just reading the new report about additional educational requirements to become a professional engineer, put forward by the National Council of Examiners for Engineering and Surveying. (NCEES report)
Essentially if you want to be a licensed engineer by 2020 (and who wouldn’t) you have to have a masters degree in engineering and a number of years of experience. (The number of years varies in the chart, in the paper, but it looks to be a minimum of 3 years)
The first part of the paper deals with how Universities are going to deal with the influx of new students seeking to gain their masters degrees. (It seems odd that the first thing NCEES worries about is the burden on Universities and not the poor students who have to fit the new requirements into their already busy lives.)
I liked this sample question:
Will bachelor’s-degree recipients with low grade point averages (GPA) have a problem
becoming licensed because their GPAs prevent them from being admitted to a master’s
Will they? How about this quote.
In the Economic Impact section, the task force considered it likely that the value of lifelong earnings would offset the cost for pursuing the proposed additional education requirements.
Since I already have the masters degree and the P.E., I am off the hook but if your a student or a parent of a future engineer, be aware of the coming requirements. Good or bad they are coming.
When I was looking into what could be done to improve the “look” of standard precast beam bridges already in service, I investigated the use of staining systems. Simply put, I looked at painting bridges.
Since bridges are huge and subject to weather extremes, it is essential to properly prepare the concrete surface and pick the right staining system. We used a Sherwin Williams Acrylic stain.
I tested the system on a nearby bridge over 8 years ago. It still looks great.
Now everybody calls my bridge the “Walmart Bridge”.
Still the bridge looks good (open to debate of course) and the paint system passed with flying colors.
So my county bridge design (see earlier posts) was finally let. The low bid appears to be just over $200,000 dollars. For a 50′ x 28′ bridge that works out to about $142 /sq. ft.
A county would have put in a high abutment bridge (then they could use non-prestressed deck panels) instead of my 50′ span. Their typical cost would be around $125 / sq. ft. (about $140,000 for a 40′ x 28′)
I think my bridge will find a market, especially if it can be installed in 5 days! But further design is required to get the bridge down to a competitive price.
I don’t know much about the webmaster of bridgehunter.com but it is full of old and historic bridges. Currently, it holds over 31,000 bridge records, gathered by a number of “bridgehunters”. The Iowa Dot also has a good website dedicated to historic bridges found throughout the state. Historic bridges of Iowa.
Scour is not a great sounding word. In bridge slang, scour means “water move soil”, seriously, look it up. (Hey I have not had much sleep since giving the exam last night and then getting up at 5:00)
Anyway, scour is one of the reasons we use pile foundations around our river systems. Essentially, high water flows removes the soil around our bridge foundations. If the exposed length of piling is too great you may experience some buckling of the piles. If you used a spread footing, the water flow may undermine and damage your bridge.
I saw this one lane truss bridge over the soldier river. It was posted for 11 tons and featured a wood plank deck.
A new crossing was being built slightly upstream, so I doubt this bridge will be around for long.
A problem on some of the bridges I looked at was the issue of strands breaking out of the ends of the beams. Fixing this will take a little thought.
One more photo of the truss bridge below the fold.
ASCE has a website dedicated to ranking the current state of our infrastructure. Apparently we need $2.2 trillion dollars to cover the cost. Yikes! It has a ranking of each state and it shows that my state has 27% structurally deficient bridges*. They also have a contest going on for photos of broken down infrastructure. Since I just got back from looking at bridges that need work, I think I am going to enter!
*Structurally deficient bridges are those that are restricted to light vehicles, require immediate rehabilitation to remain open, or are closed. Functionally obsolete bridges are those with deck geometry (e.g., lane width), load carrying capacity, clearance, or approach roadway alignment that no longer meet the criteria for the system of which the bridge is a part.1 In the 1990s, while the number of structurally deficient bridges steadily declined, the number of functionally obsolete bridges remained fairly constant.
This project has been in a lot of presentations for accelerated bridge construction. Built about 4 years ago, its a single span all precast system. They used spread footings on rock with box beams and a complete precast abutment. It seems a little complicated for me. The rock is a lucky thing, trying to put precast on piles is a little more difficult.
A quick overview of ten amazing bridges from oddee.com. (No idea who they or what they are, but the pictures are good.)
From what I understand lists are the most popular thing to put on your website. Things like top 10 this and top 5 that. I guess I will have to start the ABC top ten. (Hey that will be my next post!)
One of the things I am working on is developing a simple, cheap but strong county bridge. The idea is to design something that anyone could build, to open the construction to as many fabricators as possible. Currently, a large number of counties use high abutment single span bridge with a precast panel deck. The panels are not pretensioned or post tensioned and for that matter, may not meet current codes. What they are is cheap. Counties are concerned with first costs and a short, high abutment is often the most inexpensive bridge to build.
The criteria for the design is pretty simple.
- Simple span – starting with 40 feet, high abutment.
- Width 28 feet.
- Depth of the superstructure, 24″ or less.
- All precast, with a basic design that multiple fabricators or County personnel can manufacture.
- No pretension or post tension, if possible.
- Meet LRFD design code
- Accelerated bridge construction, if possible (precast would likely be ABC)
- Cost around $120,000 or less
One idea is to slide precast concrete panels down H-piles and then cap the piles with a precast abutment. The bridge would be shorter and hopefully cheaper than the standard spill through abutment bridge.
A longer bridge is often easier to build and keeps the substructure out of the water but it usually costs more than a high abutment bridge. The longer bridge usually requires some kind of high tensioned steel strands to make the span lengths required and that makes the precast deck a specialized product to manufacture. That increases the cost and it is all about costs when you have a large number of bridges to replace.
Happy Easter, great picture of the swamp Rabbit Pedestrian Bridge from Bridgepix.com. (get it rabbit – easter..)