I have written a few posts about adding landscaping to bridges and I think you will see this type of design becoming more prevalent. Some have already been built and I see it often in design concepts, the concept of livable bridges. The positives are obvious, flowering plants and green trees add to any bridge experience. But a bridge, carrying its loads on small supports, is very expensive real estate and a designer has to be careful what they put on the deck.
The downside is often pointed out by engineers. You need special design details for planters on a bridge. How do you protect the planter from freeze/thaw, how do you drain the water, how do you handle the extra weight, how do you handle debris, how do, well you get the idea…..
UPDATE: It was pointed out to me that I forgot to put dead load on the adjacent spans for my STAAD analysis. oops, but I still think the analysis is even more conservative without the dead load on the other spans, since the DL on the other spans would reduce the moments on the spans I loaded. Or so I think…
ACI concrete code moments and shear coefficients are really old, (Section 8.3) and I can not find the background material showing how they were developed. I usually give my students a homework problem asking them to compare the ACI coefficients to a STAAD analysis. Sometimes STAAD is more conservative and sometimes the ACI coefficients. Go figure.
The students asked for a little help, so I made the following videos, very quickly. Get that, quickly, so they are really rough. (and how is that different from my other videos you ask in a snarky Peewee Herman voice..)
“The manual divides sustainable practices into eight categories: planning, design, environmental, water quality, transportation, lighting, materials, and innovation.
In the materials category, for instance, if a contractor recycles on-site during a project, instead of hauling material off and back on again, the project is awarded points. In the design category, if a project minimizes earthwork by aligning grades as closely as possible, the project is awarded points. Several aspects of the design and construction processes and materials are considered.
Illinois is now one of only three states to provide this kind of framework for recognizing and promoting green practices across all key areas in road and transportation building.”
Sitting here having my coffee and looking around the web for something interesting, I ran across a number of articles claiming that “Green” design is cheaper over the long run. I’m not sure that is true but I do know that most bridge costs are evaluated as first costs. Meaning what does it cost now?
Every engineer I know asks that question first, “Oh ya green design is great but it always costs more, go hug a tree.” (I added the tree part..)
I mentioned you can save money now by using higher strength materials and removing a beam line. But it is difficult to change the geometry of a standard bridge. For example, say all I need for a design is a 28″ concrete column, typical formwork only comes in even 1/2 foot dimensions. So I design a 30″ column. Is the extra concrete wasted? I could reduce the amount of steel but I will probably leave it in (need my 1% min.) and have a stronger bridge. (Way strong is what us structural engineers like…Hey we have to sign it)
Can a green bridge design cost less than a traditional bridge right out of the box? Or is only after decades will we see the savings?
On another note, I have to design an impractical bridge concept so impossible that I will get tons of internet buzz. Like this one, and this one.
Bridges are engineered to be three times stronger than needed, so the additional 23 pounds per square foot of load will be absorbed on the base structure with no additional load cost.
Why do we design it so strong? Stupid engineers…
“The project combines the esthetical, the functional, and the business minded. This winning proposal is architecture in high, high class.”
A reader, Kitty Snow, sent me some newspaper clippings which describe how her aunt Kathleen Lynch become the first bridge engineer in Virginia. The clippings are a little hard to read but I will post as many as I can.
It is amazing how Ms. Lynch learned mechanical engineering during the second world war by designing artillery and then after the war moved into bridge design.
(That is a slide rule she is holding, for the younger crowd. Think pre-pre-calculator…)
Another break, another bridge. Just playing around to see how fast I can draw something out. I like the idea of a pointed nose so only one person can fit in the spot. (Makes it a place when people want to visit.)
Don’t expect too much for a 15 minute bridge…I’m not sure it would even work!
I was thinking at lunch that I need to concept some fun bridges. (well fun to me)
So channeling a designer trying to sell you a concept, may I present the Wristwatch Bridge!
It has narrow pathways to an open center.
The narrow pathways represent the struggle people face everyday, fighting through crowds, meetings and life in general to get to a center of calm. The middle of the bridge is a large open circle where you can meet your friends, relax and enjoy the view.
I was thinking about how the world of engineering moves and from what I see it moves really slow. So how do you speed things up? No really, how do you do it?
When I speak to other engineers they often agree that things should change but they don’t actually want to change. So incremental change is the order of the day but I hate it! (Maybe I am wishing for the moon.)
I wrote in an earlier post about how you can save money by removing a beam line when you design a bridge. That is an example of what a structural engineer can do after a bridge concept is finalized….
The biggest savings come when you first concept a bridge and the early decisions are typically made by someone other than the final design engineer.
The decisions made about materials, size and structure type are huge and will determine if your final design is a sustainability success.
One of the tools you can use when you start a bridge concept is a simple benefit/cost analysis. The New York State DOT has a worksheet that helps a designer narrow down the cost and type of structure required for a location. (Click on the image below to see a sample of the worksheet.)
Four-foot-diameter caissons were drilled into the ground adjacent to the stream bed. Below a depth of 10 feet, the soil temperature is between 50 and 55F. Heat is extracted from the caissons through heat exchangers as a glycol fluid is pumped through the system.
The heat is transferred via closed loop three-quarter inch stainless steel pipes, embedded in the concrete deck, which weave up and down — six inches apart — across the 100-foot span. The glycol then warms the deck, melting ice and snow. Depending on the outside temperature, auxiliary flash boilers are activated to increase the glycol’s temperature, speeding the melt.
Since the project began in 2000, more than 15 million tonnes of CO2 have been injected into the Weyburn oilfield. The CO2 increases reservoir pressure and recovery rates from mature oilfields, such as Weyburn, which was discovered in the mid-1950s.
A good overview of sustainable bridge design on structuremag.org. Daniel Whittemore suggests that a rating system is needed to “measure” a sustainable design. (Which I think is true) So it is a good thing that ASCE is developing a new rating system which will be rolled out later this spring!
So, in practice, sustainable bridge design is not about strictly environmental concerns, or only about energy conservation. Instead, it is a more holistic – top to bottom review and evaluation of a bridge project’s merit and compatibility with the indigenous human and wildlife populations on both the micro and macro scale. As such, it has the potential to be a useful tool to quantify and determine the true scale of even indirect or unintended deterioration done to our environment, society and the community at large.
I literally just read about the Dharma Wheel, which is often used to represent the Noble Eightfold Path. This is essentially a “how to live” guide for Buddhists and something I will shamelessly morph into a discussion of sustainability in bridge design and a way of living for engineers. (I think I am little preachy in this discussion, its like a smoker who quits and now wants everyone to quit…..)
(Note: material is taken from Wikipedia and adapted to my skewed perspective.)
1) Right View
It is the right way of looking at life, nature, and the world as they really are. It is to understand how reality works. It acts as the reasoning for someone to start practicing the path. It explains the reasons for human existence, suffering, sickness, aging, death, the existence of greed, hatred, and delusion.
I have uploaded a couple of bridge images that I am going to “improve” in Photoshop (or Gimp). If anyone wants to take a shot at making them look cool, go ahead and then send it back to me for posting. I will even give you credit! (Click on the image for the large view.)
From a USAToday article, see how much your state lost. (If earmarks are indeed lost money.)
The problem is so pervasive that almost 1 in 3 highway dollars earmarked since 1991 — about $13 billion — remains unspent, federal data show. “We call them orphan earmarks,” says Michael Covington of the South Carolina Department of Transportation. “They don’t have a home.”
You probably have heard that phrase a million times. The idea of buying local produce and products helps the local economy, reduces carbon emissions, (less trucks hauling long distances) and helps build your community, by keeping the money in house. It is a strategy that seems to be transforming organic food production and is a big drawing card for local restaurants. (shameless plug below)
Would this work for bridges? (HP touched on the concept in my previous post.)
It would work this way. If your community needed a bridge you would design it with local materials in mind. If your state was a precast concrete state like mine is, you would lean heavily towards concrete bridges, that could be constructed with local forces. Steel bridges would be a last resort because the material and fabrication would be outsourced to another state and trucked back in. You would not see any of that money in your community. Then a specialized work force would come in and erect the structure. (Obvious it would be the opposite way if you where a steel making state and you had to import concrete.)
Is this an ethical sustainability practice for bridges? Even if you had to pay more, but the money stayed locally, would this be a good idea?
How do you make a typical highway bridge sustainable? Most engineers would probably argue that a small pretensioned precast beam bridge is the best you can do in terms of economy and design efficiency. Where it falls down is in the social or community aspect of the structure.
Typical highway bridges are not attractive and there is little you can do to make it blend into the community. But they are inexpensive (for the most part) and easy to design.
I just saw this before bed. A group has formed to promote awareness of three potential corridors for a new interprovincial bridge near Ottawa, Ontario. (Canada….)
As far as I can see they are lobbying for more discussion and a rational solution, based on the principles of sustainability. I’m not sure who is right but I like the public getting involved.
Sustainable Solutions/Solutions durables believes that none of the currently proposed bridge corridors provide a real solution to the long standing and unacceptable situation of 2500+ inter-provincial heavy trucks per day transiting downtown Ottawa. Furthermore it is our position that it will be unacceptable to build a bridge costing $500M or more (initial estimates from Phase 1) which does not provide a solution to this interprovincial truck problem.
Our goal is to raise awareness of this issue and build consensus among the affected communities to lobby the study proponents (NCC, MTO, & MTQ along with the Cities of Ottawa and Gatineau) to widen the scope of the study to include a proper evaluation of additional options that could provide a better solution to this truck problem.