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…)