Monday, August 3, 2015

Strange Uses for Bridges (2)

Rendering of Juncal Viaduct with Turbines (Oscar Soto, ZECSA)
My sister sent me an article from Smithsonian Magazine about installing wind turbines on bridges to create electricity. In the drawing above, mechanical engineer Oscar Soto imagines how turbines could be installed on the Juncal Viaduct in the Canary Islands. He said that any place with wind speeds between 6 and 25 meters per second would work.

I imagine that bridges spanning mountain canyons like we saw in Mexico would have sufficient clearance for a wind turbine. However, tall bridges have enough trouble resisting high winds without having to resist the additional drag forces from having deep longitudinal diaphragms installed between their piers.

Sunday, August 2, 2015

Unbuilt Bridges (2)

Visionary artists often come up with bridge designs to illustrate their ideas and/or philosophies. Sometimes their bridges are built during their lifetimes, or after they're gone, but usually they remain tantalizing ideas that only exist in books. The architect Paolo Soleri believed that humans were migratory creatures and wanted to design high density cities (to minimize their impact on the environment) where they could stop between their travels. He built Arcosanti in the Sonoran Desert to test his ideas. His 'Beast' bridge (shown above) was designed to help carry his imagined tribal societies on their journey. It's a continuous concrete structure with the superstructure folded upward at midspan and folded downward at the supports. It actually looks a lot like Frank Lloyd Wright's 'Butterfly' bridge, which isn't surprising since they worked together at Taliesen in the 1940s. Most likely, they influenced each others designs. This bridge was in 'The Architecture of Bridges," a book that The Happy Pontist rated highly in a blog last week.
Buckminster Fuller developed a philosophy of tensegrity with structures composed of prestressed tension cables (on the outside) and isolated compression struts (in the middle). These truss-like structures are composed of elements loaded axially without any bending, shear, or torsion. Although a tensegrity bridge was never built in Buckminster Fuller's lifetime, the Kurilpa Bridge in Brisbane, Australia is said to have been designed (by Cox Rayner Architects and Ove Arup Engineers) using tensegrity principles.
Frank Gehry's structures are easily identifiable because of their undulating stainless steel surfaces. The BP (Millennium Park) Pedestrian Bridge in Chicago is a long steel box girder bridge (designed by SOM) that supports Frank Gehry's design. To help in the design and construction of his structures, Gehry's uses Grasshopper programming software, which is good at creating intricately folded surfaces. If you are a famous architect, most cities are happy to own your bridge (although even Gehry had to go through many iterations before his design was finally accepted).

Friday, July 31, 2015

Unbuilt Bridges (1)

I was reading a book, "AAD - Algorithm-Aided Design" by Arturo Tedeschi and on the last page was a computer generated drawing for a 'Cloud Bridge.'  This picture reminded me of the many other lovely bridge designs that were never built because they were too whimsical or too expensive.
For instance, the Ruck-A-Chucky Bridge was designed by TY Lin when he was working at Skidmore, Owings, and  Merrill. It was to go across the Middle Fork of the American River (in California) when the state was planning to built the Auburn Dam in the 1970s. Because the bridge was to be built in a steep canyon, it was thought that a curved superstructure hanging from cables anchored into the rocks above would be an economical alternative with the least environmental impact to the area. When it was decided not to build the dam, they also decided to abandon the bridge project.
Similarly, Frank Lloyd Wright had been interested in designing a bay crossing between the San Francisco to Oakland Bay Bridge and the San Mateo to Hayward Bay Bridge. His first drawings were made in 1949. The design had an sinuous, organic shape with 2000 ft long arch spans supporting a garden in the middle of the Bay. It was called the 'Butterfly Bridge,' perhaps because it resembled the flight of a butterfly. Several attempts were made to finance this 'Southern Crossing' but the state of California eventually rejected the idea as being too costly.

There are many other designs for bridges that were never built because they were perceived to be impractical for some reason. It seems like if you have a nice hand for drawing landscapes or for doing 3D computer graphics you can create something intriguing, but it requires something more to get your design built. We'll take a look at some more unbuilt bridge designs in my next post.