Daniel Whittemore, AI Engineers, Inc., Middletown, CT
Kurilpa Bridge in Brisbane, Austrailia. Photo: Pulv (Wikimedia Creative Commons)
Water powered lights on bridge in Ballybofey, Ireland.Photo: L&H Ecotech
As "green design" has become mainstream, examples of bridges with notable "green" features can now be found all over the world. . The Kurilpa Pedestrian Bridge in Brisbane, Australia, designed by Cox Architects, uses an array of 84 solar panels to power LED lights to illuminate its deck. In Ballybofey, Ireland, engineers have installed a water-powered light system powered by the currents of the river it crosses. And in San Diego, California, engineers have proposed a new structure that has an LED light show powered every night by 100% renewable sources including wind turbines. Do these stately, impressive crossings represent the leading edge of sustainable bridge design?
Before we can begin to answer that question, we need to first define the term "sustainable bridge." I suspect this term evokes images of structures like those listed above in the minds of many of my fellow bridge engineers when they hear that term. Or, perhaps they imagine picturesque glued-laminated wooden structures blending harmo- niously with their surroundings deep in a national park. Notably, the one common thread would be that these images would appear to have very little applicability to the real world, day-to-day problems faced by bridge owners or bridge professionals. Being pragmatic, many of us would then quickly dismiss the concept of a sustainable bridge as something impractical, or at best, of limited usefulness outside of the arena of green design.
The Triple Bottom Line
Example of Sustainability Triple Bottom Line
In reality, such images and the basic assumptions behind them are off the mark. To reframe the discussion, a sustainable design of any stripe is commonly defined as "development that meets the needs of the present without compromising the ability of future generations to meet their own needs." Extrapolating from this basic definition, a sustainable engineering project such as a bridge can therefore be defined as one that is conceived, designed, constructed, operated, maintained, and eventually put out of service in such a fashion that these activities demand as little as possible from the natural, material and energy resources of the surrounding supporting community.
Hartford, CT, USA. In order to reconnect downtown Hartford back to the Connecticut River that birthed it, the city literally built a greenway right over Interstate I-91 (Seen running left and right in the photo).
The concept suggested by this definition is often described as the sustainable triple bottom line. In this visualization of sustainability, what we are looking for are engineering projects that have the most positive impact at the intersection of the People it intends to serve, the Planet on both a micro and macro scale, and the long-term Profit of everyone involved throughout the life of the project. By this test, a sustainable bridge can't be one that serves the people it serves, but imposes a high lifetime cost. Nor could it be an ecologically friendly and economical crossing that serves noone. Rather, a completely sustainable bridge is one that strives to serve the people that use it and the environment it is connected to at a palatable long- term cost. A sustainable bridge isn't, then, defined by any one feature on the crossing, but by looking at the structure in its entire context.
Are the bridges in the first paragraph sustainable? The answer is: they might be, but the features mentioned above, by themselves, don't tell the complete story about each bridge's impact to the triple bottom line. With a definition in hand, we can now start to look at any of the structures above or a proposed bridge project and begin to measure, and hopefully plan for, its sustainability.
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