The Zakim Bunker Hill Bridge, a cable-stayed span constructed in conjunction with Boston’s Big Dig highway relocation project, is an excellent example of how a distinctive design can become a symbol of a city. It is now virtually mandatory for people engaged in television interviews originating from Boston to be shown with that bridge as backdrop.
Among the most dramatic of newer cable-stayed bridges is the Millau Viaduct, which carries vehicle traffic high over France’s wide and deep Tarn Valley. The bridge’s roadway is so high off the ground that it appears on occasion to float above the clouds that form beneath it, but the bridge earns equal distinction for the gently arcing curve of its deck and its overall striking appearance. I have lost count of how many correspondents have sent me still and moving images they took while driving over this bridge, but I never tire of admiring their pictures.
Not all striking bridge designs are towering, long-span highway bridges. Many pedestrian bridges of exceptional aesthetic value have been designed and built in recent years. Among the most widely known is the London Millennium Bridge, the design of which was the collaborative effort of the Arup engineering firm, Foster and Partners architects, and the sculptor Anthony Caro. It resulted in a striking low-slung suspension bridge, which to many people is hardly recognizable as one. Unfortunately, the bridge became somewhat of an embarrassment when its walkway swayed so much that it had to be closed within three days of its opening. The problem was fixed by retrofitting the bridge with stiffening struts and dampers, and it has become one of the most popular new tourist attractions on the River Thames.
Among the most highly anticipated of new bridges is the replacement for the east span of the San Francisco -- Oakland Bay Bridge, which was damaged in the 1989 Loma Prieta earthquake. Rather than spend $1 billion to retrofit the old structure, the California Department of Transportation argued, the money could be better spent on a new and distinctive span. The centerpiece of the new bridge, whose final cost will likely exceed $6 billion, is an unusual structure -- a self-anchored suspension bridge, one over whose single tower cables are draped and then connected to the ends of the roadway. Expected to be completed next year, the structure is sure to bring bridge enthusiasts and their cameras to San Francisco Bay.
I expect I may be the recipient of some photos of the new Bay Bridge, and I will welcome them. Different people have different opportunities to see different structures from different perspectives under different environmental conditions. Unlike the fine art masterpieces hanging in a museum under controlled temperature, humidity, and lighting, bridges must be works for all seasons. And the best of them truly are.
I think Mydesign has an excellent point: ancient engineers built amazing, beautiful structures, many of which have lasted hundreds or thousands of years, without any of today's sophisticated design tools. In fact, many prehistorians are still arguing about just how some of the oldest ones got designed and built, meaning what tools the engineers actually had in the way of mathematics and physical tools such as a string and chalk for laying out some of the more sophisticated megalithic monuments.
I just visited the arch bridge over the New River Gorge in West Virginia, where We went across the bridge on the catwalk below the deck. That is a very interesting tour. It is difficult to grasp the magnitude of the structure until you see it that close up. All of that steel loaded in compression is an awsome thing indeed.
The bridges with structual elements in tesion are also amazing, but it is clear that they require a great deal more attention and maintenance to remain safe, since tensile failure modes are usually much faster than compressive failure modes, at least that is my understanding. It would be quite educational to have an explanation of how corrosive failure of the suspension elements is prevented.
I grew up not far from the Golden Gate Bridge in San Francisco, with a 4,200-foot suspension span built in 1937. Regular painting is done to prevent corrosion, and those paint jobs are the main form of maintenance, according to this site: http://goldengatebridge.org/research/facts.php
Ann, I agree completely. In 2009 my wife and I traveled to Madrid to celebrate our 40th anniversary. While there, we took a side trip to visit Toledo, an ancient city with many extrodanary structures, one being an aqueduct running close to three miles in length. The workmanship was stunning and how the engineers accomplished the uniform downward slope with the tools they had at their disposal amazes me. The stones were all laid by hand, each one carefully placed. Thousands upon thousands of carefully cut and placed stones. I would love to climb into Mr. Peabody's way-back machine just to see how some of these ancient monuments were constructed. It would certainly be a real treat.
I have add in my two cent to this architectural love-fest on bridges. There is something magical about the way they "work" without actually "doing" anything. Sort of like the human equivalent of a spider's web - constantly balancing forces through a series of aesthetic arcs and supports. All in plain view. Thanks for highlighting these marvels of engineering.
Bob, those aqueducts that have lasted 2000-plus years are pretty amazing, aren't they? I've seen lots of good illustrations that show how they work, but none about the exact building methods used. Does anyone else know any?
Ann, our ancient civil engineers and draftsman had done excellent works in designing and building bridges and roads without any analytical and design software/tools. They had used their brain and skills to complete the task, without depending any man made tools. In my country we had a more than a dozen of bridges built by the great British engineers in 19th century. Still most of them are in good condition and public is widely using it and some other are protecting as heritage monuments.
Mydesign, if I remember correctly, you're in India, right? That country has some incredibly well-built, very ancient public structures and multi-story houses in Mohenjo-Daro and Harappa I've read about (and seen reconstructions of), from the Indus Valley civilization of a few thousand years ago. I don't know if they are still standing, fully or partially, but from the archaeological reconstructions I've seen they were both beautiful and well-engineered.
Ann, you are right. Whatever the things possible are preserved and keeping as monuments by the archeological department. Apart from Mohenjo-Daro and Harappa, all the buildings with more than 100 years old are preserving by government and archeological departments, irrespective of it's a private or public building.
The legacy endpoint devices that control our critical infrastructure (utility systems, water treatment plants, military networks, industrial control systems, etc.) are some of the most vulnerable devices on the Internet.
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.