邓文中院士关于桥梁设计创新的文章—Innovation

Innovation Summary Innovation can be defined simply as “invention, improvement or incorporation” but must also offer “increase in value.” These make up four of the “I’s” in Innovation. If the invention, improvement, or incorporation does not offer an increase in value, it is only an alternative, and not an innovation. Innovation can be achieved through a process of asking oneself “Why, why not, and what if?” Keywords: Innovation, improvement, incorporation, San Francisco-Oakland Bay Bridge, bridge innovation. 1. Definition A few hundred thousand years ago, human beings lived just like animals, roaming the planet to survive. Today, there is a great distinction between how we live and how other animals live. The difference is that human beings have achieved an advanced state of intellectual and cultural development, e.g., we’ve become civilized. Consequently, we have dominated the world! There is also a huge difference between people’s lifestyles 5,000 years ago and our lifestyles today. The difference is 5,000 years of civilization. Human beings have the wisdom and courage to innovate; along the way, we have found ways of improving our civilization. So, civilization can be defined as a sort of accumulation of bits and pieces of innovations over the span of human evolution. Without civilization, we would still be living like animals. Without innovation, we would not even have a civilization! What is innovation? Merriam-Webster’s Dictionary defines innovation as “to introduce something new, to effect change in the established order.” In my opinion, this definition is not complete. An innovation is a change, but, it must bring with it added value. If it does not bring any added value, it is only an alternative, not an innovation. Therefore, a discussion about innovation must start with value. 2. Value of bridges The four basic requirements of a bridge are “safety, functionality, economy, and aesthetics.” Each of these has its own individual value, that is, the value of safety, the value of functionality, the value of economy and the value of aesthetics. An idea can only be qualified as an innovation if it increases the total sum of these values. It is the sum that is important because, in many cases, we may have trade-offs between these values. For example, we may enhance the beauty of a bridge, but at the same time spend more money to do so, thus increasing the value of aesthetics and decreasing the value of economy. We may also enhance the functionality of a bridge and, at the same time, increase the cost or affect the aesthetics. The safety of a bridge can never be compromised. A bridge must be safe under all design conditions. Some people believe that a bridge can only be either safe or unsafe, so its value in terms of safety cannot be changed. It is true that making an already safe bridge twice as safe typically does not carry much meaning. However, in reality, safety is not an absolute term, but rather a relative one. Our design is based on reliabilities and probabilities. For example, the current AASHTO standard specifications recommend that a bridge be designed for an ultimate seismic event with an estimated return period of 2,500 years, which corresponds to a probability of an B.Sc. 1959, Chu Hai College, Hong Kong, Dipl.-Ing. (1963) & Dr.-Ing. (1965), Techn. University Darmstadt, Germany. Structural engineer, major in bridges. Man-Chung TANG Chairman of the Board T.Y. Lin International San Francisco, USA Mtang@tylin.com   1Innovative Infrastructures - Toward Human Urbanism occurrence at 2% in 50 years. Clearly, this does not mean a stronger earthquake is not possible. It would bring additional value if a bridge could resist a much stronger earthquake at no added cost. This brings peace of mind. And peace of mind has value! Durability also falls under the category of safety as an issue. Indeed, making a bridge more durable increases the value of a bridge. If we can assure the safety of a bridge beyond its design life, the value of the bridge increases. Functionality is the primary reason why a bridge is built. A bridge must satisfy the function it is designed for. A six-lane bridge must have six proper traffic lanes. However, functionality is also a relative element. For example, a lane can be 3.50m wide, or 3.75m wide, or sometimes only 3.00m wide. There are also sight distances and other factors to consider. If an innovation can create better driving conditions, it certainly adds value. Economy is directly related to the value of a bridge. If a bridge can be built at a lower price than anticipated, that savings is an added value. The value of aesthetics is certain but hard to determine due to differences in perception of beauty. Still, people can and do differentiate between a so-called beautiful bridge and an ugly one. The aesthetics of a bridge is not limited to the bridge itself. A bridge can be seen as part of a city. Landmark bridges like the Golden Gate Bridge in San Francisco and the Alexander III Bridge in Paris definitely contribute to the beauty and history of their cities. In fact, they are the main attraction for visitors and tourists. If we want a beautiful city that we can be proud of, the bridges of our cities must also be beautiful. Each of the above mentioned values vary in their importance under different circumstances and in the minds of different people. But in most cases, they can still be readily recognized. 3. What constitutes innovation? We can simply say that innovation is either “invention, improvement, or in-corporation,” while satisfying the requirement of an “increase in value.” This may be called “The Four “I’s” in Innovation!” “Invention” is the creation of a totally new idea. The light bulb, for example, was an invention. Putting reinforcement into concrete to form reinforced concrete was an invention. These ideas were new at that time and offered significant value to society, the industry, and the built world. Prestressing was an important invention; so was the segmental construction method. “Improvement” means to modify what we already have and to make it better. Precasting is a different way of casting concrete, but under certain circumstances, it can save time and costs, and/or improve quality; therefore, it is an innovation. The concept of a cable-supported form traveler, which uses the front cable to support the traveler (to reduce the bending moment in the traveler and the girder of a concrete cable-stayed bridge) saves costs and increases safety. Thus, it too is an innovation. The Sony® Walkman was an innovation because it allowed us to listen to music while walking down the street. The iPod was an innovation because it improved upon the way we listen to music compared to other products like the Sony® Walkman. “In-corporation” means to combine existing ideas to create something new. Steve Jobs once said, �Creativity is connecting things.” The iPhone is not an invention. It is a combination of various existing components, or technologies. By incorporating them into a single phone that is better than all other phones, it provides more value to its users; so, it is an innovation. The diesel engine is an important invention. It allows the use of lower-grade fuel extracted from oil. Since its inception, there have been many improvements made to the original diesel engine. So, there have been many accompanying innovations in connection with the diesel engine. Incorporating the diesel engine into an automobile, for example, is yet another innovation. As previously mentioned, reinforced concrete is an invention. That was patented by Joseph Monier in 1867 about 150 years ago. In the mean time, the strength of both concrete and steel has been increased through improvements, and there have also been many innovations to improve the usefulness and applications of reinforced concrete 2 18TH CONGRESS OF IABSE, SEOUL, 2012 A concrete, cable-stayed bridge is an innovation that incorporates the existing components of reinforced concrete, cables, and other components such as bearings and piles into a bridge that can span longer distances at lower costs. In sum, any of these inventions, improvements, or incorporations can be defined as innovations because they are unique and they also increase the value of the final product. By increasing the value of the product, it results in a reduction of its actual cost. 4. Process of innovation Engineering is not science. Science is very strict and deals only with the truth of nature. Truth is immutable. That is, scientists cannot change the rules of nature. By contrast, engineering is an art and humans alter their environment to improve on what nature has given us so that we can live more comfortably on this planet--we build houses to shelter us from sun, rain and other adverse weather conditions; we build ships so that we can navigate and reach land; we build bridges to cross rivers and valleys. Art is flexible and allows for alternatives. This offers ample room for innovation. But how do we innovate? Innovation has been the topic of discussions and research for a long, long time. So, there have been many teachings, theories, and concepts on the methods of innovation. To make it more understandable, I believe the process of innovating can be simplified into finding answers to three specific questions: “Why? Why not? and, What if?” The question “Why?” challenges the status quo. In school and in society, we were taught to follow many rules and procedures. Most of the time, we never ask why. In engineering, there are codes and specifications for designers to follow. Most engineers just follow them and never ask questions. But as mentioned above, the foundation of engineering is experience. Experience is never complete. Codes and specifications are a product of accumulated experience. So, they are not perfect or complete either. Codes and specifications are constantly being modified to reflect the latest knowledge learned from experience. To be able to improve on what is prevailing in the codes and specifications, we must ask why! This question enables us to understand the reasons behind these rules. All rules are manmade. They can be wrong. There can also be better alternatives. However, we can only find out if we ask why! But to be able to ask why, or to be able to understand why, we must have sufficient knowledge. If we are not able to understand a problem after asking the question, then there is no answer and the line of questioning ends. Take the San Francisco-Oakland Bay Eastern Span Replacement (for convenience, we’ll call it the Bay Bridge). For example, the bridge is located in one of the highest seismic zones in the United States. Bay Area residents preferred a single pole tower shape, which, according to prevailing judgment at the time, was not possible in such a high seismic area. A portal-type tower with two columns and cross girders would have been the “proper” choice. To make a single pole tower acceptable in this area, our process began with the question of why? Why is a single pole tower considered seismically unsafe? It is because a single pole tower is non-redundant. During an earthquake, the cross girder of a portal tower can form plastic hinges which can dissipate energy while leaving the vertical columns elastic so that they can continue to carry the vertical loads. On the other hand, a single pole tower becomes unstable and falls down once a plastic hinge is formed; so, it is deemed unsafe. This can easily be seen from a simple push-over analysis. To make a single pole tower acceptable for the design of Bay Bridge, we had to find a solution to this problem. Fig.1: The Bay Bridge Fig.2: Portal and single pole Fig.3: Modification The question, “Why not?” helps one present a new idea.   3Innovative Infrastructures - Toward Human Urbanism If a change is preferable, there must be a better idea to replace what is currently being used. For every engineering task there are always multiple possible solutions. This leaves much room for innovation. From an array of possible alternatives, we need experience and knowledge to pick the most promising one. In the case of the Bay Bridge, since a portal tower was acceptable, we then asked why we couldn’t place the entire portal tower in the middle between two roadways. We narrowed the portal tower as much as possible so that the bridge deck would not be too wide. This way, the tower is still a portal tower, and only the cross girders are shorter. This shape satisfied the desire of Bay Area residents with respect to the issue of aesthetics. One advantage in using such a configuration was that we were able to put as many cross girders between the vertical columns as we liked, and at any location, as we felt appropriate. They do not interfere with roadway traffic because they are between the two superstructures. The new bridge configuration retained the same total width with 10 lanes, thus, it also satisfied the functionality of the bridge. In addition, the Owner accepted the preliminary cost estimate. “What if?” is a group of questions to ascertain that the newly introduced concept is workable. With bridges, safety is a major concern. An innovation always takes a step beyond what has been done before. Are there any hidden weaknesses we have not discovered? A bridge is built for and used by the public. It must be unquestionably safe. We raised many questions with respect to the Bay Bridge’s tower configuration, including but not limited to: What would happen if the cross girders did not yield in bending as in a portal frame? What would happen if the cross girders do not yield in bending but did yield in shear? What would happen if the cross girders did not have sufficient ductility? What would happen if the columns yielded before the cross girders yielded in the event of an earthquake? What would happen to the already yielded cross girders if a strong aftershock hit after the initial quake? What would have to be done after the earthquake if some cross girders yielded? And, How would the tower perform under high wind conditions and if the cross girders already yielded during an earthquake? Fig.4: Shear link test Fig.5: Push-over result Fig.6: Tower cross-section In order to answer these questions, we carried out extensive analyses and laboratory tests. This work confirmed that the concept was safe and acceptable for the Bay Bridge. The final tower configuration actually has four columns connected by a number of short cross girders we call “shear links.” These shear links show excellent ductility in laboratory tests. They are connected to the columns using high-strength bolts that are replaceable if they deformed after an earthquake. Because the tower is located between the two roadways, the replacement of these shear links would not interfere with traffic—one of the design criteria. Analyses show that only one of the many shear links will yield under the ultimate safety design earthquake. The tower has significant reserve in ductility because there are many shear links 4 18TH CONGRESS OF IABSE, SEOUL, 2012 between the columns. Dividing the single pole into four columns reduces the stiffness of the individual columns so that they can suffer a large deformation without any yielding in the columns. By answering the questions, Why, why not, and, what if? we created a single pole look-alike tower for the Bay Bridge that is safe, functional, economical and beautiful as desired by residents. All innovators undergo this same process in order to achieve their goal. 5. Partially cable-supported girder bridge In a conventional cable-stayed bridge, the girder is typically very slender. As a result, its carrying capacity is neglected. The towers must carry the total load of the entire bridge through its cables. For a relatively short span bridge, the girder alone may be able to carry a large portion of the load. So we asked, “Why do we have to transfer all of the loads to the towers?” We then asked, “Why can’t we use the towers to carry the portion of load over and above what the girder can carry?” Based on this idea, we went on to design a bridge where the tower carries only about 50% of the load. This design concept is now called a “partially cable-supported girder bridge”. It is partially a cable-stayed bridge and partially a girder bridge. Fig.7: Taijiang Bridge This concept of a “partially cable-supported girder bridge” was applied in the design of the Taijiang Bridge in the City of Sanming, Fujian, China. The bridge has twin main spans of 110m each. The City desired a signature bridge at the newly developed commercial and recreation area and the scheme shown in Fig.7 was selected. To save on construction costs, the girder could only be concrete because a steel box girder would have been too expensive for the available budget. To design the bridge as a regular cable-stayed bridge would have required a much stronger tower and that would have been too expensive. By reducing the load to the tower by about 50%, we gain sufficient savings to make the bridge scheme economically possible. We certainly went through many “what ifs” to ascertain that the concept was applicable and the bridge was safe. Otherwise, this bridge would not have been built. 6. Conclusion For any engineering task, there are always a variety of solutions and alternatives that allows opportunities to innovate. Finding answers to the questions: Why, why not, and, what if? is a simple way for engineers to innovate. 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