Aesthetics in Bridge Design英1.docx

Aesthetics in Bridge DesignThe appearance of the bridge is dominated be the shapes and sizes of the elements controlled be the engineer - the structural elements themselves, not by details, color, or surfaces. The Golden Gate Bridge owes its appeal to the graceful shape of its towers and cables, not to its reddish color. If the towers were ugly, painting them red would not make them attractive.Periodically the suggestions is made that the engineers should delegate responsibility for the appearance of bridge to architects or other visually trained professionals such as urban designers, landscape architects, or sculptors, the notion being that this would result in better-looking structures. This is rarely successful. The usual result is an overly elaborate and overly costly structure, without a significant improvement in appearance. There are two reasons for this. The first is that the visual professional doesnt understand the special limitations and problems of bridge or, even more important, the aesthetic opportunities of modern engineering materials structural types. So, the designer falls back on the familiar conventions of architecture or sculpture and makes something that looks like a building or a piece of sculpture, not a bridge.The second reason is that the delegation can never be complete. In the United States, engineers have the professional and legal responsibility for bridge. The organizations that commission, finance, and build bridges are usually run be engineers. None of these people are willing or legally able to delegate complete responsibility for a bridge to a nonengineer, no matter how talented. This usually means that the “important” (structural) aspects of the bridge are reserved for the engineers, while the “window dressing” (surface details, color) is left to the visual professional. Although the details are an important part of a structures aesthetic impact, it is the structure itself - its spans, proportions, and major elementsthat has the largest role in creating its effect. If the engineer does a poor job with these major elements, no amount of architectural add-ons will compensate.Engineer must control the structural elements - that is their job. However, for the bridge to be a complete aesthetic success, the details, colors, and surfaces have to be in tune with the structural concept. Therefore, the engineers should control those as well. That said, visual professional who are willing to take the time to understand the special nature of bridge can offer a positive contribution to engineers be acting as aesthetic advisors or critics. Their role is comparable to that of other specialists, such as geologists or hydrologists, on whom the engineer may call for advice. Engineers have accepted a responsibility to society for bridge design. For that reason, no engineer would knowingly build a bridge that is unsafe. For the same reason, no engineer should knowingly build a bridge that is ugly.Aesthetic ability is not some mysterious quality bestowed by fate on a fortunate few. Though many engineers are not well prepares by their education or experience for the visual aspects oftheir responsibilities, they can learn what makes bridges attractive and they can develop their abilities to make their own bridges attractive.Many tools are available to help engineers improve their abilities in the aesthetic aspect of engineering. Many books present a series of guidelines and the principles that underlie them. It is useful base from which to consider the appearance of structures. But the guidelines are only a beginning. Engineers should form their own opinions about what looks good, and work to develop their own aesthetic abilities.Bridges must safely carry their loads for a long enough time to repay the investment made in them. This basic fact imposes a hierarchy on design making:Performancestructural capacity, safety, durability, and maintainabilityCostconstruction and maintenanceAppearanceThat said, this statement often leads to the assumption that three criteria are necessarily in conflict, that one must be sacrificed for the other. This is not true. For example, many people think improved appearance will automatically add cost. They believe good appearance derives from add-ons, like an unusual color, special materials such as stone or brick, or ornamental features. In fact, the greatest aesthetic impact is made by the structural members themselvesthe cables, girders, and piers. These things have to be there anyway. If they are well shaped, the bridge will be attractive, without necessarily adding cost.Many of the greatest bridge engineers were able to create that are beautiful, structurally sound, and less expensive than any alternative, all at the same. In decisions about appearance, as in decisions about strength and durability, the challenge is to achieve an improvement without an increase in cost. It can be done.Now lets discuss the next item on the specific requirements for bridge aesthetics.Conformity with EnvironmentA bridge must conform with its surroundings and environment. The setting or surroundings greatly affect its appearance. Those that are exposed to the river view are seen and appreciated more than others that are partly hidden by adjoining objects.Generally, a structure must be in harmony with its environment and not appear as an intrusion. To secure harmony between the structure and its environment means the merging of its general outlines with those of the landscape. It should be remembered that the bridge will likely be seen from various angles, and that each viewpoint will cause its own individual impression.The rule, generally, is to make the bridge more striking than its surroundings, so the eye will naturally be attracted to it. A good method is to make separate photographs of the site and the design to the same scale, and after placing the proposed bridge in the landscape view, to rephotograph the combination. Features of the design that fail to conform to the surroundings will then appear, and changes can be made until it is satisfactory.Economic Use of MaterialEconomic use of material is another standard of excellence. Beauty exists in every structure which is designed according to the principles of economy, with the greatest simplicity, the fewest members, and the most pleasing outline consistent with construction.Exhibition of Purpose and ConstructionThe purpose of the bridge should be plainly evident, and generally the construction should be revealed. Expressiveness, to many people, is the main source of beauty. Strength and boldness should predominate.Pleasing Outline and ProportionsA bridge is beautiful if its primary form or outline and its relative proportions are well and properly chosen. The proportions must satisfy the eye and the aesthetic feeling, and have optical harmony. Good general lines are necessary as a basis; a consistent scale or proportion of parts should follow. A form that admits of no explanation cannot be beautiful. It must have and show some purpose in its general relation. Each part of a bridge structure should be treated in such a way that its function therein is apparent and emphasized according to its importance. The different kinds of materials used in structures call for different treatment and varying aesthetic standards.The underlying thoughts connecting these precepts is that the structure must be fitted for the work it is to do, that it should express the truth, and that falsities are erroneous and outside the realm of rational aesthetics.The achievement of good general lines is best attained by a study of the profile of the structure. The feature of a bridge is so pleasing to the eyes of all observers, cultivated and ignorant alike, as perfect symmetry in the layout of spans; consequently is involved thereby. Unfortunately, the connections are not always favorable to the perfect symmetry of design. In such cases it becomes necessary to do the best one can with the unfavorable conditions, and to make the structure aesthetically pleasing, if not symmetrical.Appropriate but Limited Use of OrnamentMere ornamentation generally affronts the sense of harmony and fitness. In many bridges what would otherwise be a pleasing outline is spoiled by the introduction of massive ornamental portals at the ends. It is not advisable to correct the hard, rigid outline of a span by the use of additional parts that falsely proclaim a different function for the members or confuse their action in the structure. Ornament is not architecture, and a bridge of beautiful outline may easily be spoiled with an excessive amount of details. Super