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发布日期:2020-02-02 21:59:20来源:土木工程网推荐:土木龙

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《高层建筑展望及建筑结构,毕业设计外文中文》 ThefutureofthetallbuildingAndstructureofbuildings Zoningeffectsonthedensityoftallbuildingsandsol



The future of the tall buildingAnd structure of buildings
    Zoning effects on the density of tall buildings and solar design may raise ethical challenge. A combined project of old and new buildings may bring back human scale to our cities. Owners and conceptual designers will be challenged in the 1980s to produce economically sound, people-oriented buildings.
In 1980 the Level House, designed by Skidmore, Owings and Merril1 (SOM) received the  25-year award from the American Institute of Architects “in recognition of architectural design of enduring significance”. This award is given once a year for a building between 25and 35 years old .Lewis Mumford described the Lever House as “the first office building in which modern materials, modern construction, modern functions have been combined with a modern plan”. At the time, this daring concept could only be achieved by visionary men like Gordon Bunshaft , the designer , and Charles Luckman , the owner and then-president of Lever Brothers . The project also included a few “first” : (1) it was the first sealed glass tower ever built ; (2) it was the first office building designed by SOM ;and (3) it was the first office building on Park Avenue to omit retail space on the first floor. Today, after hundreds of look-alike and variations on the grid design, we have reached what may be the epitome of tall building design: the nondescript building. Except for a few recently completed buildings that seem to be people-oriented in their lower floors, most tall buildings seem to be a repletion of the dull, graph-paper-like monoliths in many of our cities. Can this be the end of the design-line for tall buildings? Probably   not. There are definite signs that are most encouraging. Architects and owners have recently begun to discuss the design problem publicly. Perhaps we are at the threshold of a new era. The 1980s may bring forth some new visionaries like Bunshaft and Luckman. If so, what kinds of restrictions or challenges do they face?
Zoning  Indications are strong that cities may restrict the density of tall buildings , that is , reduce the number of tall buildings per square mile . In 1980 the term grid-lock was used for the first time publicly in New York City. It caused a terror-like sensation in the pit of one’s stomach. The term refers to a situation in which traffic comes to a standstill for many city blocks in all directions. The jam-up may even reach to the tunnels and bridges .Strangely enough, such as event happened in New York in a year of fuel shortages and high gasoline prices. If we are to avoid similar occurrences, it is obvious that the density of people, places, and vehicles must be drastically reduced. Zoning may be the only long-term solution.
Solar zoning may become more and more popular as city residents are blocked from the sun by tall buildings. Regardless of how effectively a tall building is designed to conserve energy, it may at the same time deprive a resident or neighbor of solar access. In the 1980s the right to see the sun may become a most interesting ethical question that may revolutionize the architectural fabric of the city. Mixed-use zoning became a financially viable alternative during the 1970s, may become commonplace during the 1980s, especially if it is combined with solar zoning to provide access to the sun for all occupants.
Renovation   Emery Roth and Sons designed the Palace Hotel in New York as an addition to a renovated historic Villard house on Madison Avenue. It is a striking example of what can be done with salvageable and beautifully detailed old buildings. Recycling both large and small buildings may become the way in which humanism and warmth will be returned to buildings during the 80’s. If we must continue to design with glass and aluminum in stark grid patterns, for whatever reason, we may find that a combination of new and old will become the great humane design trend of the future.
Conceptual design   It has been suggested in architectural magazines that the Bank of America office building in San Francisco is too large for the city’s scale. It has also been suggested that the John Hancock Center in Boston in not only out of scale but also out of character with the city. Similar statements and opinions have been made about other significant tall buildings in cities throughout the world. These comments raise some basic questions about the design process and who really make the design decisions on important structures-and about who will make these decisions in the 1980s.
Will the forthcoming visionaries-architects and owners-return to more humane designs?
Will the sociologist or psychologist play a more important role in the years ahead to help convince these visionaries that a new, radically different, human-scaled architecture is long overdue? If these are valid questions, could it be that our “best” architectural designers of the 60’s and 70’s will become the worst designers of the 80’s and 90’s? Or will they learn and respond to a valuable lesson they should have learned in their “History of Architecture” course in college that “architecture usually reflects the success or failure or failure of a civilized society”? Only time will tell.
A building is closely bound up with people, for it provides people with the necessary space to work and live in. As classified by their use, buildings are mainly of two types: industrial buildings and civil buildings. Industrial buildings are used by various factories or industrial production while civil buildings are those that are used by people for dwelling, emplovment, education and other social activities.
    The construction of industrial buildings is the same as that of civil buildings. However, industrial and civil buildings differ in the materials used, and in the structural forms or systems they are used.
    Considering only the engineering essentials, the structure of a building can be defined as the assemblage of those parts which exist for the purpose of maintaining shape and stability. Its primary purpose is to resist any loads applied to the building and to transmit those to the ground.
    In terms of architecture, the structure of a building is and does much more than that. It is an inseparable part of the building form and to varying degrees is a generator of that form. Used skillfully, the building structure can establish or reinforce orders and rhythms among the architectural volumes and planes. It can be visually dominant or recessive. It can develop harmonies or conflicts. It can be both confining and emancipating. And, unfortunately in some cases, it cannot be ignored. It is physical.
    The structure must also be engineered to maintain the architectural form. The principles and tools of physics and mathematics provide the basis for differentiating between rational and irrational forms in terms of construction. Artists can sometimes generate shapes that obviate any consideration of science, but architects cannot.
    There are at least three items that must be present in the structure of a building: stability, strength and stiffness, economy.
    Taking the first of the three requirements, it is obvious that stability is needed to maintain shape. An unstable building structure implies unbalanced forces or a lack of equilibrium and a consequent acceleration of the structure or its pieces.
    The requirement of strength means that the materials selected to resist the stresses generated by the loads and shapes of the structure(s) must be adequate. Indeed, a “factor of safety” is usually provided so that under the anticipated loads, a given material is not stressed to a level even close to its rupture point. The material property called stiffness is considered with the requirement of strength. Stiffness is different from strength in that it directly involves how much a structure strain or deflects under load .A material that is very strong but lacking in stiffness will deform too much to be of value in resisting the forces applied.
    Economy of building structure refers to more than just the cost of the materials used.Construction economy is a complicated subject involving raw materials ,fabrication ,erection ,and maintenance .Design and construction labor costs and the costs of energy consumption must be considered .Speed of construction and the cost of money (interest) are also factors .In most design situations ,more than one structural material requires consideration .Completive alternatives almost always exist ,and the choice is seldom obvious .
    Apart from these three primary requirements ,several other factors are worthy of emphasis .First ,the structure or structural system must relate to the building’s function .It should not be in conflict in terms of form .For example ,a linear function demands a linear structure ,and therefore it would be improper to roof a bowling alley with a dome .Similarly ,a theater must have large , unobstructed spans but a fine restaurant probably should not .Stated simply , the structure must be appropriate to the function it is to shelter .
    Second, the structure must be fire-resistant. It is obvious that the structural system must be able to maintain its integrity at least until the occupants are safely out. Building codes specify the number of hours for which certain parts of a building must resist the heat without collapse. The structural materials used for those elements must be inherently fire-resistant or be adequately protected by fireproofing materials. The degree of fire resistance to be provided will depend upon a number of items, including the use and occupancy load of the space, its dimensions, and the location of the building.
    Third, the structure should integrate well with the building’s circulation systems. It should not be in conflict with the piping systems for water and waste, the ducting systems for air, or (most important) the movement of people. It is obvious building systems must be coordinated as the design progresses. One can design in a sequential step-by-step manner within any one system, but the design of all of them should move in a parallel manner toward completion. Spatially, all the various parts of a building are interdependent.
    Fourth, the structure must be psychologically safe as well as physically safe. A high-rise frame that sways considerably in the wind might not actually be dangerous but may make the building uninhabitable just the same. Lightweight floor systems that are too: ”bouncy” can make the users very uncomfortable. Large glass windows, uninterrupted by dividing motions, can be quite safe but will appear very insecure to the occupant standing next to on 40 floors above the street.
    Sometimes the architect must make deliberate attempts to increase the apparent strength or solidness of the structure. This apparent safety may be more important than honestly expressing the building’s structure, because the untrained viewer cannot distinguish between real and perceived safety.
    The building designer needs to understand the behavior lf physical structures under load. An ability to intuit or “feel” structural behavior is possessed by those having much experience involving structural analysis, both qualitative and quantitative. The consequent knowledge of how forces, stresses, and deformations build up in different materials and shapes is vital to the development of this “sense”.
    Structural analysis is the process of determining the forces and deformations in structures due to specified loads so that the structure can be designed rationally, and so that the state of safety of existing structures can be checked.
    In the design of structures, it is necessary to start with a concept leading to a configuration which can then be analyzed. This is done so members can be sized and the needed reinforcing determined, in order to: a) carry the design loads without distress or excessive deformations (serviceability or working condition ); and  b)to prevent collapse before a specified overload has been placed on the structure(safety or ultimate condition).
    Since normally elastic conditions will prevail undue working loads, a structural theory based on the assumptions of elastic behavior is appropriate for determining serviceability conditions. Collapse of a structure will usually occur only long after the elastic range of the materials has been exceeded at critical points, so that an ultimate strength theory based on the inelastic behavior of the materials is necessary for a rational determination of the safety of a structure against collapse. Nevertheless, an elastic theory can be used to determine a safe approximation to the strength of ductile structures (the lower bound approach of plasticity), and this approach is customarily followed in reinforced concrete practice. For this reason only the elastic theory of structures is pursued in this chapter.
    Looked at critically, all structures are assemblies of three-dimensional elements, the exact analysis of which is a forbidding task even under ideal conditions and impossible to contemplate under conditions of professional practice. For this reason, an important part of the analyst’s work is the simplification of the actual structure and loading conditions to a model which is susceptible to rational analysis.
    Thus, a structural framing system is decomposed into a slab and floor beams which in turn frame into girders carried by columns which transmit the loads to the foundations. Since traditional structural analysis has been unable to cope with the action of the slab, this has often been idealized into a system of strips acting as beams. Aldo, long-hand method have been unable to cope with three-dimensional framing systems, so that the entire structure has been modeled by a system of planar subassemblies, to be analyzed one at a time. The modern matrix-computer methods have revolutionized structural analysis by making it possible to analyze entire systems, thus leading to more reliable predictions about the behavior of structures under loads.
    Actual loading conditions are also both difficult to determine and to express realistically, and must be simplified for purposes of analysis. Thus, traffic loads on a bridge structure, which are essentially both of dynamic and random nature, are usually idealized into statically moving standard trucks, or distributed loads, intended to simulate the most severe loading conditions occurring in practice.
     The most important use of structural analysis is as a tool in structural design. As such, it will usually be a part of a trial-and error procedure, in which an assumed configuration with assumed dead loads is analyzed, and the members designed in accordance with the results of the analysis. This phase is called the preliminary designed ; since this design is still subject to change, usually a crude, fast analysis method is adequate. At this stage, the cost of the structure is estimated, loads and member properties are revised, and the design is checked for possible improvements. The changes are now incorporated in the structure, a more refined analysis is performed, and the member design is revised. This project is carried to convergence, the rapidity of which will depend on the capability of the designer. It is clear that a variety of analysis methods, ranging from” quick and dirty to exact”, is needed for design purposes.
 An efficient analyst must thus be in command of the rigorous methods of analysis, must be aware of available design and analysis aids, as well as simplifications permitted by applicable building codes. An up-to-date analyst must likewise be versed in the bases of matrix structural analysis and its use in digital computers as well as in the use of available analysis programs or software



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