英文翻译2020届毕业设计17

1、Copyright ASCE 2004Structures 2000 Advanced Technology in Structural Engineering Robustness and Redundancy Design for Tall Buildings Ahmad K.Abdelrazaq Robert C.Sinn Abstract Post-modern architecture has moved significantly from directly expressing the structural systems of tall buildings, which sym

2、bolized their strength and stability.Tall buildings have become more slender, require large open views along their perimeter, include multiple setbacks, and have been proposed for regions with potentially large wind forces and seismic events. These factors have influenced structural system selection

3、 significantly. In an effort to reduce the structural cost, and to resist overturningforces,several structural systems have been proposed that are nearly determinate andthushave relatively little redundancy. These structures are highly efficient, from a material expenditure standpoint. The issue of

4、redundancy as it relatestotheunderlying robustness of the structural system has traditionally been left to the discretion of the individual engineer. Unlike highly redundant framed tube structures such as the Sears Tower, Chicago, and the World Trade Center Towers, New York, unpredictableevents and

5、design forces, including acts of terrorism, could have a large impact on these nearly determinate systems. Research is needed to study the approach and philosophy that engineers should adopt to evaluate the redundancy and robustness of these systems and toestablishdesigncriteria. Computer Technology

6、 and StructuralSystem Optimizations Present computer technology and readily available commercial programs have allowed structural engineers to develop and propose structural systems that would not have been attempted even a few decades ago. During the 1960 s and early1970 s,structural engineers prop

7、osed systems that could be computed by simplemethodsduetothe limited capacity of high speed computers at that time. While these structural systems were innovative and sophisticated, their structural behaviors were also simple to understand, analyze, and construct. The simplicity and the purity of th

8、ese structural systems led to the integration of the structural solution and the architectural expression. While the structural solution is critical in tall building planning, the present architectural approach to tall building design is beginning to lean toward finding an architectural design witho

9、ut regard to the structural requirements at the early stage ofthedesign. Commercially available structural engineeringsoftware has allowed engineers to propose 1 Downloaded from by Nanjing University of Technology on 01/13/13. Copyright ASCE.Forpersonal use only; all rights reserved.

10、 Copyright ASCE 2004Structures 2000 Advanced Technology in Structural Engineering structural system solutions where the fundamental behavior is at times a complicated interaction of sub-systems and materials. Optimizing such systems is limited to member size refinement rather than an overall system

11、optimization. Computer optimization programs and methods allow engineers to eliminate the structural material fatand redistribute the structural material to the most efficient location in resisting the lateral forces (see Figure 1) 1. These optimization programs may often lead to the elimination of

12、some members. Thus, in the search for structural optimization, highly sophisticated optimization programs may create more determinate systems. The structural engineering effort at the early stage of the design might be better limited to overallsystem optimization rather than member optimizations on

13、one selected structuralconcept. System optimization can be viewed as the art of distributing the structural material to resist gravity loads with minimum premium for resisting lateral and stability load requirements. Overall system optimization can be performed without affecting the redundancy and r

14、obustness of the design. ImpactofPresentMaterialsandConstructionMethodsonStructuralSystemSelections Technological advances and the introduction of new materials have alwaysbeenthe source of structural system innovation in tall buildings. Present concretematerial technologies have allowed the advance

15、ment of new structural systems thatwere previously not thought possible. The use of composite steel/high strength concrete elements has lead into the development of innovative and veryefficientstructural systems that consist of mega-braced frame systems. In thesemega-structures,the majority of the b

16、uilding design loads are supported by a few mega-columns,that are located at the perimeter of the building to maximize the effective moment of inertia and the resistance of the building to lateral and stability loads. The overturning moments are typically resisted efficiently by the axial deformatio

17、n of the mega-columns and the lateral and stability horizontal shears are resisted by a structural steel bracing system between themega-columns. When these structural principles are used with the latest developments in high strength concrete and concrete construction technology, it is possible to de

18、velop reinforced concrete systems that have very clear structural behavior, are economical, easyto construct, detail, and design. The reinforced concrete elements of these systems are proportioned so that the gravity load flow is channeled to the members, which also resist lateral loads. The structu

19、ral system optimization is thus achieved in concept andvery little computation is required other than the detailed verification ofthestructural elements. The reinforced concrete stiffened web system is an example of a system that allowsfor the flow of gravity loads to the mega-columns, or a series b

20、undled columns, without needing a major transfer system. See Figure 2 for an illustration ofthisstructural concept2. The reinforced concrete members in the stiffened shear panel are nearly the 2 Downloaded from by Nanjing University of Technology on 01/13/13. Copyright ASCE.Forperson

21、al use only; all rights reserved. Copyright ASCE 2004Structures 2000 Advanced Technology in Structural Engineering same size throughout the building height. In addition, the use of high strength concrete has allowed reduction in the mega-concrete column sizes, thus increasing the vulnerability of th

22、ese members, in the case of unpredictable events. Research for such systems should be focused on the minimum stiffness required for the stiffened shear panel system to maintain a minimum level of redundancy and robustness in the overall system. Smart materials are beginning to be developed that alte

23、r the fundamental building dynamic characteristics providing additional stiffness, strength, or damping. Incorporating these materials for the shear panel between the mega-columns could be of great benefit to the structural behavior of the system. Research is needed, however, to study the short and

24、long term behavior of these efficient structural systems. Redundant Systems vs. OptimumSystems The late Dr. Falzur R. Khan, former partner at Skidmore Owings all rights reserved. Copyright ASCE 2004Structures 2000 Advanced Technology in Structural Engineering ReviewofCodeRequirementsforRobustnessand

25、Redundancy Present building codes address the issue of redundancy through minimum design and detailing requirements. In addition, building codes provide a limit on selecting structural systems depending on the characteristics of the building including its height and geometric characteristics. Innova

26、tions in structural engineering often extend the building system beyond the current limits of the code. In such instances, engineers are left with the necessity to create their own criteria. Both the city of London, England, and New York City building codes 3,4, among others, identify key structural

27、 elements which require special design provisions to prevent progressive collapse under abnormal load. The New York City code identifies critical elements as supporting 1,000 square feet horizontally over at least three stories, while the city of London building regulations specify elements supporti

28、ng at least 70 square meters of tributary area. In each case the designer is left with an option of either providing an alternate load path for the key elements in case of failure, or designing the element to receive an equivalent static pressure of 5 psi (34 KN/m2) applied over the projecting surfa

29、ces of the element. In either case, redundancy and robustness is designed into the system of the key structural elements. The latest analytical and computational research in blast-resistant design may be brought to bear in critical instances to determine the level of vulnerability of key structural

30、elements in tall buildings. Some of the latest building codes address the issues of redundancy and minimum stiffness requirements for damped systems. However, these minimumrequirementsmaynot apply to special projects and special structural systems, such as supertall buildings, in which the code prov

31、isions could be extended. Conclusion With the aid of continued improvements in structural materials and constructionmethods, many forward-thinking structural engineers are proposing unique, innovative, and efficient systems for tall buildings in the future. While developing suchsystems,structural en

32、gineers are challenged to ponder the unexpected and ensure the ultimate safety of the building and its occupants in an extreme event. Research is needed to better understand the impact of such unlikely scenarios on individual members and entire systems. This research would likely involve input from

33、many members of the design and building community including structural engineers, architects, and experts in the field of materials technology, blast protection, and uncertainty analysis. The result of such research would be a more rational approach to the issue of redundancy and robustness in tall

34、building structuraldesign. 4 Downloaded from by Nanjing University of Technology on 01/13/13. Copyright ASCE.Forpersonal use only; all rights reserved. Copyright ASCE 2004Structures 2000 Advanced Technology in Structural Engineering References 1WilliamF. Baker, Lawrence C. Novak, Robert C. Sinn, John R. Viise, Structural Optimization of 2000 Tal