تفاوت روش‌های طراحی بر اساس نیرو و تغییر مکان در قاب‌های خمشی بتنی در برابر زلزله

نوع مقاله : Articles

نویسندگان

1 گروه مهندسی عمران، دانشکده مهندسی، دانشگاه کاشان

2 دانشگاه کاشان

3 دانشگاه سمنان

چکیده

امروزه روش‌های طراحی بر اساس عملکرد با دو رویکرد مستقیم و غیرمستقیم انجام می‌شوند. در رویکرد مستقیم، ویژگی‌ها و مشخصاتی مثل مکانیسم مطلوب، میزان دوران مفاصل، تغییر مکان نسبی طبقه هدف و محدودیت کرنش مصالح که متناظر با سطح عملکرد مورد نظر هستند از همان ابتدا در فرآیند تحلیل و طراحی گنجانده شده‌اند. یکی از روش‌های طراحی بر اساس عملکرد با رویکرد مستقیم، طراحی مستقیم بر اساس تغییر مکان است که در آن سازه با فرض مکانیسم و عملکرد مطلوب تحلیل و طراحی می‌شود. در این پژوهش ابتدا مبانی روش طراحی مستقیم بر اساس تغییر مکان بیان شده و سپس قاب‌های خمشی بتنی ۴، ۸، ۱۲ و ۱۶ طبقه با روش طراحی بر اساس نیرو و این روش، طراحی شده‌اند که مقایسه‌ی آنها نشان می‌دهد ستون قاب‌های روش تغییر مکان ابعاد بزرگ‌تر یا مساوی و آرماتور خمشی بیشتری نسبت به ستون قاب‌های روش نیرو دارند. علاوه ‌بر این میزان آرماتور وسط دهانه‌ی تیرهای قاب‌های روش تغییر مکان نسبت به دو انتهای آن (محل‌های احتمالی تشکیل مفاصل پلاستیک) بیشتر است. همچنین در ستون قاب‌های طراحی‌شده با روش طراحی مستقیم بر اساس تغییر مکان نسبت به طراحی بر اساس نیرو وزن کل بتن به‌کار رفته تا ۲۸ درصد و وزن آرماتور به‌کار رفته ۴۵ تا ۸۲ درصد بیشتر است، حال آن‌که در تیرها وزن بتن به‌کار رفته تا ۱۸ درصد کمتر و وزن آرماتور به‌کار رفته ۳ تا ۳۱ درصد بیشتر است.

کلیدواژه‌ها


عنوان مقاله [English]

Difference of Force-Based and Displacement-Based Seismic Design of RC Frames

نویسندگان [English]

  • Hassan Ostadhossein 1
  • Seyed Mohammad Hossein Kamel 2
  • Mojtaba Henteh 3
1 Department of Civil Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran
2 Department of Civil Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran
3 Department of Civil Engineering, University of Semnan, Semnan, Iran
چکیده [English]

Considering the performance of a structure in design procedure as an initial explicit and primary assumption is a valuable achievement, which enable the client to decide about acceptable cost and risk. In traditional Force Based Design (FBD) method after limitation of internal forces to the strength limits of members, performance of a structure will be checked as a secondary goal of design procedure. While actually it is the damage level that is defined by desired performance, it is the main concern of design as well. Performance based design methods are categorized into direct and indirect approach. In direct approach, in spite of indirect one, structure features and characteristics are predefined such that the desired mechanism, rotation of hinges, target story drift and material strain limits correspond to the desired performance level, have been included from the beginning of the analysis and design process. Direct Displacement Based Design (DDBD) is a direct performance method in which desired mechanism of inelastic deformation and optimal performance for frames are considered as initial and essential assumptions of the design procedure. According to predefined acceptable total drift of the structure as an index of performance, base shear will be determined by using displacement spectra considering nonlinearities and damping effects. After that, the calculated base shear will be distributed throughout the stories of structure according to predominant mode shapes. Internal forces of structural members will be calculated based on a plastic analysis considering assumed mechanism. In this paper, four concrete special moment frames with two 5 m bays and 4, 8, 12 and 16 stories with height of 3 m were designed by direct displacement based method and were compared with force based design method results. According to base shear calculation relation of DDBD, it is required to predefine the total drift as a performance indicator. The total drift for life safety performance level is suggested to be 2% in FEMA 356 for concrete moment resistant frame. It was observed that DDBD base shear was greater than FBD one. Besides, by increasing the height of the structure, the difference of base shear in DDBD and FBD become greater. It was concluded that columns dimensions and longitudinal reinforcement of DDBD are equal or greater than FBD. As a general conclusion, it has been understood that the issue of weak ductile beam against strong column that is the main design topic in special moment frame design is more feasible in DDBD approach. In fact, in direct displacement based design procedure, plastic hinges are assumed to be formed in beams ends, explicitly. This consideration leads DDBD columns to have more concrete volume and longitudinal reinforcement weight compared to FBD columns. Moreover, beams of DDBD have longitudinal reinforcement weight more than FBD beams but they have less concrete weight. In addition, it was observed that in DDBD method, obtained reinforcement arrangement in columns and beams and section dimensions are such that the formation of hinges in columns or beams mid span is prevented. Finally, it is concluded that DDBD leads to a more efficient design.

کلیدواژه‌ها [English]

  • Direct Displacement-Based Design (DDBD)
  • Force-Based Design (FBD)
  • Concrete Moment Frame
  • Base Shear
  • Favorable Mechanism
  1. Priestley, M. (2000) Performance based seismic design. Bulletin of the New Zealand Society for Earthquake Engineering, 33, 325-346.
  2. Bertero, V.V. (2000) Performance-based seismic engineering: conventional vs. innovative approaches. Proc. Memorias 12vo Congreso Mundial de Ingenieria Sismica.
  3. GCR, N. (2009) Research Required to Support Full Implementation of Performance-Based Seismic Design. Washington, DC.
  4. Sejal, D.P., Vasanwala, S. and Desai, A. (2011) Performance based seismic design of structure: A review. International Journal of Civil and Structural Engineering, 1, 795.
  5. Priestley, M., Calvi, G. and Kowalsky, M. (2007) Direct displacement-based seismic design of structures. Proc. 5th New Zealand Society for Earthquake Engineering Conference.
  6. Shibata, A. and Sozen, M.A. (1976) Substitute-structure method for seismic design in R/C. Journal of the Structural Division, 102, 1-18.
  7. Dwairi, H.M., Kowalsky, M.J. and Nau, J.M. (2007) Equivalent damping in support of direct displacement-based design. Journal of Earthquake Engineering, 11, 512-530.
  8. Blandon, C.A. (2004) Equivalent Viscous Damping Equations for Direct Displacement Based Design‏ .Master, Rose School.
  9. Pettinga, J.D. and Priestley, M.N. (2005) Dynamic Behaviour of Reinforced Concrete Frames Designed with Direct Displacement-Based Design. Master, Rose School.
  10. Della Corte, G. and Mazzolani, F. (2008) Theoretical developments and numerical verification of a displacement-based design procedure for steel braced structures. Proc. Proceedings of the 14th world conference on earthquake engineering, Beijing, 12-17.
  11. Pennucci, D., Calvi, G. and Sullivan, T. (2009) Displacement-based design of precast walls with additional dampers. Journal of Earthquake Engineering, 13, 40-65.
  12. Sullivan, T.J. (2009) Direct displacement-based design of a RC wall-steel EBF dual system with added dampers. Bulletin of the New Zealand Society for Earthquake Engineering, 42, 167.
  13. Garcia, R., Sullivan, T.J. and Corte, G.D. (2010) Development of a displacement-based design method for steel frame-RC wall buildings. Journal of Earthquake Engineering, 14, 252-277.
  14. Maley, T.J., Sullivan, T.J. and Corte, G.D. (2010) Development of a displacement-based design method for steel dual systems with buckling-restrained braces and moment-resisting frames. Journal of Earthquake Engineering, 14, 106-140.
  15. Sullivan, T. and Lago, A. (2012) Towards a simplified direct DBD procedure for the seismic design of moment resisting frames with viscous dampers. Engineering Structures, 35, 140-148.
  16. Sullivan, T.J. (2013) Direct displacement-based seismic design of steel eccentrically braced frame structures. Bulletin of Earthquake Engineering, 11, 2197-2231.
  17. Ostad Hossein, H., Kamel, S. and Henteh, M. (2017) Performance of concrete moment resisting frames of direct displacement based against force based design. Journal of Structural and Construction Engineering (in Persian).
  18. Peng, C. and Guner, S. (2018) Direct displacement-based seismic assessment of concrete frames. Computers and Concrete, 21, 355-365.
  19. Muljati, I., Kusuma, A. and Hindarto, F. (2015) Direct displacement based design on moment resisting frame with out-of-plane offset of frame. Procedia Engineering, 125, 1057-1064.
  20. Priestley, M., Grant, D.N., and Blandon, C.A. (2007) Direct displacement-based seismic design. Proc. 2005 NZSEE Conference.
  21. FEMA, P. (2000) 'Commentary for the seismic rehabilitation of buildings'. In: Book Commentary for the seismic rehabilitation of buildings, Washington, DC.
  22. Priestley, M., Calvi, G. and Kowalsky, M. (2007) Displacement‐based seismic design of structures. 1st edn. IUSS Press, Pavia, Italy.
  23. ACI (2014) Building Code Requirements for Structural Concrete (ACI 318-14) and Commentary (ACI 318R-14). American Concrete Institute.
  24. ASCE (2010) Minimum Design Loads for Buildings and Other Structures (ASCE 7-10). American Society of Civil Engineers.
  25. Bommer, J.J., and Elnashai, A.S. (1999) Displacement spectra for seismic design. Journal of Earthquake Engineering, 3, 1-32.
  26. Massena, B., Bento, R., Degee, H. and ICIST, R. (2010) 'Direct Displacement Based Design of a RC Frame–Case of Study'. In: Direct Displacement Based Design of a RC Frame–Case of Study.
  27. Massena, B., Bento, R. and Degee, H. (2012) Assessment of Direct Displacement–Based Seismic Design of Reinforced Concrete Frames. Proc. 15th WCEE Conference.
  28. Paulay, T. (1995) The philosophy and applications of capacity design. 2nd International Conference On Seismology and Earthquake Engineering, Tehran, Sharif University of Technology.