Case Study on Seismic Performance of Soft Stories in Short Steel Structures and Replacement of Braces with Equivalent Moment Resisting Frame

Document Type : Research Article

Authors

Civil Engineering Department, Sadra Institute of Higher Education, Tehran, Iran

Abstract

Many of changes in ground floor of buildings may result in elimination of braces.This phenomenan, which called “soft story”, decreases the stiffness of stories and leads to collapse of building under severe earthquakes. Study of last earthquakes such as Bam on December 26 ,2003 and chichi-Thaiwan on September 20 ,1999 shows that many peaple missed their life because of soft stories created due to elimination of structural infills by changing residential buildings to commercial or architectural reasons.
In this research, the soft story studied in short steel buildings with four stories by removing X-braces at first and second stories using nonlinear static and dynamic analyses. After removing braces, the stiffness of soft story increased gradually by providing rigid connections and using moment resisting frame and the replacement of braces with equivalent moment frame (with different stiffnessess) studied. The seismic design parameters such as transient and inherent dissplacements, ductility and energy dissipation capacity calculated and compared in various diagrames. In addition, the sttiffness of X-braced and moment resisting frames calculated using classical relations of solid mechanics and discussed. According toobtained results, the replacement of X-braces by an equivalent moment frame in a building leads to excessive drifts and less energy dissipation capacity. In addition, the findings of this paper is coin with specification requirements to avoid soft stories in buildings by avoiding stories with stiffness of 70 percent relative to above story.

Keywords

Main Subjects

References

[1] Wibowo, A., et al. (2010). "Collapse modelling analysis of a precast soft storey building in Australia." Engineering Structures 32(7): 1925-1936.
[2] Moehle, J. P. and L. F. Alarcon (1986). "Seismic analysis methods for irregular buildings." Journal of Structural Engineering 112(1): 35-52.
[3] Valmundsson, E. V. and J. M. Nau (1997). "Seismic response of building frames with vertical structural irregularities."Journal of Structural Engineering 123(1): 30-41.
[4] Chintanapakdee, C. and A. K. Chopra (2004). "Seismic response of vertically irregular frames: response history and modal pushover analyses." Journal of Structural Engineering 130(8): 1177-1185.
[5] Le-Trung, K., et al. (2008). Seismic Behavior and Evaluation of Steel SMF Buildings with Vertical Irregularities. 14th World Conference on Earthquake Engineering, China.
[6] Pirizadeh, M. and H. Shakib (2013). "Probabilistic seismic performance evaluation of non-geometric vertically irregular steel buildings." Journal of Constructional Steel Research 82: 88-98.
[7] Ghale-Noei, M., et al. (2011). Evaluation of the Effect of Soft-story on Performance of Structures with the Capacity Spectrum Approach. Sixth National Conference on Civil Engineering, Semnan, Iran.
[8] Code-2800 (2006). Iranian Code of Practice for Seismic Resistant Design of Buildings, Standard No. 2800, Road, Housing and Urban Development Research Center.
[9] National-Code (2005). National Building Code of India. Structural Design.
[10] National-Code (2002). National Standard of the Peaple ‘s Repubic of China. Code of Seismic Design of Buildings.
[11] ASCE7 (2010). Minimum Design Loads for Buildings and other Structures.
[12] Turkish-Standard (2007). Turkish_Earthquake_Code.
[13] Eurocode-8 (2003). Design of structures for earthquake resistance.
[14] National-Code (2006). "National Iranian Code No. 6."
[15] Silva, P. and S. Badie (2008). "Optimum beam-tocolumn stiffness ratio of portal frames under lateral loads." Struct. Mag.
[16] FEMA356 (2000). Prestandard and Commentary for the Seismice Rehabilitation of Buildings.
[17] Taghinejad, R. (2010). Design and seismic rehabilitation of structures based on performance using pushover analysis.
[18] http://peer.berkeley.edu.
[19] ATC40 (1996). "Seismic evaluation and retrofit of concrete buildings." Applied Technology Council, report ATC-40. Redwood City.
Amirkabir Journal of Civil Engineering
Volume 49, Issue 2
August 2017
Pages 237-250

Files

Share

How to cite

Statistics