Assessment of Spectrum Modification Factor for Design of Steel Moment Frames in Near Fault Regions

Document Type : Original Article

Authors

1 Assistant Professor, Civil Engineering Department, Semnan University, Semnan, Iran

2 Associate Professor, Faculty of Civil Engineering, Semnan University, Semnan, Iran

3 PhD Student, Civil Engineering Department, Semnan University, Semnan, Iran

Abstract

Iranian Seismic design code (standard No. 2800) increases the design spectrum ordinates by a modification factor (N factor), to consider the damaging effects of near fault ground motions in design procedure of structures. Accordingly, the spectrum modification factor depends on fundamental period of vibration and seismicity level of the region. In this paper, the preciseness of the expression given by Iranian seismic design code for calculation of spectrum modification factor is examined and estimations are suggested for N factor by evaluating the near fault effects on inelastic seismic response of steel moment-resisting frames. For this purpose, the response spectrum shape and nonlinear seismic response of sample structures are evaluated for one set of far fault and three different sets of near fault ground motions. Incremental dynamic analysis is utilized to obtain the seismic response of the sample frames (including five steel frames with 3 to 15 stories) in various intensity levels. The results of the study demonstrate that modification factors provided by standard No. 2800 does not precisely take account the effects of near fault excitations on inelastic seismic response of steel moment-resisting frame structures. Also, it was found that there is no meaningful relationship between spectrum modification factor and structural period.

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References

[1] Building & Housing Research Center, (2015). Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No. 2800) 4th edition. Tehran.
[2] Somerville, PG. (2005). Engineering Characterization of near-fault ground motions. In: NZSEE Conference, Planning and Engineering for Performance in Earthquake. Taupo, New Zealand.
[3] Kalkan, E.; Sashi, K.; Kunnath. (2006). Effects of Fling Step and Forward Directivity on Seismic Response of Buildings. Earthquake Spectra, 22(2), 367-390.
[4] Gerami, M.; Siahpolo, N.; Vahdani, (2015)., Effects of higher modes and MDOF on strength reduction factor of elastoplastic structures under far and near-fault ground motions. Ain Shams Engineering Journal, In Press.
[5] Somerville, PG.; Smith, NF.; Graves, RW.; Abrahamson NA. (1997). Modification of empirical strong ground motion attenuation relations to include the amplitude and duration effects of rupture directivity. Seismological Research Letters, 68(1), 199–222.
[6] Alavi, B.; Krawinkler, H. (2001). Effects of near-fault ground motions on frame structures. Report No. 138. California: The John A. Blume Earthquake Engineering Center, Stanford University.
[7] Sehhati, R.; Rodriguez-Marek, A.; ElGawady, M.; William, F. (2011). Effects of near-fault ground motions and equivalent pulses on multi-story structures. Engineering Structures, 33.  767–779.
[8] Su, F.; Anderson, JG.; Zeng, Y. (2006). Characteristics of ground motion response spectra from recent large earthquakes and their com- parison with IEEE Standard 693. In: Proceedings of the 8th United States National Conference on Earthquake Engineering (8NCEE), San Francisco, CA.
[9] Gerami, M.; Abdollahzadeh, D. (2012). Estimation of forward directivity effect on design spectra in near field of fault. Journal of Basic and Applied Scientific Research, 2(1), pp. 8670–8686.
[10] Gillie, JM.; Rodriguez-Marek, A.; McDaniel, C. (2010). Strength reduction factors for near-fault forward-directivity ground motions. Engineering Structures, 32, 273–285.
[11] Soltangharaei, V.; Razi, M.; Gerami, M. (2016). Comparative Evaluation of Behavior Factor of SMRF Structures for Near and Far Fault Ground Motions. Periodica Polytechnica Civil Engineering, 60(1), 75-82.
[12] Iwan, WD. (1997). Drift spectrum: Measure of demand for earthquake ground motions. Journal of Structural Engineering, 123 (4), 397–404.
[13] Dixiong, YJP.; Gang, L. (2010). Interstory drift ratio of building structures subjected to near-fault ground motions based on generalized drift spectral analysis. Soil Dynamics and Earthquake Engineering, 30. 1182–1197.
[14] Ghobarah, A.; ElSheikh, AI. (2003). Response of structures to near-fault ground motion. In: 4th International Conference of Earthquake Engineering and Seismology. Tehran.
[15] Baker, JW. (2007). Quantitative Classification of Near-Fault Ground Motions. Bulletin of the Seismological Society of America, 97(5), 1486–1501.
[16] Shahi, SK.; Baker, JW. (2014). An efficient algorithm to identify strong velocity pulses in multi-component ground motions. Bulletin of the Seismological Society of America, 104(5), 2456–2466.
[17] Kumar, M.; Stafford, PJ.; Elghazouli, AY. (2013). Seismic shear demands in multi-storey steel frames designed to Eurocode 8. Engineering Structures, 52, 69–87.
[18] Rathje, EM.; Faraj, F.; Russel, S.; Bray, JD. (2004). Empirical relationships for frequency content parameters of earthquake ground motions. Earthq. Spectra, 20(1), 119–44.
[19] Ministry of roads and Urban Development, (213). Iranian National Building Code for Steel Structures-Part 10. Tehran.
[20] SeismoStruct. A computer program for static and dynamic analysis for framed structures, Version 7.0.4, Available in URL: www.seismosoft.com(online)(2015)
[21] Scott, MH.; Fenvese, GL. (2006). Plastic hinge integration method for force-based beam-column elements. ASCE Journal of Structural Engineering, 132(2), 244-252.
[22] Stewart, JP.; Chiou, SJ.; Bray, JD.; Graves, RW.; Somerville, PG.; Abrahamson, NA.( 2001). Ground Motion Evaluation Procedures for Performance-Based Design. Research Report Conducted Under Grant no.EEC-9701568 from the National Science Foundation. University of California: Berkeley, CA, 63–88.
[23] National Institute of Standards and Technology, NIST GCR 11-917-15, (2011). Selecting and Scaling Earthquake Ground Motions for Performing Response-History Analyses,  NEHRP Consultants Joint Venture, Page 56.
[24] Lin, KC.; Lin, CJ.; Chen, JY.; Chang, HY. (2010). Seismic reliability of steel framed buildings. Structural Safety, 32, 178-182.
[25] Baker, JW.; Cornell, CA. (2008). Vector-valued intensity measures for pulse-like near-fault ground motions. Engineering Structures, 30, 1048-1057.
 

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History

  • Receive Date: 04 February 2017
  • Revise Date: 03 June 2017
  • Accept Date: 14 June 2017

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