Probabilistic Seismic Assessment of Moment Resisting Steel Buildings Considering Soft-story and Torsional Irregularities

Document Type : Original Article


1 Department of Civil Engineering Faculty, University of Semnan, Semnan, Iran

2 Department of civil engineering, Shahrood University of Technology, Shahrood, Iran


In this study, the fragility curves were developed for three-, five-, and eight-story moment resisting steel frame structures with considering soft story and torsional irregularities during the earthquake mainshock to assess the probabilistic effects of irregularities in plan and height of steel structures. These models were designed according to Iranian seismic codes. 3D analytical models of steel structures were created in the OpenSees software platform and Incremental Dynamic Analysis (IDA) was conducted to plot the IDA curves. The maximum value of inter-story drift was selected as the demand parameter and the capacity is determined according to the HAZUS-MH limit states; and finally, the corresponding fragility curves were developed. The results of the 3D nonlinear dynamic analysis indicated that the damage state of the structure due to soft story irregularity was decreased with increasing stories. On the other hand, the damage caused by torsional irregularity in plan was increased by increasing the height of the structure. For example, in the 3-story structure, soft-story effect on damage probability was more dominant than torsional irregularity.


  1. Pahlavan, H., Zakeri, B. and Ghodrati Amiri, G., "Probabilistic performance assessment of retrofitted horizontally curved multi-frame rc box-girder bridges", Journal of Earthquake and Tsunami, Vol. 11, No. 04, (2017), 1750010,
  2. Kennedy, R.P., Cornell, C.A., Campbell, R., Kaplan, S. and Perla, H., "Probabilistic seismic safety study of an existing nuclear power plant", Nuclear Engineering and Design, Vol. 59, No. 2, (1980), 315-338,
  3. Kircher, C.A., Nassar, A.A., Kustu, O. and Holmes, W.T., "Development of building damage functions for earthquake loss estimation", Earthquake spectra, Vol. 13, No. 4, (1997), 663-682,
  4. Anagnos, T., Rojahn, C. and Kiremidjian, A.S., "Nceer-atc joint study on fragility of buildings", (1995),
  5. Ozturk, B., Sahin, H.E. and Yildiz, C., "Seismic performance assessment of industrial structures in turkey using the fragility curves", in 15th World Conference on Earthquake Engineering, Lisbon, Portugal. (2012), 1-7.
  6. Naseri, A., Pahlavan, H. and Ghodrati Amiri, G., "Probabilistic seismic assessment of rc frame structures in north of iran using fragility curves", Journal of Structural and Construction Engineering, Vol. 4, (2018), 58-78, doi: 10.22065/JSCE.2017.78827.1095. .
  7. Pahlavan, H., Shaianfar, M., Ghodrati Amiri, G. and Pahlavan, M., "Probabilistic seismic vulnerability assessment of the structural deficiencies in iranian in-filled rc frame structures", Journal of Vibroengineering, Vol. 17, No. 5, (2015), 2444-2454,
  8. Ozturk, B., "Seismic behavior of two monumental buildings in historical cappadocia region of turkey", Bulletin of Earthquake Engineering, Vol. 15, No. 7, (2017), 3103-3123,
  9. Hwang, S.-H. and Lee, K., "Probabilistic seismic demand assessment of steel moment-resisting frame buildings with ordinary and essential occupancy uses", International Journal of Steel Structures, Vol. 20, (2020), 1230-1240,
  10. Kassem, M.M., Nazri, F.M., Farsangi, E.N. and Ozturk, B., "Improved vulnerability index methodology to quantify seismic risk and loss assessment in reinforced concrete buildings", Journal of Earthquake Engineering, (2021), 1-36, doi.
  11. Fattahi, F. and Gholizadeh, S., "Seismic fragility assessment of optimally designed steel moment frames", Engineering Structures, Vol. 179, (2019), 37-51,
  12. Taiyari, F., Mazzolani, F.M. and Bagheri, S., "Damage-based optimal design of friction dampers in multistory chevron braced steel frames", Soil Dynamics and Earthquake Engineering, Vol. 119, (2019), 11-20,
  13. County, C., "Federal emergency management agency", FEMA Community, No. 170132, (2013).
  14. Abkar, G. and Lorki, A.A., "Evaluation of progressive collapse in steel structures designed based on iranian code of practice for seismic resistant design buildings (standard no. 2800), and iranian national building code'inbc', part 10", Journal of civil Engineering and Materials Application, Vol. 2, No. 4, (2018), 192-200.
  15. Trombly, B., "The international building code (ibc)", CMGT 564-Term Paper, (2006),.
  16. ASCE, "Minimum design loads for buildings and other structures, American Society of Civil Engineers. Vol., No., (2005).
  17. Malley, J.O., "The 2005 aisc seismic provisions for structural steel buildings", Engineering Journal-American Institute of Steel Construction, Vol. 44, No. 1, (2007).
  18. Lignos, D.G., Krawinkler, H. and Whittaker, A.S., "Prediction and validation of sidesway collapse of two scale models of a 4‐story steel moment frame", Earthquake Engineering & Structural Dynamics, Vol. 40, No. 7, (2011), 807-825,
  19. Mander, J.B., Priestley, M.J. and Park, R., "Theoretical stress-strain model for confined concrete", Journal of Structural Engineering, Vol. 114, No. 8, (1988), 1804-1826, doi.
  20. Li, Y., Song, R. and Van De Lindt, J.W., "Collapse fragility of steel structures subjected to earthquake mainshock-aftershock sequences", Journal of Structural Engineering, Vol. 140, No. 12, (2014), 04014095,
  21. Banazadeh, M. and Jalali, S.A., "Probabilistic seismic demand assessment of steel moment frames with sideplate connections", Amirkabir Journal of Civil Engineering, Vol. 44, No. 2, (2013), 47-64,