Effect of Minor Variations in Characteristics of Beam on the Safety of 2D Steel Moment Frame under Dynamic Loads

Document Type : Research Article


1 University of Qom

2 Civil Engineering, University of Qom, Qom, Iran


Increasing the strength of members or enhancing the redundancy does not jeopardize the overall safety of the structure. This can be proved under static loads by the safe theorem, which is one of the fundamental theories of plastic analysis. Although this theorem has not been proved in the case of dynamic loads, it has been widely applied to the design of systems under dynamic loads. Therefore, this paper aims to make use of the results of this theorem in the numerical analysis of structures subjected to dynamic loads. Since the structural instability mechanism and collapse do not occur under transient loads, an adequate level of ductility demand has been assigned to the structural components to ensure the safety of the structure. For this purpose, the plastic rotation of the members is determined after a minor variation in strength and stiffness of the beams in a 2D five-story steel moment-frame structure by performing dynamic analysis. To compare the ductility demand obtained by the dynamic analysis with the criteria values, the performance of the structure is also evaluated by conducting nonlinear static analysis. The analysis results showed that the increase in the strength of the beam members generally leads to a lower ductility demand; however, in some cases, the maximum ductility demand increased by about 7.3%. With the increase in the stiffness of the beams, the ductility demand increased by up to 16%. It can be concluded that with the increase in the stiffness and strength of the beams, a lower ductility demand is obtained by the dynamic analysis compared to the static analysis, and thus the structural collapse has not occurred under dynamic loads.


Main Subjects

[1] Drucker, D.C., Greenberg, H.J., Prager, W., 1951. In: J1. Appl. Mech.
[2] Greenberg, H.J., Prager, W., 1951. Journ. Struct. Div., Prec. ASCE.
[3] Baker, J., Baker, L., Heyman, J., 1980. Plastic design of frames 1 fundamentals, CUP Archive.
[4] Aziminejad, A., Moghadam, A., 2007. “Effects of strength distribution on fragility curves of asymmetric single story building”, Proceedings of the Ninth Canadian Conference on Earthquake Engineering Ottawa. Ontario, Canada.
[5] Eshghi, S., Maki abadi, M., 2013, “Developing Theoretical Fragility Curves for Conventional Mid-rise Concrete Buildings in Iran”, University of Science & Culture, Tehran. (in Persian)
[6] Mosleh, A., Rodrigues, H., Varum, H., Costa, A., 2016. Arêde, A., “Seismic behavior of RC building structures designed according to current codes”, Structures. 7, 1-13.
[7] Faisal, A., Majid, T.A., Hatzigeorgiou, G.D., 2013. “Investigation of story ductility demands of inelastic concrete frames subjected to repeated earthquakes”, Soil Dynamics and Earthquake Engineering. 44, 42-53.
[8] Samimifar, M., Oskouei, A.V., Rofooei, F.R., 2015. “Deflection amplification factor for estimating seismic lateral deformations of RC frames”, Earthquake Engineering and Engineering Vibration. 14(2), 373-384.
[9] Christidis, A.A., Dimitroudi, E.G., Hatzigeorgiou, G.D., Beskos, D.E., 2013. “Maximum seismic displacements evaluation of steel frames from their post-earthquake residual deformation”, Bulletin of Earthquake Engineering. 11(6), 2233-2248.
[10] Azhdarifar, M., Meshkat-Dini, A., 2015. “Study on the Seismic Response Parameters of Modular Tube Steel Mid-Rise Buildings under Effects of Near Field Ground Motions”, SID. (in Persian)
[11] Sivandi-Pour, A., Gerami, M., Taghdisi, M., 2019. “Assessment of the effect of column base connection rotational stiffness on seismic behaviour of the steel moment frames”, Sharif journal of civil engineering. 35.2, 2.1, 83-92. (in Persian)
[12] Stillmaker, K., Lao, X., Galasso, C., Kanvinde, A., 2017. “Column splice fracture effects on the seismic performance of steel moment frames”, Journal of Constructional Steel Research. 137 93-101.
[13] Stillmaker, K., Magdaleno, A., Nazari, M., Kanvinde, A., 2018. “Assessment of column splice fracture influence on seismic performance of steel moment frames”, Eleventh U.S. National Conference on Earthquake Engineering. 25-29.
[14] Song, B., Galasso, C., Kanvinde, A., 2019. “Advancing fracture fragility assessment of pre‐Northridge welded column splices”, Earthquake Engineering & Structural Dynamics.
[15] Instruction for Seismic Rehabilitation of Existing Buildings (No. 360), 2005. Management and Planning Organization Office of Deputy for Technical Affairs, Tehran.