Journal of Constructional Steel Research 65 (2009) 314–325 Contents lists available at ScienceDirect Journal of Constructional Steel Research journal homepage: www.elsevier.com/locate/jcsr Self-centering MRFs with bottom flange friction devices under earthquake loading J. Iyama a,b,∗ , C-Y. Seo b , J.M. Ricles b , R. Sause b a Department of Architecture, Graduate school of Engineering, The University of Tokyo, Japan b ATLSS Center, Department of Civil and Environmental Engineering, Lehigh University, PA, USA article info Article history: Received 28 September 2007 Accepted 20 February 2008 Keywords: Post-tensioning Self-centering moment resisting frame Friction Steel moment connection abstract A bottom flange friction device (BFFD) has been developed as an energy dissipation device for self- centering post-tensioned steel beam-to-column connections for moment-resisting frames (MRFs). The BFFD is located beneath the beam to avoid interference with a floor slab. Since the BFFD is attached to only one flange, a connection with a BFFD has an asymmetric behavior with different positive and negative moment capacities. To investigate the behavior of a self-centering MRF with BFFDs, static and dynamic analyses were performed, and the results were compared to those of a similar frame with connections that have a symmetric behavior. It was found that the asymmetric behavior of the MRF with BFFDs leads to increased inelastic strain in the beam top flange, which may lead to beam flange buckling. These inelastic strains can be reduced by using longer top flange reinforcing plates. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Recent major earthquakes (e.g., 1994 Northridge Earthquake, 1995 Kobe earthquake and 1999 ChiChi earthquake) showed that improved steel moment resisting frame (MRF) connections were needed to prevent unexpected premature fractures in their welded beam-to-column connections. Improved welded connection details were developed [1,2, e.g.,], however, the use of these improved MRF connections will not prevent damage and permanent drift in the MRF during a major earthquake. To avoid damage and permanent drift in MRFs under earth- quake loading, Ricles et al. [3] developed a self-centering (SC) post- tensioned (PT) steel beam-to-column moment connection utilizing high-strength steel strands running parallel with the beam, with bolted top and seat angles as primary energy dissipation (ED) de- vices. Fig. 1 shows a schematic elevation of an SC MRF. The SC MRF has SC beam-to-column moment connections, where PT strands run across a number of bays and are anchored as shown in Fig. 1. It has been shown [3] that a properly designed frame with SC con- nections has a self-centering capability without damage and per- manent drift during a major earthquake, and beams and columns remain essentially elastic while ED devices provide energy dissipa- tion. Similar SC connections with different details have been devel- oped by Christopoulos et al. [4], who utilized plastic deformation of ∗ Corresponding address: 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan. Tel.: +81 3 5841 6191; fax: +81 3 5841 6189. E-mail address: iyama@arch.t.u-tokyo.ac.jp (J. Iyama). Fig. 1. Schematic elevation of self-centering post-tensioned frame. steel bars for energy dissipation. ED devices used in both systems become damaged and need to be replaced after the earthquake. To overcome this disadvantage of these ED devices, the use of friction devices has been investigated. These devices are not damaged and would not need to be replaced after the design- level earthquake. Morgen and Kurama [5] showed that friction devices are as effective as the energy dissipation device for SC MRFs. Rojas et al. [6] proposed a post-tensioned friction damped connection (PFDC) for SC MRFs, where friction devices are located along the top and bottom flanges of the beams, as shown in Fig. 2(a). Rojas et al. [6] compared the seismic response of a SC MRF with PFDCs (PFDC-MRF shown in Fig. 5, and discussed later) with the response of a MRF with conventional welded connections (FR- MRF). Both MRFs were subjected to an ensemble of eight ground motions scale to the design basis earthquake (DBE) and maximum considered earthquake (MCE) hazard levels. The MCE has a 2% probability of exceedance in 50 years [7]. The intensity of the DBE is 2/3 the intensity of the MCE [7]. Rojas et al. [6] reported that for some ground motions the PFDC-MRF developed a larger drift response, however, even when the PFDC-MRF developed a 0143-974X/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcsr.2008.02.018