جستجو در تالارهای گفتگو

Cyclic Testing of Chevron Braced Steel Frames with IPE Shear Panels Seyed Mehdi Zahrai, School Civil Engineering, the University of Tehran and Research Associate at the University of Ottawa, mzahrai@ut.ac.ir (Received , Revised , Accepted ) Abstract. Despite considerable life casualty and financial loss resulting from past earthquakes, many existing steel buildings are still seismically vulnerable as they have no lateral resistance or at least need some sort of retrofitting. Passive control methods with decreasing seismic demand and increasing ductility reduce rate of vulnerability of structures against earthquakes. One of the most effective and practical passive control methods is to use shear panel system working as a ductile fuse in the structure. Shear Panel System, SPS, is located vertically between apex of two chevron braces and flange of floor beam. Seismic energy is highly dissipated through shear yielding of shear panel web while other elements of structure remain almost elastic. In this paper, lateral behavior and related benefits of this system with narrow-flange link beams is experimentally investigated in chevron braced simple steel frames. For this purpose, five specimens with IPE (narrow-flange I section) shear panels were examined. All of the specimens showed high ductility and dissipated almost all input energy imposed to the structure. For example, maximum SPS shear distortion of 0.128-0.156 rad, overall ductility of 5.3-7.2, response modification factor of 7.1-11.2, and finally maximum equivalent viscous damping ratio of 35.5-40.2% in the last loading cycle corresponding to an average damping ratio of 26.7-30.6% were obtained. It was also shown that the beam, columns and braces remained elastic as expected. Considering this fact, by just changing the probably damaged shear panel pieces after earthquake, the structure can still be continuously used as another benefit of this proposed retrofitting system without the need to change the floor beam. Keywords: IPE shear panel, vertical link beam, chevron braced simple frame, cyclic testing, ductility ratio, energy dissipation, response modification factor. منبع: [Hidden Content] دانلود: [Hidden Content] papers_Zahrai-SCS-Revised_1.pdf

Study of an innovative two-stage control system: Chevron knee bracing & shear panel in series connection S.M. Zahrai1a and A.K. Vosooq2 1Center of Excellence for Engineering and Management of Civil Infrastructures, School of Civil Engineering, Faculty of Engineering, The University of Tehran, Iran 2Department of Structural Engineering, Faculty of Civil Engineering, Tafresh University, Tafresh, Iran (Received May 16, 2012, Revised July 30, 2013, Accepted September 18, 2013) Abstract. This paper describes analytical investigation into a new dual function system including a couple of shear links which are connected in series using chevron bracing capable to correlate its performance with magnitude of earthquakes. In this proposed system, called Chevron Knee-Vertical Link Beam braced system (CK-VLB), the inherent hysteretic damping of vertical link beam placed above chevron bracing is exclusively utilized to dissipate the energy of moderate earthquakes through web plastic shear distortion while the rest of the structural elements are in elastic range. Under strong earthquakes, plastic deformation of VLB will be halted via restraining it by Stopper Device (SD) and further imposed displacement subsequently causes yielding of the knee elements located at the bottom of chevron bracing to significantly increase the energy dissipation capacity. In this paper first by studying the knee yielding mode, a suitable shape and angle for diagonal-knee bracing are proposed. Then finite elements models are developed. Monotonic and cyclic analyses have been conducted to compare dissipation capacities on three individual models of passive systems (CK-VLB, knee braced system and SPS system) by General-purpose finite element program ABAQUS in which a bilinear kinematic hardening model is incorporated to trace the material nonlinearity. Also quasi-static cyclic loading based on the guidelines presented in ATC-24 has been imposed to different models of CK-VLB with changing of vertical link beam section in order to find prime effectiveness on structural frames. Results show that CK-VLB system exhibits stable behavior and is capable of dissipating a significant amount of energy in two separate levels of lateral forces due to different probable earthquakes. Keywords: two-stage earthquake resisting system, vertical link beam, knee elements, stopper device Structural Engineering and Mechanics, Vol. 47, No. 6 (2013) 881-898 DOI: [Hidden Content] منبع: [Hidden Content] دانلود: [Hidden Content] _VPIxzlt.pdf

Study of an innovative two-stage control system: Chevron knee bracing & shear panel in series connection S.M. Zahrai1a and A.K. Vosooq2 1Center of Excellence for Engineering and Management of Civil Infrastructures, School of Civil Engineering, Faculty of Engineering, The University of Tehran, Iran 2Department of Structural Engineering, Faculty of Civil Engineering, Tafresh University, Tafresh, Iran (Received May 16, 2012, Revised July 30, 2013, Accepted September 18, 2013) Abstract. This paper describes analytical investigation into a new dual function system including a couple of shear links which are connected in series using chevron bracing capable to correlate its performance with magnitude of earthquakes. In this proposed system, called Chevron Knee-Vertical Link Beam braced system (CK-VLB), the inherent hysteretic damping of vertical link beam placed above chevron bracing is exclusively utilized to dissipate the energy of moderate earthquakes through web plastic shear distortion while the rest of the structural elements are in elastic range. Under strong earthquakes, plastic deformation of VLB will be halted via restraining it by Stopper Device (SD) and further imposed displacement subsequently causes yielding of the knee elements located at the bottom of chevron bracing to significantly increase the energy dissipation capacity. In this paper first by studying the knee yielding mode, a suitable shape and angle for diagonal-knee bracing are proposed. Then finite elements models are developed. Monotonic and cyclic analyses have been conducted to compare dissipation capacities on three individual models of passive systems (CK-VLB, knee braced system and SPS system) by General-purpose finite element program ABAQUS in which a bilinear kinematic hardening model is incorporated to trace the material nonlinearity. Also quasi-static cyclic loading based on the guidelines presented in ATC-24 has been imposed to different models of CK-VLB with changing of vertical link beam section in order to find prime effectiveness on structural frames. Results show that CK-VLB system exhibits stable behavior and is capable of dissipating a significant amount of energy in two separate levels of lateral forces due to different probable earthquakes. Keywords: two-stage earthquake resisting system, vertical link beam, knee elements, stopper device source: [Hidden Content] Download: [Hidden Content] Dbeowzz7.pdf