مهندسی عمران شریف (Feb 2016)
RESPONSE MODIFICATION FACTOR FOR DUAL SYSTEM OF MEDIUM DUCTILITY STEEL MOMENT FRAME CONCENTRIC BRACED WITH PALL FRICTION DAMPER
Abstract
The response modification factor in analysis and design standards, used to reduce design forces, represents seismic energy absorption from the time of creating the first plastic hinge until the collapse mechanism. Various parameters are effective in the determination of Such reduction factor, the strength factor and the redundancy factor. Dampers act, as means of seismic retrofit, induce energy dissipation, and the use of such dampers is proposed in order to reduce structural damage during an earthquake. Much research has been done on the response modification factor; but the role of the friction damper and its effects on the parameters of such factors have not been fully investigated.In this paper, by considering a pall friction damper in stories using nonlinear analysis, the impact of dampers on the response modification factor of two-dimensional 3, 6 and 9-story steel moment frames, with 3, 5 and 7 bays (designed based on Standard No. 2800 (Ver. 4), the latest version of the 6th and 10th Iranian codes and the 1st revision of Standard No. 361), is investigated. The side frame structure studied here has a span of 5 meters and a story height of 3 meters. The next step is to consider concentric braces in the middle bays of the frame with medium ductility, followed by re-analysis and design.For the damper model, plastic elements (WEN) are used in SAP2000 software. In this study, first, nonlinear static analysis is undertaken, and to check the actual behavior of structures and for better assessment of results, Nonlinear Incremental Dynamic Analysis (IDA) is used, considering step by step increasing acceleration until reaching the life safety limit. In all cases, the force displacement curve of increasing dynamic analysis indicates compatibility with the results of static analysis.Based on obtained results, considerable improvements in the response modification factor up to 100\% are observed in the dual system of the steel moment frame and concentric brace with a pall friction damper. Finally, a strength factor of 3.55, ductility factor of 3.37 and response modification factor of 12 are proposed for the frame systems with dampers studied here, due to a high energy absorption capacity, based on a minimum amount.
