Civil and Structural Engineering Computing: 2001
Chapter 15 J. Gluck+ and Y. Ribakov*
+Structural Engineering Division, Faculty of Civil Engineering, Technion - Israel Institute of Technology, Technion City, Haifa, Israel *Department of Civil Engineering, Faculty of Engineering, College of Judea and Samaria, Ariel, Israel Keywords: amplifying braces, dampers, structural control, earthquake response, seismic design, structural dynamics
This paper deals with application of supplemental damping systems for improvement of structural seismic behavior. In order to achieve economical earthquake-resistant buildings, structures must be able to absorb and dissipate a large amount of seismic energy. Passive energy dissipating systems [1,3,4] have been installed in existing buildings resulting in an improved structural response to earthquakes. Active systems have wider ranges of operation compared to passive systems, however they require relatively large amount of energy for real time system adjustment, which is critical during seismic events when the main power source may fail. The advantages of the recently developed magnetorheological (MR) damper is its ability to operate over a wide range of temperatures, and that the MR fluid can be controlled with a low current-driven power supply of 12-24 volts and 1-2 amps [2]. An attractive way for further improvement of the structural behavior can be achieved is by connecting the dampers to amplifying braces (AB) at various locations in the structure. This leads to a decrease of the energy required for active and semi-active control. According to the proposed approach, the damper is connected to the top and bottom floor diaphragms by means of bars. The required control force in the dampers during an earthquake is obtained by using instantaneous optimal control theory with velocity and acceleration feedback [5]. In order to examine the efficiency of the proposed AB a seven-story shear framed structure with stiff beams was analyzed under different earthquakes for the following cases: uncontrolled structure, structure with active friction dampers (FD) connected to chevron braces, structure with FD connected to AB, structure with MR dampers connected to AB. The following four seismic excitations were used as input in order to examine the behavior of the structure: El Centro S00E, 1940, Taft N21E, 1952, Kobe NF17, 1995 and Eilat EL 1226NS, 1995. For all earthquakes the peak response of the damped structure is significantly improved compared to that of the uncontrolled one. The reductions of the peak displacements in the friction damped and MR damped structure compared to the uncontrolled one varies from 67% to 74%. Using the proposed damping systems yields significant reduction in roof accelerations. There is no significant change in the base shear forces in a damped structure. The numerical example has demonstrated high efficiency of the amplifying braces in reducing the energy required for control. It shows that it is possible to obtain the same structural response by using dampers connected directly to the chevron braces or to the amplifiers, however in the second case the control forces will be significantly reduced. These results make the proposed system with amplifying braces very attractive for practical applications.
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