Bracing Configuration in Earthquake Resistant Structure

Abstract eng:
Technological advances in the seismic design of energy dissipation systems raise the issue of the codes dominated capacity design of structures. Building code requirements that describe the dynamic behavior, modeling and analysis of structures with different types of energy dissipation systems are currently under review. A new seismic design approach, described in the current paper, adds to the current research activities of the authors on passively controlled systems with integrated hysteretic damper and cable bracings. The control system considers at first place the effect of added stiffness when conventional bracings are added to structural frames that are necessary for the integration of the damping devices. An increase in the systems stiffness may result to a reduction of the peak displacement, i.e. peak pseudo-acceleration, and thus to an increase of the shear forces. In addition, an increase in damping can significantly influence the response of elastic and inelastic systems. The new system proposed aims at both, energy dissipation and damage control. It consists of an energy dissipation device and a portal cable bracing mechanism with a kinetic closed loop, working only in tension. The closed bracing mechanism does not practically affect the initial stiffness of the system, i.e. the concept relies on two completely “separate” systems: a primary for the vertical- and wind loads and a secondary for the earthquake loads. Analysis model considerations for describing the physical behavior of the system in computational language are presented, by incorporating the SAP2000 program, revealing step by step the procedure followed for the resulting desired dynamic performance. Based on the energy balanced equation at each time-step, the hysteretic energy dissipation demand is reduced when the supplemental damping system is utilized. An Effective Toughness Index, in accordance to the timedependence of the hysteretic energy dissipation is proposed to characterize the portions of the input energy dissipated by the control system. The predominant parameters that characterize the system’s seismic behavior are derived on the basis of a parametric analysis under selected international strong ground motions. Finally the systems behavior is verified in respect to the mechanical properties of the control elements under the action of ten selected earthquake excitations of the Greek-Mediterranean region. The parametric analyses of the system’s seismic behavior conclude with a proposed preliminary design methodology for the passively controlled SDOF models.

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