قراردهی بهینه میراگر ویسکوز برای سازه های MDOF
Abstract
1- Introduction
2- Optimal damper placement with respect to transfer function amplitude at natural frequency and optimal damper placement under critical double impulse
3- Plastic deformation characteristics of building structures with optimal damper locations for increasing level of critical double impulse
4- Conclusions
References
Abstract
The effectiveness of the optimal viscous damper placement for elastic-plastic multi-degree-of-freedom (MDOF) structures under the critical double impulse is demonstrated through the comparison with the optimal damper placement for elastic MDOF structures designed with respect to transfer function amplitudes at natural frequencies. The method for optimal viscous damper placement was proposed for elastic-plastic MDOF structures subjected to the critical double impulse as a representative of near-fault ground motions in the previous paper [1]. The double impulse is composed of two impulses with opposite directions and the critical interval is determined by using the criterion on the maximum input energy. The critical timing of the second impulse was found to be the timing which requires the vanishing of the sum of the restoring force and the damping force in the first story. Three models with different story stiffness distributions of main structures are treated to demonstrate the effectiveness of the optimal viscous damper placement under the critical double impulse. The double impulse pushover (DIP) procedure proposed in the previous paper for determining the input velocity level of the critical double impulse is examined further in this paper. It is demonstrated that the optimal viscous damper placement for elastic-plastic MDOF structures under the critical double impulse is more effective for pulse-type recorded earthquake ground motions than the optimal damper placement designed with respect to transfer function amplitudes at natural frequencies because several higher modes arising in the elastic-plastic response under pulse-type recorded earthquake ground motions can be well controlled by the design for the double impulse.
Introduction
Viscous, visco-elastic and hysteretic dampers have been used as effective passive dampers installed at interstories. It is commonly understood that hysteretic dampers are effective in general for impulsive ground motions with short duration [2–6] and viscous dampers are useful for long-duration ground motions. Recently, it is reported after devastating earthquakes that near-fault ground motions of impulsive type with short duration are apt to cause large damage to building structures. Although viscous dampers are not necessarily effective for near-fault ground motions, they have advantages to be able to reduce both displacement and acceleration. It seems, therefore, preferable that, when designing viscous dampers, they can reduce the earthquake response to small-to-moderate level ground motions and prevent excessive deformation to large level ground motions, such as long-period ground motions. Many useful researches on optimal damper placement have been accumulated so far (see Refs. [7–9]). Takewaki [10] proposed an optimality criterion-based approach including an incremental inverse-problem formulation in which the transfer function amplitude in terms of the sum of the interstory drifts at the fundamental natural frequency is minimized under the constraint on total damper quantity. This approach has an advantage that the algorithm is simple and the obtained result is independent of input ground motions. Aydin [11] extended this approach to the transfer function amplitude in terms of the base shear at the fundamental natural frequency. Fujita et al. [12] developed an optimization method for minimizing the maximum interstory drift in the transfer function under a constant total damper quantity. Adachi et al.