دانلود رایگان مقاله انگلیسی خواص مودال و رفتار لرزه ای ساختمان های مجهز با چارچوب های محکم شیب دار - الزویر 2018

ABSTRACT

This paper deals with the seismic protection of building frames by means of external dissipative systems. Dampers and external framing system can be arranged in several configurations, involving different kinematic behaviours and seismic performances. This study analyses a recently-developed solution called “dissipative tower”, which exploits the rocking motion of a steel braced frame, hinged at the foundation level, for activating the dampers. This system aims at controlling both the global response and the local storey deformation of the frame, by using a reduced number of viscous dampers. A state space formulation of the dynamic problem is presented in general terms, together with the solution of the seismic problem via the modal decomposition method. A parametric study is carried out to evaluate the influence of the added damping and of the braced frame stiffness on the modal properties and seismic response of a benchmark reinforced concrete frame retrofitted with the external dissipative towers. It is shown that the addition of the towers yields a regularization and reduction of the drift demand along the building height, but it may induce significant changes, not always beneficial, in the distribution of internal actions of the frame and in the absolute storey accelerations.

Conclusions

This paper investigates the seismic performance of existing buildings frames coupled with external dissipative towers consisting of a steel truss, hinged at the foundation level, whose rocking motion promotes the dissipation of energy by means of viscous dampers. The system at hand is non-classically damped, being the energy dissipation concentrated at the tower base, and a suitable formulation is proposed for its analysis. In particular, a state-space approach and a complex modal analysis of the coupled system is proposed to evaluate the influence of the added tower stiffness and damping on both the dynamic and seismic behaviour, by highlighting the contribution of each of the complex vibration modes to the global seismic response. In order to evaluate benefits and drawbacks of the system, a parametric study is carried out, by considering several retrofit configurations which differ for the levels of added stiffness (tower-to-frame stiffness ratio κ = 1 and κ = 0.5) and dissipation capacity (damping ratio ξadd = 0.15 and ξadd = 0.3). The cases of the bare building (Uncontrolled) and of an infinitely stiff tower (Stiff), providing an added damping contribution of 30%, are also considered for comparison purposes.