Modal properties and seismic behaviour of buildings equipped with external dissipative pinned rocking braced frames

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.

Seismic retrofitting of braced frame buildings by RC rocking walls and viscous dampers

“…In the present parametric analysis, the viscous dampers of each system S1 are designed to obtain a total equivalent viscous damping factor equal to 35%. To this end, the equivalent viscous damping factor ξ str of the braced structure is first evaluated by Equations (13) to (16) in the case of CBFs and by Equation (20) in the case of EBFs. Then, the additional equivalent viscous damping factor ξ d is calculated as the difference between 35% and ξ str , and the viscous damping…”

“…To avoid unfavourable impact on the outermost parts of the rocking wall base, the interface between the rocking wall and the foundation consists of an explicit pin bearing in the middle of the wall. Details regarding this bearing or the connection of the wall to the deck are reported in other papers . Post‐tensioned tendons are embedded in the wall to increase the crack resistance of concrete .…”

“…Details regarding this bearing or the connection of the wall to the deck are reported in other papers. 14,17,18,20 Post-tensioned tendons are embedded in the wall to increase the crack resistance of concrete. 17 Linear viscous dampers are added, if required, to reduce the lateral displacement demands of the system and are located between the sides of the rocking walls and adjacent reaction columns.…”

A Design Method for Viscous Dampers Connecting Adjacent Structures

“…The dissipative coupling of adjacent structures also includes the case of existing structures connected to new external systems. This retrofit measure has been recently investigated in different studies (Gioiella et al, 2018a;Reggio et al, 2019), because it presents several advantages compared to other methods (e.g., dissipative braces inserted within the frames), thanks to the reduced interferences with the existing frame and the low downtime associated with the installation of the retrofit measure. There can be different arrangements for the external protection system, which can be for example a new external reaction tower or an exoskeleton structure wrapping the building to be protected.…”

“…There can be different arrangements for the external protection system, which can be for example a new external reaction tower or an exoskeleton structure wrapping the building to be protected. The study reported in (Gioiella et al, 2018a), investigated the modal properties and the seismic response of an r.c. frame building coupled with an external pinned-rocking truss equipped with linear fluid viscous at its base and connected at the floor level with the building to protect.…”