Concordia's Library Building (LB) incorporates 150 friction dampers designed to dissipate the destructive energy of major earthquakes.

image taken from the website of the University of Concordia for more information on the following link photo: http://www.bcee.concordia.ca/index.php/Pall's_friction_dampers

SEISMIC RESPONSE OF A NINE-STORY STEEL FRAME WITH FRICTION DAMPED CROSS-BRACING

lan D. Aiken', James M. Kelly2 , and Avtar S. Pall3

1 Graduate Student, Dept. of Civil Engineering, University of

California, Berkeley, USA

2 Professor, Dept. of Civil Engineering, University of California,

Berkeley, USA

3 President, Pall Dynamics Limited, Montreal, Quebec, Canada

SUMMARY

A passive energy dissipation system that incorporates friction damping devices in the cross-bracing of a medium-rise steel moment resisting frame is investigated. Earthquake simulator tests and an analytical study of the system are performed and the response characteristics compared with those of equivalent moment resisting and eccentric braced frames. An existing scale model 9 story steel moment resisting frame (MRF) was modified to include friction damped bracing as part of the lateral load resisting system. The frame is one bay wide and three bays long and represents a typical section in the weak direction of a steel frame building of approximately one quarter scale. It was observed that the friction damped braced frame (FDBF) system had the ability to behave in a nonlinear fashion without demanding inelastic behavior in the frame itself. This implied continued integrity of the structure during and after a seismic event. Analytical results and experimental observations confirmed that for small variations of the slip loads from the optimum loads the overall response of the frame remained essentially unchanged. 

Pall Friction Dampers For Seismic Control Of Buildings

This page is the official website of Pall Dynamics, a manufacturer of frictiondampers for seismic control of buildings

http://www.palldynamics.com/

Important facts when using friction dampers in buildings

Denis Lefebvre, eng., M.A.Sc.

The utilization of friction dampers may considerably reduce the base shear, axial forces in the columns, and

vertical reactions on foundations. However, a good calibration of the dampers is necessary to have adequate control over interstorey deflections. Engineers who wish to use friction dampers (Pall) are compelled to analyze the structure with a non linear model in order to study the behavior under earthquake loading. The choice of an appropriate accelerogram is required and represents a second difficulty. The method proposed by Ibrahimbegovic et Wilson (FNA : Fast Nonlinear Analysis) and used by SAP2000 is based on a modal superposition technique that is very fast and requires only one computation of eigenvalues and eigenvectors. However, the friction dampers vertical components that are transferred to the columns are included in the results only if a sufficient number of modes have been considered in the analysis. It is recommended to use a sufficient number of modes (or all the modes), but it is a difficult task for the engineer to do so or to choose the good ones. Buildings having thousands of degrees of freedom generally possess a vertical stiffness that is greater than the translation stiffness. The result of this is that the modes providing an important contribution to the behavior in translation are listed at the beginning, while modes acting on vertical forces (ex. : friction

dampers vertical component) are listed at the end. To get round this problem, the engineer is forced to ask a great number of modes, which is not always possible for it costs much time and memory. Elements that increase the vertical component on one column are the calibration of friction dampers, their number, and their vertical components. For a building having a few friction dampers (1 or 2) attached to the columns, the error is quite small (10%) and passed unnoticed. However, if there are many friction dampers, the error may be important. If you are using the standard FNA method, important erroneous results may occur in the calculation of axial forces in the columns and vertical reactions on the foundations, because it is impossible to choose a great number of modes for an analysis, except for small structures. The method presented in VisualDesign is a variation of the original FNA method. With this method, engineers will only need to study two or three modes per storey as they would do when using a standard linear analysis in order to get a minimum of 90% of the participating mass. In this non linear analysis, we simultaneously apply the FNA method for the calculation of horizontal forces applied to the structure and a static method is used for the calculation of the friction dampers vertical components. The method suggested in VisualDesign offers an alternative that will allow the engineers to get more accurate results (correct axial forces in the columns and vertical reactions on foundations) while choosing fewer number of modes.

(A french copy of this paper is available on our web site)

Design of a bracing-friction damper system for seismic retrofitting

Sung-Kyung Lee

Department of Architectural Engineering, Dankook University, Seoul, Korea

Ji-Hun Park

Department of Architectural Engineering, University of Incheon, Incheon, Korea

Byoung-Wook Moon, Kyung-Won Min* and Sang-Hyun Lee

Department of Architectural Engineering, Dankook University, Seoul, Korea

Jinkoo Kim

Department of Architectural Engineering, Sungkyunkwan University, Korea

(Received March 20, 2007, Accepted December 11, 2007)

Abstract: This paper deals with the numerical model of a bracing-friction damper system and its deployment

using the optimal slip load distribution for the seismic retrofitting of a damaged building. The Slotted Bolted

Connection (SBC) type friction damper system was tested to investigate its energy dissipation characteristic. Test results coincided with the numerical ones using the conventional model of a bracing-friction damper system. The placement of this device was numerically explored to apply it to the assumed damaged-building and to evaluate its efficiency. It was found by distributing the slip load that minimizes the given performance indicies based on structural response. Numerical results for the damaged building retrofitted with this slip load distribution showed that the seismic design of the bracing-friction damper system under consideration is effective for the structural response reduction.

Key words: bracing-friction damper system; slotted bolted connection type; slip load distribution; damaged

building.