Maziar Jamshidi - School of Civil Engineering, Sharif University of Technology, Azadi Ave.,
Mehdi Ahmadizadeh

An effective method is developed for design of passive viscous fluid dampers for structural control, considering the flexibility of braces used for installation of dampers. In the first stepof this method, a suitable damping ratio is determined based on the optimization results of single-degree-of-freedom systems with various natural periods and brace stiffness ratios. Theoptimization is carried out using an objective function that is a weighted combination ofmean squares of inter-story drift and absolute acceleration responses. The search for optimum damping ratio is carried out for a set of scaled ground motion records, and the mean of theresulting record-specific optimum damping ratios is then adopted as the optimum dampingratio. By repeating this procedure for a range of natural periods and brace-to-story stiffness ratios, a set of control design spectra is generated that yield the suitable damping ratios forany given single-degree-of-freedom system. Next, the usage of this method is extended tomulti-degree-of-freedom shear building systems by adding the above-mentioned optimumdamping ratio to the inherent damping of the first natural vibration mode. Finally, assumingstiffness-proportional classical damping for the structure, the new damping matrix of the system is determined and used to find the required damping coefficients of viscous fluiddevices. In order to demonstrate the application and effectiveness of the proposed designmethod, control systems are designed for an example 7-story structure and the achieved performances are compared to that of other design methods. It is shown that the control systems, designed using the proposed method, provide responses close to those of optimumsystems, while greatly simplifying the design process.

passive control, viscous fluid damper, brace flexibility, design spectra