טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentBahnasy Abedalkreem
SubjectOptimal Seismic Design of Buildings using Nonlinear Viscous
Dampers
DepartmentDepartment of Civil and Environmental Engineering
Supervisor Professor Oren Lavan
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

One of the technologies available for seismic retrofitting relies on energy dissipation devices. Out of the variety of such devices, viscous dampers gained special attention in the context of seismic retrofitting. This is because they are velocity-dependent; hence, large energy dissipation would be activated with small inter-story drifts. Moreover, the forces these velocity-dependent dampers produce are out of phase with columns axial forces and bending moments due to displacements. Therefore, a retrofitting scheme with viscous dampers will not usually require column and foundation strengthening. The third advantage of the viscous dampers is the long history of military application that proves system reliability. Unlike metallic yielding dampers or friction dampers, viscous dampers do not result in residual internal forces due to yielding or slippage. In addition, with a careful design, it seems that the use of such dampers may reduce both drifts and accelerations simultaneously

 

In order to assist the engineering community, many methodologies for the design and the optimal design of seismic retrofitting using viscous dampers were proposed. Some of the advanced design methodologies are easy to implement in design offices without any special requirement of optimization theory or software. Most of the methodologies consider linear viscous dampers. These could then be replaced by nonlinear equivalent ones.  This is done based on equating the energy dissipation of each linear damper with that of a nonlinear damper under harmonic response with the peak inter-story drift. Nonetheless, a simple optimal design methodology appropriate for the direct design of nonlinear viscous dampers is not available. Furthermore, there has been a long debate between earthquake engineers throughout the world on whether linear fluid viscous dampers are superior to nonlinear fluid viscous dampers for seismic mitigation or vice versa. Those to side with linear viscous dampers indicate that the forces they produce are out of phase with forces due to deformations, hence, reducing the need for columns and foundation strengthening. On the other hand, those to side with nonlinear viscous dampers indicate that the dependency of their peak forces on the maximum velocity is smaller. Hence, in the case of a stronger earthquake than designed for, the forces in the dampers would not significantly increase peak forces on brittle elements and connections.

 

The aim of this research is twofold. First, a practical methodology that was proposed by Lavan and Levy (2005, 2006) for the optimal design of linear viscous dampers is modified here for the direct design of nonlinear viscous dampers. It's designs are further compared to those obtained using Genetic Algorithms, to minimize either the sum of added damping or the sum of damper's peak forces, with good agreement. Then, a rigorous comparison is conducted of the seismic behavior of structures optimally retrofitted with linear viscous dampers versus that of structures optimally retrofitted with nonlinear viscous dampers. Linear and nonlinear viscous dampers are first optimally designed for various types of frame buildings located in various seismic environments. Then, their behavior in terms of various responses of interest is examined to reveal their pros and cons.