טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentPollini Nicolo
SubjectOptimization-Based Approach for a Realistic Minimum-Cost
Seismic Retrofitting of Frames with Viscous
Dampers
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Oren Lavan
Professor Oded Amir


Abstract

The research thesis discussed herein focuses on the establishment of a novel optimization-based approach for the simultaneous placement and sizing of added viscous dampers for the seismic retrofitting of generic structures subject to seismic excitation. The main idea is to couple a realistic and practical formulation of the problem, including the associated costs, with material interpolation techniques from the field of Topology Optimization, into a computationally efficient approach.

Earthquakes have always posed a secular threat and challenge for engineers. With traditional seismic protective systems engineers have been able to guarantee expected levels of safety to a structure during frequent, occasional, or strong earthquakes. Typically, these techniques rely on the concept of energy dissipation by means of irreversible plastic deformations in the structure.

This may result in additional costs after a seismic event. Alternatively, seismic protection systems can significantly enhance the behavior of a structure during an earthquake. Moreover, retrofitting structures for a high performance during strong ground motions, by means of traditional seismic protective systems, might be not economical, and in many cases not feasible. In these cases, seismic protection systems are the only solution.

Out of the variety of seismic protection systems, passive fluid viscous dampers proved to be effective in reducing both structural and nonstructural damage levels, with a reasonable additional cost. However, their distribution in a structure can significantly affect their efficiency.

Thus, many researchers focused on developing new methodologies for the optimal design and distribution of added dampers in structures subject to earthquakes. In this context, the present research intends to produce an additional contribution with the development of a practical and efficient approach for the optimal seismic retrofitting of generic framed structures with viscous dampers optimally distributed and sized. Practical meaning that the optimal solutions may be used "as is". Efficient meaning that the proposed methodology requires a reasonable computational effort.

After a thorough study of the available literature, it became clear that it was not yet available a methodology that could identify practical minimum-cost dampers’ distributions, with a reasonable computational cost. Thus, in the present research a new realistic cost function is formulated, considering all the cost components involved in the design problem. This function is the objective function to be minimized in the optimization problem presented herein. The problem is formulated as a mixed-integer programming problem, and it is solved with a continuous and computationally efficient approach. In the solution phase, material interpolation techniques play an important role in achieving final discrete solutions.

Valuable results have been obtained and they are discussed further in this thesis. They highlight the main advantages and challenges of the proposed methodology, and pave the way for further developments of this work. The proposed optimization-based approach interests those practitioners involved in the retrofitting of structures with viscous dampers, having to comply at the same time with limitations on the budget and on the structural response. Potentially, the methodology could also be extended so to include other seismic protection systems.