UC Berkeley

Abstract

Toward Performance-based Design of Seismically Isolated Structures

By

Benshun Shao

Doctor of Philosophy in Civil and Environmental Engineering

University of California, Berkeley

Professor Stephen A. Mahin, Chair

Seismic isolation is an efficient structural system to achieve higher performance objectives in seismic design. It has been widely studied and used in practice. However, it is not always the case that seismically isolated structure is designed and engineered to achieve desired performance. Use of seismic isolation must be accompanied by correct engineering design concept and methodology. To address this issue, a performance-based design procedure for seismically isolated structure is needed for practical application. The dissertation work is aimed to enhance the understanding, to solve the remaining challenges and to provide guidance and support toward the development of performance-based design for seismically isolated structures.

As the basis for design, a Two-level fundamental performance objective for seismically isolated structure is firstly proposed. It requires the design to satisfy a L1 performance objective which is to minimize damage and to achieve continued functionality under design level seismic event. At the same time, a L2 performance objective is required which is to achieve required safety reliability under rare seismic event.

The main challenge for development of performance-based design for seismically isolated structure is to conduct preliminary design and to address the fundamental Two-level performance objective. The key is to select design parameters of upper-structure and isolation system efficiently and systematically with correct design concept. By numerically investigating responses of different seismically isolated structures considering different loading conditions, the dissertation work provides guidance on preliminary design of seismically isolated structure to achieve the Two-level performance objectives proposed.

The dissertation work is divided into two parts. The first part focuses on investigating preliminary design of seismically isolated structure to achieve L1 performance objective. By investigating responses of different seismically isolated structures (Chapter 4 considers seismically isolated SDOF model, Chapter 5 considers seismically isolated tall building, Chapter 6 considers seismically isolated nuclear power plant) under different design parameters of isolator and upper-structure, this part of study focuses on understanding how change of design parameters will affect responses and provides systematic guidance on preliminary design.

The second part focuses on investigating preliminary design of seismically isolated structure to achieve L2 performance objective which is to achieve safety reliability. By conducting numerical analysis on an archetype seismically isolated structure, the study shows current design regulation for seismically isolated structure does not achieve required safety level. Addition capacity of isolation system is needed. By investigating different types of enhanced isolation system, it is found that using seismic isolator with stiffening behavior is the most efficient solution to provide enough capacities for achieving safety reliability. To implement this concept in practice for general design case, a probabilistic design procedure has been developed.

The analyses work conducted in the two parts of the dissertation redefines the concept for design of seismically isolated structure, and it provides guidance for conducting preliminary design of seismically isolated structure to achieve desired performance. The work provides basis for further development of performance-based design of seismically isolated structures.