Reliability-Based Optimal Aseismic Design of Reinforced Concrete Buildings

The assurance of structural performance against excessive damage or collapse under moderate and severe earthquakes is the major objective of earthquake-resistant design of structures. It is universally recognized and accepted that to require absolute safety or performance in the design under all earthquake intensities would be prohibitively expensive. Some level of risk or probability of non-performance has to be accepted, and indeed underlies the philosophy of current earthquake-resistant design. The determination of proper level of safety (or performance), therefore, would require trade-off between structural performance and economic consequences under an earthquake environment.

Also, in light of unavoidable and significant uncertainty and randomness in earthquake loadings, and in structural behavior and response, proper measures of seismic safety and performance require consideration of probability or risk. Accordingly, proper criteria for seismic resistant design may be formulated for acceptable risk or prescribed target reliability.

The study has developed the necessary reliability framework for the systematic determination of the acceptable risk for the earthquake-resistant design of reinforced concrete buildings in Tokyo. Acceptable risks (or target reliabilities) for design to control damage and prevent collapse under earthquake loads have been, determined quantitatively on the basis of minimum life-cycle cost. To achieve these objectives, the following specific studies were required:
- Application of a systematic approach for integrating the important technical and economic factors in the determination of the optimal target reliabilities for the earthquake resistant design of reinforced concrete structures.
- Formulation of credible and realistic cost relationships that are explicitly functions of risk or reliability.
- Practical methods for the quantitative assessments of structural damage and reliability under earthquake loadings, which may be modeled as random processes. These methods must include calculations of structural responses involving nonlinear and hysteretic behavior of reinforced concrete elements including shear walls.
- Realistic modeling of the behavior of important structural elements, as well as of the structural system, for the purpose of the response analyses under earthquake loadings.
- Practical methods for the optimal aseismic design of reinforced concrete buildings satisfying prescribed target reliabilities.