Displacement-Based Seismic Design of Bridges

This paper provides a summary of the displacement-based seismic design method as applied to bridge structures. A brief introduction is devoted to the shortcomings of traditional force-based design methods, followed by a discussion of the seismic input for displacement-based design and by the fundamentals of the method. The essential objective of the approach is to provide a design methodology that engineers can employ to accomplish the goals of performance-based earthquake engineering (PBEE), the primary objective of which is to design a structure in order to achieve predictable levels of performance under defined levels of seismic input, within definable levels of reliability, as stated by SEAC in 1999. It is thus essential that the design procedures used are capable of controlling structural performance. Such a requirement is the primary limitation of traditional force-based methods. Structural performance can be characterized by various parameters such as strains, curvature, rotations, displacement, drift, or ductility which are of course all deformation quantities. This is of obvious importance since structures are designed to respond inelastically under even moderate earthquakes. Forces, however, are poor indicators of damage potential and any attempt to control inelastic structural behavior by controlling forces is likely to fail.