Chapter 20 - Seismic component devices

Abstract

This chapter introduces seismic component devices that are widely used to protect bridges from severe damages during earthquakes by absorbing or dissipating input seismic energy. These devices can generally be classified as seismic isolators and damping systems. Seismic isolators reduce peak seismic demand on bridge piers through dynamic isolation of the deck from piers. This is done by placing flexible seismic isolation bearings between the deck and piers, thereby elongating the first natural period of the bridge beyond the spectrum of predominant earthquake periods. Damping systems are installed in parallel with isolators to limit excessive displacement of the deck. Four common types of isolators, low-damping rubber bearing (LDRB), high-damping rubber bearing (HDRB), lead rubber bearing (LRB), and friction pendulum system (FPS), are discussed in detail. The mathematical concept behind seismic isolation using a simple bridge model is also explained. The design method of seismic isolation in bridges based on the current design codes is briefly described. Typical passive damping systems used in bridges and other structures are fluid viscous damper (FVD), friction damper (FD), and magnetorheological damper (MRD). This text describes advantages and disadvantages of these dampers. Applications of isolators and damping systems are illustrated through some examples of bridges equipped by seismic component devices around the world.