Bridges

A series of shake table tests on an isolated bridge model included low and high damping elastomeric isolation systems, and low damping elastomeric systems with added linear and nonlinear viscous dampers. Each of these configurations could withstand much stronger seismic excitations than the non-isolated configurations. A set of low intensity tests was conducted to form a basis for comparison with the non-isolated configurations and also to test the effectiveness of these systems under low intensity excitation. The results of these tests are presented, followed by a discussion of the effects of scragging, the benefits of seismic isolation, and the significance of damping, the importance of added damping in near source seismic excitation and on the benefits and drawbacks of using nonlinear viscous damping.

This report describes an experimental study of the behavior of a bridge seismic sliding isolation system consisting of flat sliding bearings and fluid restoring force/damping devices. Earthquake simulator tests were performed on a model bridge structure both with isolators and without. The experimental results demonstrate a marked increase of the capacity of the isolated bridge to withstand earthquake forces. Analytical techniques are used to predict the dynamic response of the system and the obtained results are in very good agreement with the experimental results.

This paper describes the first part of a project to produce a class of passive sliding seismic isolation systems for bridges. This includes experimental verification of the systems by large scale shake table testing, analytical techniques for interpretation of the experimental results, and design procedures for sliding bridge isolation systems. A quarter length scale bridge model was tested on a shake table. Restoring force was provided by various means. First, spherically shaped sliding bearings (known as FPS bearings) were used to provide restoring and frictional forces within a compact unit. Next, flat sliding bearings were combined with various devices placed between the deck and the pier to provide restoring force and additional energy dissipation capacity. These devices were in the form of: a) arc-shaped rubber elements between a moving central rod and a cylindrical housing, b) wire rope springs, c) fluid spring-damper devices and d) fluid viscous dampers.

This unpublished paper by Dr. Michael Constaninou describes the seismic protection of a steel multi-girder highway bridge. Three types of base isolators are included; high damping rubber, lead-rubber and Friction Pendulum. The effect of added viscous damping is also investigated, and is found to greatly enhance the performance of the isolators, even though the dampers required are rather small. This classic paper is hand written by Dr. Constantinou and includes his calculations and his sketches of the bridge, isolation devices and dampers.