Ian G. Buckle

Seismic Isolation: History, Application, and Performance—A World View

The concept of seismic or base isolation as a means of earthquake protection seems to be more than 100 years old. However, until very recently, few structures were built using this principle. Today the concept has matured into a practical reality and is taking its place as a viable alternate to conventional (fixed base) seismic resistant construction. This paper reviews some of the history of isolation and restates the basic elements of a modern isolation system. It then proceeds to review current activity, worldwide. Progress in the United States is discussed first followed by that in China, France, Greece, Italy, Japan, New Zealand and the Soviet Union. Directories of isolated structures in the United States, New Zealand and Japan are also included. Finally the performance of a selection of these structures during actual earthquakes is given.

Impediments to the implementation of seismic isolation

There are over 125 civil engineering structures worldwide that have been constructed using the principles of seismic isolation and 15 of these are in the United States. Although use of the technology is increasing in the United States it is significantly less than that seen in Japan and New Zealand. Some of the impediments that have been encountered, such as design codes, economics and government leadership are discussed and the paper provides a summary of the status of some of the solutions required for its more widespread use in the United States. A comparison with the Japanese implementation process is also provided.

Structural Performance of Bridges in the Tohoku-Oki Earthquake

Including minor nonstructural damage, over 1,500 highway bridges and numerous rail bridges were damaged during the Tohoku-oki earthquake of 11 March 2011. The causes of this damage can be broadly classified in two categories: ground shaking, including ground failure (liquefaction); and tsunami inundation. Damage included span unseating, column shear and flexural failures, approach fill erosion, liquefaction induced settlement, and failed steel and elastomeric bearings. Since many bridges in the north Miyagi-ken and south Iwate-ken suffered extensive damage during the 1978 Miyagi-ken-oki earthquake, bridge performance during the 2011 earthquake is of particular interest. Advances in design and retrofit may be assessed by looking at the performance of bridges designed to post-1990 codes and those retrofitted since the Kobe earthquake in 1995. In both categories, bridge damage due to ground shaking was minor, thus validating the provisions in the post-1990 codes and the Japan bridge retrofit program. Damage that did occur due to ground shaking was mainly to bridges not yet retrofitted or only partly so. Tsunami-related damage included complete loss of span and erosion of backfills. However, many bridges survived, despite being totally submerged, and their performance gives insight into the potential design of tsunami-resistant bridges.

Structural Performance of Bridges in the Offshore Maule Earthquake of 27 February 2010

Of the nearly 12,000 highway bridges in Chile, approximately 300 were damaged in this earthquake, including 20 with collapsed spans. Typical failure modes include damage to connections between super- and substructures, unseating of spans in skewed bridges due to in-plane rotation, and unseated spans with some column damage due to permanent ground movement. Unusual failure modes include unseating of spans in straight bridges due to in-plane rotation, plate girder rupture due to longitudinal forces, scour and pier damage due to tsunami action, and collapse of a historic masonry bridge. The most common damage mode was the failure of super-to-substructure connections (shear keys, steel stoppers, and seismic bars), which is the most likely reason for the low incidence of column damage. Whereas the fuse-like behavior of these components is believed to have protected the columns, the lack of adequate seat widths led to the collapse, or imminent collapse, of many superstructures.