Practices of Seismic Damage Control Design of Bridges in Japan and Some Lessons From 2011 Tohoku Earthquake

Abstract eng:
Seismic damage control technology has advanced rapidly and been widely applied to not only new construction but also retrofit of existing bridges, especially after 1995 Kobe Earthquake. At the first part of paper, development of design and performance evaluation of base-isolated bridges before 2011 Tohoku Earthquake are reviewed. In Kobe Earthquake, elevated viaducts in metropolitan Kobe area were most severely damaged, which neutralized transportation function of the entire city. Since observed severe damage were due mainly to damage of columns, strengthening measures of bridge columns were aggressively pursued. Isolation between bridge column and girder was found effective to reduce seismic damage without altering major geometry, and was widely applied to newly built and existing elevated viaducts. Base-isolation effect for elevated bridges is extensively studied and verified by numbers of field observation. Effects of soil conditions and details of isolation devices were studied in depth based on observed data. The design concept has further been extended to seismic damage control and applied to seismic retrofit of long span bridges. Minato Bridge, whose central span of 510[m] is the longest truss bridge in Japan, was retrofitted with extensive use of seismic damage control concept. In the retrofit, floor deck systems were isolated from main truss frame and energy absorbing braces with low yield point steel were attached to reduce main frame response. In Yokohama Bay Bridge, possible damage scenarios were identified and countermeasures were taken for each scenario to prevent worst consequences resulting in human loss. In 2011 Tohoku Earthquake, most structures designed by post-Kobe code were not damaged by ground motion. However in some bridges designed by post-Kobe code, rubber bearings and dampers were severely damaged. Although recorded ground motion continued over 300 seconds, and the peak ground acceleration is very large, in most records the response acceleration around 0.5 – 2.0 second was less than design spectra. Cracks of rubber bearings were observed in the wide region and rupture of bearings were occurred in two highway viaducts. The damage was concentrated near the edge of continuous girders. In some bridges, the attachments of dampers were damaged..

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