MCEER Visits Iceland to Investigate Performance of Seismically-Isolated
On October 9-10, 2000, Michael Higgins, MCEER’s Senior Program Officer
for Transportation Research, and Benedikt Halldorsson, Ph.D. candidate in
the Department of Civil, Structural and Environmental Engineering at the
at Buffalo, and member of the Student Leadership Council, visited the
Earthquake Engineering Research Center, University of Iceland (EERCUI), to
the performance of isolated bridges during two recent earthquakes.
The earthquakes, magnitudes
6.5 and 6.4, respectively, occurred on June 17
and June 21, 2000, along a
strike slip fault in a rural area
of the South Iceland Lowlands
near the village of
Thjorsa bridge in the South Iceland Lowlands was subjected
to a peak ground acceleration of 0.84 g.
The events took place
after 88 years of relative seismic
quiescence in the South
Iceland Seismic Zone (SISZ)
where, based on historic
records, damaging earthquakes have repeatedly taken place.
characteristic of the SISZ is that every 100-140 years or so, strong
earthquakes tend to occur in sequences over a period ranging from a
few days to a few years, releasing tectonic strain over a large part of the SISZ. Although this summer’s earthquakes released
considerable strain, it is still possible that an event of comparable size will take place in the near future.
Damage to infrastructure was minor and no significant injuries were reported.
The Iceland Public Roads Administration has
been using seismic isolation on bridges for several years, and four isolated bridges were located in the epicentral area.
A team, including Mr. Higgins, Mr. Halldorsson, Einar Haflidason, Head of the Bridge Division, Public Roads
Iceland, and Bjarni Bessason and G.I. Balduinsson, EERCUI, visited the isolated bridges and one non-isolated bridge.
All of the bridges were fully operational after the earthquakes, and suffered only minor damage.
One of these bridges, the Thjorsa Bridge, was located 5 km from
the June 21st epicenter and only 2 km from the closest surface fault.
The bridge consists of three spans: two approach spans with slab
on girder construction and one center span consisting of a 270
footsteel truss arch (see photos). Only the center span was isolated.
The bridge was instrumented with accelerometers, and
during the June 21st earthquake, the maximum recorded peak
ground acceleration was 0.84 g. It suffered minor permanent displacements
in both the lateral and longitudinal directions.
The EERCUI is presently analyzing the data recorded by several
accelerometers on the Thjorsa Bridge to fully quantify the benefits
of seismic isolation and compare the results from their models
to the actual performance of the structure. It is anticipated that
the results of this study will be published in early 2001.
view (left) shows where
the elastomeric seismic isolation bearings are
in the Thjorsa Bridge; above
is a close-up of one of
More information on the Iceland earthquakes and ensuing research
efforts will be made available through MCEER and the EERCUI.
Check the Highway Project section of our web site at