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Performance of Bridges during the 2010Darfield and 2011 Christchurch EarthquakesLiam Wotherspoon, Aaron Bradshaw, Russell Green, Clinton Wood, Alessandro Palermo, Misko Cubrinovski, and Brendon BradleyLiam Wotherspoon, 1 Aaron Bradshaw, 2 Russell Green, 3 Clinton Wood, 4Alessandro Palermo, 5 Misko Cubrinovski, 5 and Brendon Bradley 5INTRODUCTIONThe region in and around Christchurch, encompassingChristchurch city and the Selwyn and Waimakariri districts,contains more than 800 road, rail, and pedestrian bridges.Most of these bridges are reinforced concrete, symmetric, andhave small to moderate spans (15–25 m). The 22 February2011 moment magnitude (M w ) 6.2 Christchurch earthquakeinduced high levels of localized ground shaking (Bradley andCubrinovski 2011, page 853 of this issue; Guidotti et al. 2011,page 767 of this issue; Smyrou et al. 2011, page 882 of thisissue), with damage to bridges mainly confined to the centraland eastern parts of Christchurch. Liquefaction was evidentover much of this part of the city, with lateral spreading affectingbridges spanning both the Avon and Heathcote rivers.The majority of bridge damage was a result of liquefaction-inducedlateral spreading, with only four bridges sufferingsignificant damage on non-liquefiable sites. Abutments,approaches, and piers suffered varying levels of damage, withvery little damage observed in the bridge superstructure.However, bridges suffered only a moderate amount of damagecompared to other structural systems. Because some bridgescritical to the city infrastructure network sustained substantialdamage, extensive traffic disruption occurred immediately followingthe event.This paper presents a summary of field observations andsubsequent analyses on the damage to some of the bridges inthe Canterbury region as a result of the Christchurch earthquake.Reference is also made to the performance of bridgesfollowing the 4 September 2010 M w 7.1 Darfield earthquake(Gledhill et al. 2011), and details of damage progression are presentedwhere applicable. The ground motion characteristics forboth events and the regional soil conditions are first described.We provide descriptions of the damage at each selected bridgesite and compare observations of liquefaction with predictedresponse using in situ test data.1. University of Auckland, New Zealand2 . University of Rhode Island, Kingston, Rhode Island, U.S.A.3. Virginia Tech, Blacksburg, Virginia, U.S.A.4. University of Arkansas, Fayetteville, Arkansas, U.S.A.5. University of Canterbury, Christchurch, New ZealandLOCAL GEOLOGYThe city of Christchurch, shown in Figure 1, is located alongthe central coast of the Canterbury Plains, an approximately50-km-wide and 160-km-long region created by the overlappingalluvial fans of rivers flowing east from the SouthernAlps. Interbedded marine and terrestrial sediments up to 40m deep overlie 300 to 400 m of late Pleistocene sands andgravels (Brown and Weeber 1992). Much of the city was originallyswampland, beach dune sand, estuaries, and lagoons,which were drained as part of the settlement and expansion ofthe city (Brown et al. 1995). A high water table, one to twometers below the ground surface in the east of the city, graduallyincreases in depth moving across the city to the west. Tothe south of the city are the Port Hills, formed from volcanicactivity (Brown and Weeber 1992).Two spring-fed meandering rivers, the Avon and theHeathcote, cut through Christchurch (Figure 2). The AvonRiver passes through the city from west of the Christchurch▲ ▲ Figure 1. Overview of Christchurch city and its surroundings,with the epicenters of the Darfield and Christchurch earthquakesshown by stars. Boundaries of moderate bridge damageduring the Darfield earthquake at Lincoln and Kaiapoi arerepresented by circles. The region of interest for Christchurchbridges presented in Figure 2 is bounded by the dashed whiterectangle (Google Inc. 2011).950 Seismological Research Letters Volume 82, Number 6 November/December 2011 doi: 10.1785/gssrl.82.6.950