Performance of bridges during the 2010 Darfield earthquake

This paper presents a summary of the performance of the over 800 road, rail and pedestrian bridges in the Canterbury region of New Zealand during the M_w7.1 Darfield earthquake. This event occurred on September 3 2010 (UTC) with an epicentre 40 km west of central Christchurch. Information is based on the visual inspections of fifty five bridges carried out by the authors, as well as information provided by other institutions involved in the post-earthquake inspections. Out of the total bridge stock, eight road bridges required closure following the event, mainly due to approach damage caused by liquefaction induced lateral spreading. Of these bridges, only one suffered significant damage to the superstructure. Six pedestrian bridges suffered damage as a result of lateral spreading loads and will likely require replacement. The superstructure stiffness of these bridges was much less than the road bridges and they were therefore unable to resist compressive loads induced by lateral spreading. The two major factors that contributed to the good performance of the bridge stock were first, most bridges in the Canterbury area had small to moderate spans that generally exhibit a sturdy seismic response, due largely to their symmetry and limited reactive mass. Secondly, newer bridges were generally designed to resist forces larger than the demands imparted by this earthquake.