Lucas Hogan

Dynamic Field Testing of a Three-Span Precast-Concrete Bridge

AbstractThere has been little full-scale physical experimentation to support the findings of numerous computational studies regarding the contribution of various substructure components to overall bridge-foundation system behavior. In response to this lack of experimental data, a field testing program was undertaken to investigate the in situ dynamic characteristics of a 27-m-long, three-span, precast-concrete bridge. Forced vibration testing and system identification were used to characterize the dominant modal behavior of the bridge-foundation system in each loading direction, leading to identification of the likely force-transfer mechanisms between the structure and the substructure components. It was determined that both the transverse and longitudinal responses of the bridge were dominated by the abutment stiffness, with the passive resistance of the buried settlement slab contributing significantly to the transverse response and the backfill passive resistance dominating the longitudinal response.

Seismic Performance of Concrete Bridges during Canterbury Earthquakes

In less than six months the city of Christchurch, experienced two major earthquakes on September 4, 2010 and February 22, 2011. The former was generated by rupture of the previously unknown Greendale fault releasing a magnitude (Mw) 7.1 earthquake at 30-40km away from the city, while the latter event, a Mw 6.2, was less than 10km from the Central Business District on a buried fault at beneath of the city. Lifelines sustained widespread damage in Christchurch City and the closest districts of Selwyn and Waimakariri. However, no major bridge collapses were registered, and only twenty bridges required closure due to damage caused by the two earthquakes. Canterbury soils are susceptible to liquefaction, and the resulting lateral spreading caused extensive damage to roads/bridge approaches and the associates lifelines. Authors aim to provide a seismic damage assessment overview of Canterbury bridges, emphasizing unexpected issues that are still not properly detailed in New Zealand and overseas standards.