Reinforced Concrete Bridge Columns Tested Under Long and Short Duration Ground Motions

Abstract eng:
Recent earthquakes in Indonesia (2004), Chile (2010), and Japan (2011) are reminders of the possible occurrence of a longduration, large-magnitude earthquake in the Cascadia subduction zone along the Pacific Northwest Coast of the United States. The importance of studying the effect of ground motion duration on structural performance has been highlighted by these earthquakes. Current seismic design specifications do not consider this effect. Conclusions from previous research with regard to duration have been conflicting. This paper describes a comprehensive experimental study to investigate the effect of duration on reinforced concrete (RC) bridge columns. The results of shake table tests of three identical large-scale RC bridge columns are discussed. The columns were tested using spectrally equivalent long and short-duration ground motions. A cumulative damage metric is used to define columns damage states. This metric was correlated against damage states obtained from published data on more than 25 bridge columns that had been tested to failure. The results showed that the columns subjected to long-duration motions were more highly damaged than those with short-duration motions. The reinforcing steel in the columns subjected to longer motions had a significantly larger number of plastic strain cycles, which caused the bars to fracture at lower displacements compared to the columns subjected to short-duration motions; i.e. ground motion duration affected the collapse capacity of these columns. Therefore, it is recommended that duration effects be considered in the seismic design of bridges, especially in regions where long-duration earthquakes may occur.

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