The laboratory testing and inelastic computer analysis are described for a 1936-designed bridge which is typical of many of the older, reinforced-concrete, multi-span bridges in New Zealand. The structure has plain-round (undeformed) reinforcing bars and anchorage details, shear strength, and column-transverse reinforcement that are potentially deficient. Despite the suspected seismic deficiencies, the testing and analysis of the bridge show that its seismic performance will be good.
The results indicate that (a) seismic retrofitting for the subject bridge is not warranted, (b) code criteria applicable to the design of new structures, with deformed reinforcing, can be overly conservative when used for the assessment of existing structures, and (c) plain-round reinforcing bars under seismic forces suffer extensive bond deterioration resulting in pinched hysteretic response which, for earthquakes with strong pulses, can lead to greater seismic damage. Also records show that some earthquakes have a much higher potential to cause damage than the earthquake levels that have typically been assumed in bridge design and retrofitting.
Keywords: Bond, bridges, capacity design, concrete, earthquakes, New Zealand, plain bars, reinforcing steel, retrofitting, seismic evaluation, seismic testing, structural engineering, time-history analysis