Quick Release Pullback Testing and Analytical Seismic Analysis of a Six Span Composite Girder Bridge.

摘要

A six span four hundred and fifty foot long continuous composite girder bridge has been subjected to extensive dynamic testing to identify its structural dynamic properties. Transverse motions were induced by quick release pullback testing and vertical motions were induced by normal vehicular traffic. Analysis of the data obtained indicates that this type of dynamic testing is very effective for bridge structures of this type. After obtaining the experimental dynamic properties, a linear analytical model was used for purposes of comparison with the experimental results and for estimating the seismic forces induced by small to moderate earthquakes having recurrence times on the order of 30to 40years in Western Nevada. Results of this analysis indicate that the earthquake forces prescribed by the AASHTO specifications (1961),under which this bridge was designed,are too low for seismic regions of the Western United States. The 300-pound per linear foot minimum transverse wind load controlled in the design,but dynamic seismic analysis indicates that lateral forces in excess of four or five times those caused by the wind loads would be expected to occur every 30to 40years. The peak ground motions associated with the earthquakes used in this study are about 14percent of the largest ground motions ever recorded during an earthquake.