| Summary: | 碩士 === 逢甲大學 === 土木工程學系 === 102 === The interdisciplinary academic integration of rock mechanics and fault mechanics has made the mechanism and effect of rock slipping along the fault plane more and more clarified. Under such circumstances, it has been proven in more and more practical cases that, in addition to the bridge damage caused by ground motions during earthquakes, the area of localizations of deformations will also lead to damages to bridges with seismic resistant designs.
In view of the above, bridges constructed both before and after the promulgation of seismic design specifications of bridges have studied in this research. In each case, three bridges in the disaster area of 311 earthquake in Northeastern Japan which were not affected by the tsunami have selected. Results from this dissertation indicate that, as long as the influence of shear banding is excluded, even bridges before the promulgation of seismic design specifications did not show any obvious damage during a severe earthquake. On the contrary, if the influence of shear banding is not excluded during a huge earthquake, even bridges after the promulgation of seismic design specifications showed obvious damages during the major earthquake.
It has been shown by the mechanism of fault propagation that the slipping of active fault will lead to various fractures associated to brittle shears surrounding the active fault, and the rapid shearing fracture process will trigger the volume expansion of rock. This will then increase the degree of brittle fracture of rock, which will directly damage the bridge foundation or indirectly cause horizontal and vertical relative movements for the foundations of each two adjacent piers, thus leading to shear planes of brittle fractures among various components of bridges due to localizations of deformations. These facts have proven to be the main cause of damages to vibration reducing components of some bridges during a severe earthquake after the promulgation of seismic design specifications of bridges.
With the discovery of the actual reason leading to bridge damage during a major earthquake in this dissertation, the author has suggested that future bridge seismic design specifications should take into consideration the shear banding caused by localizations of deformations in order to avoid widespread damages to the bridges (which are in compliance with seismic design specifications) over curved incised riverbed during a major earthquake.
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