Seismic Analysis Of Frame And Bridge Under Near-field Earthquake Ground Motions

Recently near-field earthquake has become a hot point of earthquake engineering and structure engineering. Focused on the characteristics of near-field ground motions and performances of structures under them, this thesis involves the following work:1. The characteristics of near-field ground motions are discussed and conclusions can be made that the definitation of near-field zone within 20km can be better to consider the special action effects of near-field earthquakes. Besides directivity effects, hanging-wall effects and with velocity pulses,the vertical accelation of near-field earthquakes is very large. So the calculation of vertical earthquake actions need detailed research and furtherly improvement when carrying on seismic design of near-field earthquakes.2.《Code for seismic design of buildings》,《General rule for performance-based seismic design of buildings》,《Specifications of earthquake resistant design for highway engineering》,《Specifications of seismic design for hydraulic structures》,《Code for seismic design of buildings of TaiWan》,《Uniform Building Code 1997》and《Building Standard Law of Japan》are introduced and compared in the aspects of seismic fortification of near-field earthquakes. It is indicated that the code for seismic design of buildings, the specifications of earthquake resistant design for highway engineering and the specifications of seismic design for hydraulic structures still need to be furtherly improved.3. The response of a 10-story frame structure under near-field ground motions is furtherly discussed by nonlinear time history analysis firstly. It shows that the response under near-field ground motions is far larger than that under general ground motions. Peak ground acceleration,PGV/PGA(the ratio of peak ground velocity to Peak ground acceleration) and velocity response spectrum could be the preferred considerations. The seismic response of the structure is obtained using Pushover analysis. Comparing with the results of nonlinear time history analysis, it is illustrated that the method of Pushover analysis can not accurately evaluate the seismic performance of structures subjected to near-field ground motions.4. The analysis of responses of a bridge under a group of ground motions also shows that the importation of near-field ground motions can also cause great impact of force and displacement to bridges. The maximum input energy of near-field ground motions is far greater than that of general ground motions, and most of the energy is produced in such a short time that the structure can not make good use of the internal damping to do the periodic vibration, thus the possibility of the structure destruction will obviously be increased. The near-field earthquake puts forward much higher requirement to the ductility. The elastic-plastic response spectrum of the near-field effect established by the traditional method will underestimate the elastic-plastic displacement of structure, and can not satisfy the deformation requirement of the structure.