Research On Seismic Performance Of PC Frame Structures Under Extremely Rare Earthquakes

With the implementation of the fifth generation of ‘Seismic ground motion parameters zonation map of China’(GB18306-2015),it has explicitly proposed the concept of ‘four grades of earthquakes’,which the extremely rare earthquakes is added on the basis of small earthquakes,medium earthquakes,and rare earthquakes.It puts forward higher requirements for the seismic performance of building structures.Then,the prestressed concrete(PC)frames structures is widely used in major engineering,but there are still few studies on the seismic performance of PC frames under extremely rare earthquakes.Therefore,this paper systematically studied the PC frames’ seismic performance under extremely rare earthquakes,with the seismic resistance grades of I,II,III,which are designed in code.And it is expected to provide reference for the design of PC frames or the new prestressed code’s revision.The research contents and conclusions are as follows:(1)Six PC frame structures,including the seismic resistance grades of I,II,III and different size of beam section,are designed according to the current Chinese code.The models based on nonlinear fiber beam-column finite element are established in Open Sees.The period and mode of vibration are compared with the PKPM model.By simulating the existing low-cycle horizontal reciprocating load test,the hysteresis curve and skeleton curve of the test results are well matched.Therefore,the applicability of the model is verified.(2)By improving the existing harmony search method for ground motion selection,dynamic time-history analysis is performed for two differently periodic PC frame structures.Then it is compared with the periodic point method,the dual-band method and the area method for calculation results.The results show that using the results of the improved harmony search method to selecte ground motion is a preferably match for the site and structural characteristics.It is applicable to both elastic time-history analysis and elastoplastic time-history analysis.The dispersion of structural response parameters small,which is close to the code’s result.(3)Through Pushover analysis,it can obtain the Pushover curve of each PC frame and the distribution of plastic hinges at the performance points.The performance status of each PC frame under rare and extremely rare earthquakes is analyzed.The results show that the PC frame is difficult to realize the ‘strong-column and weak-beam’ under rare earthquakes,and the bottom column is easy to get out of the hinge first.By appropriately reducing the beam section size,it is possible to effectively improving the ductility and hinge-out sequence of the structure that is conducive to the realization of seismic energy dissipation and the ‘strong column and weak beam’.At the performance points of rare and extremely rare earthquakes,the maximum inter-layer displacement angle of the PC frames can meet the limit of 1/50,and it has good seismic performance.(4)Through incremental dynamic analysis and vulnerability analysis,it can obtain the IDA curve,vulnerability curve and the structure’s collapse resistance reserve under far-field and near-field earthquakes.And it analyzes the failure probability under far-field and nearfield extremely rare earthquakes.The results show that under the same ground motion intensity,the structural response and the failure probability under near-field earthquakes is greater than far-field earthquakes’.Under extremely rare earthquakes,the collapse failure probability of each PC frame is small,which meets the seismic fortification requirements of ‘no collapse under rare earthquakes’.Then,the failure probability of PC frames with a seismic grades of III is much smaller than others,and it has the largest anti-collapse reserve factor under extremely rare earthquakes,which indicate its seismic performance is the best under seismic fortification requirements.