Research On The Seismic Performance Factor Of Post-tensioned Unbonded Precast Concrete Frame Structure Based On Pushover And IDA Method

The post-tensioned unbonded precast concrete frame structure is a fabricated structural system with good node integrity and strong self-reset capability,which is of great significance to the development of fabricated structures in China.Although the domestic and foreign researches on the post-tensioned unbonded precast concrete frame structure have achieved great results,the seismic performance evaluation and seismic design recommendations of this type of structure have not yet been perfected.Chinese seismic code adopts elastic design method for frequent earthquakes,which includes a unified response modification coefficient of 2.86 for all structures,ignoring the differences in ductility and energy dissipation capacity of different structures,which is unfavorable for the post-tensioned unbonded precast concrete frame structure.In order to study the seismic performance and seismic design method of posttensioned unbonded precast concrete frame structure,Pushover and IDA methods are used to study the seismic response and seismic performance factors of post-tensioned unbonded precast concrete frame structures in this paper,and the recommended design value of seismic performance factors is given.The main research work is divided into the following several parts:(1)Design post-tensioned unbonded precast concrete frame structures with different number of layers and different fortification intensity that meets the requirements of current Chinese code.Based on the design results,the initial rotational stiffness of different joints and the constitutive curve of the custom joint plastic hinge are calculated through finite element analysis.(2)Based on on the results of step(1),the post-tensioned unbonded precast concrete frame structure analysis models were established,and Pushover analysis under inverted triangle distribution,uniform distribution,and incremental dynamic analysis under 10 natural ground motion records were carried out respectively.(3)Based on the results of the two analysis methods,analyze the seismic response of the post-tensioned unbonded precast concrete frame structure,and analyze the difference of results under different analysis methods.The seismic performance factors under the two methods were calculated respectively,and the recommended values were given.Through the above research content,the main conclusions are as follows:(1)Based on the concept of FEMA plastic hinge,a constitutive model of prefabricated beam column joints is proposed.(2)Under the two analysis methods,post-tensioned unbonded precast concrete frame structures with different floors and different fortification intensities can meet the displacement requirements of frequent earthquakes and rare earthquakes in Chinese codes,and the posttensioned unbonded precast concrete frame structures can under the horizontal force,the plastic hinge at the beam end yields before the column hinge,which conforms to the design concept of "strong column and weak beam".(3)For post-tensioned unbonded precast concrete frame structures,the single horizontal lateral force distribution mode of the Pushover method will cause differences in the development of plastic hinges and actual seismic actions,resulting in differences between Pushover results and IDA analysis results.Therefore,the horizontal lateral force distribution mode of pushover analysis needs to be selected according to the height of the structure.The suggestions for using Pushover method to analyze these structures were given in the paper.(4)Combining the calculation results of the two methods,the recommended values of the seismic performance factors of the post-tensioned unbonded precast concrete frame structure are as follows: The value of the structural over-strength coefficient should be above 2.0;the value of ductility reduction coefficient should be 4.0;the value of response correction factors should be 10.0;the displacement magnification coefficient should be 14.0.