Application Of IDA Method In Seismic Fragility Analysis Of Unbonded Prestressed Concrete Frame Structures

Unbonded prestressed concrete,as a a new technology in the field of concrete,not only can speed up the construction progress,reduce the self-weight of structure and save steel,but also can improve its overall efficiency,which is a trend in the development of the building structure.In recent years,although researches on the seismic performance of unbonded prestressed concrete structures have achieved a lot,but the application of such structures in seismic fortification area is little and its performance-based seismic researches are few.In order to improve the seismic performance of unbonded prestressed concrete structures effectively and to promote the application of such structures in seismic fortification areas,in this paper,the performance-based seismic study of unbonded prestressed concrete frame structures is carried out by incremental dynamic analysis method,then the structural collapse resistance and seismic economic losses are evaluated by seismic fragility analysis.The prestressing force applied in the unbonded prestressed concrete structure can be expressed by the prestressed degree,which can directly affect the seismic performance of the structure.Therefore,in this paper,considering the influence of prestressed degree,a five-story two-span unbonded prestressed concrete frame is taken as the research object,and the incremental dynamic analysis of the structural model with prestressed degree of 0.4,0.6,0.8 and 1.0 is carried out by using MIDAS / gen finite element software.At the same time,the IDA curves are established,with spectral acceleration 1(,3%)aS T and the maximum drift angle max? as the earthquake intensity index and structural damage index.In the end,from the analysis data of IDA curves and the seismic performance of the structures are studied,the results show that: in the elastic stage,with the increase of prestressed degree,the strength and stiffness of the unbonded prestressed concrete frame structure becomes larger,and the seismic performance of structure is improved;in elastic-plastic phase,when the structure reaches CP limit state,the spectral acceleration of the structure with the prestressed degree of 0.6 is the largest,and the intensity and stiffness of the structure decrease slowly with the increase of the spectral acceleration,so that the seismic performance of the structure is the best for the application in the area of anti-earthquake.Based on the theory of seismic fragility,this paper summarise the analysis procedure of structural seismic fragility based on IDA analysis.The fragility curves of different prestressed degree structures under different performance levels are analyzed,then the anti-collapse ability and the earthquake economic loss are evaluated.The results indicate that the prestressed degree on fragility curves of structural changes in IO and LS limit state is not significant.For the fragility curve of the structure in the CP limit state,when the prestressed degree is 0.6,structural fragility curve is the most gentle.The probability of surpassing the CP limit state under the same level of rare earthquakes is small,indicating that the structure exhibits good plastic deformation capacity and ductile energy dissipation performance after entering the elastoplastic stage;From the anti-collapse reserve coefficient of the structure,it can be seen that the structure with the prestressed degree of 0.6 has the highest anti-collapse reserve coefficient,indicating that the unbonded prestressed concrete structure has strong anti-collapse ability and high safety reserve under the medium prestressed degree,and the direct economic loss of the structure is the least when it is subjected to a definite annual frequency earthquake,which is beneficial to the application of the structure in the earthquake-resistant area.