Study On Seismic Performance Of ECC-Reinforced Concrete Composite Piers

As the main vertical load-bearing component of bridge structure,pier often adopts reinforced concrete(RC)structure.Under the earthquake load,the major part of bridge structure is often damaged or even collapsed due to the damage of RC pier.The Engineered Cementitious Composites(ECC)is a fiber-reinforced cement-based material with the feature of high ductility and multi-cracks cracking.The application of ECC in the plastic hinge area of RC piers can give full play to the excellent properties of ECC materials and improve the seismic performance of piers.Supported by the National Key R&D Program of China(2016YFC0701202),through pseudo-static test and Open Sees finite element modeling,the seismic performance of ECC-RC composite pier and the influence of several parameters on its seismic performance were investigated and analyzed,which provides reference for future theoretical research and practical engineering application.The main research work and conclusions are as follows:1)Based on the existing research on the seismic performance of RC piers,the failure mode and the corresponding seismic performance research methods under the earthquake load are analyzed,and the mechanical properties of ECC materials are studied.By summarizing of the existing research on the seismic performance of ECC-RC composite pier,the newly ECC-RC composite pier,only the plastic hinge area on the bottom of which is covered by ECC material,is put forward.Four ECC-RC composite pier specimens,with different ECC heights and different ECC thicknesses,and one cast-inplace RC pier specimens were designed and tested.2)The failure mode,hysteretic curve,skeleton curve,bearing capacity,ductility,stiffness characteristics,energy dissipation capacity and residual displacement of each specimen are analyzed through pseudo-static test.The results show that the hysteretic curve of ECC-RC composite pier is fuller,the peak loading is higher and the energy dissipation capacity is stronger than that of the RC pier,and the cumulative energy consumption in the ultimate state is about two times of that of the RC pier.Due to the existence of ECC,the integrity in ultimate state and the ductility of ECC-RC composite pier is better than that of the RC pier.Compared with the increase of ECC thickness,the increase of ECC height can improve the ductility of the specimen more effectively.But the increase of ECC height or thickness has little effect on residual displacement.3)Based on Open Sees,the ECC-RC composite pier is simulated,and the hysteretic curve and skeleton curve obtained from the FE analysis are compared with the test results,which verifies the validity of the model.The influence of ECC height,ECC thickness,axial compression ratio,slenderness ratio,longitudinal reinforcement ratio,yield strength of longitudinal reinforcement,ECC compressive strength and concrete strength on the seismic performance of ECC-RC composite pier is further analyzed through FEM.The results show that the higher height and thickness of ECC,the higher peak loading of the specimen,the better ductility,but the effect will be weakened when it is increased to a certain extent.With the increase of axial compression ratio,the ultimate load of specimen increases,but the excessive axial compression ratio leads to the brittle failure and lower ductility of the specimen.With the increase of slenderness ratio,the peak loading of specimen decreases,and the ductility increases.With the increase of longitudinal reinforcement ratio,the stiffness,peak load and ductility of specimen increase.While it has little effect on the seismic performance of specimen.The increase of ECC compressive strength can increase the peak load of specimen and change the trend of downward part of skeleton curve,but the concrete strength has little effect on the seismic performance.