Research On Seismic Performance Of High Strength Fiber-Reinforced Concrete Columns

As modern buildings move towards high-rise,long-span and lightweight,more and more projects choose to use high-strength reinforced concrete or even ultra-high-strength.However,high-strength reinforced concrete has fatal disadvantages: high brittleness and poor ductility.In order to overcome this disadvantages,adding appropriate amount of PVA fiber to high-strength reinforced concrete can significantly improve its ductility.At the same time,under tensile and bending loads,PVA fiber-reinforced concrete shows quasi-strain-hardening characteristics and multi-crack cracking characteristics to a certain extent.In this study,seven columns using PVA fiber-reinforced concrete in column end region and one high-strength reinforced concrete specimens for comparison were designed,and a pseudo-static test was performed on them.Then,the seismic performance was evaluated according to the seismic performance index,and compared with the simulation results.Finally,the lateral displacement angle limits of PVA fiber concrete columns at different performance levels were obtained through statistical analysis.The specific work is as follows:(1)The effects of axial compression ratio,shear span ratio and the content of PVA fiber on the hysteretic characteristics,bearing capacity,deformation capacity,energy dissipation capacity and the law of strength and stiffness degradation of the specimens were studied by pseudo-static test,and their seismic performance was evaluated.The results showed that the axial compression ratio and shear span ratio have a significant effect on the seismic performance of the specimens,and the content of PVA fiber has a great influence on them.Compared with the high-strength reinforced concrete column,the hysteretic hoops of PVA fiber concrete column are more full,its ductility increases obviously,its energy dissipation capacity is better,and its strength degradation is slower.(2)Based on the finite element simulation software OpenSees,a rotation spring element and a shear spring element were added to the fiber model to simulate the bond-slip effect of the steel in the plastic hinge zone and the shear deformation of the specimens.Then the simulation data was compared with the experimental data to verify the accuracy of the OpenSees model.On this basis,the axial compression ratio and shear span ratio were analyzed expansively.The results showed that with the increase of the axial pressure ratio(from 0.2 to 0.6),the decline of the skeleton curve accelerates,the peak load gradually increases,the ductility and the ultimate displacement angle decrease linearly;with the increase of the shear span ratio(from 1.84 to 5.07),the skeleton curve changes very clearly,the peak load decreases rapidly,and the ultimate displacement angle gradually increases.(3)The Kunnath model was used to calculate the damage index of the PVA fiber-reinforced concrete column,and compared with the range of the measured damage index,the agreement was good.In order to apply the performance-based seismic design ideas to PVA fiber-reinforced concrete column structures,the seismic performance levels were divided into five levels,namely: normal use,temporary use,use after repair,life safety,and near collapse.Through statistical analysis of relative frequencies,the PVA fiber-reinforced concrete columns corresponding to 5 performance levels and lateral displacement angle limits exceeding 85%safety guarantee rate were obtained,which were 1/300,1/150,1/80,1/55 And 1/40.