| Recently,a series of buildings with important social impact have been built with the rapid development of China’s economy.A lot of new technologies and materials have been utilized in these buildings extensively.Especially,as a new type of building material,high strength concrete(HSC)has been employed extensively.However,a lot of post-earthquake disaster investigations indicate that brittle shear failure occurs generally in reinforced high strength concrete columns or high strength concrete filled thin-walled steel tubular columns.This results in that the high strength concrete component cannot dissipate the earthquake input energy by fully use of ductility and it threatens the safety of people’s lives and properties seriously.Therefore,it is necessary to investigate methods to improve the seismic performance of high strength concrete members from structural design,construction measurement and material properties and then improve the survivability of important buildings suffered from strong earthquake loads.After that,the loss of people’s lives and properties and social impact will be reduced in the maximum extent.Especially,the improvement of material properties is one effective method to overcome the brittleness of high strength concrete,improve the seismic performance of high strength concrete members,and prevent collapse of buildings from strong ecarthquake load.Ultra-high-performance concrete is an innovative cement-based composite material with excellent mechnacial properties.Therefore,it is a beneficial attempt to apply ultra-high-performance concrete to the field of seismic-resistant performance of engineering structures.However,few of investigations on the seismic performance of ultra-high-performance concrete members are reported recently.Therefore,the seismic behaviors of high strength reinforced ultra-high-performance concrete columns and ultra-high-performance concrete filled thin-walled steel tubular columns are investigated systematically by a large number of experiments,numerical simulations and theoretical analysis.The primary work and achievements include the following several aspects:(1)An innovative ultra-high-performance concrete is developed with compressive strength ≥ 150 MPa and flexural strength ≥20MPa.The effect of nanomaterial and steel fiber on the compressive strength and flexural strength of this innovative material is investiaged by compressive and flexural tests.The results indicate that the type of nanomaterial should be selected reasonably to prepare ultra-high-performance concrete.Meanwhile,the results also illustrate that steel fiber could improve the mechanical properties of ultra-high-performance concrete and the improving effect is more significant with increasing of volume ratio of steel fiber.In addition,the improving effect of twist fiber is best when volume ratio of steel fiber is constant.A meso-sacle FE model of ultra-high-performance concrete is developed to investigate the compressive properties including damage mechanism and steel fiber reinforced mechanism.Meanwhile,massive parametric studies are conducted to investigate the effect of volume ratio of steel fiber,length of steel fiber,shape effect and size effect on the compressive properties of ultra-high-performance concrete.(2)The seismic behaviors of high strength reinforced ultra-high-performance concrete columns are investigated.The failure mode,hysteresis curve,envelop hoops,degradation of strength and stiffness,ductility and energy dissipation of high strength reinforced ultra-high-performance concrete columns under revers cyclic lateral loading are investigated in detail.Meanwhile,the effect of main design parameters including axial compression ratio,reinforcement ratio,stirrup ratio,type of stirrup and shear span ratio on the seismic behavior of high strength reinforced ultra-high-performance concrete columns is also investigated in detail.Eventually,the calculation formula of bending capacity and shear capacity of high strength reinforced ultra-high-performance concrete columns suffered form reverse cyclic lateral loading is derived based on the experimental datas.A precise FE model of the high stregnth reinforced ultra-high-performance concrete columns under monotonic lateral loading is developed to further investigate the effect of main design parameters by massive parametric studies.Meanwhile,the plastic hinge length of the high strength reinforced ultra-high-performance concrete columns is investigated by this precise FE model.Similarly,the effect of axial compression ratio,reinforcement ratio,shear span ratio and volume ratio of steel fiber on the plastic hinge length is also investigated by massive parametric studies.(3)The seismic behaviors of ultra-high-performance concrete filled thin-walled steel tubular columns are investigated.The failure mode,hysteresis curve,envelop hoops,degradation of stiffness,ductility and energy dissipation of ultra-high-performance concrete filled thin-walled steel tubular columns under revers cyclic lateral loading are investigated in detail.Meanwhile,the effect of main design parameters including axial compression ratio,steel ratio,volume ratio of steel fiber and slenderness on the cyclic behavior of ultra-high-performance concrete filled thin-walled steel tubular columns is also investigated in detail.Meanwhile,the seismic behaviors of ultra-high-performance concrete filled thin-walled steel tubular columns are comprared with that of high strength concrete filled thin-walled steel tubular columns and normal strength concrete filled thin-walled steel tubular columns.The results indicate that the seismic behaivors of ultra-high-performance concrete filled thin-walled steel tubular columns is much better.A fiber model is developed to further investigate the seismic behaviors of ultra-high-performance concrete filled thin-walled steel tubular columns by parametric study after validating the fiber model. |
PDF Full Text Request