The Confinement Effect And Configuration Optimization Of Circular Hollow RC Columns

Incorporating hollow sections to bridge columns for long-span and high-elevation concrete bridges has gaining popularity due to its advantages over solid sections,such as reduced self-weight,effective section propertied,and good quality control during construction stage.The current practice for seismic design of reinforced concrete bridges is to establish inelastic flexural mechanism in bridge columns that are required to be detailed with adequate transverse reinforcement in plastic hinge regions,so that they can behave in a ductile manner when subjected to earthquake loads.Therefore,the influence of confinement configurations on seismic performance of RC bridge columns are studied by experimental and numerical simulation in this paper,which provides valuable suggestions for the engineering application of circular hollow RC columns.The main research of this thesis including:(1)Two large-scale circular hollow concrete columns were tested under a constant axial load and a cyclically reversed horizontal load.The primary investigated parameter was the ratio of inner-to-outer layer of transverse reinforcement amount.One column was designed based on the current practice that equal amount of inner and outer layer of transverse reinforcement amount was provided,while the other column was detailed with an inner-to-outer transverse reinforcement amount ratio being 4:9.The failure of the column unit confined with a 5:5 inner-to-outer ratio was characterized by crushing of confined concrete near the outside concrete wall.And the failure of the column unit confined with a 4:9 inner-to-outer ratio was characterized by fracture of outer longitudinal reinforcement.(2)The flexure behavior and confinement effect were investigated.The test results showed that both column units presented satisfactory hysteretic response.The column unit confined with a 4:9 inner-to-outer transverse reinforcement ratio showed more stable response under cycles of load reversals with lower amount of confined concrete crushing and higher level of ductility.The demand developed on the inner circular hoops are smaller than the outer circular hoops for hollow columns confined with two layers of transverse reinforcement.In addition,arrangement of cross-ties was optimized to facilitate construction.Design of alternately arranged cross-ties was proposed based on the test results.(3)A reliable numerical simulation method was developed to simulate the nonlinear behavior of circular hollow RC columns under earthquake loading.The simulation response showed a satisfactory agreement with the measured responses of the column units,indicating that the selected calculation method of confined concrete could predict the flexural behavior of circular hollow RC columns.