To study the eccentric compression performance of ultra-high performance concrete (UHPC) columns,seven UHPC columns and one high-strength concrete (HSC) column were tested.Variation parameters include:the steel fibers volume of UHPC,load eccentricity and stirrup ratio of columns.The failure mode,bearing capacity and deformation capacity of the specimens with vertical loading were studied,and the following conclusions were drawn.It is demonstrated that the failure mode of UHPC eccentric compression columns includes large eccentric tension failure and small eccentric compression failure.Large eccentric tension failure mainly showed the following three characteristics:the tensile longitudinal reinforcements were yield,fine cracks appeared in tension zone and the UHPC in compression zone was crushed.However,small compression eccentric failure mainly showed the following two characteristics:less and slighter cracks appeared in tension zone and the UHPC in compression zone was crushed,without the yield of tensile longitudinal reinforcements.Due to the "bridging" effect of steel fibers,the development of cracks were delayed,the number of cracks increased significantly,and the width decreased.The load-deflection curves of large eccentric columns shows a gentle descending section,which shows that the specimens have good ductility.Comparing with HSC column,the cracking loads of UHPC columns increased 44.5% and 59%,and the ultimate loads increased 30.2% and 58.9%.With the increase of steel fiber volume,the carrying capacity of UHPC columns increased by 13.3%~58.9%,and the failure deflection increased by 14.3%~146.5%.With the increase of stirrup ratio,the carrying capacity of UHPC columns increased by 6.2%~11.4%,and the failure deflection increased by 14%~14.8%.The increase of steel fiber volume and stirrup ratio has an effective effect on improving bearing capacity and deformation capability of UHPC columns.Due to the high tensile capacity of UHPC,the contribution of UHPC tensile strength to carrying capacity was considered in bearing capacity formula.And an equivalent rectangular stress diagram was used to simplify the calculation.The theoretical calculation results agree well with the test results.It can provide a theoretical basis for engineering application.
