| The use of Ultra high performance concrete(UHPC)in bridge structures can effectively solve various diseases that are prone to occur in traditional prestressed concrete bridges and improve the durability of bridge structures.The section of UHPC beam is slender,and the traditional steel strand will lead to dense steel strand spacing,which affects the construction quality.The application of 17.8 mm larger diameter strand is significant.However,there are few studies on the combination of UHPC and 17.8 mm steel strand.In this paper,the bonding properties of UHPC and 17.8 mm steel strand are studied by drawing test.The influencing factors of bonding properties and the distribution of bonding stress in the range of bonding length are studied.The main work is as follows.(1)Nine groups of 27 pullout specimens were designed to observe the failure mode and analyze the influence of different influencing factors on the bonding performance.The results show that :(1)The bond-slip curve of UHPC and larger diameter strand can be divided into three stages: rising stage,strengthening stage and sliding stage.(2)The load-slip curve of UHPC and larger diameter strand did not show a significant decline,and the anchorage failure mode was stiffness failure.(3)The bond length has a great influence on the bond strength and the peak value of bond stress between UHPC and larger diameter strand,while the thickness of protective layer and stirrup only have a great influence on the peak value of bond stress.(4)The bond stress between UHPC and larger diameter strands is unevenly distributed within the bond length range,and increases with the bond length.The uneven trend will also increase.(2)Based on different influencing factors of bond strength,the bond strength calculation formula of UHPC and larger diameter strand was obtained by fitting,and the bond strength calculated by the formula was close to the experimental value.At the same time,according to the characteristics of bond-slip curve,the bond-slip constitutive relationship between UHPC and larger diameter strand is given(3)Combined with the proposed bond strength calculation formula,the recommended anchorage length of larger diameter strand in UHPC is given by using reliability theory and approximate calculation method,which improves the economy of design.(4)With the help of finite element analysis software ABAQUS,three groups of models and beam models corresponding to the drawing test are established and the parameters are analyzed.The results show that the bond strength increases with the increase of concrete strength,and UHPC can significantly improve the bond strength between concrete and steel strand.At the same time,the calculated transfer length of larger diameter strand is far less than the standard value,indicating that the bonding performance between UHPC and larger diameter strand is better. |
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