| With the advancement of building industrialization,prefabricated frame structure,as the main structural system for the in-depth development of prefabricated buildings,the study of its seismic performance is increasingly put on the agenda,and the problem of node connection is an important factor affecting the development of prefabricated frame structure.As the beamcolumn joint belongs to a relatively weak area,and the force in the core area of the joint is complex,once damaged,it is easy to cause the collapse of the whole frame structure,so the connection of the beam-column joint is the top priority.As a kind of ultra-high performance concrete,the modified activated powder concrete(MRPC)is based on the activated powder concrete(RPC),adding steel fiber and polypropylene fiber(PP fiber),and then improving the ratio.It has excellent mechanical properties such as high strength,good toughness,ductility and energy dissipation.When applied to the post-pouring area of prefabricated frame structure,it can effectively improve the mechanical properties such as tensile and cracking resistance of frame joints.In this thesis,starting from the types of steel fibers,low-cycle cyclic load tests were carried out on 5 prefabricated beam and column middle nodes to explore the influence of MRPC on the seismic performance of prefabricated frame nodes under different types of steel fibers.The main research contents and conclusions are as follows:(1)Based on the design theory of reactive powder concrete(RPC),MRPC was improved and formulated.The mixing ratio was optimized by adjusting the mixing amount of each matrix material,and the positive mixing effect of hybrid fibers was ensured by controlling the volume mixing amount of steel fiber and polypropylene fiber.By adjusting the water-binder ratio and the mixing amount of water reducing agent,the optimal ratio with moderate fluidity,good bonding performance and suitable strength was obtained.(2)Under the action of cyclic loading,the test phenomena and data of each specimen are compared and analyzed.The results show that the beam end bending failure occurs in all specimens,but the crack width of the cast-in-place specimen is large and the damage degree is high,accompanied by the phenomenon of large-scale spalling of concrete and exposed steel bar at the main crack of the beam end.The prefabricated specimens only have slight peeling and crisp concrete,and the joint core area is mostly fine oblique cracks,so the structural integrity is well maintained.Moreover,the prefabricated specimens basically achieve the same or even better than the seismic design requirements of cast-in-place members in terms of energy dissipation,ductility,cracking resistance,tensile resistance and deformation resistance.(3)The seismic performance indexes such as hysteretic characteristics,stiffness degradation,ductility and energy dissipation capacity of the prefabricated specimens are compared and analyzed.The results show that the comprehensive seismic performance of SFZP-1 doped copper-plated linear steel fiber is the worst.The specimen with wavy steel fiber SFZP-4 has the lowest bearing capacity,but the highest energy dissipation capacity.The SFZP-2 specimens of doped end-bent steel fibers have small slip degree,excellent bonding property of matrix materials,strong energy dissipation ability under earthquake,slow and gentle stiffness degradation rate,excellent ductility and deformation resistance,and effectively improved seismic performance.Therefore,compared with different types of steel fibers,The end-bent steel fiber can exert its excellent mechanical properties more effectively and is relatively optimal.(4)Based on test data processing and analysis,"influence coefficient" was added to modify the calculation formula of crack bearing capacity of MRPC prefabricated frame joints under different types of steel fibers.The results show that the calculated values of the shear capacity are in good agreement with the test values,which provides a theoretical basis for the subsequent application of MRPC to the prefabricated frame joints to improve the seismic performance index. |
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