| In order to further enhance the structural load-bearing capacity and meet the social demands for the development of the construction industry,Coarse Aggregate Ultra-High Performance Concrete(UHPC-CA)is gradually being applied to engineering construction.However,when UHPC is used in conjunction with ordinary reinforced steel bars,it cannot fully exert its excellent bending and tensile properties.This not only fails to reflect the actual performance of UHPC structures,but also results in a waste of resources.The combination of UHPC and HRB600-grade reinforced steel bars is more conducive to the performance of its bending and tensile properties.This structural form also has the advantages of high strength and durability,but the reliability of the steel bar connection becomes a key issue.Considering that the bonding performance between UHPC and high-strength steel bars is better than that of ordinary concrete,the simplest overlap form can be used for the connection of steel bars in UHPC.To further promote the application of UHPC-CA and high-strength steel bars,it is necessary to conduct research on their overlap performance.This study explored the impact of overlap length,protective layer thickness,reinforcement ratio,coarse aggregate content,and steel bar diameter on the steel bar overlap performance through tensile tests.Through regression analysis,the calculation formulas for the overlap bonding strength and overlap length of HRB600-grade reinforced steel bars in UHPC-CA were obtained,and the applicability of the formula was analyzed through beam tests,with good results.The formula was simplified according to the function form of the current Chinese regulations for overlap length calculation.The specific research content and conclusions of this article are as follows:(1)By conducting tension tests,the study explores the factors influencing the performance of steel bar splices.An analysis of the splice failure mechanism reveals that UHPC’s exceptional tensile properties induce higher and uniform tensile stress in the concrete surrounding the steel bars,effectively balancing radial fracture stress.Consequently,it exhibits superior splice performance.A computational formula is proposed for the bond strength and critical lap length of HRB600-grade steel bars in UHPC-CA.(2)The critical lap length formula is utilized to calculate the lap length value for the design of the beam test.This simulation accounts for the most unfavorable load conditions and involves steel bar splicing in the tension zone of the test beam.A three-point loading test on the beam is employed to validate the applicability of the lap length formula in actual structural components.The test results demonstrate that a beam with a lap length of 12 d,when reinforced with stirrups,exhibits crack development,distribution,failure mode,ultimate load,and deflection that are essentially similar to those of a non-spliced beam.Hence,it meets the requirements for splice performance,and there is good agreement between the calculated lap length value and the experimental value.Increasing the lap length and appropriately configuring the reinforcement in the splice region effectively improve the crack propagation and failure mode of the test beam,thereby enhancing its stiffness and ductility.(3)By incorporating the fundamental material properties of UHPC and HRB600-grade steel bars into lap length calculation formulas from different countries,a comparative analysis is conducted.The results indicate that the lap length specified by the American code significantly exceeds the experimental values,whereas the lap length specified by the Chinese code closely approximates the experimental values.Taking the formula format from the Chinese code as the primary basis,simplification of the obtained lap length formula is carried out,along with a comprehensive investigation of design values.This enhances the accuracy and safety of lap length calculation for HRB600-grade steel bars in UHPC-CA. |
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