| Steel-normal concrete composite beams commonly suffer from diseases such as cracking of bridge decks and corrosion of shear connectors,leading to reduced structural bearing capacity and shortened service life,seriously threatening the safety of bridge operation.Steel fiber reinforced concrete(SFRC)has excellent crack resistance and toughness enhancement performance,highly meets the performance requirements of bridges in harsh service environments,and can ensure the safety and reliability of the entire life cycle of the structure.However,there is currently limited research on the application of SFRC in steel-concrete composite structures,and the design theory of shear connectors in steel-SFRC composite structures is still incomplete.This article combines experimental research,numerical simulation,and theoretical analysis to study the shear performance of different forms of connectors in steelSFRC composite structures.The following innovative research work has been completed:(1)Pull-out tests were conducted considering the content of steel fibers in concrete and the diameter of steel bars.The failure modes of different specimens were analyzed,revealing the mechanism of bond-slip failure of steel bars and SFRC.The distribution characteristics of bond-slip curves of pull-out failure specimens were clarified,and a constitutive model for bondslip of steel bars and SFRC was proposed considering the influence of steel fiber content and steel bar diameter.Based on the single spring connection element method,a finite element model considering the bond-slip between steel bars and steel fiber reinforced concrete was established.The results showed that the single spring connection element defined by the bondslip curve can accurately simulate the bond-slip behavior of steel bars and SFRC.(2)Push-out tests were carried out to investigate the shear performance of stud shear connectors in steel-NC and steel-SFRC composite structures,taking into account parameters such as steel fiber content,stud diameter,and length.The difference in the shear performance of shear connectors s in steel-NC and steel-SFRC composite structures was studied,and the failure modes of shear connectors and strain distribution characteristics of various structural components during loading were elucidated.The influence of parameters such as stud diameter,yield strength,and weld seam on the shear bearing capacity of stud shear connectors was analyzed,and proposed a calculation method and load slip curve formula for the shear bearing capacity of stud shear connectors considering the influence of steel fibers.The results indicate that due to the bridging effect of steel fibers,the shear performance of shear connectors in steel SFRC composite structures has been significantly improved.(3)Push-out tests were performed on the shear performance of PBL shear connectors,taking into account parameters such as steel fiber content,number of openings,and diameter of penetrating steel bars.The difference in mechanical properties and failure mechanism of PBL shear connectors in two types of concrete materials were studied,and the crack resistance and toughening mechanism of steel fibers in steel-SFRC composite structures were clarified.The crack propagation and failure mechanism of concrete slabs under load were revealed.A finite element model was established to consider the bond-slip between H-shaped steel and concrete slabs,as well as the bond-slip between steel bars and concrete tenons.The influence of key design parameters on the shear bearing performance of PBL shear connectors was explored.A calculation method for the shear bearing capacity of PBL shear connectors in steel-SFRC composite structures was proposed,which comprehensively considers the contributions of the steel concrete bond effect,reinforced concrete tenons,and perforated steel plates.(4)A new type of composite shear connector with stud and PBL was proposed,and composite shear connector push-out tests were conducted considering the arrangement of studs and the number of studs and penetrating steel bars.The failure mode and damage mechanism of the composite shear connectors were revealed,and the synergistic bearing mechanism of the stud and PBL shear connector was elucidated.A method for determining the shear stiffness of the composite shear connector was constructed.A finite element model considering the slip effect of the steel-concrete bond was established to analyze the influence of the diameter and yield strength of studs and penetrating steel bars on the shear performance of composite shear connectors.The results showed that considering the slip effect of the steel-concrete bond can significantly reduce the calculation error of shear stiffness of composite shear connectors.A calculation method for the shear bearing capacity of composite shear connectors considering the slip effect of the steel-concrete bond was proposed.(5)Mechanical performance tests were carried out on steel-NC and steel-SFRC composite beams connected by stud shear connectors in the negative moment zone,verifying the inhibitory effect of SFRC on crack propagation in the steel-concrete composite beams.The results show that there are not many cracks in the concrete slab after the failure of the steel-NC composite beam,but the crack width is relatively large;The cracks in the steel-SFRC composite beam appeared relatively late,with a small crack width and slow development.Local buckling deformation occurred in the flange plate of the steel beam.The neutral axis of the steel-NC composite beam remains stable within the range of 160 mm of the web,while the neutral axis of the steel-SFRC composite beam remains at a height of 190 mm.The parameter analysis of the finite element model shows that the bending capacity of the steel-concrete composite beam connected by composite shear connectors,PBL shear connectors,and stud shear connectors decreases sequentially.The thickness and width of the concrete slab,as well as the height of the H-shaped steel beam web,have a significant impact on the bending capacity of the steelconcrete composite beam,while the increase in the thickness of the steel beam web has limited improvement in its bending capacity. |
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