Study On Mechanical Behavior Of FRP Concrete Composite Beams With Perforated Plate Connectors

FRP concrete composite structure is a new type of composite structure which uses FRP instead of traditional steel.Because of its light weight and good corrosion resistance,it has a wide application prospect in engineering structure.For FRP concrete composite structure,reliable interface connection is an important prerequisite to ensure the cooperation between them.At present,scholars at home and abroad mainly focus on the connection of two materials in FRP concrete composite structure,such as bolts and cementation.However,due to the need of drilling holes,the integrity of fiber will be damaged by using bolt connectors,and it is difficult to quantitatively grasp the bearing capacity of cemented layer when using cementation.The FRP perforated plate connector has the advantages of better integrity,controllability,and more excellent mechanical properties,which can effectively solve the problems of the above connection.However,there are few researches on its mechanical properties at present,and there is a lack of a complete theoretical system and calculation method.Therefore,supported by the national key R & D Program(2017YFC0703005),this paper studies the mechanical properties of FRP perforated plate connectors.The push out tests of 11 FRP perforated plate connectors were carried out to study the effects of diameter of perforated bars,opening size,opening spacing,concrete strength,presence or absence of perforated bars and number of opening rows on failure mode,ultimate bearing capacity and shear stiffness of FRP perforated plate connectors.The test results show that the specimens show three failure modes: I.shear failure of concrete tenon and bending failure of perforated reinforcement;II.Failure of bond surface between FRP I-beam and FRP perforated plate;III.bending failure of perforated reinforcement on one side and failure of concrete tenon,and interlaminar shear failure on the other side.Through the analysis of the influencing factors of the shear performance of the connector,it can be concluded that: when the diameter of the perforated steel bar increases from 6 mm to 8 mm,the ultimate bearing capacity increases by 8%,and the shear stiffness increases by 19%;when the opening diameter of the FRP perforated plate increases from 20 mm to 25 mm,the ultimate bearing capacity increases by 10%,and the shear stiffness increases by 20.9%;when the opening spacing increases,the stress at the FRP opening will spread more evenly,When the spacing increases from 100 mm to 200 mm,the ultimate bearing capacity increases by 26.3% and the shear stiffness increases by 87.8%;when the concrete strength changes from C40 to C50,the ultimate bearing capacity increases by 5.8% and the shear strength increases by 23.4%;when the through reinforcement is set,the concrete in the hole will be in the triaxial compression state,which makes the ultimate bearing capacity increase by 19.7% and the shear stiffness increase by 15.6%;when the hole is opened,the concrete in the hole will be in the triaxial compression state When the number of rows increases from two to three,the ultimate bearing capacity of the member increases by 19.8%,but the improvement of shear stiffness is less,and the increase of the number of rows leads to the superposition of stress,reduces the utilization rate of openings,and reduces the single hole bearing capacity by 25.4%.The nonlinear finite element model of the push out specimen is established and verified by the test results.Based on the Hashin failure criterion,the tensile and compressive damage of fiber and matrix are output,and the failure state of FRP perforated plate at different stages is determined.The results show that in the FRP perforated plate,the matrix compression failure and matrix tension failure expand fastest in the region where they appear,and the ultimate failure degree is high,and the ultimate failure range covers the whole area around the hole.Through the parameter analysis of the factors influencing the shear resistance of FRP open-hole plate connectors,it can be concluded that the ratio of the diameter of the through steel bar to the size of the opening has a greater impact on the shear performance.When the opening is greater than 20 mm,the ultimate bearing capacity and shear stiffness appear peak value,exceeding the peak point.With the increase of the diameter,the effect of improving the shear resistance is smaller and smaller.When the opening hole diameter is 35 mm,the opening range is more than half of the width of the FRP opening plate.At this time,the stress at the opening diffuses to the edge of the opening plate.The failure mode of FRP plate extrusion damage occurs on the opening plate.The stress performance of the connector of the opening plate is not fully developed,which leads to the decrease of bearing capacity.Therefore,the diameter of the opening matching the width of the opening plate should be selected in the actual project;With the increase of the spacing between holes,the ultimate bearing capacity and shear stiffness show exponential increase,which is due to the different distribution of FRP fibers,the distance between the holes will affect the transfer of the force between the holes;The increase of concrete strength makes the shear force that concrete tenon can bear in the hole increase,and the ultimate bearing capacity and shear stiffness increase with the increase of concrete strength,showing a non-linear growth trend.The thickness,ultimate bearing capacity and shear stiffness of the open-hole plate show an exponential growth trend.Based on the experimental results,combined with the results of finite element analysis,regression analysis of the failure mode of concrete tenon shear failure and perforated steel bending failure is carried out,and the calculation formula of the bearing capacity of FRP perforated plate connector is obtained and verified.Based on the anti sliding mechanism of perforated plate connector in steel-concrete composite structure,the shear stiffness calculation formula of perforated GFRP perforated plate connector in elastic rising stage is obtained,which is verified by finite element results and has good accuracy.