Study On Flexural Properties Of BFRP-Steel Tube Confined High-Strength Mortar Composite Components

With the rapid development of infrastructure construction in China,the inventory scale of Bridges and tunnels keeps increasing,and the related maintenance demand also increases rapidly.With the increase of service years,Bridges will lose strength and stiffness in different degrees,and there will be long-term diseases such as bending cracking of beam body.The concrete structure of tunnel lining will deform and crack with the aging of time,which will seriously affect the safety of bridge and tunnel structure.BFRP-steel tube confined high-strength mortar composite profiles can better meet the needs of bridge and tunnel concrete structure reinforcement,effectively improve the strength and stiffness of the original structure,with good corrosion resistance,construction convenience and economy,as an improved and optimized reinforcement method has a good application potential.In this study,the bending property change mechanism of BFRP-steel tube confined high-strength mortar composite profiles under the influence of multiple factors was studied by the composite profile component test,theoretical calculation and finite element simulation.The main research contents include:(1)Four-point bending test of BFRP-steel tube confined high-strength mortar composite profiles was carried out to study the influence of six factors on the flexural performance of BFRP-steel tube confined high-strength mortar composite profiles.The section strain distribution,deflection variation along length and the relationship between curvature and deflection are analyzed.The bending process can be divided into three stages: elastic stage,elastic-plastic stage and strengthening stage.The increase of section size and steel tube thickness significantly improves the flexural capacity,while the decrease of steel tube wall thickness accelerates the stiffness loss of specimens.BFRP constraints have a weak effect on the stiffness improvement,but can effectively reduce the stiffness loss with the increase of deflection.(2)The combined axial compressive strength and plastic development coefficient of BFRP-tube confined high-strength mortar composite profiles were determined,and the calculation method of flexural bearing capacity of the composite profiles was proposed.Axial compression tests and finite element models were designed to verify the modified formula of axial compression capacity,and the functional relationship between the combined constraint coefficient and plastic development coefficient of integrated BFRP and steel tube was established.The calculation formula of flexural capacity obtained has good accuracy.The influence of various factors on plastic development coefficient is analyzed by the calculation model,and the improvement degree of ultimate bearing moment of specimens under the constraint of BFRP and steel tube is clarified.Based on the principle of superposition,a practical calculation method of BFRP-steel tube confined high-strength mortar composite profiles was proposed,and different reduction coefficient values were determined in the calculation of initial bending stiffness and service bending stiffness of core grouting mortar and BFRP.The final calculation method was in good agreement with the test results.(3)Based on the finite element analysis method,the BFRP-steel tube constrained high-strength mortar composite profiles under the influence of multiple factors were studied,and the effectiveness of the finite element analysis method was verified by comparing the test results.In the bending failure process of composite profile specimens,the BFRP fails to reach the tensile strength at the yield of steel,the internal mortar cracks at oblique section,and the lateral stress between the loading point and the support is concentrated.Studied the cross section dimension,section height to width ratio,steel tube thickness,thickness of BFRP,perfusion mortar strength,steel strength BFRP-pole constraints under multiple factors affect high strength mortar composite profile bending performance changes,the results show that increasing the cross section size and aspect ratio is the effective measure to improve strength and stiffness,ductility of the specimens are also improved;With the increase of mortar proportion and the decrease of aspect ratio,the strength of specimen will decrease greatly when entering the yield section.Increasing the thickness of steel tube can improve the strength and stiffness.BFRP wrapping can improve the bending capacity of composite profile specimens to a certain extent,but increasing the number of BFRP layers does not significantly improve the strength and stiffness.The use of high-strength steel pipe can only improve the bending capacity and the maximum deformation of the elastic section,but has no effect on the stiffness.