Experimental Study Of UPC Beams Strengthened With Aluminun Alloy Plate With Inorganic Matrix

Although the external bonding of FRP sheets and steel sheets is a technology of reinforcing the concrete structure by bonding externally that is widely used currently,the lower elongation of FRP sheets will lead to certain brittle failure of the reinforced structure and the corrosiveness of the steel will also limit the durability of the structure reinforced by bonding steel plate externally.Due to its properties,such as light weight,high strength,corrosion resistance and good elongation,etc.,aluminum alloy sheets have received increasing attention in the field of civil engineering structure.Reinforcing the concrete structure by bonding the aluminum alloy sheets externally has certain advantages in the transformation and reinforcement of concrete structures in coastal,and erosion,wet and high temperature environments,etc.In this paper,six damaged unbonded prestressed（UPC）beams that have undergone ultimate load were selected to be reinforced by bonding the aluminum alloy plate with inorganic glue after repaired,and then used for the three-point static loading test.Based on the test results,the properties of crack development,rigidity and bearing capacity,and the reinforcement design method of unbonded prestressed beams reinforced by aluminum alloy plate were preliminarily studied.Firstly,the mechanical properties of 5083 aluminum alloy were measured and its constitutive relation was proposed.Magnesium phosphate cement was selected as the reinforced structure glue in the test through double shear test comparison.Moreover,the bonding strength,effective bond length and bond-slip constitutive relationship of aluminum alloy-concrete interface bonded with sulphoaluminate cement,magnesium phosphate cement and alkali-activated slag were proposed.Secondly,based on the test results,a method for calculating the stress increment of unbonded rebar when the ordinary tensile rebar with the composite reinforcement index and the ordinary tensile reinforcement index as the parameters yielded was put forward.The influence coefficient of considering the effect of unbonded rebar and aluminum alloy plate was introduced,and the equivalent stress and strain nonuniform coefficient of ordinary tensile rebar considering the influence coefficient were proposed.Based on the statistical analysis of the test results,the short-term load crack expansion coefficient suitable for UPC beam reinforced by bonding aluminum alloy was proposed,and then the calculation and design method of average crack spacing and width of UPC beam reinforced by bonding aluminum alloy plate was proposed according to the normative ideas.Thirdly,the influence of the composite reinforcement index β₀ on load-deformation relationship was discussed in accordance with the test results.The double-fold line method was used to propose the calculation method of elasto-plastic stiffness coefficient after cracking with the composite reinforcement index as the parameter and the calculation method of stiffness under short-term load after cracking,as well as preliminarily propose the calculation method of stiffness of UPC beam reinforced by bonding aluminum alloy plate.Finally,through the analysis of the test results,it is found that the aluminum alloy fully exerted its strength in the reinforcement,and the influence of the aluminum plate slip can be ignored.The limit stress calculation formula of unbonded rebar with the aluminum alloy plate reinforcement index,prestressed rebar reinforcement index and composite reinforcement index as the parameters was derived,and then the calculation method of the bearing capacity of UPC beam reinforced by bonding aluminum alloy plate with inorganic glue was proposed.In this paper,the test results show the feasibility and effectiveness of using inorganic glue to bond the aluminum alloy plate to reinforce UPC beam,and the proposed calculation theory will provide a theoretical reference for further research of UPC beam reinforced by bonding aluminum alloy plate.