Pull Out And Tensile Mechanical Properties Of The FRP Reinforced LECC Research On Key Influencing Parameters

Fiber Reinforced Polymer(FRP)composites are high-performance materials with excellent durability and mechanical properties.When FRP is combined with epoxy resin glue or cement mortar,two reinforcement systems are formed.Due to the easy aging and structural incompatibility of epoxy resin and the brittle fracture of cement mortar,the reinforcement efficiency of FRP is seriously affected.In order to solve the above problems,a reinforcement method combining FRP with Lightweight Engineered Cementitious Composites(LECC)is proposed.LECC has the characteristics of ductility and multi-cracks of Engineered Cementitious Composites(ECC),and at the same time has the advantages of light weight and heat insulation.Advantages,it has application prospects in high-rise buildings and long-span structures.At present,scholars have studied the tensile mechanical properties and pull-out behavior of FRP-reinforced ECC through key influencing parameters such as FRP type,textile grid size,and FRP reinforcement rate.The results show that key parameters affect the tensile reinforcement effect and the bond-slip law of the sample.However,traditional FRP materials have brittle characteristics and low ductility,which limits their use in structures that require seismic resistance.At the same time,the reinforcement mechanism of FRP in the ECC matrix needs to be reasonably explained by pull-out tests.Therefore,this paper explores the key influencing parameters of the pull-out behavior of FRP in the LECC matrix and the tensile mechanical properties of the large-strain FRP reinforced LECC matrix.The research content and results of this paper are as follows:1.The pull-out behavior of the FRP material embedded in the LECC matrix was investigated by a center-asymmetric pull-out test.The test results show that adding epoxy coating can effectively improve the bonding stress and bonding stiffness of FRP materials in LECC matrix,and the interface bonding between FRP textile grid and LECC matrix is the key factor affecting the bonding performance.The type of FRP material,the anchorage length and the thickness of the matrix jointly affect the failure type of the samples.BFRP textile grid usually has three failure modes: pull-out,pullout-fracture and textile fracture,and the failure mode of BFRP tendon is different from that of BFRP textile mesh.There are usually three failure modes of splitting,peeling-splitting and peeling failure.Compared with the test results,the improved model established is in good agreement with the test curves,and can accurately describe the behavior of the residual segment.2.The uniaxial tensile test of FRP textile-reinforced LECC composite(TR-LECC)was carried out,focusing on the influence of key parameters such as FRP material type and FRP reinforcement rate on the axial tensile mechanical properties of TR-LECC composite.The stress-strain curve and failure mode of FRP reinforced LECC materials were analyzed,and the bonding performance and strengthening mechanism between FRP materials and LECC matrix were clarified by combining SEM method.The results show that the tensile strength of TR-LECC specimens is significantly increased with the increase of the reinforcement rate of FRP materials,but the reinforcement effect of FRP without epoxy coating is far less than that of coated FRP materials,and the utilization rate of FRP materials is lower than that of coated FRP materials.The ultimate strain of the traditional FRP grid reinforced LECC matrix is about 2%,and the failure mode has certain brittle failure characteristics.The large strain PP grid reinforced LECC shows 8% ductility,and its energy dissipation capacity is significantly greater than that of traditional FRP materials.3.Based on the finite element analysis method,the crack development and failure mode of the tensile model sample were studied,and the stress and strain distribution of the FRP grid and LECC matrix material were analyzed in detail.The results show that the crack propagation and failure form simulated by finite element are basically consistent with the phenomena observed in the tensile test,with a high degree of agreement.As the number of BFRP grid layers increases,the stress and strain values in the tensile region of the specimen decrease,and the stress form of the matrix is improved.Through the stress cloud diagram of the BFRP grid,it can be clearly observed that the weft yarn bears the load on the warp yarn anchoring effect.