Research On Shear Behavior Of RC Beams Strengthened With Prestressed FRP Grids

For reinforced concrete beams with deteriorated shear resistance,the engineering community often uses techniques such as pasting steel plates and pasting fiber cloth to repair and strengthen them to extend their service life.However,while these methods effectively strengthen the structure,there are also certain shortcomings.Bonded steel plate reinforcement has poor fire resistance and weather resistance,and high maintenance costs in the later period.Externally sticking fiber cloth reinforcement requires high construction requirements,and the performance of the reinforcement interface will be degraded.In view of this,scholars have developed a new type of reinforcement technology with better applicability,namely FRP grid-polymer mortar reinforcement technology.This technology has many advantages such as convenient construction,good durability,and reliable reinforcement quality.However,there are still insufficient research in the field of shear reinforcement,low material utilization,and lagging strength of reinforcement materials that need to be resolved.Based on the above background and actual needs,this paper chooses green and environmentally friendly and cost-effective basalt fiber（BFRP）grid as the reinforcement material.The relevant factors affecting the shear reinforcement effect of FRP grid are systematically studied,and the application of prestressing is attempted.To solve the defects of low utilization rate of grid materials and lagging force,I hope this research can provide reference for subsequent engineering applications.The main research contents of this paper are as follows:（1）Test the materials and prestressed FRP grid anchors involved in the grid reinforcement technology,and design the anchorage structure.The results show that: chopped fiber can enhance the toughness and energy dissipation capacity of polymer mortar;the anchoring efficiency of flat friction anchors is more than 70%,the long-term prestress loss is less than 5%,and the anchoring effect is related to the pre-tightening bolt arrangement and eccentric force.The degree is related.（2）Experiments on the shear-strengthened concrete beams with ordinary BFRP grids are carried out,and the effects of reinforcement amount,matrix material toughness,interface treatment methods and construction methods on the shear resistance of test beams are analyzed.The results show that the shear bearing capacity of the reinforced beam is increased between 20%-45%,and the bearing capacity increases with the increase of the BFRP mesh reinforcement.After adding chopped fibers to the matrix material for toughening,the crack development of the component is suppressed,but the shear bearing capacity is not improved.When using grid reinforcement,an interface agent must be used to ensure the interface bonding strength.The interface agent used can be resin or bonding mortar.Using on-site pouring construction and prefabricated board pasting construction can achieve the same shear reinforcement effect.（3）Experiments on shear-strengthened reinforced concrete beams with pre-stressed BFRP grids are carried out,and the influence of pre-stressing on the shear performance of test beams is analyzed.The results show that applying prestress to the BFRP grid can greatly increase the rigidity of the beam members during normal use and inhibit the development of cracks,but the bearing capacity of the members is only increased by 8.4%.（4）Numerical simulation and theoretical calculation of BFRP mesh shear-strengthened concrete beams are carried out,and the influence of mesh stiffness,reinforced structure concrete strength and prestressing direction on the reinforcement effect is analyzed,and the bearing capacity of BFRP mesh shear-strengthening reinforcement is proposed.Calculation method.The results show that the bearing capacity of beam members increases with the increase of grid stiffness.FRP grid reinforcement technology is more effective for low-grade concrete beam components.Applying prestress in different directions will improve the shear resistance of beam members at different stress stages.The ACI549.4R guideline and the related formula proposed by Triantafillou et al.are used to predict the shear capacity of BFRP grids well,with an error of less than 20%.