Study On Mechanics Behavior Of RC Slab Strengthened With NSM FRP

Due to some reasons such as service life,design and emergency,the structure is damaged without losing its function.Considering the economic impact,it is necessary to strengthen the structure or components.Near-surface mounted FRP strengthening method is a new type of strengthening method which develops rapidly in recent years.It has the advantages of convenient construction,shortening construction period,saving project cost and ideal strengthening effect,and it can prevent fire,man-made or environmental factors from damaging buildings.It has a broad development prospect in practical projects.Reinforced concrete slab is one of the important structural components,which plays an irreplaceable role in building floor,bridge deck and some structures.In the strengthening field,reinforced concrete slab is also a member that often needs to be strengthened,and the flexural behavior and punching performance are the basic mechanical properties of concrete slab.Using near-surface mounted FRP strengthening method for the concrete slab,its flexural behavior and punching performance are studied,which has a good guiding role for the application of the strengthening method in practical projects.In this paper,the flexural performance of one-way concrete slabs strengthened with NSM-CFRP bars is conducted.The stress process and failure mode of the slabs are compared and analyzed.The load-deflection curve and load-strain curve of the slabs are studied.The strengthening effect of the slabs on the bearing capacity,ductility and rigidity is analyzed,and the influence of different amount of CFRP bars and the reinforcement ratio of tensile bars in the slabs on the flexural performance of the strengthened beams is studied.The results show that the cracking load,yield load and ultimate load of the strengthened specimens are higher than those of the control specimens,and the maximum increase of the ultimate load of the concrete slab strengthened by NSM-CFRP bars is achieved.In the aspect of restricting the development of cracks,the embedded CFRP reinforcement has a certain advantage.ABAQUS software is used to carry out the finite element simulation of concrete one-way slab,and the simulation results are compared with the test results to verify the reliability of the simulation analysis;then,the amount of FRP bars,FRP type,FRP diameter,concrete strength and reinforcement ratio are used as parameters for in-depth simulation analysis.The influence of each parameter on the flexural strengthening effect is studied.The simulation results show that the bearing capacity of the strengthened slab increases with the amount of FRP,FRP diameter,concrete strength and reinforcement ratio,among which the amount of FRP and FRP diameter have obvious effect.At the same time,FRP type is an important factor to change the failure mode of the specimen,and the strengthening effect of the embedded CFRP bars is the best.On the basis of experimental research and numerical simulation analysis,the flexuralcapacity of one-way concrete slabs strengthened with NSM-FRP bars is analyzed theoretically,and the calculation formulas of flexural capacity of slabs under different failure modes are established.The comparison results between calculation results and test results show that they are in good agreement.Finally,a composite strengthening method of two-way concrete slab with FRP strip and FRP bar is proposed in this paper.The flexural and punching behavior of the two-way concrete slab are analyzed by finite element method,and the load-deflection curve and the development law of concrete tensile damage are studied.The results show that the composite strengthening method can not only improve the flexural capacity and punching capacity of the members,but also increase the early stiffness and reduce the mid-span deflection of the members.