Numerical Simulation Of RC Beams Strengthened By External Prestressing With Ordinary Rebar

With the average living area of China close to 40 square meters,the new construction industry will gradually shrink,replaced by the maintenance and reinforcement industry,external prestressed reinforcement as a kind of simple and effective reinforcement method.It belongs to the post-tensioned unbonded prestressed structural system.The reinforcement method has the advantages of eliminating stress lag,reinforcing material weight is light,having small influence on the structure clearance,and so on,therefore obtained rapid development.At present,the external prestressed tendons tend to use steel strand,because of its high yield strength,when reinforced beam is damaged,the external prestressed tendons is still far from yield,If using ordinary steel bar instead of steel strand,reasonably control the amount of tension,the longitudinal reinforcement of beam bottom and external prestressed tendons in the process of applied load can yield at the same time,avoiding the waste of materials,and because the construction is simple,it has great practical significance for engineering reinforcement.At present,there are few researches on the reinforced concrete beams strengthened with ordinary steel bars in external,and the factors such as the stress degree of reinforcing steel bars,the number of tensile steel bars,the form of tension and the degree of pre-stress should be determined.In this thesis,the finite element model is established from the existing experiment,considering the discordant deformation of the external prestressed tendon and the concrete beam,the non-linearity of the material,choosing the reasonable constitutive relation,and using the birth and death element to simulate the actual load on the beam before prestressing,carried out the following research:1)The simulation is carried out by using ANSYS software to simulate the whole process of a simply supported beam with external prestressed strengthening experiment,for the question of whether or not to considering concrete crushing,slip of steel bar was simulated and compared with the experimental value,a reasonable and feasible model is obtained;2)Based on the analysis of the test beam finite element model,extract the beam mid-span's load-displacement curve,the load-stress curve of the external prestressed tendons.Considering the holding load level of the beam before strengthened,the height and number of the steering block,the anchorage height and the prestressing degree of the prestressed tendons in the beam and other factors,yield load and ultimate bearing capacity of reinforced beam body are analyzed;3)The external prestressed tendons are replaced by steel strands into ordinary steel bars,according to the load level of the beam before reinforcement,the stress level of the original steel bars is calculated.The premise of the longitudinal reinforcement at bottom of the beam and external prestressed reinforced yield at the same time,the relationship between the stress of the original steel bar and the initial stress of the prestressed tendon was established,and the change law of the external load when the prestressed tendon and the longitudinal reinforcement at bottom of the beam was yielded.Studies have shown that using finite element method simulation in external prestressed reinforcement concrete beam is feasible,with ordinary steel bar instead of steel strand,reasonably control the amount of tension can make the longitudinal reinforcement at bottom of the beam and external prestressed tendons yield at the same time in the process of applying external forces,thus avoiding waste materials and has certain guidance for actual reinforcement engineering.