Experimental Study On Flexural Behavior Of Damaged RC Short Beams Strengthened With FRP Sheets

Due to the influence of steel corrosion,natural disasters,long construction time and other factors,a large number of active reinforced concrete(RC)structural buildings in China have been damaged and their bearing capacity has decreased.However,the economic cost and time of demolition and reconstruction of buildings are too high,so reinforcement and reconstruction will become the focus of future development of China ’s construction industry.Fiber Reinforced Polymer(FRP)has become a hot research topic in the field of reinforcement at home and abroad due to its high strength and good cooperative performance with the research structure.At present,the research at home and abroad is focused on the undamaged shallow beams strengthened with CFRP,and there are few reports on the flexural performance of damaged RC short beams strengthened with different types of FRP sheets.Therefore,in this paper,four-point bending tests were carried out on damaged RC short beams strengthened with different types of FRP sheets to analyze and evaluate the flexural performance of the strengthened short beams.The specific research contents and conclusions are as follows :(1)One ordinary RC short beam,six damaged and undamaged RC short beams strengthened with CFRP,GFRP and BFRP were designed and manufactured,and four-point bending test was carried out.The test results show that bonding FRP can effectively improve the distribution of cracks,reduce the number of cracks and reduce the width of cracks.Bonding FRP sheet can effectively improve the ultimate load and initial stiffness of the reinforced beam,but it will reduce the ductility of the component,and the ductility of the damaged reinforced beam is the best.Anti-stripping failure is the key factor to give full play to the tensile properties of FRP sheets.Even if the closed hoop or other anchoring measures are used,the debonding failure cannot be completely avoided.On the premise of giving full play to the tensile strength of FRP sheets,the effect of CFRP strengthening damaged RC short beams is the best.As deep flexural members,the cross-sectional strain of RC short beams strengthened with various types of FRP sheets no longer conforms to the plane section assumption.(2)According to the calculation method of flexural capacity of deep flexural members in’ Code for Design of Hydraulic Concrete Structures ’ SL191-2008,the calculation formula of flexural capacity of damaged RC short beams strengthened with FRP is given based on the section analysis method.Based on the modified strut-arch model,another formula for calculating the flexural capacity of FRP strengthened beams is given.Comparing the calculated values obtained by the two formulas with the experimental values,the results show that the calculated values of the bearing capacity calculation formula based on the section analysis method are in better agreement with the experimental values.In order to avoid the flexural failure or shear failure of RC short beams caused by excessive FRP reinforcement,this paper proposes a calculation method for the reasonable limit value of FRP reinforcement.The influence of parameters such as concrete strength,steel strength,damage degree and FRP cloth type on the limit value of reinforcement is quantitatively analyzed,and the applicability of the calculation method is evaluated.(3)ABAQUS finite element simulation software was used to simulate the bending test of RC short beams strengthened with CFRP sheets with better reinforcement effect.The finite element simulation results were compared with the test results,and the accuracy of the finite element simulation was better.The finite element software accurately simulates the bending process of FRP reinforced RC short beams.The establishment of the model is feasible,the setting of parameters is reliable,and the simulation results are credible.The quality of the glued layer has a great influence on the reinforcement effect.In order to study the influence of the glued layer on the reinforcement effect,the finite element simulation analysis of the three parameters of the glued layer was carried out.It also provides a reference for further research on the finite element simulation analysis of other types of FRP cloth reinforced RC short beams.