Study On Bearing Capacity And Environmental Durability Of RC Beams Strengthened With CFRP Based On Piezoelectrical Impedance Method

Externally bonded carbon fiber reinforced polymer（CFRP）reinforcement is an effective reinforcement technology,which can effectively improve the bearing capacity of concrete bridge structures.The repair effect of reinforced structure depends on the bond between CFRP and concrete.In South China,the reinforced bridge structure has been in service under the environment of high temperature and high humidity for a long time.CFRP and structural adhesive will gradually deteriorate,resulting in the continuous decline of interface bonding.In addition,the reinforced bridge structure will inevitably suffer from the long-term action of self weight and vehicle load,the degradation of interface bonding performance will further aggravate,and the safety and durability of the structure can not be guaranteed.In this thesis,considering the combined action of dry wet cycle and long-term load,piezoelectric impedance（EMI）technology is used to monitor the damage evolution behavior of reinforced beam interface in damp heat load test;The four point bending test of the strengthened beam is carried out to study the interface peeling process and flexural mechanical properties of the strengthened beam after load holding.The specific research contents and results are as follows:（1）EMI technology is used to monitor the health of the strengthened beam under the coupling of load holding and dry wet cycle for 270 days,and the damage evolution behavior of the interface of the strengthened beam is studied.The deflection,concrete and CFRP strain of the load-bearing beam in indoor and humid and hot environment increase with the load-bearing time;The damage index（RMSD）of the end of the load bearing beam showed an upward trend under indoor and humid and hot environment;The RMSD value in the middle of the span of the load bearing beam shows a downward trend in the indoor environment,while the RMSD value in the middle of the span of the load bearing beam shows an upward trend in the humid and hot environment.The results show that the damage degree of the strengthened beam interface caused by load holding is small,but the damage degree of the strengthened beam interface caused by the coupling effect of load holding and dry wet cycle is large.Both EMI technology and strain gauge measurement can monitor the interface damage of the strengthened beam under the coupling action of load holding and dry wet cycle,and EMI technology is more sensitive to the slight interface damage.（2）The static load test of the strengthened beam after the coupling action of load holding and dry wet cycle is carried out to study the flexural mechanical properties of the strengthened beam.The peak load of the strengthened beam is less than the RMSD of the reference beam,and the peak load of the strengthened beam is less than the RMSD of the reference beam;Load holding will damage the interface of the strengthened beam and reduce the ultimate bearing capacity of the strengthened beam;Dry wet cycle will deteriorate the interface and improve the strength of concrete.The results show that EMI technology can effectively characterize the development process of interface performance damage in static load test,and can distinguish the existing damage of strengthened beams in the process of dry wet cycle.（3）Different failure modes of reinforced concrete beams strengthened with CFRP are studied theoretically,and the calculation formula of ultimate bearing capacity of reinforced beams is obtained.On this basis,the bearing capacity of the strengthened beam corresponding to different failure modes is calculated.The results show that the average ratio of the theoretical value to the measured value of the test beam is 0.95,and the coefficient of variation（COV）is 3.7%.In conclusion,based on EMI technology,this thesis reveals the damage evolution behavior of the interface of CFRP strengthened beams under the coupling of long-term load `In conclusion,based on EMI technology,this thesis reveals the damage evolution behavior of the interface of CFRP strengthened beams under the coupling of long-term load and dry wet cycle;The static load test is carried out to study the flexural mechanical properties of the strengthened beam after coupling action;Through the theoretical study of different failure modes of reinforced beams,the calculation formula of ultimate bearing capacity of reinforced beams is obtained.The results of this thesis will provide theoretical basis and test data for relevant design and specifications,and promote the research and application of EMI technology in structural health monitoring.