Experimental Study On Loading Failure Process Of Reinforced Concrete Beams Based On Acoustic Emission Technology

For a long time,people have been trying to understand the development process of internal damage of reinforced concrete beams,so that they can make early warning before danger occurs.As a non-destructive testing method,acoustic emission technology can capture the internal damage signal of reinforced concrete structure well,so as to obtain the development of internal damage without causing damage to components,which has broad application prospects in the field of non-destructive testing of bridges.In order to explore the development and change of internal damage of reinforced concrete simple-supported beams,the compression tests under three working conditions were designed and carried out.Acoustic emission was used as the main technical means.Meanwhile,the damage development law of reinforced concrete simple-supported beams in the whole process of failure was explored based on the relevant data such as mid-span deflection,mid-span strain and pre-stress changes in beams obtained during the test process.The main work and achievements of this thesis are as follows.(1)The acoustic emission signals collected during the whole failure process of model test beams under three working conditions are analyzed by means of parameter analysis and waveform analysis,and the characteristics of each stage of failure are obtained.Especially when the critical load is reached,that is,when the crack occurs,the acoustic emission signal will have obvious characteristics.(2)The graded loading of the pre-stressed reinforced concrete beams shows that the critical load often occurs at about 80% of the ultimate load.At this time,the deflection will slow down with the increase of the load,and the energy and ringing count of the acoustic emission signal will increase greatly.At this time,the central frequency of the acoustic emission signal mainly concentrates on about 150 kHz and 300 kHz.(3)Through trapezoidal cyclic loading of pre-stressed reinforced concrete beams,it is found that the ultimate load of model beams under cyclic loading can be reduced by about 20% compared with that under step loading.Moreover,after the test beam reaches the critical load under cyclic load,there will still be acoustic emission signals during the unloading process,which can be used as a criterion to determine the critical load.(4)The ultimate load of ordinary reinforced concrete beams is reduced by about 40% compared with that of pre-stressed reinforced concrete beams under step loading,which shows that pre-stress can effectively improve the flexural strength of reinforced concrete.(5)By comparing the load tests of model beams under three working conditions,it is found that the critical load of pre-stressed RC beams usually occurs at about 80% of the ultimate load,while that of ordinary RC beams occurs at about 40% of the ultimate load.The load should not exceed the critical value in normal use,otherwise it is easy to be dangerous.