Experimental Study On Damage Monitoring Of RC Exterior Frame Joints Based On Embedded Piezoelectric Ceramic

Beam-column joint, as the zone of intersection of beams and columns, is thecritical region of reinforced concrete frame structure. Under seismic loading, the jointcore may be subjected to both horizontal and vertical forces which are much largerthan the beam or column elements. The functional requirement of a joint is to enablethe adjourning members to develop and sustain their ultimate capacity. With thevigorous development of urban construction, the demand for high-strength concrete isincreasing in practical engineering. The application of high-strength concretedecreases the cross section sizes of structural members, thus rendering the joint coreweaker than the adjoining members. Since the1960s, earthquakes in different parts ofthe world have revealed that failure in the beam-column joint is a main reason forstructural damage and seismic disaster. Consequently, how to monitor the damage ofRC beam-column joints becomes a major concern for disaster prevention.In this thesis, a total of7exterior beam-column joint specimens in reinforcedconcrete frame structure were tested under cyclic loading to investigate the damagedeveloping tendency, including parts of research as follow:(1) Based on the material character of piezoelectric ceramic (PZT) and previousresearch on “smart aggregate”, a new kind of sensor, functional piezoelectric unit,was described in details. The new smart sensor had the function of piezoelectricceramic and was capable of solving the problem caused by the combination ofstructure and piezoelectric ceramics.(2) A total of7specimens, suffered different failure patterns, were tested toinvestigate the damage development of RC exterior beam-column joints underdifferent loading and cyclic level. The test result showed that damage in RC structurecould be effectively identified by means of the health monitoring technique based onthe piezoelectric unit.(3) Response signals were analyzed through amplitude and energy decrease whilegenerating sine excitation signals and sweep signals for the RC exterior jointspecimens internally. The experimental result showed that the signal amplitude andenergy were sensitive to the damage. That is, the signal amplitude and energydecreased while damage developed. Damage situation and position were effectivelydetected through the piezoelectric unit embedded inside the specimens. (4) With the square root index as characteristic parameters, response signalsreceived by the sensor inside the RC exterior joint were analyzed by means of thefrequency response function while generating pulse excitation signals for the RCexterior joint specimens. The test results showed that the presence of damage resultedin a frequency shift in the frequency response function. Moreover, the frequencyoffset increases as damage aggravates. The damage developing tendency of RCexterior joints was effectively reflected by the square root index.(5) A comparison of damage investigation and the situation of crack damage waspresented. The test results were agreed with the damage situation. It indicated that thepropose method could reflect the developing tendency of damage effectively and itwas suitable for health monitoring of reinforced concrete structure.