Experimental Study On Damage Monitoring Of Concrete-filled GFRP Tube Composite Column Based On Piezoceramics

Glass fiber reinforced polymer(GFRP)has good corrosion resistance and tensile properties,and it is widely used in the design and development of new composite structures.In addition,GFRP is also used to reinforce existing structures.Concrete-filled GFRP tube composite column is a new type of composite structure and which is composed of GFRP tube and the concrete in the tube.Concrete-filled GFRP tube composite column can be used in hydraulic structure or the areas with poor environmental conditions due to its superior mechanical properties and corrosion resistance,in addition,it can also replace concretefilled steel tube columns as vertical or axial load-bearing members in large-scale engineering structures.Therefore,the health monitoring and damage diagnosis of buildings with this new composite column show a very broad application prospect.Based on this point,this paper proposed an active monitoring method which combines the external lead zirconate titanate(PZT)patch and the embedded piezoelectric smart aggregate(SA),and use this method to identify and monitor the damage of concrete-filled GFRP tube composite columns from the pouring to the service period(Including the forming stage and the service stage,and the service stage includes the normal service condition and the extreme load condition).Mainly including the following contents:(1)Forming stage——A group of concrete-filled GFRP tube columns(CFGC)with two SA embedded inside were made,and the strength development process of concrete in the tube was monitored in 28 days.It was found that there were three stages of concrete strength development in 28 days:the first stage is 1～4 days,during which the concrete strength increased slowly,reaching only about 11%of the maximum strength in 28 days.The second stage is the 5～14 days.At this stage,the power spectral density and wavelet packet energy of concrete increase rapidly,and the strength of concrete also fast increases.On the 14th day,the strength of concrete is close to 90%of the maximum in 28 days.The third stage is the 15～28 days.In this stage,the concrete strength increases slowly with a small amplitude and tends to be stable.The wavelet packet energy and power spectral density of the monitoring signal close to their maximum values and fluctuate in a small range.The test can provide a reference for monitoring of the pouring quality of concrete in CFGC in practical engineering.(2)Normal service condition——Affected by factors such as shrinkage and creep of concrete,fatigue effects of materials,and long-term effects of loads,under normal service conditions,the contact interface between GFRP tube and concrete may be debonding,which affects the joint work of the two and reduces the mechanical properties of concrete-filled GFRP tube composite column.Based on this,two groups of CFGC specimens with SA embedded inside were designed,and each group of specimens was set with four different levels of artificially simulated interface debonding damage.The piezoelectric transducers were used to monitor the interface damage of the composite columns,and it is found that the amplitude and the wavelet packet energy of monitoring signal both decrease with the increase of the interface damage.The damage index(DI)based on wavelet packet analysis was used to quantitatively evaluate the level of interface damage,and it is found that DI increases with the increase of the degree of interface damage.This test verifies the feasibility and effectiveness of the active sensing method based on piezoelectric ceramics for monitoring the interface debonding damage of concrete-filled GFRP tube composite structure.(3)Extreme load condition——Using the monotonic loading and reciprocating loading to simulate the extreme load condition of the composite column.Two double tube concrete columns(DTCC)were fabricated,and 4 SAs were pre-embedded before pouring.After curing for 28 days,two DTCC specimens were subjected to monotonic loading and reciprocating loading tests.It is found that the active monitoring method piezoelectricity based can better identify the real-time damage of core concrete and sandwich concrete of DTCC under monotonic and reciprocating axial compression,and the amplitude of the monitoring signal and the root mean square damage index DI based on wavelet packet analysis are sensitive to the damage development process.Both of the amplitude and DI of the monitoring signal can be used to evaluate the damage level of DTCC under axial compression.(4)The finite element software ABAQUS is used to model DTCC,and the load-displacement curves obtained by finite element method are in good agreement with the test results.The compression damage coefficients of core concrete and sandwich concrete of DTCC were extracted from ABAQUS.It is found that the change trend of the damage coefficients is basically consistent with the damage index(DI)based on wavelet packet energy.This result also further verifies the scientificity and effectiveness of the active monitoring method piezoelectric materials based to identify the real-time damage status of core concrete and sandwich concrete of DTCC during the loading process.The results show that the structural health monitoring technology based on piezoelectric transducers can realize the health monitoring and damage identification of the concrete-filled GFRP tube composite structure from pouring to service period.The damage index proposed is more sensitive to damage level.The research results can provide a reference for real-time damage assessment of GFRP-concrete composite structures in practical projects.