Damage Diagnosis And Evaluation For Steel-Concrete Composite Beams Based On Wave Detection Methods

Composite structures is vigorously promoted in China,with the advantages of low cost,high performance,large rigidity-to-weight ratio,and convenient for construction et al.,has been widely used in high rise building,complex spatial structures,and bridge structures et al.Composite beam is the important transverse load-bearing components of composite structures,the safety and stability of composite beam is of vital to ensure the health of structures.In this paper,the damage detection and evaluation of the steel-concrete composite beam was studied based on the wave detection methods(Ultrasonic and Acoustic Emission)and numerical simulation method.Four key issues were studied,i.e.,the diagnosis and evaluation of local hiden damages,the influence of initial damages on mechanical properties and aging characteristics,the overall damage assessment,and damage pattern recognition.The main research contents and conclusions are as follows:(1)The wave based method was proposed to detect the damages of shear studs in steel-concrete composite beams,and a baseline-free wave identification method was developed.Different test schemes were used to analyze the effects of stud's damage on ultrasonic wave signals,and the wave propagation mechanisms was revealed.The proposed amplitude variation index(AVI),energy variation index(EVI)and wavelet packet energy index show linear relationship with the damage degree.To overcome the shortcomings of imprecise and unstable of EVI index when the number of test points is not sufficient,the R-EVI index was calculated based on the novel iterative method,the baseline-free damage identification of shear studs in steel-concrete composite beam was achieved.(2)The wave based method was proposed to detect the damages of interface in steel-concrete composite beams,and the quantitative estimation method of interface damage was developed.The improved energy variation index and wavelet packet energy index were calculated based on the proposed iterative algorithm,the interface damage area was identified accurately,and the propagation path and mechanism of ultrasonic wave were disclosed.Based on the change of propagation path and propagation time of ultrasonic wave signal under different damage condition,the Akaike information criterion was proposed to determine the wave arrival time and wave velocity,and the interface damage size was estimated with a maximum error of not more than 8%.(3)The refined solid sliding FE modeling method for steel-concrete composite beam was proposed,the mechanical degradation and long-term aging characteristics of the composite beam with initial damage were explored.By overcoming the difficulties such as irregular shape meshing and interface contact definition,the refined solid sliding FE model for steel-concrete composite beams was developed in ABAQUS software and verified by the test results.The effects of different damage conditions on structural mechanical properties were researched from the aspects of bearing capacity,bending stiffness and interface sliding distribution.Based on the viscoelastic creep constitutive model and the effective modulus adjustment of concrete,the long-term aging characteristics of composite beams under the coupling effect of initial damages,concrete shrinkage and creep were analyzed.The damage mechanisms of shear studs and the nearby concrete were revealed,and the vertical deformation,cross-sectional stress growth and prediction models for composite beams were proposed.(4)The acoustic emission(AE)technology was proposed to monitor the damage evolution of the novel FRP/steel-concrete composite beam,and the critical state warning and quantitative damage assessment method were proposed.Through the analysis of characteristic parameters such as AE energy and amplitude,the damage evolution and stiffness degradation of the novel FRP/steel-concrete composite beams was revealed.Based on the analysis of AE activity parameter(b-value)and damage parameter(D),the occurrence of major structural damage was identified,and the critical state warning of composite beams was realized.By establishing the "strength analysis diagram",the damage degree of the novel FRP/steel-concrete composite beams was divided into five grades,a quantitative assessment method of damage degree was put forward.The nonlinear logarithm fitting model was proposed based on the correlation between the AE energy and the deformation and local strain of the composite beam,the integrated monitoring and evaluation of local and overall damage of composite beams was realized(5)The parameter selection method(LSMI)and self-adaptive real-time clustering method(SASC)were put forward,the damage pattern recognition of FRP/steel-concrete composite beams were realized.Based on the Laplace score and Shannon's entropy,the clustering parameter selection method(LSMI)was developed.By breaking the limitation of repeated iteration of traditional clustering methods,and introducing the parameter R and C to control the split and merge between clusters,the novel self-adaptive cluster method(SASC)was put forward.The AE amplitude,peak frequency and counts were selected based on the LSMI method.By conducting the novel SASC algorithm,the damage signals of the FRP/steel-concrete composite beam were classified into three clusters.The dominant damage types of each damage stage were identified,and the range of typical AE characteristic parameters corresponding to different damage types was obtained.