Research On Delamination Detection In Prefabricated Superimposed Slab Using Impact-echo Method

Compared with the cast-in-place slab in the traditional construction mode,the prefabricated superimposed slab belongs to the secondary forming component.In the castin-place operation,the composite surface may retain residual soil,floating slurry,water,etc.These factors can have a certain impact on the bonding performance of the composite surface,which is usually manifested as the interface layering between the cast-in-place layer and the prefabricated layer.Once the layering occurs,the bearing capacity of the structure will change.Furthermore,it affects the reliability of the composite components and even the structure.Therefore,timely discovery and accurate detection of interface stratification becomes an urgent problem to be solved in the development of prefabricated superimposed slab.Therefore,on the basis of the impact echo detection method,this paper conducts tests on the layered defects of the prefabricated superimposed slab under different working conditions and conducts researches combined with numerical simulation.The main research work and conclusions are as follows:(1)Aiming at the interface layering problem of prefabricated superimposed slab,we designed prefabricated superimposed slab specimens with square and rectangular layers of different sizes,divided measuring areas and measuring lines at the defects,collected echo signals of measuring points at different positions and converted them into frequency domain signals through fast Fourier transform(FFT),and analyzed the spectrum diagram to obtain: The impact echo method is feasible to detect lamination defects in prefabricated superimposed slab.The test results show that the long side size of lamination defects and the knock position often determine the modal order and frequency value of the test excitation,and the relative amplitude of the excitation mode is also affected by the test position.Therefore,the order of excited modes,the frequency value of excited modes and the relative amplitude of excited modes can be commonly tested to predict the layering size,measuring point and relative position of the layering.(2)Based on the above test results,a finite element model for the delamination defect detection of two-dimensional prefabricated superimposed slab was established.Transient analysis method in finite element software ABAQUS/Explicit was used to study the relationship between the impact echo spectrum characteristics and interface delamination in different working conditions,and the finite element simulation and test results were compared and analyzed.The finite element simulation is in good agreement with the experimental results.At the same time,the modal analysis of the 200 mm layered model was carried out.The ABAQUS linear perturbation analysis was carried out on the local concrete with defects in the floor,and the fifth-order natural vibration frequency of the structure was extracted.It was found that the fifth-order modal frequency value was consistent with the peak value of the test spectrum diagram under the 200 mm layered condition.Numerical simulation verifies the validity and accuracy of the impact echo method to detect the lamination defect test data of the prefabricated superimposed slab.(3)According to the above test and simulation results,the corresponding relationship between different lamination defect conditions of prefabricated superimposed slab and test spectrum characteristics is established.The reliability of this relationship is verified by measuring irregular lamination defects,and the accuracy of impact echo method in detecting lamination defects of prefabricated superimposed slab joints is further illustrated.To sum up,the impact echo method can effectively detect the lamination defects of prefabricated superimposed slab,and effectively identify the outer boundary contour,adjacent outer edge region and defect center region of lamination defects in view of the problem that it is difficult to quantify lamination.This study lays a good foundation for the impact echo method to detect the stratification problem of prefabricated superimposed slab joint surface.Figure [210] table [8] reference [52]...