Experimental Study On The Influence Of Laminated Surface Defects On The Mechanical Behavior Of Prefabricated Concrete Laminated Slabs

Compared with the cast-in-place concrete members,the laminated members are easy to form a weak surface at the overlapping surface.When the laminated surface is roughened,the mechanical properties can be approximated to the cast-in-place.If the treatment is not handled properly,it is equivalent to cold seams.In addition,during the construction of the laminated members,there may be defects such as floating pulp,oil stains,muck soil,and water accumulation on the laminated surface.These factors may have a certain influence on the bonding performance of the laminated surface,thereby affecting the quality of the stack,the reliability of the combined components and even the structure.In this paper,the truss reinforced concrete laminated slabs commonly used in engineering are taken as the research object,and the influence of the physical and mechanical properties of the concrete laminated surface and the quality defects of the laminated surface on the mechanical properties of the laminated slab is studied.The main contents and achievements of this paper are as follows:1.Through the literature research,several common concrete roughness detection methods and roughness characterization parameters that can be used are summarized.The limitations of existing detection methods are pointed out,and the 3D laser scanning technology is applied to the quality evaluation of concrete laminated surface.A total of 8 specimens were obtained for the four rough surface treatment methods.The point cloud data was obtained by laser scanning method,and the feasibility of the method for quantitative characterization of the superimposed surface was evaluated.2.For the 80 laminated core samples and 20 comparative core samples with a height to diameter ratio of 1:1,the splitting tensile test is carried out.The rough surface treatment considers in ways of artificial pulling,punching,natural vibration,and embossed steel plate indentation and steel bar indentation.The roughness is quantitatively evaluated by sand filling method.The test results show that the rough surface forming process has a great influence on the splitting and tensile properties of the laminated surface.The sanding method has a certain limitation on the depth of the laminated surface.This parameter cannot reflect the proportion of the rough surface aggregation.And the distribution situation should not be used as a unified method to measure the processing quality of different laminated surface forming processes.The new evaluation method should be studied in combination with parameters such as contour amplitude and contour spacing.3.Through the static test of 14 laminated plate specimens,the influence of the quality defects of the laminated surface on the mechanical properties of the precast concrete laminated slab is studied.The defect characteristics such as positional parameters and area parameters,as well as the effects of rough surface treatment,truss tendon and other parameters on the bearing capacity,deformation and crack performance of the laminated plates are considered.The test results show that the defect characteristics of the laminated surface have a significant influence on the normal use of the laminated plate,such as the crack resistance,and the impact on the bearing capacity is relatively reduced.The rough treatment process directly affects the roughness of the laminated surface and further affects the laminated plate.For the mechanical properties,it is necessary to conduct a more in-depth study on the overlapping faces of different roughness;the truss tendon bar as a shear bond has a relatively small effect,mainly after the laminated plate is subjected to cracking.4.The results of nonlinear finite element analysis for 4.2m span laminated plates using ABAQUS software are in good agreement with the experimental results.The simulation results of the laminated plates with no defects,25% defects at the ends of the plates and 50% defects in the middle are close to the test results,and can accurately simulate the variation of the stiffness of concrete after cracking.For the laminated plates with 100% defect and no truss ribs,after the concrete is cracked,the finite element simulation displacement results are significantly larger than the test results,because the actual laminated surface has a certain adhesive force and friction,and the laminated surface was considered smooth during the simulation.Defects have a certain influence on the deformation performance of the laminated plates after cracking,and the stiffness is reduced.The larger the defect area under normal use conditions,the greater the deformation of the mid-span deflection,but the smaller the ultimate bearing capacity is.