Research On Mechanical Properties Of Dowel Action Considering The Coupled Damage Effect Of Concrete

Dowel action is the main resisting mechanism at the construction interfaces and joints.These interfaces and joints may turn out to be critical planes in the operation of the load-resisting mechanism and govern the ultimate strength,ductility and enery absorption capability of an entire structure.To assure the safety of the RC structure,it is of great importance to research on the mechanical behavior of the dowel action.In this thesis,a three-dimensional steel-to-concrete bond model considering the coupled damage effect was proposed based on the mechanism analysis and experimental research.Through the analysis of the mechanism of fatigue damage,the model was further extended to predict the fatigue properties of the dowel action.This study mainly includes:1.In this research,a total of 15 specimens were tested to investigate the effect of the bar diamtters,concrete compressive strengths,pre-tension and concrete cover on the dowel action.The effect of the damage degree of concrete and the coupled damage effect on the dowel action were quantified and the experimental data were used to calibrate and develop the proposed model.2.A steel-to-concrete bond model considering the coupled damage effect of concrete was proposed based on the analysis of the mechanism of the interaction between steel bar and concrete.The local strain of steel bar was chosen as an indicator of the damage level of the surrounding concrete due to axial slip,while the local strain of concrete was chosen as the quantitative index of the localized crushing and fractures due to shear displacements.A quantitative calculation method was proposed to characterize the coupled damage effect.Verification of the model was conducted by comparing the analysis results with experimental data obtained in this study and from the literature,and satisfactory agreement was obtained.3.Baed on the experimental data and analysis results,a computional model for the bearing capacity of the dowel action considering the damage effect was proposed.The damage effect due to localized crushing of concrete was determined and employed to improve the accuracy of the proposed formulae based on the parameter damage factor.Through a series of FEM cases with different bar diameter and thickness of concrete cover,the influence factor of the concrete cover was determined to characterize thestress state and damage mechanism of concrete when the failure mode is transformed.Verification of the model was conducted by comparing the analysis results with experimental data.It was found that the proposed model give good predictions for both failure mechanisms.4.Fatigue tests with different bar diameters were carried out to study the fatigue performance and failure mode of the dowel action under fatigue loads.The quantitative calculation method of fatigue damage accumulation coefficient was proposed to represent the effect of fatigue loading on the dowel action.Based on the static model,the bond model considering the fatigue damage is established,and verification of the model was conducted by comparing the analysis results with experimental data.