Research On The Influence Of Grouting Defects On The Tensile Performance Of A Fully Grouted Sleeve Connector

As the Precast Concrete（PC）technology continues to thrive in the construction industry,there is a constant need to ensure the safe transfer of loads at the connection during the erection of the structure and in its lifetime service.While there are various ways of connecting PC members,the use of grouted sleeve connection is more common in the construction industry all over the world but much more in China.During the construction process,however,it has been reported in some cases that the grouting process does not fully occupy the inner volume of the sleeve leaving room for some voids known as defects.Though research has confirmed the structural resilience of this connection,the presence of defects weakens the performance of the connector and threatens the structural integrity of the structure at the connection.The current trend of research on grouting defects is much more inclined to half-grouted sleeve connections and rarely considers the fully grouted joint.Furthermore,the existing research does not fully address the influence of the location of the defect in compromising the stress distribution between the components of the connection.This work presents a comprehensive study on the influence of the grouting defect on the mechanical properties of the fully grouted sleeve connector.The objective of this study is to assess the influence of these defects on the performance of the fully grouted sleeve connection.The aim of this study was achieved through a combination of both experimental and numerical approaches to study the different ways defects influence the mechanical performance of the grouted sleeve connection.The control specimen had no defects and the main anchorage length was 8d（d is diameter of the bar）.The systematic approach presented in this dissertation can be subdivided in contents as follow:（1）Tensile experiment on the full grouted sleeve with inbuilt defects.Defects of different sizes where predesigned in different locations of the connector to make 7 configurations.72 specimens were prepared following the Chinese standard for testing materials and,were subjected to a uniaxial tensile loading test.The results revealed two main failure modes including the fracture of the bar and its slip out.A comparative analysis of the non-defective and defective specimens was conducted.When the defect size is less or equal to 3d,the highest drop in capacity is 18%compared to the non-defective specimen.However,the performance of the connection is highly sensitive the location of the defect.For instance,when the defect of size 3d is located in the midspan of the anchorage length the connection fails by pullout and its capacity decreases by 18%while when the defect of the same size is located at both ends of the sleeve the drop in capacity is about 2%and the connection fails by fracture.In addition,the sole pullout failure when the size of the defect is 2d was experienced when the defect is located at the mid-span of the anchorage length.Thus,defects of equal size influenced the mechanical performance of the connection differently based on the location of the defect.Based on the response and sensitivity of the connector to the location of the defects,the connection was divided into three main zones to indicate the severity of the defect based on the location.（2）Numerical model establishment and validation.Based on the experiment models,the corresponding finite element models were established in Abaqus to simulate and further analyze the specimens.The comparative analysis of the load-displacement curves and the failure modes of the connector indicate that the results of the finite element modelling are consistent with the experimental findings and reflects the actual load-bearing capacity and failure modes of the connection.Furthermore,the stress distribution in the connector is symmetric between the two ends of the reinforcement and the defect compromises this distribution by creating an overstressed zone in grouting materials around the location of the defect which caused the pullout failure of the connector in some configurations.（3）Parametric study on the influence of defects.Based on the validated finite element models,a parametric study was conducted to analyze the interaction between defects and the diameter of the bar,the ratio of the diameter of the sleeve to that of the bar（d_s/d）and the location of the defect.The outcome of the parametric study revealed that as the diameter of the reinforcement increases the bearing capacity of the connection increases gradually,but the sensitivity of the connector to the defects and the induced impact of the defects remains almost the same regardless of the change in the diameter.In contrast,different values of the ratio of the sleeve diameter to that of the bar have a significant impact on the performance of the connection.As the value of the ratio decreases the bearing capacity of the connection increases and as the value of the ratio increases the capacity of the connection decreases significantly.For instance,when the defect of size 3d is located at the midspan of the anchorage length and d_s/d is 2.66,the equivalent drop in the ultimate capacity is 12%compared with the non-defective specimen while,with the same configuration of the defect and d_s/d is 3.55,the corresponding drop in capacity is 44%compared to the same control specimen.Furthermore,with the increase in d_s/d the failure mode of many specimens changed from fracture to pullout.The location of the defects determines its impact on the performance of the connection.When the defect is located in the mid-span of the anchorage length,the maximum impact of the defect is attained when it is exactly located at a distance（3d）from the edge.（4）Structural monitoring guidelines and design suggestions.Based on the findings of this research,this dissertation puts forward suggestions for the monitoring and maintenance of the connection.This study suggests a sequential process toward the required action when the defect is located in the sleeve.These actions consist of first use non-destructive testing（NDT）to detect the location and the size of the defect,determine the severity of the defect based on the proposed catalogue in this study and then conduct the required maintenance action.Furthermore,this study proposes a constant of safety in the calculation of the average bond strength which accounts for the impact of the location of the defect and the confinement on the bond strength.In conclusion,some suggestions were made on the design and construction of the grouted sleeve connection to provide a reference for the development of the grouted sleeve connection and precast concrete structures.