Sleeve Connection Research Articles

Slight Looseness Detection of Reinforcing Bar’s Threaded Sleeve Connections Using Convolutional Neural Network Trained by Magnetostrictive Guided Wave Signals

The threaded sleeve connection (TSC) is widely used in the connection of reinforcing bars and the looseness is difficult to observe directly. The guided wave (GW) can be used to detect TSC’s looseness due to its ability to propagate to invisible regions, which is difficult to identify with traditional signal processing methods if the looseness is slight. In this study, we employ the convolutional neural network (CNN) to process the magnetostrictive GW signals for the detection of TSC’s slight looseness. Experiments are carried out on the thread-sleeve-connected reinforcing bars to obtain the passing GW signals as the dataset to train the CNNs and the states of the TSC contain tighten and slight looseness in which loosening angle is less than 5°. In order to improve the time–frequency resolution of CNN, a CNN with multi-scale kernel size is built. For comparison, another three CNNs with one kernel size are built. Using the GW signals, we train these four CNNs and then these four trained CNNs are employed to analyze the testing data. Only the CNN with multi-scale kernel size can achieve 100% slight looseness detection accuracy. The results show that the CNN can be used to detect the slight looseness of reinforcing bar’s TSC and the CNN trained with multi-scale kernel size performs better.

Experimental investigation on the post-fire cyclic behavior of grouted sleeve connections

Grouted sleeve connections have been widely used in precast construction for joining rebar. In order to study their post-fire seismic performance, grouted sleeve connections, which are heated first to elevated temperature and then cooled down to room temperature, are tested under both monotonic and cyclic loadings. For comparisons, the same tests are also carried out on continuous rebar. The failure modes, skeleton curves and compression strength of the specimens are analyzed to study the influence of temperature on the seismic performance of the grouted sleeve connections. The results show that buckling occurs to all the grouted sleeve connections under cyclic loading. It is also found that the skeleton curves, compressive and buckling strength of both the connections and the continuous rebar decrease with the increase of temperature up to 600 °C. From the test results and on the basis of the GMP and GA hysteric constitutive models of steel, a modified model for cyclic constitutive law of the continuous rebar and the grouted sleeve connections is presented and validated. The results demonstrate that the modified model is capable of accurately simulating hysteretic properties of steel rebars and grouted sleeve connections.

基于反应谱法的灌浆套筒连接装配式桥墩抗震性能研究

基于反应谱法的灌浆套筒连接装配式桥墩抗震性能研究

Monolithic equivalent stiffness of precast columns with grouted splice sleeve connections

abstract The aim of this paper is the validation of monolithic equivalent stiffness applied to precast columns with grouted splice sleeve connections, wherein spliced precast elements have been compared with continuous monolithic elements. The experimental investigation has been carried out with bending tests for two spliced elements (L1 and L2), comparing the deflections along these elements with the results obtained from two monolithic elements (M1 and M2). The grouted splice sleeve connections have been characterized by their rotational stiffness (moment-rotation relationship), ultimate strength, and ductility, allowing the calibration of the equation for the secant stiffness according to ABNT NBR9062:2017. Based on the experimental results, the effective deformation length within the connection zone obtained was Led = 20ϕ, corresponding to a secant stiffness of Rsec = 77,785 kN∙m/rad. Although relative rotations have been observed at the grouted splice joint, the deflections along the precast spliced elements were very close to the deflections along the monolithic elements. A strong convergence for all phases of the load x displacement curves has been observed, as well as good approximation in terms of rotational stiffness, strength and ductility. Therefore, based on the analysis of the experimental results, the requirement to define the monolithic equivalent stiffness for the precast columns has been met.

Experimental study on grout defects detection for grouted splice sleeve connectors using stress wave measurement

Grouted splice sleeve (GSS) connectors have been widely employed to connect rebars in prefabricated concrete (PC) structures. However, grout defects may occur due to manual operation miss or poor control approaches for quality, which weaken the efficient embedment of rebars in GSS connectors and lead to a negative effect on mechanical properties of PC structures. The development of reliable and efficient grout defect detection methods for GSS connectors is challenging because its inaccessibility and inner structure complexity. In this paper, an active grout defects detection approach for GSS connectors using direct stress wave measurement is proposed, where piezoelectric-lead-zirconate-titanate (PZT) patches are mounted on the surface of the sleeve as actuators and sensors, and experimental study is carried out to validate its feasibility. Stress wave propagating along the GSS connectors excited by the surface-mounted PZT actuator is measured with PZT sensors. In order to investigate the effect of grout defects on stress wave measurement, four GSS specimens with different degrees of mimicked grout defects are designed and analysis on the PZT sensor measurement with a pitch and catch pattern is carried out. By comparing the PZT sensors measurement of different specimens without and with different grout defects under an identical impulse excitation signal, the grout defect is detected. The relationship between a normalized defect evaluation index (DEI) determined by the use of the PZT sensor measurement and the grout defect severity is analyzed. Experimental results indicate grout defect leads to increase in PZT sensors measurement compared with that of specimen without grout defect. The results show that the proposed approach based on stress wave measurement is efficient in detecting grout defect and the stress wave measurement is sensitive to the dimension of grout defect in GSS.

GROUTED SLEEVE CONNECTION FOR PRECAST CONCRETE MEMBERS

Precast concrete structures have gained preference in the modern construction industry because of the multiple advantages they offer. The connection of precast members is an important aspect to consider in the design of structures with precast components. Grouted Sleeve connection, one of the famous connector types, is made of the trio of reinforced bars, high strength grouting materials and a ductile iron cylinder. This article compares the finding of recent experimental research findings on grouted sleeve connection and establishes the relationship between the three components of the connector to enhance the performance of the splicing agent. It is found that the tensile performance of the connector increases with the embedded length of the bar for a normal sleeve. An effective embedded length set between 6 and 8 times the diameter of the bar will maximize the tensile performance of the connector. The increase in diameter of the sleeve cylinder, the compressive strength of the grout and the length of the bar embedded and its surface will affect the bond performance and the mode of failure under tensile load.

Shear strength and cracking mechanism of precast bridge columns with grouted sleeve connections

Precast columns are widely adopted in Accelerated Bridge Construction (ABC) due to its fast construction speed, environment amity and little interference to existing traffic. The bending behavior of precast columns with grouted sleeve connections under seismic effect has been widely studied. However, studies on the shear behavior of this kind of columns (for example, short columns under seismic effect) are limited, which restricts the application of ABC in seismic regions. This study proposes an approach for evaluating the shear cracking mechanism of sleeve region and the shear strength of precast columns with grouted sleeve connection. In this approach, the sleeve units and concrete units in the sleeve region are established according to the different stiffness between sleeve and concrete, individually. The cracking angle of membrane element of units is solved based on the Modified Compression Field Theory (MCFT). Thus, the crack developing diagram is drawn in light of the cracking range of units. An improved model for computing the shear strength of precast columns with grouted sleeve connection is presented by the predicted cracking method in this paper. A skeleton curve prediction method based on the principal compressive strain in compression zone has also been proposed and verified. In general, the improved MCFT method given in the paper is effective for predicting shear failure of precast bridge columns with sleeve connection.

Seismic performance of pre-fabricated segmental bridge piers with grouted splice sleeve connections

Accelerated bridge construction (ABC) has been increasingly popular in recent decades, due to various potential advantages compared with traditional cast-in-place (CIP) construction. Grouted splice (GS) sleeve is one of the most widely adopted techniques connecting the pre-fabricated segmental bridge columns and pier footings/caps. Therefore, the behavior of segmental piers with GS should be investigated carefully, especially under earthquake events. This paper investigates the seismic performance of GS piers, considering the influence of columns heights that is scarcely incorporated in previous numerical and experimental studies. The results show that the distribution of plastic regions and hysteretic responses of GS piers are similar to the CIP ones, except for GS regions remaining elastic. The ultimate lateral forces of GS piers are increased by about 10%, since the implementation of GS improves the corresponding section stiffness. While the yield displacement of GS piers accounts over 90% of CIP ones, the displacement capacity and ductility are 40–60% lower, caused by the strain penetration of steel bars and shifting of plastic deformation into grouted beds, as well as shorter plastic regions. Additionally, investigation on coupler rigid length factor (β) proposes for the first time that this parameter could be affected by the pier height, H, and might be related to other factors. Suggestions concerning the seismic design of GS piers are finally proposed according to the above results.

Behavior and design formulation of steel CHS with sleeve connections

Structures with tubular profiles gain space in civil construction due to their excellent response under tension, compression, and torsion. They are widely used in structural trusses, especially in large lengths. The profiles have a limited size due to the manufacturing and transport process. Therefore, there is a need to use some mechanism to perform the joint of profiles and obtain the desired length. This work aims to develop a new type of bar splice in circular hollow section (CHS) connection called sleeve connection, composed of two tubes connected with another smaller diameter tube with bolts arranged in a line (staggered bolts). This research presents an experimental, numerical, and parametric study of sleeve connection in CHS under centric axial tension. A numerical model was developed using the finite element method (FEM) considering sleeve connection with staggered bolts. From the numerical results, it was possible to analyze the connection behavior and failure modes: yielding gross cross-section, fracture through the effective net area, bolt shear failure, bearing failure of the plate, and bolt bending failure. This way, formulations were proposed to predict the sleeve connections' behavior with staggered bolts as a function of the failure modes.

Seismic behaviour of full-scale prefabricated RC beam–CFST column joints connected by reinforcement coupling sleeves

This study evaluated a new type of joint for connecting reinforced concrete (RC) beams with a concrete-filled steel tube (CFST) column that consists of U-shaped steel end plates and longitudinal reinforcement coupling sleeves. The proposed joint configuration was designed to fully realise the advantages of prefabricated structures, including a short construction period, easy construction control and low environmental impact. Low-cycle reversed loading tests were conducted to evaluate the seismic behaviour of three full-scale joint specimens, namely a cast-in-place joint and two prefabricated RC beam–CFST column joints connected using reinforcement coupling sleeves. The results indicate that the prefabricated joints exhibited plumper load–displacement curves and a good connection behaviour. The prefabricated joints failed in bending, thereby resembling the failure of the cast-in-place RC beam–CFST column joint. The failure region was concentrated in the area outside of the U-shaped end plate. The coupling sleeve connection was reliable, and the plastic hinge at the beam end moved further outward. Compared to the cast-in-place joint, the prefabricated RC beam–CFST column joints exhibited a similar bending capacity. The ductility coefficients of the prefabricated RC beam–CFST column joints increased about 5.2% and 2.6%, respectively. The average energy dissipation coefficient increased by 0.71% and 1.74%. The cumulative energy consumption and working index showed no significant difference.

Experimental and Analytical Study of Grouted Sleeve Splice Under Axial Tensile Load

Paper Compared to traditional cast-in-place concrete structures, the precast Concrete structures are usually constructed in a controlled environment , i.e. plants, and then assembled through certain links at the construction site. The concrete precast concrete structures can therefore have better concrete quality and help to reduce labor costs and increase construction speed. Because of these advantages, in recent years the precast concrete structures have received much attention. This research work therefore presents a reasonable procedure for designing a grouted sleeve splice connection using a simple material such as standard pipes with little workmanship which gives the design a good advantage compared to just using selection tables for expensive proprietary similar connection. Such splices’ mechanical behavior is a function of two essential mechanisms: bar-to-grout bond behavior, and sleeve-to-grout bond behavior. To achieve the purpose of this analysis work , three arrangements were manufactured and checked under incremental axial tensile load with an all-out number of 66 grouted splice sleeve specimens. While experimental methods of investigation are extremely useful in obtaining information about the grouted splice sleeve connection behavior, the use of numerical models helps to develop good comprehension of behavior at lower cost. Models of non-linear finite-element analysis for grouted splice sleeve connection were presented in this research. The research utilized the commercial Finite Element modeling software (ANSYS) to study the effects of some parameters that are important in the bond behavior of the grouted splice sleeve connection and compare the analytical results with the experimental results to confirm the analytical model. The average efficiency of the finite element models using ANSYS was 92.5%. Having the finite element model validated, a parametric study was performed using ANSYS to evaluate the effect of the following parameters on the behavior of grouted splice sleeve: bar diameter, embedded length, grout compressive strength, sleeve wall thickness, and sleeve inner diameter.

Identification of Grout Sleeve Joint Defect in Prefabricated Structures Using Deep Learning

A grout sleeve connection is a typical kind of joint in prefabricated structures. However, for construction and manufacturing reasons, defects in this kind of joint are usually inevitable. The joint quality of a prefabricated structure has a significant influence on its overall performance and can lead to structural failure. Due to the complexity of various types of materials used in grout sleeve connection, traditional non-destructive testing methods, such as Acoustic Emission (AE), Ultrasonic Testing (UT), Guided Wave Testing (GW), are facing great challenges. The recent development of deep learning technology provides a new opportunity to solve this problem. Deep learning can learn the inherent rules and abstract hierarchies of sample data, and it has a powerful ability to extract the intrinsic features of training data in complex classification tasks. This paper illustrates a deep learning framework for the identification of joint defects in prefabricated structures. In this method, defect features are extracted from the acceleration time history response of a prefabricated structure using a convolutional neural network. The proposed method is validated by vibration experiments on a half-scaled, two-floor prefabricated frame structure with column rebars spliced by different defective grout sleeves.

Nondestructive testing of strength of sleeve grouting material in prefabricated structure based on surface hardness method

The strength of the sleeve grouting material plays a key role in the performance of the entire sleeve connection in prefabricated structures. Detecting this strength efficiently, reliably, and nondestructively is a difficult problem. In this research, the correlation between the surface hardness and compressive strength of a sleeve grouting material was studied first. Then, rubber stoppers with flat ends were creatively used to plug the grouting material to obtain qualified inspection surfaces, and the relationship curve between the surface hardness and compressive strength of the grouting material in PVC pipes was established. Finally, the nondestructive testing method was applied to laboratory and field testing. Results showed that the relative error between the actual values of the compressive strength obtained by the compressive tests and the conversion values of the compressive strength of the grouting material calculated from the surface hardness and strength curve was small, which satisfied the needs of practical engineering applications. The feasibility and reliability of estimating the strength of the sleeve grouting material based on the surface hardness method were further verified.

Ultrasonic inspection of grouted splice sleeves in precast concrete structures using elastic reverse time migration method

Precast concrete (PC) structure has been widely employed for building construction in recent years, and grouted splice sleeve is commonly used for component connection. The compactness of the grouted splice sleeve connections plays a decisive role in structural safety, especially for its capacity to resist an earthquake. In this study, an ultrasonic imaging method is proposed for inspecting the grouted splice sleeves in PC structures using reverse time migration (RTM) algorithm based on an elastic wave equation. Numerical and laboratory experiments are carried out to assess the feasibility of our proposed method. In the numerical experiment, three numerical models, i.e. three-quarter grouted, fully-grouted, and non-grouted, are established. The results show that the proposed RTM method can reconstruct images of the buried sleeves with a higher resolution and a greatly-improved accuracy, compared with the traditional ultrasonic imaging method. Moreover, the grouting condition in the three models can be readily distinguished and even the interface between the grouting material and the air defect in the three-quarter grouted model can be clearly identified. In the laboratory experiment, two sleeves, one is fully-grouted and the other one is insufficiently-grouted with certain air defects, are embedded in a concrete model. The top of the two sleeves can be clearly imaged, and the insufficiently-grouted sleeve has a reflection, which is about 9 dB stronger than the other one. We conclude that the proposed ultrasonic imaging method can be used for inspecting the grouting quality of splice sleeves in PC constructions in field.

Experimental study on seismic response of precast bridge piers with double-grouted sleeve connections

In recent years accelerated bridge construction (ABC) has become increasingly popular all over the world because of its good quality, cost effectiveness and decreasing bridge construction time. Much attention has been paid to substructure connections for ABC systems. Grouting sleeve (GS) is one of the most widely used connection methods. In this study, three 1/4 scale column models with two joints connected by different technique were conducted according to an actual precast bridge project. Two precast columns (B2, C2) were made to study the location effect of GS. One conventional cast-in-place (CIP) column (A2) was conducted as reference specimen. The seismic performance of the columns was investigated and compared. Experimental results showed that cracks for B2 with GS connectors in the column foot were less and plastic hinge had shifted to the ends of GS. The energy dissipation capacity of B2 was lower than that of reference specimen. Specimen C2 with GS connectors in the pier foundation appeared similar seismic performance to reference CIP A2, and the peak load of each cycle was higher due to the high-strength grout reinforced the interface bonding behavior between column and base. The displacement ductility coefficients for A2, B2 and C2 were 6.87, 5.14 and 6.42 respectively, and the GS connecting technique like B2 was not suggested for application in the high seismic area. The column-cap beam joint of all specimens remained intact throughout the testing from the strain results of the longitudinal bar.

Shake table study on precast segmental concrete double-column piers

Seismic capacity, including the ultimate load-carrying capacity and ultimate deformation capacity of precast segmental concrete double-column (PSCDC) piers with steel sleeve (SS) connection or grouted corrugated-metal duct (GCMD) connection, has been verified to be similar to those of cast-in-place (CIP) piers by quasi-static tests. However, the lack of knowledge of seismic response characteristics and damage process of PSCDC piers has limited their application in high-intensity seismic areas. Therefore, shake table tests, using variable types and intensities of seismic ground motions, were performed to investigate the seismic behavior of connection joints and to evaluate the seismic performance of PSCDC piers with SS and GCMD connections. Also, a finite element analysis (FEA) model was developed to study the influence of design parameters on the seismic behavior of the piers. The results showed that the main damage in PSCDC piers was caused by the cyclic opening and closing of connection joints. Under high-intensity ground motions, the PSCDC piers had a lower seismic performance than the CIP piers due to a significant decrease of their integrity and stiffness. The seismic performance of PSCDC piers is comparable to CIP piers when using an appropriate initial stress of the prestressing tendons.

Tension analysis of bolted sleeve connection between pultruded GFRP tube and steel member considering adhesion

Pultruded Glass fibre reinforced polymer (GFRP)-steel hybrid structures have become increasingly popular in civil infrastructures. However, the connection between GFRP and steel members is one of the key issues limiting the development of the innovative structure. This paper presents tensile capacity of bolted sleeve connection between GFRP and steel members. With consideration of the pre-loaded bolt effect, the appropriate fastening torque was proposed by finite element investigation. The adhesive effect was also considered and investigated by cohesive zone method. The bolted sleeve connection provides a good solution for the tubular and large-span structures.

Axial load resistance of grouted sleeve connection for modular construction

Abstract Modular construction has become popular for its advantages in construction efficiency and reduced manpower on site. Steel modules are typically connected using bolted connections which often suffer from inadequate allowable tolerances to accommodate imperfections due to vertical alignment of modules. To solve these problems, a shear-keyed grouted sleeve connection (SK-GSC) is proposed to connect the square hollow section (SHS) columns between the upper and lower modules. This paper investigates the axial performance of SHS SK-GSCs, specifically on their resistance and load transferring mechanism. To study the effect of shear key spacing, grout strength, and grout thickness, fifteen specimens were tested, and numerical models were calibrated against the test results to gain insight into the failure mechanism. It was found that the load-bearing resistance of SHS SK-GSCs was contributed by the frictional bond at the steel-grout interface and the diagonal compression struts developed in the grout. The proposed connections have sufficient axial resistance, stiffness and ductility to integrate the module columns vertically as compared to existing bolted connections. They were robust enough to withstand potential tension force due to accidental action in the design of modular buildings.

Bearing failure in bolted sleeve connections with circular hollow sections under compression

Abstract This article analyzes sleeve connections between circular hollow sections. This type of connection is composed of two tubes connected by bolts to an inner tube with a smaller diameter, and explores the efficiency, aesthetics and resistance of hollow sections subjected to tension and compression. In previous researches, sleeve connections with aligned and crossed bolt dispositions and under axial tension were studied. Herein, the behavior of sleeve connections with aligned bolts and under compression was analyzed. A model to represent the connection using the finite element method was developed, which allowed a numerical analysis with geometric property variations. In the numerical/parametric results, bearing failure was observed in all cases, either in the outer or inner tube. Limiting the number of bolts to 6 and considering that connections have a lower outer thickness than the inner tube, a formulation was proposed to determine the ultimate bearing capacity of sleeve connections under compression and with bearing failure.

Experimental study on seismic performance of an improved precast reinforced concrete column-to-column joint

The seismic performance of an improved column-to-column connection in the precast concrete frame is studied in this article, including five precast specimens and one cast-in-place specimen. The traditional reinforced concrete tenon connection of precast concrete frame columns is replaced by the concrete-filled steel tubular tenon. The welding or cold extrusion sleeve connection of the column longitudinal bars is replaced by rolling straight thread sleeve connection. The six-frame column specimens were fabricated and tested subjected to low-reversed cyclic loading. Efforts have been made to study the characteristics of an improved tenon column joints, such as the failure mode, the hysteretic curves, the skeleton curves, the stiffness degradation, the ductility, and the energy dissipation. The test results show that the seismic performance of the precast columns with the suggested tenon connection is similar to that of the cast-in-place columns.