Rebar Connection Research Articles

Experimental and numerical study on cyclic behavior of precast segmental railway bridge columns with lap-spliced rebar connections using UHPC wet joints

A novel lap-spliced connection with ultra-high performance concrete (UHPC) was proposed to connect precast railway bridge column segments with footings or cap beams. Two 1:3 scaled specimens were tested under cyclic loads. Specimen PC-LS was a precast column with lap-spliced rebar connection and UHPC wet joints. Specimen CIP was a monolithic column as a reference specimen. The test results revealed that the plastic hinge region of the precast specimen shafted to the upper surface of the UHPC wet joint. The failure mode of the precast specimen was exhibited as the crushing of the core concrete and the buckling/fracture of the longitudinal rebars. Specimen PC-LS experienced larger lateral force, initial stiffness, comparable ductility, and energy dissipation compared to specimen CIP. Additionally, the validated finite-element (FE) models considering the bond-slip effect between concrete and reinforcements were developed. The parametric studies were carried out to further investigate the cyclic behavior of specimen PC-LS. Analytical results demonstrated that the variation of the compressive and tensile strength of UHPC showed little influence on the cyclic behavior of the precast segmental column, which indicated that UHPC with natural curing and lower volume content steel fibers could be used as the wet joint. The precast segmental column had similar lateral force and stiffness with the cast-in-place column when the lap splice length was 10 times of the rebar diameter.

Development of a Multi-Robot System for Pier Construction

The construction industry is a challenging field for the application of robots. In particular, bridge construction, which involves many tasks at great heights, makes it difficult to implement robots. To construct a bridge, it is necessary to build numerous piers that can support the bridge deck. Pier construction involves a series of tasks including rebar connection, formwork installation, concrete pouring, formwork dismantling, and formwork reinstallation. These activities require working at heights, presenting a significant risk of falls. If bridge construction could be performed remotely using robots instead of relying on human labor, it would greatly contribute to the safety of bridge construction. This paper proposes a multi-robot system capable of remote operation and automation for rebar structure connection, concrete pouring, and concrete vibrating tasks in pier construction. The proposed multi-robot system for pier construction is composed of three robot systems. Each robot system consists of a robot arm mounted on a mobile robot that can move along rails. And to apply the proposed system to a construction site, it is essential to implement a compliance control algorithm that adapts to external forces. In this paper, we propose an admittance control that takes into account the weight of the tool for the compliance control of the proposed robot, which performs tasks by switching between various construction tools of different weights. Furthermore, we propose a synchronization control method for the multi-robot system to connect reinforcing structures. We validated the proposed algorithm through simulation. Furthermore, we developed a prototype of the proposed system to verify the feasibility of the suggested hardware design and control.

Pullout test for PC column-capital grouted rebar connection with corrugated duct

Double-beam precast concrete (PC) structures require large capitals to support a wide PC girder. In this study, a segmented PC column-capital system is developed to overcome the disadvantages of conventional PC columns in terms of manufacturing, transportation, and construction. In the proposed segmented PC column-capital system, large PC capitals are assembled with PC columns using the proposed corrugated rebar connections filled with grouted mortar. To verify the load-transfer capacity of the proposed corrugated rebar connections, pullout load tests are conducted under various test parameters, including the mortar compressive strength, curing time, bond length, and embedment length. To enable rapid construction, a relatively short curing time of 1–2 days is addressed. The test results indicate that the pullout performance of the proposed corrugated rebar connection is primarily affected by the mortar compressive strength fm’ and embedment length ld. When fm’ > 7.9 MPa and ld = 800 mm, the proposed corrugated rebar connection transfers tensile loads corresponding to construction loads. When fm’ > 21.0 MPa and ld = 800 mm, the proposed rebar connection can resist the tensile yielding load of the connected vertical rebar even after one-day of curing. However, when ld is less than 800 mm, bond-slip failure occurs because of the insufficient bond length. Based on the test results, a parametric analysis is conducted using a finite-element model. Similar to the experimental result, the numerical result shows that the bond strength of the proposed rebar connections is significantly affected by fm’ and ld. Hence, a bond-strength model of less-hardened grouted mortar with a bond stress of τb = 0.20 fm’ is suggested based on the previous and present test results as well as parametric analysis results.

Experimental analysis on the out-of-plane structural performance of single-face superposed shear walls with different horizontal connections

Single-face superposed (SFS) shear wall is a novel precast concrete sandwich panel (PCSP) wall that can be used as load-bearing walls in high-rise buildings and underground structures in seismic zones. This paper investigates the out-of-plane structural performance of SFS shear walls with different horizontal connections. Three SFS shear walls with different lap-spliced rebar connection configurations at the horizontal connections were designed and tested to compare their out-of-plane structural performance with that of a cast-in-place specimen, in terms of failure modes, cracking patterns, load-displacement curves, stiffness degradation curves, ductility, and force transfer mechanism of lap-spliced rebar connections. The test results showed that the SFS shear wall specimens exhibited and maintained a high level of composite action until failure, and the studied three different horizontal connections can allow effective force transfer between the upper shear walls and the lower. The stiffness, ductility, and ultimate bearing capacities of SFS shear walls under out-of-plane monotonic loading were significantly higher than those of cast-in-place shear walls. The bearing capacity was found to depend to a large extent on the location of additional vertical connecting rebar, the displacement mainly caused by rigid body rotation and related to crack width at joint. A calculation method of the ultimate bearing capacity of a SFS shear wall under out-of-plane horizontal loads was proposed. Finally, some suggestions on the setting of the vertical connecting bar are put forward.

Interface Microstructure and Properties of Vacuum-Hot-Rolled 55#/316L Clad Rebars

The existing process for the preparation of cladded rebars is too complicated for large-scale industrial production. Therefore, this paper proposes a 55#/316L rebar preparation method based on vacuum hot rolling. The microstructure and mechanical properties of the composite interface of the rebar, along with the connecting technique, were studied using transmission electron microscopy, X-ray diffraction, and Vickers hardness testing. The obtained results showed that the minimum thickness of the 55#/316L rebar cladding was 0.25 mm, which was twice that of the M 329M/M 329-11 design standard used in the United States of America. Due to the diffusion of carbon, large numbers of second-phase particles were precipitated on the stainless-steel side, which resulted in intergranular chromium depletion. After multi-pass hot rolling, the minimum bonding strength of the composite interface reached 316.58 MPa, which was considerably higher than the specified value of 210 MPa. In addition, we designed three different types of rebar connection joints: sleeve, groove-welded, and bar-welded. According to the tensile test, the bar-welded joint had higher yield strength (385 MPa) and tensile strength (665 MPa) than the base rebar (376.6 MPa and 655 MPa), as well as a very high corrosion resistance.

Interfacial shear performance of UHPC-strengthened RC structures using post-installed rebar connections: Experiments and analyses

The reliable bonding effect between the ultra-high performance concrete (UHPC) layer and the existing reinforced concrete (RC) components is always expected when UHPC is used to rehabilitate deteriorated RC structures. The post-installed rebar connection has been demonstrated to possess robust mechanical performance. However, no research to date clarifies how to design the post-installed rebar connection in engineering practice. To this end, this study conducted 34 push-out tests to investigate the interfacial shear performance of UHPC-strengthened RC structures using post-installed rebar connections. The primary variables in the tests included strengthening form, embedded depth of rebar, rebar diameter, rebar spacing, and substrate type. Based on the test results, three different failure modes were identified. The analytical results indicate that the embedded depth of the rebar has a significant influence on the performance of the post-installed connection. A formula was proposed to determine the minimum embedded depth, and its accuracy was validated by the physical experiments. The load-bearing mechanisms were revealed based on the experimentally measured force–displacement curves. The shear capacity of the connection mainly comprises the adhesive effect, rebar shearing, and friction. The connection capacity can be approximated by the rebar shear capacity due to its robust shear resistance. Also, a formula was proposed to estimate the shear capacity of the rebar. The experimental and theoretical results facilitate the design and application of post-installed rebar connections in UHPC-strengthened RC structures.

Research on the out-of-plane mechanical performance of double-face superposed shear walls with different horizontal connections

The horizontal connections play a critical role in resisting gravity and lateral loads in precast concrete sandwich panel shear wall structures and it's important to fully understand their behavior under various loading conditions. This study aims to investigate the out-of-plane mechanical behavior of double-face superposed shear walls with horizontal connections featuring different lap-spliced rebar connection configurations. Three full-scale double-face superposed shear walls were tested to investigate their out-of-plane structural performance with that of a cast-in-place shear wall in terms of failure modes, cracking patterns, strain analysis, deformation analysis, load-displacement curves, and force transfer mechanism of lap-spliced rebar connections. The double-face superposed shear walls displayed and maintained a fully composite manner until failure, and the examined three different horizontal connections can allow effective force transfer between the shear walls and the main structure. The final crack distribution and failure mode of double-face superposed shear walls were almost similar to that of the cast-in-place shear wall all exhibiting obvious out-of-plane bending failure characteristics. While the initial stiffness, ultimate bearing capacity and displacement ductility capacity of double-face superposed shear walls were higher. A mathematical model predicting the ultimate bearing capacity of the double-face superposed shear wall under out-of-plane horizontal loads was proposed.

교각 시공을 위한 모바일 매니퓰레이션 시스템 개발

A pier is a structure that supports the bridge girder as the lower structure of the bridge. Concrete piers are generally constructed by connecting rebars, installing formwork and then pouring concrete. Pier construction is performed by repeating rebar connection work, formwork installation work, concrete pouring work, formwork dismantling work and formwork installation work. Such pier construction requires work at height and falls frequently occur during the operation of the above procedures. An automation system is being developed to reduce the risk of accidents, shorten the construction period and improve the quality of the pier construction work; automation is being attempted to some of the pier construction tasks. Most of the pier construction work, however, is still performed by workers and these tasks are not easy to automate. This paper proposes a mobile manipulation system that can support rebar structure connection work, concrete pouring and concrete vibrating work in pier construction work. We developed a prototype of the proposed system and verified its applicability through driving experiments.

Experimental study on seismic behavior of precast concrete beam-column joints using UHPC-based connections

Ultra-high performance concrete (UHPC) with high bond characteristics with reinforcing bars could significantly shorten the lap splice length of rebars. UHPC-based rebar lap splice connections offer larger tolerance and simpler operation than traditional rebar connection approaches, which could ease and accelerate the on-site construction process of precast concrete structures. This paper characterizes the seismic behavior of precast beam-column joints where the longitudinal rebars of columns are connected using UHPC with a lap length of 15 times rebar diameter (15db). Full-scaled cyclic tests on two precast joints and two corresponding monolithic joints to compare were carried out keeping a high axial compression ratio (n) at 0.5. It was demonstrated that the beam-column subassemblies failed characterized by flexural failure of beam end instead of the column or joint core. The arch-like load–displacement curves and stable hysteretic behavior were still captured considering the p-delta effect. The proposed precast beam-column joints with UHPC-based connections could achieve similar bearing capacity, ductility and stiffness degradation rule to the monolithic counterparts. The degenerated four-linear restoring force model was presented and verified. Moreover, the numerical simulation was also performed, and the predicted structural behavior was in agreement with the experimental results.

Seismic performance of ceramsite concrete T-shaped composite wallboard joints under cyclic loading

The external wall insulation and fire prevention problems are hard to solve due to the lack of economical insulating and flame-retardant materials. By taking the wallboard structure as the cut-in point, a novel ceramsite concrete composite wallboard is proposed in this study, which inputs the insulation materials inbetween two wallboards to not only solve the fire prevention problem of the insulation materials thoroughly, but also prevent peeling-off of insulation wall during the construction and using processes. In order to apply this type of wallboard in shear wall structure, a T-shaped joint component of the new ceramsite concrete composite wallboard that adopts U-shaped rebar connection way is proposed in this paper as well. Three same specimens and one contrast specimen are designed in total. Meanwhile the seismic performance of the joint is also studied through the low-cyclic reversed loading experiment. And both the experimental phenomenon and the failure mechanism show that, shearing failure is the failure form of the specimen. The core area of the joint plays a dominating role during the stress process. By analyzing the seismic parameters of the specimen, such as hysteresis, skeleton, ductility and energy consumption, conclusions are made that the specimen is featured in good overall seismic performance, meeting the design requirement of “strong joint, weak component” in the specifications. The study on the T-shaped joint of the novel ceramsite concrete wallboard complements the connection methods of this new type of insulation wallboard, and provides a reliable basis for applying this type of wallboard in practical construction.

Research on Application Practice of Rebar Mechanical Connection

The development of rebar connection technology is the key to improve the construction quality of construction projects, and the application of related technologies can also improve the construction quality and efficiency of construction projects. The connection process of mechanical connection of steel bar requires higher requirements, which is different from the welding and binding connection of steel bar. The quality of mechanical joint also needs strict inspection. At present, grade I joints are widely used in high-rise buildings. How to ensure the quality of mechanical connection has become one of the key points of high-rise building quality control. Combined with specific engineering projects, this paper mainly analyzes the practical application of rebar mechanical connection technology in construction, and elaborates on rebar processing, product protection, quality control, etc., in order to provide technical reference for the work of relevant personnel in the field of construction engineering.

Influence of reinforcement arrangement details on mechanical behavior of precast concrete barrier with loop connection

Concrete bridge barriers are installed as road safety facilities to prevent vehicles or pedestrians on the road from exiting the lane or entering the opposing lane. Deterioration due to the aging of reinforced concrete members, vehicle crashes, and renovation/extension of bridges necessitate the repair and reinstallation of barriers. A precast concrete barrier solution is used to replace old deteriorated barriers to enable fast and effective completion of structures. This precast barrier is connected to a highly durable cementitious mortar injected into the loop rebar connection. This research shows that a beam specimen can be utilized to understand the detailed behavior of the connection. The results of the experimental study indicate that the configuration of the loop reinforcement provides excellent anchoring capacity and a failure mode that is more stable and capable of greater energy absorption than the existing system. It is revealed that the cracking pattern and mechanical behavior of the reinforcement are highly influenced by the re-arrangement of the reinforcement in the connection. The reinforcement congestion and stress concentration at the edge can be resolved safely by the details proposed in this study, and it can be used effectively for the design of impact loading conditions. The outcomes of this work will lead to important design guidelines for the connection of precast concrete barriers with deck slabs.

Experiment and analysis on mechanical properties of Fully-Grouted sleeve connection at elevated temperatures

The performance of the prefabricated concrete (PC) structures at elevated temperature becomes an important focus, once a fire occurs. The failure in fire of fully-grouted sleeve connection (FGSC) that extensively used in PC members will cause serious consequences. To fill this knowledge gap, the present work presents the experimental results of 15 FGSC specimens and 15 single rebar (SR) specimens by static tension. The results show that the mechanical behavior of FGSC specimens at high temperature is affected by the temperature and similar to that of SR. Two types of failure modes appear in the FGSC specimens, namely, rebar tension fracture and bond failure. The bond failure was observed at 600 °C. Based on the test results, the tension constitutive relation curves was established, and the bond strength design of FGSC at elevated temperatures were put forward to avoid the bond failure. A new prediction method for calculating mechanical property of prefabricated rebar connection at elevated temperature is proposed.

Research on pseudo-static cyclic tests of precast concrete shear walls with vertical rebar lapping in grout-filled constrained hole

In this paper, the seismic behaviors of four precast shear wall specimens and one cast-in-place shear wall specimen are investigated by pseudo-static test method. For the precast shear wall specimens, a new type of assembled rebar lap splices with prepared grout-filled holes and constraining spiral hoops were applied. Different vertical rebar lap splice positions and different rebar lap lengths at the horizontal assembly joints of the precast specimens were designed and fabricated in order to compare their seismic behaviors with the cast-in-place specimen. The geometric size and rebars of four precast specimens are totally same as those of the cast-in-place specimen. By analysis of test results including the load-lateral drift hysteresis curves, crack propagation and rebar strains, the failure modes, bearing capacity, hysteretic characteristics, ductility, rigidity degeneration and energy dissipation of all specimens were obtained and compared. The test results show that the precast concrete shear walls with horizontal assembly joints by this kind of rebar connection have good seismic behaviors and could be equivalent to the cast-in-place shear walls on the conditions of specified construction details.

Experimental Investigation on the Seismic Behavior of Newly-Developed Precast Reinforced Concrete Block Masonry Shear Walls

Typically, a special type of concrete block with cleaning holes is used in the bottom layer of traditional reinforced masonry shear walls (RMSWs) for mortar cleaning and vertical rebar connection, which results in reduced integrity and weakened structural behavior. In this paper, a precast construction technology was introduced to overcome these shortcomings. The cleaning-hole blocks were eliminated in the newly-developed precast RMSWs. Quasi-static tests on two traditional and two precast fully grouted RMSWs were conducted. The results showed that the flexural capacity of precast walls exhibited about a 10% increase when compared to traditional RMSWs under the same axial compression. Precast RMSWs that failed in flexural mode showed favorable deformation capacity and the displacement ductility value corresponding to 15% strength degradation reached 4.9. The wall stiffness degraded rapidly to 50% of the initial stiffness, K0, at 0.2% drift and, at 0.5% drift, the corresponding stiffness decreased to about 21% K0 at a more gradual rate. Furthermore, precast RMSWs exhibited significant energy dissipation capacity. The experiment suggests that precast RMSWs have a satisfactory seismic performance.

DETERMINATION AND RANGING OF ORGANIZATIONAL AND TECHNOLOGICAL FACTORS THAT DEFINE THE RATIONAL DECISIONS OF RE-BARS CONNECTION

Purpose. The paper proposes: 1) determination and formulation of factors that influence the choice of rational method for joining re-bars of vertical support members of reinforced concrete frame; 2) determination of factor parameters; 3) ranging of factors by the expert evaluation (Delphi) method. Methodology. In order to achieve research objectives, it is necessary to carry out analysis of existent rebar connection methods, determination of factors and parameter variation limits for each of the methods. Performing factor ranking by the expert evaluation method. Findings. The results of the questioning materials of 14 experts in the area of monolithic construction allowed setting the following: when choosing the rational re-bars connections, the most significant values are the factors that define the time parameters: possibility of carcassing, time of joining the re-bars, length of rebar cage, prior operation run time, operation time of main lifting equipment. Herewith the factors that define the rebar cage parameters have a direct relation to the work performance time, as they determine the amount of bar connections in the course of building erection over wide range. Economic factors – rebar connection cost and quality control cost – have the less value. It is obvious that in the conditions of considerable construction expenses it is advantageous for an investor to increase the rebar joining cost for the work growth rate. Structural and technological factors have the least value: origin of eccentric load transmission between re-bars, possibility of use of the thermally work-hardened re-bars of А500 and higher grades, work category for implementation of works, necessity to use the scaffold and appurtenances for re-enforcement of constructions. The reason is analogical: a contractor is ready to go to complication of technology with the purpose of reduction of the facility erection terms. As the calculated Pearson’s matching criterion χ2 = 47.24 is higher than the tabular one (22.36203), then the obtained concordance coefficient W=0.26 is not casual value, and that is why the obtained results make sense and can be used in further researches. Originality. The author obtained factors that influence the choice of the rational method for re-bars connection the most. Practical value. Ranging of factors will allow objective approaching to the problem of choice of re-bars connection method, optimizing the labour and material costs, and also reducing the construction time.

Experimental Study on Steel Jacket–Concrete Composite Connections

AbstractSteel–concrete composite frame bridges have larger structural stiffness, lower cost, and faster construction speed than traditional bridges because a combination of steel–concrete composite girders, concrete piers, and steel–concrete composite connections is used. In this type of composite bridge, the most important part is the connection joint between the steel–concrete composite girder and the concrete pier, which is formed by a steel plate, core concrete, shear connectors, and rebars. Taking a five-opening (110 m × 5) steel–concrete composite frame bridge with five 40-m-high piers as a prototype structure, three specimens, including two steel jacket–concrete composite connections with different construction details and one traditional rebar connection, were designed to study the load transfer mechanism in different types of composite connections. Results of the reversed cyclic load tests on the three specimens indicated that the steel jacket composite connections have better structural performa...

Strengthened and flexible pile-to-pilecap connections for integral abutment bridges

Pile-to-pilecap connection performance is important as Integral abutment bridges (IABs) have no expansion joints and their flexible weak-axis oriented supporting piles take the role of the expansion joint. This connection may govern the bridge strength and the performance against various lateral loads. The intention of this study is to identify crack propagation patterns when the pile-to-pilecap connection is subjected to lateral loadings and to propose novel connections for improved performance under lateral loadings. In this study, eight different types of connections were developed and modeled, using Abaqus 6.12 to evaluate performances. Three types were developed by strengthening the connections using rebar or steel tube: (i) PennDOT specification; (ii) Spiral rebar; and (iii) HSS tube. Other types were developed by softening the connections using shape modifications: (i) cylindrical hole; (ii) reduced flange; (iii) removed flange; (iv) extended hole; and (v) slot hole connection types. The connections using the PennDOT specification, HSS tube, and cylindrical hole were shown to be ineffective in the prevention of cracks, resulting in lower structural capacities under the lateral load compared to other types. The other developed connections successfully delayed or arrested the concrete crack initiations and propagations. Among the successful connection types, the spiral rebar connection allowed a relatively larger reaction force, which can damage the superstructure of the IABs. Other softened connections performed better in terms of minimized reaction forces and crack prevention.

Cyclic Loading Test for Exterior Beam–Column Joints of CEFT Columns

AbstractA cyclic loading test was performed to investigate the seismic performance of exterior beam-column joints of concrete-encased-and-filled steel tubular (CEFT) columns. Two specimens with steel beams and two specimens with precast concrete (PC) beams were tested under cyclic loading. The dimensions of the column cross section were 670×670 mm, which was a two-thirds-scale model of the prototype column. The test parameters for the steel beam and the PC beam were the beam depth (488 and 588 mm) and the flexural rebar ratio (1.1% and 1.5%), respectively. In the steel beam-CEFT column joints, continuity plates were used, while in the PC beam-CEFT column joints, couplers were used for the rebar connection. The steel beam-column connections failed due to early fracture of the continuity plate, and the PC beam-column connections failed due to rebar buckling and concrete spalling after beam yielding. The strength of the steel beam-column connections was evaluated using an existing design method, and the sei...

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