Splicing Joint Research Articles

Study on the tensile properties of a novel modular splicing joint

The interconnection among module elements within a modular structure assumes a pivotal role in upholding structural integrity and stability. To address the challenges posed by existing inter-module connection joints, which necessitate operational space and may compromise the integrity of the module unit while impeding assembly efficiency, an innovative modular steel structure splicing joint is proposed. Through adjustments to the dimensions of the connection box and fastener components, four distinct spliced joints were established for axial tensile analysis. The subsequent evaluation included an examination of axial tensile capacity, strain distribution, and failure modes at critical points across various joints, providing insights into their tensile effectiveness. To comprehensively explore the influence of size parameters on tensile performance, a corresponding numerical model was developed for parametric analysis. Results indicate that tensile failure modes entail the extrication of the lower-end plate from the upper module column connection box and the cylindrical radius of the fastener. Notably, the protrusion radius of the fastener (R2), markedly influences the tensile bearing capacity of the spliced joints, with precedence over the lower end plate thickness (d0), cylinder radius (R1), sliding block thickness (d1), and limiting plate thickness (d2). The joint obviates the need for external operations to interlink module units, thereby augmenting the installation efficiency of the modular structure and mitigating complexities in design and the enigmatic transmission of forces within the self-locking joint.

Mechanical Performances of Concrete-Filled Steel Pipe Composite Segments in Complex Geological Conditions

When shield tunnels are under complex geological conditions, tunnel damage, decreased structural performance, and shield tunnel deformation and destruction may occur. Therefore, a new type of composite segment and combined splicing joint were suggested and experimentally investigated in this study. According to the test results, the new composite segment effectively enhanced the load capacity of the segment, and the yield and ultimate loads of the segment were increased. Compared with the reference specimen, the ultimate load capacities of the proposed segments with different numbers were 23.8%, 50.0%, and 64.3% greater. Moreover, the combined splicing joint enhanced the initial bending stiffness and load capacity of the segment joint, reduced the opening displacement, and improved the rotational stiffness of the segment joint. The addition of a plug-in joint at the segment joint increased its load capacity by approximately 25%. A parametric study showed that the number and posit ion of the plug-in joint clearly affected the load capacity of the segment joint. In addition to the above test results, reasonable theoretical formulas for the new composite segment and combined splicing joint are given in this paper.

Lateral hysteretic behavior of precast concrete shear walls with unjointed vertical distribution bars and opening

Precast concrete shear walls with unjointed vertical distribution bars have desirable lateral resistance compared with cast in situ concrete shear walls and much less construction cost as no sleeve splicing joint is needed. However, the influence of opening in the precast panels on their lateral hysteretic behavior has not been fully investigated. This study presents the results of cyclic loading tests of three full size precast concrete shear walls with unjointed vertical bars and opening. The test results showed that these shear walls had similar failure modes as a cast in situ concrete shear wall, such as cracking in the corners of the opening and the concrete and steel bars crushing at the bottom corners of the shear walls. The peak load of the positive and negative loading cycles and the stiffness of the unjointed shear wall with a window opening were 14.6%, 4.3% and 1.3%, respectively, smaller and the ductility ratio was 37.6% higher, than an otherwise the same cast in situ shear wall. The lateral stiffness of the unjointed shear wall with a door opening was 35% smaller than that of the one with a window opening, due to the stiffness contribution of the wall segment underneath the window opening. The development of the longitudinal strains of concrete and steel strain along the height of the wall limbs generally met the plane section assumption. However, those next to the vertical joint interface were affected by the development length of the shear force after the bedding mortar cracked under tension. The determination of the development length needs to consider the influence of the stiffness of the link beam and the wall segment underneath the opening.

A New Combined Splicing Joint for Shield Segment

A New Combined Splicing Joint for Shield Segment

Experimental study on oblique-shear performance of splicing joint for precast ultrahigh-performance concrete segmental bridges

This paper aims to study the effect of the normal stress on the shear performance of splicing joints for precast ultrahigh-performance concrete (UHPC) segmental bridges (PUSBs), an oblique-shear joint is designed to decompose the vertical force into a normal force and a shear force for the joint. The effect of the number, height and inclination angle of the keys on the bearing capacity of the joint is studied by 19 oblique-shear joints. Then, the bearing capacity and failure modes are analyzed significantly. The results show that the failure modes of the joints are shear failure, compression-shear failure and splitting failure, all showing primarily brittle failure. Moreover, the proportion of shear stress in the specimens increases with the increase of the inclination angle of the joint, and the shear capacity of the specimens decreases. Additionally, the shear capacity of the specimens increases with the increase of the height of the keys. After that, we derive a new formula for calculating the shear capacity utilizing Mohr’s stress circle theory and Mohr-Coulomb failure criterion, i.e., the interfacial frictional coefficient is 0.94 and the shear capacity of keys is 0.06. One may find the present formula shows a high guarantee by comparing with those from references. The formula established in this paper may be used to calculate the shear capacity of splicing joint of precast ultrahigh-performance concrete segmental bridges.

Experimental study on CFRP-strengthened bolted splicing modular steel plate shear wall

The seismic performance of the steel plate shear wall (SPSW) structure will be weakened by the modular splicing of the infill steel plates. To address this, carbon fiber reinforced plastic (CFRP) was used to strengthen its splicing joints. First, the specimens of CFRP-strengthened bolted joints with different CFRP laying methods were tested in uniaxial tensile control, and the corresponding design method was proposed. Next, this method was introduced into the vertical splicing joints of modular SPSWs. Three 1/3-scale SPSW specimens, with and without CFRP-strengthened modular SPSW and complete SPSW, were tested under quasi-static cyclic loading. The failure modes and hysteresis performance of the three structures were compared, and the effects of using CFRP-strengthened splicing joints on various properties of the SPSW structure were investigated. The force mechanism of the CFRP-strengthened bolted splicing modular SPSW structure was further investigated by finite element (FE) analysis. The results indicated that the CFRP strengthening vertical splicing joints can effectively reduce the stress concentration around the hole walls of the infill steel plate, improve the performance loss of wall plates due to modular segmentation, and reduce slippage of splicing joints and out-of-plane deformation amplitude of wall plate. The CFRP-strengthened vertically bolted modular SPSWs increased the stiffness and load capacity of the structure, with yield bearing capacity and stiffness increased by 11.40% and 19.57% compared with those of the vertically bolted modular SPSW, respectively.

Physical and numerical modeling of seismic soil-structure interaction of prefabricated subway station structure

Physical and numerical studies were conducted to explore the seismic performance characteristics of multi-story and multi-span prefabricated subway station structures, and to identify its weak parts and damage mode during earthquakes. A two-story three-span prefabricated subway station structure was designed and fabricated with a scale ratio of 1:10 and was subjected to a static pushover test that simulated the soil-structure interaction. The test results were interpreted to determine the horizontal resistance - interstory displacement capacity curve of the station, and the interstory displacement ratio (IDR) limit values under each seismic performance state. The experimental results revealed that the upper layer of the prefabricated subway station structure was more severely damaged than to the lower layer, and that the column ends of the upper layer were the weakest parts of the structure in terms of seismic resistance. The splicing joints were generally reliable, but the side wall-middle span splicing joint showed visible cracks. Furthermore, a finite element model was established based on the physical test configuration and was utilized to analyze the pushover tests. The numerical results indicated that the vertical load significantly accelerates the prefabricated subway station to reach the peak point and limit point of its horizontal bearing capacity. The IDR value of subway station seismic performance level 4 determined by the bearing capacity curve of the column was 30% lower than the IDR value obtained by the structural bearing capacity curve.

Experimental study on direct shear performance of prefabricated splicing joints of ultrahigh-performance concrete

Splicing joints are the weak link of precast ultrahigh-performance concrete (UHPC) segmental bridges (PUSBs). Thus, this paper conducts direct shear tests on eight groups of UHPC keyed joints to investigate the shear performance of the interface of the key. The effects of lateral compressive stress (σn) and the number of keys on the shear performance are also examined. In addition, the load–displacement curves, failure modes, cracking loads, and ultimate loads of the specimens with different parameters are presented. After that, the direct shear capacity of the joints is theoretically analyzed based on the test results and relevant specifications, and a formula for calculating the direct shear capacity is derived. The results show that the failure mode of the UHPC keyed joints is primarily brittle failure. Moreover, the failure mode is the direct shear failure along the interface of the key when the lateral compressive stress is low; however, it is the local crushing of concrete in the key when the lateral compressive stress is high. Additionally, the direct shear capacity of the specimens increases linearly with raising the lateral compressive stress. The direct shear capacity of the double-keyed joints is 17.4–29.3 % higher than that of the single-keyed joints under the same conditions. The values calculated by specifications NF P-18 710 and Eurocode 2 2011 are lower than the experimental ones. The experimental data are evenly distributed on both sides of the curve calculated by specification JSCE 2008 when the lateral compressive stress is low, posing potential hazards in this case. The value predicted by specification AASHTO 2003 is also higher than the experimental value. Finally, we derive a formula for calculating the direct shear performance of the UHPC keyed joints utilizing Mohr’s stress circle theory, and it can be applied to engineering design with high accuracy.

Seismic response analysis of rectangular prefabricated subway station structure

The development and application of prefabricated assembly technology has become an important measure to achieve industrial optimization and upgrading and sustainable development of construction engineering. The application of prefabricated assembly technology in underground engineering is in its infancy, and the seismic research on prefabricated underground structures is scarce. Therefore, this paper establishes refined finite element models (FEMs) of prefabricated and cast-in-place underground structures based on an actual project of a subway station. The developed FEMs are used to conduct a series of seismic time-history analyses considering soil-structure interaction to compare the responses of a prefabricated underground structure with rigid splicing joints or non-rigid splicing joints with that of a cast-in-place underground structure of the same structural form. In addition, the influence of the splicing properties of different parts on the inter-story displacement and internal forces of the prefabricated underground structure are systematically investigated. Tt was found that the inter-story displacement and component deformation for prefabricated underground structures with rigid joints are basically the same as those of the cast-in-place underground structure; however, both the internal force and damage at the bottom of center column decrease slightly. On the other hand, prefabricated underground structures with non-rigid splicing joints experience a slight increase (less than5%) in inter-story displacement, but more obvious mid-span deflection of the laminated slab. However, the internal force response and damage degree of their center column are significantly reduced compared to cast-in-place structures. It was also revealed that the bonding strength of new-old concrete interface of the horizontal laminated components is the main factor that reduces the lateral stiffness and causes redistribution of the prefabricated underground structures’ internal forces.

Experimental study on seismic behavior of prefabricated reinforced concrete beams with large-diameter reinforcements

This paper proposes a new beam type, i.e., a prefabricated reinforced concrete beam with large-diameter reinforcements and floor slabs, and studies its seismic performance to solve the problems that too many reinforcement joints and too dense sleeve gaps in the splicing joint of prefabricated concrete components affect the speed and quality of joint construction. Taking the large reinforcement diameter and the setting of additional connecting reinforcements as study parameters, this paper performs the low-cycle reciprocating test on four full-scale specimens so as to measure their hysteretic curves, skeleton curves, and failure modes. This work also clarifies the failure mechanism of prefabricated reinforced concrete composite beams considering the effect of floor slabs. Further, a finite element model is established utilizing ABAQUS software and verified, and the material constitutive relationship suitable for simulating the hysteretic performance of such components is proposed. The results demonstrate that under low-cycle reciprocating loading, the prefabricated concrete beams with fixed ends experiences the beam-end bending failure, the positive stiffness of the member degrades obviously when its failure, and the concrete in the compression area of the lower flange of the beam collapses. It is feasible to use a grouting sleeve to connect large-diameter reinforcements in prefabricated reinforced concrete beams. Increasing the diameter of the longitudinal reinforcement can significantly improve the cracking load, yield load, and ultimate bearing capacity of the composite beams with floor slabs. The hysteretic curves of the composite beams with the large-diameter high-strength reinforcements are full, and the setting of additional reinforcements negligibly impacts the hysteretic behavior of the composite beams. The proposed concrete damage plasticity model and Fang’s hysteretic constitutive model of steel bars can effectively simulate the hysteretic behavior of prefabricated reinforced concrete beams with large-diameter reinforcements. Although the cracking load of beam with large-diameter reinforcements is reduced by about 10 %, it has little effect on the seismic performance. The number of reinforced joints is reduced by about 50 %, which significantly improves the field assembly efficiency and pouring quality of prefabricated concrete components. It is suitable for application and promotion in prefabricated concrete structures.

Experimental investigation on flexural performance of splicing glass fiber-reinforced polymer (GFRP)-Concrete-steel sandwich composite members

In practical engineering, fiber-reinforced polymer (FRP) tubes have limited lengths due to fabrication and transportation constraints. It is needed to develop reliable splices for FRP-concrete composite member. This paper focuses on the flexural performance of splicing glass fiber-reinforced polymer (GFRP)-concrete-steel sandwich composite members. Seven spliced sandwich composite specimens connected by steel bars and a continuous sandwich specimen were tested under three-point bending. The steel ratio of connecting rebar, steel tube diameter and GFRP tube thickness were all investigated. The results show that the GFRP tube has an apparent restraining effect on the concrete at around 55% of the ultimate load (Pu), and the spliced beams degrade at about 75% Pu. The splicing method based on connecting rebar satisfies the demand that the bearing capacity of a splicing member is greater than that of a continuous member, and the splicing specimens show sufficient ductile behavior with an average displacement ductility coefficient of 4.51. The connection steel ratio greatly affects the failure mode and the steel ratio 3.66% is suggested as the optimal value in the splicing joint of the sandwich composite members, for it ensures splicing strength and provides an ideal failure mode. The inner steel tube diameter affects the stress characteristic of section and improves bending stiffness, bearing capacity and ductility to a large extent.

Flexural behavior of precast concrete beams in-span assembled with bolt-steel plate joints

The assembly of precast concrete structural components is primarily concentrated at the splicing joints of the components. Wet connections involving additional stirrups and detailing cause casting difficulties and possibly deficient joints. Herein, a new type of precast beam in-span assembled with bolt–steel plate joints (PBSPB) is proposed. A significant unique feature is the discontinuous longitudinal reinforcement in the midspan, where the U-shaped steel plate covers the web and tensile zone of the concrete beam. The steel plates and bolts are used to connect the two assembled short beams to resist both flexure and shear owing to the external effects. To investigate the effects of the steel-plate thickness and span–depth ratio on the flexural behavior of beams, a static behavior test was conducted on six PBSPBs and one cast-in-situ beam. The failure mechanisms of the PBSPBs and cast-in-situ beam were examined and compared with regard to the crack propagation, load–displacement characteristics, and strain responses. All the PBSPBs exhibited excellent performance with limited cracks under identical conditions; only minor damage was observed, which consisted of small amounts of concrete spalling and edge warping of the steel plates. Finite-element analysis (ABAQUS) models of the proposed PBSPBs were developed to verify the ultimate load and damage situations of each specimen, a simplified flexural-capacity calculation formula for the PBSPB was developed, and the theoretical results were consistent with the experimental results. The results indicated that the new precast concrete beams had favorable flexural capacities. The beam with thicker steel plates in the span had a higher strength owing to the higher stiffness. Increasing the span–depth ratio increased the ultimate load and barely affected the failure mechanism.

Seismic performance of bolted flange splicing joints for CFST columns

Bolted connections are suitable to be applied in prefabricated structures and seismic resilient structures. A series of bolted flange splicing joints were proposed for square concrete-filled steel tubular columns, and six full-scale specimens with different flange thickness and flange stiffener layouts were designed and tested under cyclic loads to study the seismic performance. The stiffness, the ductility, the bolt tension forces, the strain distributions and the hysteretic behaviors of the joints were analyzed. Finite element models were established and validated by the test results, further analyzing the joint performances. According to the results, the joints with flange stiffeners or thicker flange plates could develop larger resistance, stiffness and rotational capacity. The joint yield moments would increase with the increase of the bolt diameter, the stiffener height or the stiffener thickness, and decrease when the distances between the bolts and the column walls increase. Parametric analysis of the joint was conducted, and calculation methods of the joint yield moment were proposed accordingly and validated by the test and finite element analysis results, providing satisfactory accuracy.

Research on Modeling of Milling Force of Ball-End Mill Cutter in Multi-hardness Splicing Area of Automobile Panel Die Steel

The structure and the cavity surface hardened steel mold of automobile cover is very complex. In the stamping process, the local structure bears higher extrusion stress than the type surface, which often causes local wear and even cracking. The process of multi hardness splicing joint is applied to ensure the service life of the die according to the features of each part of the mold. The impact load caused by the repeatedly cut-in which always leads to the instability of cutting force in the whole process. The machining quality of the mold surface is reduced. Aiming at the machining process of the ball-end milling cutter in the mold splicing area, the impact at the moment of contact between the cutter and the workpiece is analyzed. The instantaneous chip thickness model that considers impact factors and the state model that calibrates the cutting state by coefficients is established. Finally, the prediction model of the milling force of the splicing area is obtained. The model is verified based on the machining cutting force measurement experiment in the case of die hardened steel Cr12MoV with single hardness and multi-hardness splicing. The average prediction error of experiments and simulation results is within 10%, which proves the accuracy of the model. The results show that the model has certain guiding significance for the actual processing of the splicing area of automobile mold cover parts.

Research on seismic behaviour of square steel tubular columns with deconstructable splice joints

In order to study the seismic performance of the square steel tubular column-to-column joints with a novel blind bolted connection, five specimens were designed. One specimen was tested under horizontal monotonic loading, and its failure mode was obtained. The mechanical performance including joint bearing capacity and displacement ductility coefficient were clarified through load versus displacement responses. The other four specimens with different design parameters were tested under cyclic loadings. Their bending moment-rotation curves, envelop curves and energy dissipation capacities were obtained. In addition, the deconstruction of the joints after their ultimate limit states being reached was validated. The finite element software ABAQUS was used to simulate the mechanical behaviour of the specimens, and the variation of the pretension within the high-strength bolts and of the friction force at the plate contact surfaces during the entire loading process were clarified. The results show that the square steel column-to-column splicing joint introduced herein is beneficial to simple configuration, convenience in installation as well as for deconstruction, and it possesses good slip-critical bearing capacity as well as ultimate bearing capacity. Good cyclic behaviour and energy dissipation capacity are also indicated. The research outcomes can provide an important basis for the subsequent research and application of deconstructable steel structures, and for further development of building industrialisation.

High-coupling efficiency and robust fusion splicing between fluorotellurite and chalcogenide fibers

We demonstrate a low-loss and high-robustness fusion splicing point between fluorotellurite fiber and arsenic sulfide-based chalcogenide fiber (As2S3) by using an asymmetric fiber splicing technology. The splicing loss of point is less than 0.55 dB at the wavelength of 1.55 μm, and the monitored tension is 129 g by tuning the distance of the fusion splicing head offset in the fusion splicing process. Using an all-fiber testing system, the fusion splicing point loss between the 1.55 μm testing light source tail fiber (silica fiber) and the fluorotellurite fiber is 0.503 dB. The output power from the As2S3 fiber is 0.91 W with a testing light source of 2 W, and the temperature of the splicing joint shows no evident increase. This finding indicates that the fusion splicing point offers excellent beam quality. This work lays a solid foundation for building an all-fiber cascaded system generating mid-infrared supercontinuum with high-coupling efficiency between mid-infrared soft-glass fibers.

Mechanical behaviour of splicing joints in shield tunnel lining subjected to fire

Shield tunnel segment joints are weak links in tunnel structures; however, studies on their fire-resisting performance are limited. In this study, scaled tests were performed on lining joints to investigate their fire-resisting behaviour in relation to installation errors. The results indicated that the lining segment with initial defects exhibited a large peeling depth, whereas those without initial defects exhibited a large spalling area and shallow depth. Moreover, the damage rate of the lining joints with initial defects was 10.52%, and the lining segment with initial defects exhibited a larger residual deformation after cooling. Furthermore, the bending and shear resistance of the lining joints decreased sharply, which was manifested by an increase in the joint opening angles. The stiffness of the lining joints with initial defects decayed faster, and the stiffness loss was greater than in those without initial defects. After the test, the remaining stiffness was reduced by 69.7% compared to that of the lining joint with no defects. The results obtained can be used to further develop the thermal–mechanical coupling of splicing joint structures in shield tunnel linings.

Seismic behaviour of precast SRC beam-CFST column joints with cantilever beam splicing

The resistance advantages of well-known high-performance components in assembly structures, such as steel reinforced concrete (SRC) beams and concrete-filled steel tube (CFST) columns, are still plagued by the connections between them, and there are a paucity of studies on the behaviour of precast joints employing such members. To fill the knowledge gap in this area, this paper reported quasi-static tests of four half-scale precast beam-column joints, each with a steel reinforced concrete (SRC) beam and concrete-filled steel tube (CFST) column. Based on the cantilever beam connector with better constructability and serviceability, the splicing position and splicing method were selected as the variables to evaluate the seismic performance of four precast joints and to reveal the feasibility of using these assembly details. The test results showed that the four joints experienced bending failures at the beam end, along with extremely plump shape of hysteresis curve. Owing to the fact that the more distant splicing position lifted the deformation restriction on the concrete at the beam end, the nonlinear deformation capacities of the distal splicing joints is better than the proximal splicing ones, by at least 14%. Except for the proximal splicing joint, the other joints had more stable carrying capacities and at least 22% lighter stiffness degradation than the referenced monolithic joint. Considering the initial stiffness values, the four joints in this study were classified as semi-rigid joints as recommended by ENV 1993-1-8. The results obtained from this study can provide a reference for the application of assembly technology to frame joints with composite members.

Research on the mechanical properties of assembled TRC permanent formwork composite columns

To further promote the prefabricated development of textile-reinforced concrete (TRC) permanent formworks, in this paper, the effects of TRC formwork form, assembly method and assembly direction on the mechanical properties of composite columns with TRC permanent formworks are studied by performing axial compression tests. The results show that the failure of these composite columns is divided into three typical failure modes, namely, corner fracture failure, bolt hole shear failure, and splicing joint crack failure. Compared with plain concrete columns, TRC permanent formwork composite columns can better control the development of cracks and improve the crack development mode under compression. A comparison of different forms of TRC formworks shows that the ultimate bearing capacity of a composite column with flat-plate TRC formworks is higher than that of composite columns with L-shaped formworks. Compared with other assembly methods, the composite column with a bolt, angle steel and high-strength nonshrinkage grouting material achieves the maximum ultimate bearing capacity. Furthermore, the bearing capacity of the composite column with the TRC formwork assembled in two directions is weaker than that of the composite column with the TRC formwork assembled in only one direction. Finally, by analyzing the bearing mechanism of the TRC permanent formwork composite column, the calculation model of the ultimate bearing capacity of the composite column is obtained, and the calculated value is in good agreement with the test value.

Analysis of Nonlinear Characteristics of Milling Force in Processing Splicing Joint Area of Automobile Mold

The structure and the cavity surface hardened steel mold of automobile cover is very complex. In the stamping process, the local structure bears higher extrusion stress than the type surface, which often causes local wear and even cracking. The process of multi-hardness splicing joint is applied to ensure the service life of the die according to the features of each part of the mold. The impact load caused by the repeatedly cutting in which always leads to the unevenness of cutting force in the whole process. The machining quality of the mold surface is reduced. Aiming at the ball-end milling process in mold splicing area, first, the impact behavior of tool workpiece cutting contact is analyzed. A prediction model for ball-end milling force in the splicing area is established by establishing the transient chip thickness model which considering the impact factors. Second, the experiment of cutting force measurement for Cr12MoV mold steel ball-end milling which is based on single hardness and multi-hardness are carried out to verify the model. Cross-correlation analysis based on data of milling force signal and machined surface roughness is carried out for getting the relevance of them in different processing states. Finally, the ApEn is used to analyze the nonlinear characteristics of the milling force signal at the multi-hardness splicing state. This explores the influence of the milling force on the machining quality. The experimental and analytical results show that the milling force signal exhibits more obvious chaotic characteristics in the multi-hardness stitching area than that in the single hardness region. This provides a basis for improving workpiece surface quality and improving cutting efficiency.