Joint Core Area Research Articles

Experimental study on the seismic behavior of a novel type of precast column‐steel beam connection with grouted corrugated metallic duct

AbstractConsidering the complicated joint details and installation difficulties of beam‐column joints, a novel type of precast joint that utilizes grouted corrugated metallic ducts was proposed. Four full‐scale specimens were prepared and subjected to the low cyclic loading test, including two precast specimens (interior beam‐column joint and exterior beam‐column joint) and two cast‐in‐place specimens for comparison. The seismic behavior of the joint was evaluated based on failure modes, hysteretic behaviors, ductility, bearing capacity, and energy dissipation. From the test results, all specimens experienced bending failures at the beam end, which kept the plastic hinge away from the joint core area. The precast assembly joints showed excellent seismic behavior, especially in terms of the bearing capacity, ductility, and energy dissipation capacity, which are better than the cast‐in‐place ones. The bearing capacity measured for each specimen was greater than the design standard, indicating that the joints are reasonably designed, and the members are safe and reliable. Parametric analysis was also conducted by finite element modeling and design advice was given accordingly.

Experimental and Numerical Investigations on the Seismic Performance of High-Strength Exterior Beam-Column Joints with Steel Fibers.

Steel fiber reinforced high-strength concrete (SFRHSC) is a composite material composed of cement, coarse aggregate, and randomly distributed short steel fibers. The excellent tensile strength of steel fiber can significantly improve the crack resistance and ductility of high-strength concrete (HSC). In this study, experimental and numerical investigations were performed to study the cyclic behavior of the HSC beam-column joint. Three SFRHSC and one HSC beam-column joint were prepared and tested under cyclic load. Two different volume ratios of steel fibers and three stirrups ratios in the joint core area were experimentally studied. After verification of the experimental results, numerical simulations were further carried out to investigate the influence of steel fibers volume ratio and stirrups ratio in the joint core area on the seismic performance. Evaluation of the hysteretic response, ductility, energy dissipation, stiffness, and strength degradation were the main aims of this study. Results indicate that the optimal volume fraction of steel fibers is 1.5%, and the optimal stirrups ratio in the joint core area is 0.9% in terms of the enhancement of the seismic performance of the SFRHSC beam-column joint.

Seismic Performance of Precast Concrete Exterior Beam-Column Joint with Disc Spring Devices

ABSTRACT To improve the seismic performance of precast concrete reinforced frame structures which are widely used worldwide, and enable a certain repairable function for the precast structure after an earthquake, this paper proposes a new type of precast concrete frame joint using a full grouting sleeve connection with a disc spring device. The disc spring device was connected in series to the longitudinal reinforcement located in the plastic hinge zone at the beam end to provide a restoring force and protect the concrete. Six exterior beam-column joints consisting of one cast-in-situ beam-column joint and five precast concrete frame joints, using a fully grouted sleeve connection equipped with or without a disc spring device, were designed and fabricated. The failure process, hysteretic characteristics, and energy dissipation capacity of the joint specimens were analyzed based on reversed cyclic loading test. The results showed that the energy dissipation and seismic performance of the newly precast concrete joints equipped with the disc spring device were better than those of the precast concrete frame joints connected by ordinary grouting sleeves without a disc spring device. The disc spring device proposed in this study plays a similar role as a damper in the precast joint during loading and has the characteristics of concentrated damage as it transfers part of the damage in the joint core area to the built-in disc spring area at the beam end. Additionally, the deformation of the precast joints under a lateral seismic load was theoretically calculated, the calculated results were in good agreement with the experimental results.

Experimental study on seismic behavior of RCS joints with asymmetric friction connections and slabs

This paper introduces a new reinforced concrete column-steel beam (RCS) joint that employs asymmetric frictional connections (AFC) to improve energy dissipation and moment transfer, reducing stress concentrations within the joint’s core. Two RCS joint specimens with AFC and floor slabs were designed and tested under quasi-static loading to analyze the impact of bolt preload on seismic performance. The experimental results demonstrate that RCS joints with AFC and slabs exhibit favorable seismic behavior in terms of bearing capacity, energy dissipation, and stiffness degradation. Increasing bolt preload enhances the bearing capacity, stiffness, and energy dissipation capacity of the joints. The failure occurred at the steel beam splice connections, while only minor micro-cracks appeared in the reinforced concrete column when the joint's bearing capacity dropped below 80% of the peak load. Displacement at the column top was primarily influenced by steel beam and column deformation, with minimal contribution from joint core deformation. The use of AFC effectively reduced deformation in the joint core area, meeting seismic design code requirements for “strong columns-weak beams.”

Hysteretic Performance Analysis of Prefabricated Steel-Concrete Composite Edge Joints Considering Floor Composite Effects

ABSTRACT This study conducts quasi-static tests and finite element (FE) analysis by using ABAQUS software to examine the effects of floor combination effect (FCE) on the seismic behavior of a novel type of prefabricated steel-concrete composite (PSCC) exterior joints. This analysis assesses PSCC exterior joints featuring bolted-welded hybrid connections, focusing on their seismic performance under the influence of FCE. The variables in this research include floor construction parameters, axial compression ratio (n), and core area concrete (CAC). The results indicated that these variables, particularly the floor construction parameters, n, and CAC, significantly influence stress distribution and magnitude within the joint core area (JCA) and the floor slab. Although the floor construction parameters exert a minor effect on seismic performance, increasing n markedly enhances the joints’ load-bearing and energy dissipation capacities. However, it also makes the joints more susceptible to brittle failure. Optimal bearing capacity and ductility for energy dissipation are achieved when n equals 0.3. In addition, CAC substantially increases the initial stiffness (IS) and bearing capacity, with a peak increase in bearing capacity of approximately 18% and an IS enhancement of around 25%. However, rising CAC strength has a relatively minor impact on seismic performance.

Experimental study on seismic performance of spatial and planar hoop-head mortise and tenon timber joints in historical architecture

This paper aims to present an experimental study investigating the seismic behaviour of spatial and planar hoop-head mortise and tenon (MT) timber joints in traditional Guangfu Ancestral Halls. The unique design of the external hoop head provides additional restraints for the tenon and mortise in these joints, endowing them with enhanced pull-out resistance and increased structural integrity compared to other types of MT connections commonly used in traditional timber-framed structures. The research commenced with material testing to determine the mechanical properties of Merbau wood used in this timber frame construction. Reversed cyclic loading tests were then performed on two planar and two spatial hoop-head MT timber joints. The experimental results demonstrated the favourable seismic performance of the hoop-head MT joints. All specimens failed within the MT joint area, exhibiting different failure modes based on varying connection configurations and tenon sizes. Furthermore, the spatial MT joints showed lower stiffness and bearing capacities compared to the planar MT joints of equivalent size. Their hysteresis curves, envelope curves, and cyclic stiffness degradation curves displayed greater asymmetry. These discrepancies can be attributed to the reduction in tenon sections necessary to accommodate the overlapping beams within the spatial joint core area.

Seismic performance of HECC/RC beam–column external joint with no stirrup and reduced anchorage length in core region

In this paper, steel–polyethylene hybrid fiber-reinforced strain-hardening cementitious composites (HECC) are applied in beam–column external joint core region to form a novel HECC/reinforced concrete (RC) composite beam–column joint with reduced anchorage length of beam longitudinal rebar and eliminated transverse rebar, and thus to alleviate rebar congestion and simplify the construction process efficiently especially for precast RC frame structures. Five external beam–column joint specimens are constructed and tested under cyclic loading to illustrate the influences of the anchorage length of beam longitudinal rebar and longitudinal rebar ratio on the seismic performance of beam–column joint. The effects of design parameters on seismic performance, including hysteresis behavior, degradation of strength, energy dissipation capacity, and cracking patterns are discussed in detail. Experimental results indicate that the replacement of normal concrete with HECC in beam–column joint core region could apparently reduce the amount of stirrups in the joint core area while maintaining reliable seismic behavior. Remarkably, specimen with no stirrups in the core area exhibits nearly equivalent seismic behavior to that of the control RC specimen. Furthermore, the application of HECC in joint core area allows for a substantial reduction of the required anchorage length for the beam longitudinal rebar to 9d, which further simplifies the construction process considerably.

Anchorage characteristics and their impacts on the seismic performance of HECC/RC composites external beam-column joint

In order to enhance the seismic performance and streamline the construction process, particularly in precast frame structures, steel-polyethylene hybrid fiber-reinforced engineered cementitious composites (HECC) is utilized to replace reinforced concrete (RC) in the external beam-column joint core area to form HECC/RC composite joints. In this study, to further alleviate rebar congestion, five no-stirrup reinforced HECC/RC composite external beam-column joints with reduced beam longitudinal rebar anchorage length (i.e., 6d-18d) in core area and one control RC specimen are designed and tested under cyclic loading. Experimental results indicate that anchorage failure occurs until the anchorage of the beam longitudinal rebar decreases to an extremely short length of 6d. In comparison with the control RC specimen, HECC/RC specimens display a reduced bond damage zone and superior bond behavior. Although relatively larger stress is transferred to the anchorage free end when anchorage length is 9d, the beam longitudinal rebar is still effectively anchored without significant slip, indicating that anchorage length of 9d in joint core area may be sufficient which needs further research. In addition, the ultimate bond strength of the rebar embedded in joint core area is lower than that observed in pullout test, underscoring the necessary of considering a safety factor in design anchorage length estimation. Lastly, the contribution of bonding condition on shear force transfer in joint core area is analyzed according to force transfer mechanism, which would promote the determination of the shear capacity of HECC joint. As the bonding damage expanded, the proportion of shear force resisted by truss mechanism decreases, emphasizing the crucial role of adequate anchoring in external joint.

Study on failure modes and calculation method of the cast steel joint with branches in treelike structure

The treelike structure links members and transfers loads via its solitary cast steel joint with branches. Therefore, the joint’s bearing capacity significantly affects the treelike structure’s stability, security, and economics. This paper utilized experimental verification and numerical modeling to examine the mechanical behavior of cast-steel joints with branches in the treelike structure under various loading conditions. Then, researchers investigated the failure process and mechanism of joints, and the three most common failure modes were outlined. Furthermore, the researchers proposed the bearing capacity calculation formula based on the common failure modes. The results show that the three common failure modes of the cast-steel joints with branches under different loading conditions are the failure in the joint core area under the axial load, the failure in the main pipe compression side under eccentric load, and the failure in the compression side of the single branch pipe root when the single branch pipe is under the uneven load. The suggested empirical calculation method can serve as a reference point for similar engineering practices design.

Influence of joint forms on the seismic behavior of concrete-filled PVC-CFRP tubular column-RC beam joints connected with core steel tubes

To examine the effects of joint forms on the failure mode, hysteretic behavior, ductility and energy dissipation capacity of concrete-filled PVC-CFRP tubular column-RC beam connected with core steel tubes (“RC beam” for short), low-cycle reversed loading tests on 13 cross-joints and 11 T-joints were designed and conducted. The findings demonstrate that the core regions of both joint types experience normal shear failure. Less flexural cracking is present in the RC beams of T-joints, but the concrete crush failure is severer in the joint core area and mostly occurs on the ends of the cantilever beams. The seismic behaviors of both joint forms alter in the same pattern with an increase in the radius-thickness ratio of the core steel tube, the joint area stirrup ratio and the steel ratio. With a rise in the axial compression ratio, the ductility of the cross joints improves but the energy dissipation capacity shows no evident change, while both decrease for the T-joints. The cross joints show better energy dissipation capacity in the whole test. As the reinforcement ratio of the beam longitudinal reinforcement rises, the cross joints show a decrease in ductility and energy dissipation capacity, while T-joints have the exact opposite effect. The seismic behavior of core steel tube joints throughout the whole test is unaffected by CFRP strip spacing.

Mechanical performance of prefabricated concrete beam-column joints with double-grouted sleeve connectors: A numerical and theoretical study

This paper presents a systematic numerical study on the structural performance of a newly developed quick-buildable beam-column joint with double-grouted sleeves considering its surface-to-surface contact behaviour between the prefabricated concrete and grouting mortar and strain penetration of the transition rebar. Theoretical analysis is also conducted to predict the load-bearing capacity of the proposed connection. After validation with experimental data, the finite element model is employed to investigate the effects of different factors including protruding beam length and grouting mortar thickness on the structural behaviour of the joint. Results indicate that the maximum stress of the reinforcing bars in the joint with no protruding beam is approximately 15.0% greater than that with a protruding beam, while the maximum stress of the joint anchorage bars decreases by around 87.0% when the short sleeves are placed completely in the joint core area. As the protruding beam length increases, the maximum crack width drops rapidly first and then slowly with a turning point of 1.36 times the short sleeve length, and the highest load-bearing capacity is achieved when the protruding beam length and short sleeve length equal. With the rising grouting mortar thickness, the maximum stress of the transition rebar reduces rapidly first and then slowly with an inflexion point of 50 mm. The change in eccentricity of the transition rebar leads to an around 3% change in the load-bearing capacity of the joint without a projecting beam. The theoretical predictions are in satisfactory agreement with numerical results and can be adopted for practical engineering design.

Seismic retrofit of severely damaged beam-column RC joints using HPFRCC

The purpose of this paper is to use high performance fiber reinforced cement composites materials (HPFRCC) in seismic repair and retrofit of the concrete exterior beams-column joints without special seismic details with severe damage, considering the effect of slab and transverse beam. For this purpose, four external beam-column joints with scale ½ have been subjected to cyclic loading. Initially, two original joints without special seismic details suffered severe damage, which led to shear failure due to unconfinement and slip of beam rebars in the core. Then the damaged joints were repaired using HPFRCC materials and a similar load history was applied to the repaired specimens. The cyclic behavior of repaired joints was evaluated with the behavior of original specimens and the results were presented in the form of load bearing capacity, stiffness degradation, ductility, and dissipated energy. The results show that the use of HPFRCC materials in the joint core area of the repaired specimens has resulted in better confinement and integrity of the longitudinal rebars of the beam and column and in addition, has caused the flexural plastic hinge in the beam. This mechanism has improved the cyclic behavior and significantly increased the bearing capacity, energy dissipation and ductility in the repaired specimens.

Experimental Study on Seismic Performance of Precast Pretensioned Prestressed Concrete Beam-Column Interior Joints Using UHPC for Connection.

The traditional connections and reinforcement details of precast RC frames are complex and cause difficulty in construction. Ultra-high-performance concrete (UHPC) exhibits outstanding compressive strength and bond strength with rebars and strands; thus, the usage of UHPC in the joint core area will reduce the amount of transverse reinforcement and shorten the anchoring length of beam rebars as well as strands significantly. Moreover, the lap splice connections of precast columns can be placed in the UHPC joint zone and the construction process will be simplified. This paper presented a novel joint consisting of a precast pretensioned prestressed concrete beam, an ordinary precast reinforced concrete (RC) column, and a UHPC joint zone. To study the seismic performance of the proposed joints, six novel interior joints and one monolithic RC joint were tested under low-cyclic loads. Variables such as the axial force, the compressive strength of UHPC, the stirrup ratio were considered in the tests. The test results indicate that the proposed joints exhibit comparable seismic performance of the monolithic RC joint. An anchorage length of 40 times the strands-diameter and a lap splice length of 16 times the rebar-diameter are adequate for prestressed strands and precast column rebars, respectively. A minimum column depth is suggested as 13 times the diameter of the beam-top continuous rebars passing through the joint. In addition, a nine-time rebar diameter is sufficient for the anchorage of beam bottom rebars. The shear strength of UHPC in the joint core area is suggested as 0.8 times the square root of the UHPC compressive strength.

Retracted] Study on Seismic Performance of Recycled Steel Fibers Locally Reinforced Cruciform Concrete Frame Beam‐Column Joint

At present, concrete frame structures are widely used, and the frame beam‐column joints are the key parts of the whole frame in seismic resistance. In previous studies, recycled steel fiber‐reinforced concrete is a new type of environment‐friendly reinforcement material, which can also be widely used in the construction industry. Therefore, in this paper, MTS electrohydraulic servo loading systems were used to carry out low‐cycle reciprocating cyclic loading tests to study the seismic performance of five 1/2 scale cruciform concrete frame beam‐column joint specimens with plain concrete, normal steel fiber‐reinforced concrete, and three recycled steel fiber‐reinforced concrete with different fiber contents in the joint core area. The results show that the addition of normal steel fibers can improve the bearing capacity, ductility, energy dissipation capacity, and shear strength of concrete frame joint specimens and delay the stiffness degradation of joint specimens, recycled steel fibers can improve the seismic performance of the cruciform concrete frame joints better than normal steel fibers, and the seismic performance increases gradually with the increases of volume ratio of recycled steel fibers. Moreover, with the recycled steel fiber content from 0.5% to 1.0% and then to 1.5%, the increased amplitude of the seismic performance of joint specimens increases. Considering the reinforcing effect of recycled steel fibers on concrete matrix and based on the design formula of shear capacity of reinforced concrete joints, the design formulas of shear capacity of recycled steel fiber‐reinforced concrete beam‐column joints were established by using the statistical analysis method and the baroclinic rod‐truss model, and the calculation results were in good agreement with the test results. This study can provide references for seismic performance research of steel fiber‐reinforced beam‐column joints and the recycling of steel wire from waste tires.

The effect of forced cooling during friction stir welding on the structure and properties of 1565ChN116 aluminium alloy joints

This paper describes the results of a study that looked at mechanical and corrosion performance of joints between 3 mm thick 1565ChН116 aluminium alloy sheets produced by friction stir welding in atmosphere and in water. It was established that a higher in-water cooling rate resulted in a higher tensile strength of the weld joint and slightly impacted its properties. It is the thermomechanical impact zone of the joint that sees fracture during tensile testing when aluminium alloy 1565ChН116 is friction stir welded in atmosphere and in water. The strength of such joint is 95 to 99% of the strength of the base metal. When conducting friction stir welding in water, the thermal impact zone is approximately 1.6 to 2.2 times shorter than when the process takes place in atmosphere. For the alloy 1565ChН116, friction stir welding conducted in water is associated with a 10 to 12% higher microhardness of metal in the thermomechanical impact zone and the stirring zone. The grain size in the stirring zone was observed to decrease from 6.8 to 4.5 μm. In this zone (the core of the joint), small angle boundaries account for approximately 15% of the total number of boundaries. This suggests that the structure mainly consists of equiaxed grains with large angle boundaries. A transmission electron microscopy study of foil obtained in the joint core area confirmed the results of phase and microtexture analysis (carried out by means of the EBSD technique) indicating that a recrystallized structure formed in the centre of the joint. A higher cooling rate during friction stir welding increases the intercrystalline corrosion resistance of all areas of the joint by approximately 1.4 to 1.7 times. The biggest increase in the intercrystalline corrosion resistance was observed in the thermal impact zone.

Numerical Simulation on Seismic Behavior of Steel Fiber Reinforced Concrete Beam-Column Joints.

Steel fiber reinforced concrete (SFRC) is a novel material of concrete, which has a great potential to be used in practical engineering. Based on the finite element software Opensees, the main objective of this paper presented a numerical simulation method on investigating the seismic behavior of SFRC–beam-column joints (BCJs) through modifying the calculation method of joint shear and longitudinal reinforcement slip deformations. The feasibility and accuracy of the numerical modeling method were verified by comparing the computed results with experimental data in terms of the hysteresis curves, skeleton curves, feature points, energy dissipation, and stiffness degradation. And then, the influences of some key parameters on the seismic behavior of BCJs were investigated and discussed in detail. The parametric studies clearly illustrated that both adding the steel fiber and increasing the stirrup amount of joint core area could significantly improve the seismic behavior of BCJs. The axial compression ratio had limited influence on the seismic behavior of BCJs. Finally, based on the main factors (steel fiber volume ratio, stirrup amount, and axial compression ratio), a formula for predicting ultimate shear capacity is derived.

Experimental study of HSS-reinforced exterior beam–column joints with different enhancement details

High-strength steel (HSS) bars are used as beam and column longitudinal reinforcements to reduce the amount of bars and thereby, prevent reinforcement congestion and insufficient concrete compaction. However, the use of high-strength steel reinforcements may induce bond failure of beam steel bars. To improve joint performance, steel fiber-reinforced high strength concrete (SFRHSC) and X-shaped reinforcement are proposed. Six full-scale specimens reinforced with steel fiber-reinforced high strength concrete and X-shaped reinforcement were designed and tested under reverse cyclic loading. The main parameters included the enhancement details, shear compression ratio, and concrete patterns. The seismic performance of the tested exterior beam–column joints (BCJs) was evaluated based on the cracking patterns, load capacity, energy dissipation, and ductility. The test results revealed that the combination of steel fiber-reinforced high strength concrete and X-shaped reinforcement significantly improved the loading capacity and energy dissipation. This was attributed to the enhancement of the shear by the X-shaped reinforcement, regulation of crack propagation by the steel fibers, and confinement of the joint core concrete by stirrups. Although the specimens displayed shear failure in the joint core area, both X-shaped reinforcement and steel fiber-reinforced high strength concrete could improve the failure modes. Here, steel fiber-reinforced high strength concrete was more effective. The bond performance of the beam longitudinal reinforcements was investigated to study the strain of the reinforcements, degradation of the bond stress, and slippage of the beam reinforcements. Anchorage methods of national codes were compared, and an anchoring recommendation was put forward.

Research on shear strength of CFSST column and H-section with beam composite joint of unequal depth

Four concrete-filled square steel tube (CFSST) columns and H-sections with beam composite joints of unequal depth were designed based on existing specifications and manufactured at ⅓ scale. A failure test of the specimens was carried out under lateral cyclic loading. Different height ratios between the left and right beam, ζ, (ζ = 0.52, 0.39, 0.26, 0.13) were tested to analyze the failure mode, hysteresis characteristics, ductility, strain, and deformation of the specimens and the damage characteristics of the structure. An equation was established to determine the shear bearing capacity of the CFSST column and H-section. The results show that shear failure in the joint core area is the dominant failure mode of the specimen. The greater the beam ratio, the smaller the yield displacement of the specimen is, and the earlier the joint core area reaches the yield strain. The damage value obtained from Chen's model is in good agreement with that obtained from the test and accurately describes the damage evolution and damage limit of the specimen from “basically intact” to “completely damaged”. The shear resistance of the joint core area is primarily borne by the steel tube web, the main concrete compression strut in the core area, and the restrained compression strut. The theoretical values and the experimental values of the shear bearing capacity of the CFSST column and H-section are in good agreement, demonstrating the accuracy of the proposed theoretical equation.

Experimental Study on the Shear Performance of Steel‐Truss‐Reinforced Concrete Beam‐Column Joints

In order to study the influence of the axial compression ratio and steel ratio on the shear‐carrying capacity of steel‐truss‐reinforced beam‐column joints, five shear failure interior joint specimens were designed. The effect of different coaxial pressure ratios (0.1, 0.2, and 0.3) and steel contents on the strain, ultimate bearing capacity, seismic performance, and failure pattern of cross‐inclined ventral and chord bars in the joint core area was investigated. The experimental results show that the load‐displacement hysteretic curves of all test specimens exhibit a bond‐slip phenomenon. With the increase of the axial compression ratio, the ultimate bearing capacity of the joint core increases by 3.4% and 5.9%, respectively. While the ductility decreases by 10.3% and 13.1%, and the energy consumption capacity decreases by 3.2% and 5.8%, respectively. The shear capacity and ductility of the member with cross diagonal ventral steel angle in the joint core are increased by 12.9% and 13.4%, respectively. The shear capacity and ductility of the joint can be significantly improved by increasing the amount of steel in the core area. The expression of shear capacity suitable for this type of joint is obtained by fitting analysis, which can be used as a reference for engineering design.

Effect of recycled aggregate concrete on the seismic behavior of DfD beam-column joints under cyclic loading

The problem of environmental pollution and waste concrete generation will be alleviated if concrete structures can be designed with both recycling and reuse strategies. In this regard, this study employed recycled coarse aggregate as the structural material in a novel beam-column joint with Design for Deconstruction (DfD) connections. Two series cyclic loading tests including pre-loading and re-loading on this frame joint was undertaken and the effect of recycled aggregate concrete (RAC) on structural behaviors was carefully evaluated. It is demonstrated that the DfD joint with RAC had favorable integrity and the influence of RAC was acceptable for practical application. Furthermore, the shear force model of the joint core area for RAC beam-column joint with DfD connections was put forward in this study, which showed good agreements with experimental results. Life cycle assessment (LCA) indicated that the carbon emission of the beam-column joint with DfD connections made of RAC increased at construction process but would reduce the total carbon emission from the perspective of lifetime.