Beam-column Joints Research Articles

Failure mechanism and dynamic response of reinforced concrete joints under impact load acting on beam ends

Beam-column joints are crucial to guarantee the integrity and ductility of reinforced concrete (RC) frame structures. Considering the strain rate effect, the failure mechanism of RC beam-column joints under impact load acting on the beam near the core area of joints was numerically investigated. Based on the verified numerical model, the differences between failure modes of joints under static and dynamic loads were compared. The deformation and damage of joints were analyzed. In addition, the effects of impact location and impact velocity were discussed. The results show that the joints that meet the shear demand under static load have shear failure under impact load. The impact load causes greater deformation and damage to the joints. The transfer of the shear force and the development of the bending moment is different as the impact location changes, resulting in various dynamic responses. As the impact location approaches the core area, the joint evolves from bending failure to shear failure. The maximum shear force only appears at the impact location when the distance between the impact location and the core area is more than 3.5 times the width of the core area (b). However, the rotation of the joint causes the yield of the stirrup in the core area. It is worth noting that when the distance is less than or equal to 2b, the maximum shear force is transmitted to the core area. With the decrease of the distance, the time history curves of impact force have multiple peaks with increased peak values while the displacement and duration decrease. The damage range of the joint is expanded when impacted with higher velocities. Meanwhile, the magnitude and duration of impact force, as well as displacement are increased. With the decrease of distance or impact velocity, more energy is consumed by concrete rather than rebars due to the smaller rotational deformation of the joint.

Study on influencing factors of hysteretic performance of cantilever fully-bolted prefabricated beam-column joint

In order to improve the construction efficiency and integrity of prefabricated RC frames, a cantilever fully-bolted prefabricated beam-column joint is proposed. Through the reciprocating loading test, the change rules of rotation characteristics, mechanical properties and stiffness degradation of this type of joint were obtained. The failure mode of the joint is found: the steel plate in the connection area undergoes a slight flexural deformation, the concrete on the outside of the connection area forms a plastic region of about 1/3 beam length, the concrete crack develops obliquely from horizontal cracking with the increase of stiffness, and the damage characteristic develops from bending damage to shear damage. The initial stiffness of the precast joint is about 1.5 times that of the cast-in-place joint, the yield load is increased by 31 %, the peak load by 52 % and the ductility coefficient by a maximum of 96 %, with significantly better mechanical properties than the cast-in-place joint. Parametric analysis was carried out based on the tests. When the flexural stiffness ratio of the cantilevered section to the reinforced concrete beam section is less than 0.5, it is a weak connection. Damage to the section cantilever section occurs, and the stiffness degrades significantly. It is recommended that the joint be designed for a strong connection, with a stiffness ratio of around 0.6. The cantilever section's length greatly influences the joint's stress transfer. It is recommended that the length be taken to be about 0.6 and no greater than 0.75 for the width of the precast reinforced concrete beam. The design process of a prefabricated RC frame is given on this basis. A research basis has been laid for the engineering application of this new type of connection.

Effects of unbonded prestressing steel tendons and slit dampers on the seismic behavior of precast concrete beam-column joints

This article proposes a novel precast concrete (PC) beam–column joint that uses prestressing steel reinforcement tendons and external steel slit dampers (SSDs) to provide self-centering and energy dissipation capabilities. The SSDs are steel plates cut to a desired shape installed under the beam ends to control their yield through energy dissipation. Three exterior beam–column joint specimens were investigated through quasi-static reversed cyclic loading tests. The specimens included a PC beam–column joint with only an SSD and two PC beam–column joint specimens using unbonded prestressing steel tendons (two in one specimen and four in the other) and an SSD. A fiber-based model using the software Ruaumoko and a code-based design were developed and validated against the experimental results. The test results showed that without the tendon, the specimen was significantly damaged, whereas using unbonded prestressing steel tendons with an SSD endowed the beam–column joint with a higher lateral load capacity of up to 40%. In addition, the ductility improved significantly up to 1.88 times. The developed model and the code-based design were in excellent agreement with the experimental results. Overall, this innovative connection type offers an alternative for seismic-resistant PC structures, and its design enables easy repair after an earthquake.

Lateral Load Behavior of Self-centering Frame with Y-Eccentrically Braced Substructure: An Experiment and Numerical Analysis

A novel self-centering frame with Y-eccentrically braced structure (SC-YEBFs) has been proposed in this paper to solve the problem that the storey drift of structure may exceed the specified limit in standards when self-centering beam-column joints are applied in high-rise and larger spans buildings, and the SC-YEBFs not only has the self-centering performance of self-centering frame system, but also has the high lateral stiffness and energy dissipating capacity of Y-Eccentrically braced frame. To study the lateral load behavior and influencing factors of SC-YEBFs, cyclic loading tests of two scaled specimens of SC-YEBFs substructure (SCS) were conducted, and seven finite element models corrected by the experiment were established to perform parametric analysis. The experiment and finite element analysis results indicated that the shear link has greatly increased the lateral stiffness and energy dissipating capacity of the self-centering structure, at the same time, it has maintained a good self-centering performance and replace ability. With an increase in the cross-sectional area and initial prestress of post-tensioned steel strands, the lateral load capacity and self-centering performance can be improved. The self-centering performance can be effectively improved by reducing the friction coefficient at the rotation connections. SC-YEBFs further extending the application field of self-centering structural systems, and making it possible to be applied to high-rise and larger spans structures.

Seismic behavior and restoring force model of precast beam-column connections with locally reactive powder concrete

In this study, an innovative approach to enhance the seismic performance of prefabricated concrete frame beam-column joints, incorporating high-strength steel bars and reactive powder concrete (RPC), was developed. The research involved the construction of four prefabricated joints and one cast-in-place node, subjecting them to low-cycle reverse load tests. The findings indicate that the inclusion of high-strength steel bars in the node core area led to a notable increase in load-bearing capacity, ranging from 9.5 % to 9.7 %. Moreover, when RPC and high-strength steel bars were simultaneously used in the node core area, the load-bearing capacity improved even further, with an increase of 19.1 %–20.8 %. Additionally, RPC was found to enhance crack resistance in columns and beams, reducing the severity of node failures. Comparing specimens with different spacing of hoops in the core area, it was observed that RPC not only ensured the seismic performance of the nodes but also addressed the issue of excessive hoop density in the core area. Through experimental data, a restoring force model for prefabricated RPC/RC composite frame beam-column joints was established using theoretical analysis. This model exhibited strong agreement with experimental results and effectively depicted the stress distribution within the proposed joints at various stages.

Review of the Structural Performance of Beams and Beam–Column Joints with Openings

The need for openings in RC structures has increased, but their presence significantly affects the performance and strength of the structures. While small openings can be managed with additional reinforcement, dealing with large openings in reinforced or pre-stressed concrete members is challenging due to the lack of technical information and specific guidelines. This research provides an up-to-date overview of RC beam–column joints that incorporate web openings and evaluates appropriate strengthening methods. The research discusses the classification of openings in RC beams, considering factors such as size and shape. Additionally, it examines the failure modes of RC beams in relation to flexural and shear behavior when web openings are present. The research also provides a comprehensive review of various strengthening techniques, outlining their advantages and disadvantages. In conclusion, larger openings in beams result in reduced strength, while increasing loads lead to higher deflection, strain, and cracking until failure. Openings are classified as small or large based on their impact on beam behavior. Multiple smaller openings are preferred over a single large opening when size becomes excessive. Optimal placement is in the middle of the section to ensure adequate concrete coverage for the chords. Sufficient concrete and depth are essential for ultimate compression during bending and effective shear reinforcement.

Seismic behavior of eccentric new RCS joints with through columns

Architectural requirements often result in beam-column joints with eccentrically framing beams. However, the fabrication of eccentric through beam-type reinforced concrete column and steel beam (RCS) joint is extremely complex due to the presence of column longitudinal reinforcement and joint confinement reinforcement. To mitigate the constructability issues associated with through-beam type RCS eccentric joints, the current study proposed a through-column type New RCS joint. The proposed New RCS joint used joint cover plates and continuity plates as additional attachments while eliminating the need for joint confinement reinforcement. Two large-scale beam column subassembly specimens were tested to evaluate the seismic behavior. Both specimens had high-strength reinforced concrete columns (New RC columns) with a design concrete grade of 84 MPa and steel reinforcement of specified yield stress 690 MPa. The experimental results revealed the asymmetric shear stress development in the joint cover plates due to joint eccentricity. Based on experimental observations, a joint shear force-deformation model was presented, which was able to capture the joint shear response with reasonable accuracy. Finally, simplified expressions were presented, which were able to provide reliable estimates of joint shear strength, which is suitable for design purposes.

Experimental and numerical research on the lateral behaviour of glued timber frame structures with and without X-type diagonal bracing

The advanced processing technology of glued wood can provide strong support for the construction and application of the modern timber structures. The modern timber structure can meet the requirements of low-carbon development goals and natural living standards, but there still exist some technical difficulties to research, such as seismic performance and design code problems. Hence, this paper presents the lateral behaviour of glued timber frame structures with and without X-type diagonal bracing by experimental and numerical research methods based on these problems. Two single-layer single-span bare glued-laminated timber (GLT) frame specimens and two GLT frames infilled with X-type diagonal bracing specimens with a 1:1.5 scale were designed to investigate the lateral behaviours under the cyclic loading tests. Three types of beam-column joint connectors (the exposed type with infilled steel plate, the coated type with infilled steel plate and the extended coated type with infilled steel plate) were designed to guarantee the effective connection between components. The failure mode, hysteretic characteristics, lateral load-bearing capacity, stiffness degradation, deformation and the lateral load resistance cooperative working mechanism between X-type diagonal bracing and GLT frame of specimens were analyzed. The test results present that the lateral behaviour of the GLT frame is significantly improved after being infilled with the X-shaped diagonal bracing, and the yield lateral load-bearing capacity and the elastic stiffness of the coated type beam-column joint connection in the GLT frame were 1.876 and 1.36 times than that of the specimen with exposed type beam-column joint connection, respectively. The beam-column joint of the bare GLT frame specimen is failure before the column-base joint. The diagonal bracing joints of the GLT frame specimen infilled with the X-shaped bracing were failures first, and then the beam-column and the column-base joints of the GLT frame were damaged. For the specimen infilled with the X-type diagonal bracing, the lateral resistance load was borne by the GLT frame and diagonal bracing, in which the percentage of the lateral load borne by the diagonal brace gradually decreases, while the percentage of the lateral load borne by the GLT frame gradually increases. In addition, the load-deformation relationships of the specimen joints were derived. Based on these relationships, the numerical analysis of the specimen was carried out to study the influences of GLT frame span-depth ratio, the slenderness ratio of GLT diagonal bracing and the wall thickness of steel tube diagonal bracing on the lateral resistance of this structural system.

Retracted: Mechanical Performance Analysis of Steel Beam-Column Joints in Fabricated Multirise Steel Structures after Fire

Retracted: Mechanical Performance Analysis of Steel Beam-Column Joints in Fabricated Multirise Steel Structures after Fire

Research on Seismic Performance of Eccentric Beam–Column Joint Retrofitted with CFRP–Steel Plate

Research on Seismic Performance of Eccentric Beam–Column Joint Retrofitted with CFRP–Steel Plate

Experimental Study on the Failure of Bamboo Laminated Hollow Section Beam-Column Joints using Glue-in-Rod Bracket

Building materials that emit pollutants, are non-renewable, and generate environmental waste require attention. Wood, a popular and natural material, is facing increasing scarcity, necessitating a substitute. Laminated bamboo emerges as the most akin and natural alternative to wood. Research into laminated bamboo encompasses diverse cross-sections, joint types, and field applications, demanding further investigation.This study aimed to ascertain failure types and damage patterns in laminated bamboo hollow section beam-column joints modified with glue-in rod-bracket connections, using petung bamboo (dendrocalamus asper). The research employed an experimental approach with descriptive analysis. Joint failures were evaluated based on moment-rotation relationships within prescribed rotational limits per standards, while joint damage was assessed through visual inspection of joint components.The study's dependent variables included thread rod diameters of 6 mm, 8 mm, 10 mm, and 4 6 embedded thread rods, while the independent variables were failure types and joint collapses. Results revealed serviceability failures in samples 8.6, 10.4, and 10.6. Joint damage across all test specimens primarily manifested as broken thread rods. The highest joint strength observed was 6.28 kNm in sample 10.6, with the lowest at 2.25 kNm in sample 6.4.Based on the findings, increasing thread rod diameters to achieve ductile joints resulted in longer rotations but did not meet the planned strength due to bracket-induced prying effects causing bolt head failure. Despite this, the collapse type aligned with the research plan. Addressing the bracket's fulcrum effect during field applications requires solutions, potentially involving enlarging the bracket's base and increasing the number of thread rod points. The tests did not damage the laminated bamboo components, emphasizing the need to consider laminated bamboo cross-sectional dimensions and thread rod fulcrum effects in subsequent tests to ensure uniform component performance.

Fire research of joint between special-shaped CFST column and U-shaped composite beam

The steel-concrete composite joint plays an important role in the building structure of transmitting load and maintaining structural stability, and the research on fire performance of composite joints is significant. The special-shaped concrete-filled steel tube (SCFST) column and U-shaped steel-concrete composite beam (USCB) have good fire resistance which is proved by authors' previous fire tests. Therefore, the fire performance of the joint between SCFST column and USCB, the temperature distribution, failure mode, fire resistance, and internal force distribution of the joint under fire are investigated based on the fire tests results of column and beam component. The results showed that the temperature of the joint zone is lower than that of the non-joint zone, which ensured that the strength and stiffness of the joint zone are higher than that of the non-joint zone (beam and column). Then the two failure modes including beam failure and column failure occurred in the composite joint in fire conditions. Furthermore, the internal force analysis indicated that internal force redistribution happens during the elevated temperature. The parameter analysis expressed that fire resistance decreases with the increase of load ratio and the beam-column moment ratio and increases with the increase of the beam-column stiffness ratio and the fire protection layer thickness. Finally, the high-temperature calculation formula for the bearing capacity of beam-column joint was proposed.

Effects of modeling assumptions on prediction of seismic demands of a single-story RC structure

This study investigates the seismic response of a single-story reinforced concrete (RC) structure subjected to strong ground motions. Effects of modeling assumptions used to idealize the reinforcement slip in beam-column joints and column footing are studied. For this purpose, the numerical model of a single-story, single-bay, three-dimensional asymmetric RC structure, tested on a shake table and its symmetric version, is analyzed. Two modeling approaches are considered to show the significance of rotation associated with the reinforcement slip. Bidirectional nonlinear time-history analyses are conducted using symmetric and asymmetric 3D models. In these analyses, 30 pairs of near-field ground motions, selected and scaled to match the target spectrum, are used. The findings indicate that the neglection of reinforcement slip in numerical model may result in an underestimation of almost 50% in story drift ratio demands.

Cyclic behavior of self-centering RCFST column to beam joints with prefabricated connectors

This paper presents the cyclic behavior of reinforced concrete-filled steel tube (RCFST) column to beam joint with prefabricated connectors. The cyclic performance of four specimens was investigated to focus on the hysteretic behavior, reinforcement tension, residual deformation, and strain distribution of joints. The equivalent viscous damping coefficients (ξeq) corresponding to the four specimens range from 0.049 to 0.087 at the yield point. And the final residual drift ratio of the specimens ranged from 3.6% to 12.9%. The tested column-beam joint specimens had good hysteretic behavior, energy dissipation, and self-centering ability. The PT steel bars without hollow channel or weakened treatment enhanced the self-centering ability and workability of joints. The finite element models were developed to verify the main mechanical properties of the self-centering RCFST column to beam joint. The average of KE/ KFEA, Mc,y/ My,FEA and Mc,p/ Mp,FEA were 0.89, 0.98, and 1.03, respectively. The FEA models could predict mechanical properties of the joints with high accuracy.

Nonlinear finite element modeling of reinforced concrete beam–column joints retrofitted using various plates configurations of carbon fiber-reinforced polymers

Nonlinear finite element modeling of reinforced concrete beam–column joints retrofitted using various plates configurations of carbon fiber-reinforced polymers

Experimental investigation using demountable steel-concrete composite reduced web section (RWS) connections under cyclic loads

This paper presents an experimental study of demountable steel-concrete composite reduced web section (RWS) connections for use in seismic areas. Four composite connection specimens were subjected to sagging and hogging moments to investigate the performance of RWS connections under reversible actions. For such purpose, a single web opening was created near the beam-column joint. Focus was made on the effects of perforation location and composite beam-slab action induced by bolted shear studs within the protected zone. Results indicate that employing RWS connections for seismic retrofit is a viable solution capable of achieving a performance similar to that observed for RBS connections in new buildings. Notably, a Vierendeel Mechanism is formed, allowing for plasticity development in the beam. All RWS connections were capable of achieving an interstory drift larger than 4%, thereby complying with the performance targets set by ANSI/AISC 358-16, ANSI/AISC 341-16 and EC8. Moreover, the deformation of beam-slab shear-transfer bolts was small enough to allow for disassembly after the tests, indicating that the proposed solution could enable reuse and post-earthquake retrofitting.

Shaking table test and numerical simulation of a precast frame-shear wall structure with innovative untopped precast concrete floors

An innovative discretely connected precast concrete floor (DCPCF) was presented, in which the adjacent precast concrete hollow or sandwich flat slabs were connected by mechanical connectors embedded in the precast concrete slabs and beams. This paper summarized the seismic performance observed during the shaking table test of a precast frame-shear wall structure adopting DCPCF. A 1/4-scale model of a 4-storey 2-bay single-span frame-shear wall structure was designed and tested on the shaking table to evaluate the dynamic characteristics and seismic responses of building structures adopting DCPCF. In addition, a finite element model, including detailed modeling of beam-column joint and slab joint connections, was established using nonlinear dynamic modeling program. The predictions on the seismic performance using the finite element model agreed well with the test results for the designed frame-shear wall structure. The precast concrete frame-shear wall structure adopting DCPCF had satisfactory seismic performance during the test process. The in-plane deformation of DCPCF was observed under the horizontal earthquakes, and DCPCF could not satisfy the requirements of rigid diaphragm assumption in most cases under design basis seismic intensity. The seismic design method based on semi-rigid floor diaphragm had large error and safety risk in calculating the seismic shear force of building structure adopting DCPCF. Additionally, design suggestions for multi-storey and high-rise building structures using DCPCF were proposed based on the observed seismic responses.

Experimental study on seismic performance of timber frame with novel energy-dissipation joints

The beam-column joints of traditional timber frames are mortise-tenon or iron hook joints, which are prone to joint damage during earthquakes, thus causing the collapse of buildings. To avoid such adverse seismic damage, this study proposes an energy-dissipation joint applied to timber frames. The energy-dissipation joints serve both as joint connections and knee braces, providing multiple lines of seismic defense. To verify the effectiveness of the energy-dissipation joints, quasi-static tests were conducted on four specimens. It is shown that the energy-dissipation joints successfully achieve the intended objective. When the inter-story drift ratio of the timber frame is small, the energy-dissipation elements in the energy-dissipation joints remain in an elastic state. As the inter-story drift ratio increases, the energy-dissipation elements in the energy-dissipation device gradually begin to yield and dissipate energy. The energy-dissipation elements cease operation when the inter-story drift ratio is relatively large, and the energy-dissipation device transforms into knee brace to provide lateral stiffness to the timber frame. Compared with the traditional timber frame, the load-bearing capacity, lateral stiffness, and energy dissipation capacity of the timber frame with the energy-dissipation joints were significantly improved, and the failure mode shifted from beam-column joint damage to timber column fracture damage, and no collapse occurred under an inter-story drift ratio of 12.86%.

Seismic behavior of prefabricated beam-column joint with π-shaped connector

An innovative beam-column π-shaped joint, which was suitable for the low-rise prefabricated lightweight steel composite structure, was proposed in this paper. Firstly, with consideration of the variables of the column type, bending stiffness ratio between the beam and π-shaped connector, π-limb length, perforated end plate thickness, and with or without web connecting plate, twelve π-shaped joint specimens were prepared and their seismic behavior was experimentally investigated in aspects of failure mode, hysteretic performances, ultimate moment, stiffness degradation, deformation capacity, energy dissipation capacity, and strain response. Then the numerical model of the π-shaped joint was established and validated with the test data, which facilitates the further investigation of the influence of the bending stiffness ratio, π-limb length, and perforated end plate thickness on the seismic performance of the π-shaped joint. The test results showed that the application of the CFST column could improve the ultimate moment, initial stiffness, and energy dissipation of the π-shaped joint compared to the SHS column. Meanwhile, the introduction of the web connecting plate could avoid the separation of beam and column, resulting in a significant improvement in the seismic performance of the π-shaped joint. The test and numerical results demonstrated that decreasing the bending stiffness ratio, increasing the π-limb length and perforated end plate thickness was beneficial to further improve the seismic behavior of the π-shaped joint, and their corresponding suggested values were also provided in the present study.

Experimental study on the structural behavior of exterior precast concrete beam-column joints with high-strength steel bars in field-cast RPC

To enhance the seismic performance of conventional precast concrete frame structures, this study introduces a novel precast high-performance concrete frame beam-column joint. We designed and conducted experiments on two full-scale precast concrete frame beam-column exterior joints, varying the presence of L-shaped steel reinforcement at the bottom of the beam-column joint. The findings reveal that the load-bearing capacity, hysteresis characteristics, stiffness degradation, and energy dissipation capacity of both joints significantly improve when using reactive powder concrete (RPC) poured into the joint connection area and L-shaped steel at the beam-column junction. A finite element model for these joints was further developed and validated based on the experimental data. Additionally, a parametric study was conducted to assess the impact of axial compression ratio and spacing of hoop bars in the joint area on joint behavior. Using an experimental fitting approach, a tri-linear skeleton curve model for the joints was established, offering a more precise representation of stress and deformation characteristics at each stage. The hysteretic curve generated from this restoring force model closely matches the experimental data, demonstrating the model’s ability to accurately depict the hysteretic behavior of beam-column joints in precast RPC/RC composite frames.