Concrete Beam-column Connections Research Articles

Experimental research on seismic performance of dry-wet combined precast concrete beam-to-column connections

In order to enhance on-site assembly efficiency and construction organization flexibility, a new type of dry-wet combined precast concrete beam-column connection was proposed. The prefabricated beams and columns were joined together using local post-tensioned tendons to create a temporary frame structure with dry connections. Subsequently, the wet connections between the prefabricated beams and slabs were established by pouring cast-in-place top concrete. A monolithic connection and four full-scale precast connections were subjected to reversal cyclic loading, with each designed incorporating distinct types of post-tensioned (PT) tendons, bonding conditions, and grouting materials. The test results indicate that the new connection exhibits flexural failure at the beam ends. In comparison to cast-in-place connections, it demonstrates enhanced deformation capacity, comparable ductility, higher stiffness, and reduced energy dissipation due to slippage of the PT tendons and steel bars. However, the viscous damping exceeds 15 %, thereby satisfying the seismic resistance requirements. The high-strength mortar grouting material satisfactorily fulfills the anchoring requirements of steel bars within the corrugated steel ducts, whereas the prestressed grouting material falls short in this regard. The overall performance of the new connection can be further enhanced by improving the grouting material and implementing local unbonded measures.

Seismic performance evaluation of exterior reinforced concrete beam-column connections retrofitted with economical perforated steel haunches

The exterior beam-column joint (BCJ) within reinforced concrete (RC) frame structures is acknowledged as a vulnerable component prone to seismic failure. This article proposes a practical and economical strengthening method for exterior BCJs using a perforated steel haunch system. This method is designed to mitigate damage in BCJs and improve the seismic performance of the structure. Employing finite element modeling (FEM) techniques, the study evaluates the impact of perforated steel haunches on the BCJs’ behavior and performance. The investigation involves creating nine distinct models, each representing a BCJ with a steel haunch system. These models include a control model without any perforations and eight variations with different levels of perforation (ranging from 10% to 50%) within the steel haunch system. Furthermore, the study analyzes the influence of perforation shapes on the connections’ performance, considering square, circular, hexagonal, and triangular shapes. The results reveal that utilizing a steel haunch without perforations significantly increases the load-carrying capacity of a BCJ by about 89%. Additionally, circular or square-shaped perforations, up to 30–35% within the steel haunch, effectively prevent the joints’ failure and promote the ductile behavior. These findings hold the potential to advance the design methodology for RC joints subjected to seismic loads, thereby enhancing the structural resilience in earthquake-prone regions.

Evaluation of the rotational stiffness of precast reinforced concrete beam-column connections

Usually, beam-column connections with steel dowels are treated as hinged connections. This approach overlooks the rotational restraining effect of the dowels. To study the behaviour of these types of connections, an experimental campaign was carried out. Three full-scale beam-column connections were tested, subjected to monotonic and cyclic displacements. The specimens were also simulated numerically to study the influence of the bond quality between the steel dowel and the grout on the stiffness of the connection. The numerical models were calibrated using the experimental results. The results showed that the restraining effect is not negligible and affects the effective length of columns, leading to smaller second-order effects.

Damage assessment of precast reinforced concrete beam-column connections using AE technology

The beam-column connection is both the critical area and the weak part for the prefabricated reinforced concrete (PC) frame structure. The ductile connection with a U-shaped shell has been well-developed for the PC cross-shaped connection. In this paper, two optimizing reinforcement methods in the U-shell were proposed to improve the seismic performance of the PC beam-column connection. Three full-scale PC beam-column connections were designed and produced. Then, reversed cyclic loading was applied to the connections with acoustic emission (AE) technology as the measuring method to investigate the failure modes and damage mechanisms under seismic actions. The results show that increasing the connecting reinforcement area can effectively promote the bearing capacity of components while setting stirrups enables improving energy-dissipating capacity. Based on the variation of AE hits, the loading process can be divided into three stages, and the optimization effects of two measures were reflected at the different loading stages. According to the Ib-value analysis, it can be seen that the cyclic development of microcrack propagation and macrocrack penetration was the main failure mode of components. Besides, the k-means algorithm was used to classify the AE signals into four clusters with different crack patterns. In addition, based on AE energy calculation, the damage prediction model was constructed for the three full-scale specimens.

Enhancing seismic resilience of reinforced concrete external beam column connection by employing an innovative prestressing method

Enhancing seismic resilience of reinforced concrete external beam column connection by employing an innovative prestressing method

Experimental Study on Seismic Behavior of Newly Assembled Concrete Beam–Column Joints with L-Shaped Steel Bars

A novel concrete beam–column connection utilizing L-shaped steel bars is proposed to address the growing demand for prefabricated buildings and to ensure good seismic performance in such beam–column structures. After positioning two prefabricated beams with L-shaped tendons into the designated connection points at the top and bottom of the columns, concrete is poured into the post-cast section of the joint and the composite beam area, realizing a connection between the beams and columns. Quasi-static tests were performed on four combined backbone curves and one cast-in-place joint to investigate their failure modes and stress mechanisms. Through low-cycle repeated loading tests, it is found that measures such as increasing the area of the post-cast concrete in the joint area, the length of the L-shape, and the concrete strength in the composite beam area can effectively improve the bonding ability between the post-cast area of the joint specimens and the precast members, to improve the ductility performance, energy dissipation capacity, and bearing capacity of the joint specimens. The initial stiffness of the joint can be effectively improved by presetting the steel pipe in the column. Concurrently, the finite element method (FEM) was employed for parameter analysis. By integrating the test and FEM results, an equation for calculating the shear capacity of the connection was derived. The findings demonstrate that the hysteresis curve of the newly assembled joints is full, and its overall performance index is roughly the same as that of the cast-in-place joints. Additionally, enhancing the post-casting area of concrete, the length of the L-shaped bars, the concrete strength in the composite beam region, the axial compression ratio, or the steel tube dimensions can effectively improve the overall performance. The derived equation for the shear-bearing capacity of the connection satisfies design and application requirements.

Hysteretic Behavior of Full-Scale Precast U-Shaped Composite Beam–Column Connections with Large-Diameter Reinforcements under High Axial Compression

This study introduces precast concrete beam–column connections comprised of composite beams, precast columns, and a monolithic joint core. The composite beams consist of U-shaped beams and floor slabs, leveraging the U-shaped beams for their lightweight nature, acceptable stiffness, and reduced demand for on-site support systems. To mitigate reinforcement congestion in the joint core, the precast connections incorporate large-diameter rebars (greater than 25 mm). This study conducted cyclic loading tests on four full-scale beam–column connections under 0.3 normalized compression, encompassing precast interior and exterior connections, along with two monolithic reference specimens, to investigate their behavior under seismic actions. The results revealed that all specimens exhibited bending failure at the beam ends, with minimal concrete deterioration observed in the joint core areas and columns. The hysteresis curves of the precast specimens and the monolithic connections exhibited a slight pinching effect. The strengths of the interior and exterior precast specimens were 13.3% and 7.8% lower than those of the reference monolithic connections, respectively. The ductility of interior precast connections and monolithic specimens stood at 2.36 and 2.23, respectively, indicating a negligible difference of less than 5%. Meanwhile, the positive and negative ductility of exterior precast connections were 3.06 and 2.34, which was approximately 8% lower than that of the reference connections. Furthermore, the stiffness degradation and energy dissipation capacity of the precast specimens aligned closely with the performance of the reference monolithic ones.

Cyclic loading response of precast concrete beam-column connections with partially bonded draped prestressing tendon

An emulative precast concrete beam-column connection consists of prefabricated columns, T-shaped composite beams with partially bonded post-tensioned (PT) tendon, and cast-in-place (CIP) core region is proposed in this study. Experimental study was carried out to examine the hysteretic behavior of four full-scale beam-column connections under a high axial compression ratio (μ = 0.4). The specimens included a precast interior connection (PC1), a precast exterior connection (PC2), and two corresponding conventional CIP control specimens (RC1 and RC2). Performance assessment of the suggested connection was conducted by evaluating various factors, including failure mode, hysteresis curve, deformation, stiffness, and energy dissipation capacity. Test results revealed that all specimens fulfilled the design objective of strong column-weak beam with flexural failure showed at beams ends. In comparison to RC1, PC1 exhibited a 6.4 % increase in peak load-carrying capacity in the positive loading process and a 7.1 % decrease in the negative loading process. On the other hand, PC2 demonstrated approximately 11.9 % higher load-carrying capacity in the positive loading and a 2.0 % lower capacity in the negative loading when compared to RC2. The ductility coefficients of PC1 and PC2 was 3.39 and 2.64, respectively, which were slightly higher than that of RC1 and RC2 (3.01 and 2.43). All specimens exhibited good deformation restoring capacity and plump hysteretic loops, demonstrating satisfactory energy dissipation capacity. Overall, the proposed connection with partially bonded PT tendon showed comparable seismic performance with their CIP counterparts, indicated its promising potential for use in practical engineering applications.

Research on Nonlinear Behavior of Local High-Performance Concrete Beam-Column Connections.

The seismic performance index of prefabricated structures is generally obtained via experimental analysis. However, in experimental research, it is impossible that every influencing factor can be taken into account. Therefore, the finite element analysis method can be used as a supplementary method for experimental research to carry out parametric analysis of joints. Based on this test, a hysteretic model of steel bars is developed on the ABAQUS platform; meanwhile, the model is used to simulate the seismic analysis of the proposed local reinforced joints. The hysteresis curve obtained via simulation exhibits a high degree of coincidence with the experimental results. Based on the validated model, a detailed parameter analysis of prefabricated local reinforced concrete frame joints is carried out. The analysis results illustrate that the axial pressure ratio at the top of the column has a minimal impact on the joint's performance. Decreasing the stirrup ratio within the core region, enlarging the diameter of the PC steel bar, and increasing the concrete strength that is poured in the keyway and the core region can raise the cumulative energy consumption of the joints, thereby reducing the damage degree of other units and improving the maximum bearing capability of the joints.

FEM Performance of Beam-Column Joint under Cyclic Loading with Column Inclination at Joint Portion

Outside non-ductile reinforced concrete (RC) beam-column connections are the primary subject of this article's analysis of their cyclic behaviour. This study utilizes experimental data and complex finite element simulations to probe the effect of angle inclination on the link. During the course of the experiment, both standard RC beam-column junction specimens and specimens with an angled column at the joint were tested. The samples were detailed for seismic activity. Physical test findings were contrasted with those obtained from computer-generated FEM simulations of similar specimens. In this research, we use the ANSYS software to perform in-depth 3D non-linear finite element (FE) simulations of beam-column junctions made of reinforced concrete (RC) at a range of inclinations. Beam-column specimens are subjected to cyclic loading in reverse with carefully calibrated amplitudes so that we can study how these parameters respond to repeated loading cycles. Finite element analysis results for energy dissipation and stiffness versus displacement are quite similar to experimental data. With its excellent ductile behaviour, ferrocement can be used as a hybrid reinforcing solution to improve the seismic performance of RC beam-column junctions. Analytical analyses supported the experimental research using finite element models developed with ANSYS software. The results show that the hysteresis simulation works well for both un-strengthened and ferrocement-strengthened specimens, proving its worth in practice.

Seismic behaviour of precast concrete beam-column connections with bolted end plates

This paper presents the seismic behaviour of a dry beam-column connection with bolted end plates for precast concrete structures. Experimental tests were carried out on one cast-in-situ connection and three precast concrete connections with bolted end plates to study the behaviour under reversed cyclic loading. The load resistance, failure mode, ductility and energy dissipation capacity were determined from experimental results. Comparisons were made among different connections to show the influence of end plates and stiffeners on the connection behaviour. Test results showed that precast concrete connections with bolted end plates mainly dissipated energy through bending of the end plate and deformation of steel bolts. The final failure of connection resulted from the yielding of the end plate or crushing of concrete in the compression zone of beams, depending on the thickness of the end plate and the presence of stiffeners. The connection with bolted end plates could achieve good ductility and energy dissipation. Moreover, failure of columns and the joint core was prevented through the use of end plates. An analytical method was also proposed to evaluate the moment-rotation relationship of connections. The contributions of joint core, steel bolts and the end plate to rotational stiffness and moment resistance were quantified in the analytical method. Comparisons with test results showed that the analytical method can estimate the moment-rotation curve of connections with bolted end plates with good accuracy when failure of connection was dominated by steel bolts or the end plate. Design recommendations were also proposed for connections with bolted end plates.

Experimental investigation on the effect of nano-silica on reinforced concrete Beam-column connection subjected to Cyclic Loading

Beam-column joints are crucial load transmission zones because they face concentrated forces from both the beams and the columns. High shear and axial stresses caused by these concentrated forces in the area of the joint may result in decreased joint strength. This article proposes a new beam-to-column connection developed for precast concrete-resisting frames. Concrete mixtures are enhanced mechanically by adding nano silica as it increases compressive strength, flexural strength, and abrasion resistance. Within the concrete, it creates a solid, gel-like matrix that fills voids and strengthens the whole construction. In this study, three reinforced concrete beam-column joint specimens were cast with fly ash, the other three with nano-silica and fly ash, and one sample with nano-silica and a control mix without admixtures was cast. Specimen cast using fly ash and nano-silica is subjected to cyclic loading after 28 days of curing. A load capacity of 100 kN was imposed on the column during testing. It was observed that a gradual increase in fly ash decreased the compressive and flexural strength of the beam-column joints. This decrease in strength was addressed by adding 2.5% nano-silica. Nano silica acts as a nucleus to bond tightly with cement particles during hydration. The results showed that the flexural strength equivalent to that of a controlled specimen can be achieved by adding nano-silica at 2.5% and fly ash at 60%. The highest loading of 38.1 kN can be applied to the specimen with nano-silica without fly ash. Although a higher axial compression ratio can improve the bearing capacity and initial stiffness, it can also reduce deformation capacity and flexibility.

Seismic Performance of Assembled Beam–Column Connections with Modified Reactive Powder Concrete under Different Steel Fiber Types in the Critical Cast-in-Place Regions

Reactive powder concrete (RPC) and reinforcements have ultra-high bonding strength and, thus, a potential advantage in improving the connection performance of assembled structures. In this study, four assembled beam–column connections using modified reactive powder concrete (MRPC) under different steel fiber types in critical cast-in-place regions, as well as a monolithic concrete beam–column connection, were tested under low-cyclic loading. The results show that MRPC application in critical cast-in-place region connections significantly improved damage tolerance capacity and load-carrying capacity. End-bent short steel fibers had the most significant crack-resistance effect. Using end-bent long fibers could improve an assembled connection’s ductility by 102%. Straight steel fibers were easily pulled out and had the least inhibitory effect on cracks. Connections using wavy steel fiber had the lowest initial stiffness and shear capacity but the highest energy dissipation capacity. Using 30 mm end-bent steel fiber is recommended for comprehensive seismic performance. The Chinese code overestimated MRPC’s shear contribution. MRPC assembled connections’ crack capacity and shear capacity models were established.

Seismic Performance Evaluation of Dry Precast Concrete Beam-Column Connections with Special Moment Frame Details

Seismic Performance Evaluation of Dry Precast Concrete Beam-Column Connections with Special Moment Frame Details

Cyclic behavior of a slit damper proposed for precast concrete beam-column connections

Since the 2017 Puebla-Morelos Earthquake, interest in limiting damage to structural components has exponentially increased in Mexico. Consequently, the use of energy dissipation devices has received renewed attention. Following that line, this paper studies an attractive solution, which is a slit damper proposed as a passive energy dissipation device for, but not limited to, precast beam-column connections. Slit dampers have been studied for their cost-effectiveness and ease of application. They present stable hysteretic behavior and dissipate substantial amounts of energy under cyclic loading while maintaining less ductile elements essentially elastic. The structural behavior of the proposed device was evaluated theoretically, followed by experimental verification. Quasi-static incremental and constant-amplitude cyclic tests were conducted on eight specimens, with two of them having non-uniform struts. Test results are presented and discussed, emphasizing ductility and energy dissipation capacity. The proposed damper showed stable hysteretic behavior and adequate seismic performance. Using non-uniform struts significantly increased the damper's deformation capacity and fatigue performance, which is desirable for seismic zones where long-duration earthquakes are expected, such as in Mexico City. Numerical modeling techniques were also validated with finite element analyses. It was shown that the proposed damper's hysteretic response could be accurately predicted using the combined non-linear isotropic and kinematic hardening model.

Evaluation Method for Ultimate Flexural State of Prestressed Precast Reinforced Concrete Beam–Column Connection with Debonded Partial Tendon

In this paper, a prestressed precast reinforced concrete (PC) beam–column connection incorporating posttensioned debonded partial tendons is introduced for PC frame structure. Compared with the conventional cast-in-place frames and many previously proposed connections for PC frames, this connection has the advantage of self-centering and low damage in strong earthquakes. In addition, the debonded partial tendons can reduce the posttensioning demand and further reduce site labor during construction and repair. In order to establish a performance evaluation method for the ultimate flexural limit of the proposed PC connection, an analytical model was developed to accurately reflect the deformation compatibility and force equilibrium conditions of the PC beam and column members, as well as the debonded partial tendons. Based on this, iterative and direct evaluation methods for the strength and deformation of the PC connections, as well as the strains of the debonded tendons, were developed. The proposed methods were verified by cyclic loading test on the beam–column connection subassemblages. It is concluded that the proposed method is sufficiently accurate and simple to be applied in engineering design, and is helpful to guarantee the self-centering and low-damage characteristics of the proposed connection against a strong earthquake.

Seismic behavior of innovative precast hybrid steel reinforced concrete beam-column connections

This study proposed an innovative partially precast steel reinforced concrete (PPSRC) beam-column connection and experimentally investigated its seismic performance. Four full-scale specimens were designed and tested under cyclic loads. Test parameters are axial compression ratio, concrete type (ordinary concrete or steel-fiber reinforced concrete), and connection type (monolithically cast or precast). Test results were discussed and evaluated, including failure modes, strength, stiffness, degradation, energy dissipation, and ductility. The results showed that the proposed connection effectively shifted the plastic hinge location away from the joint interface by longitudinal bar cut-offs. This type of connection exhibited higher strength, better ductility, and greater energy dissipation capacity compared with the moronically-cast connection. The addition of steel fibers effectively controlled crack propagation and enhanced connection performance, while increase in axial load increased the brittleness of the joint.

Progressive collapse resistance of reinforced concrete beam-column connection under fire conditions

To reveal the reinforced concrete (RC) structural response under fire-induced progressive collapse scenarios, 3D finite element (FE) models were developed to investigate the effect of high temperatures on the collapse resisting mechanisms of RC beam-column connections. To describe the behavior of RC connections at elevated temperatures, temperature-dependent thermal and mechanical properties of concrete and reinforcing steel were adopted in the 3D FE model. The sequentially coupled thermal–mechanical analysis was performed with the explicit solver in a quasi-static manner. The concrete damaged plasticity (CDP) and ductile damage for metals (DDM) were adopted to better describe the failure of concrete and steel rebar, respectively. The proposed numerical model was validated by experimental data at different temperatures from literature. To understand better the collapse resistance of RC beam-column connections, a new loading scheme was adopted in the developed model. The load capacity of RC connection under fire conditions was investigated analytically and numerically. The effects of top and bottom reinforcement ratios, concrete strength, beam depth and fire severity on the collapse resisting mechanisms were investigated. The regulated chord rotation failure criteria recommended by the U.S. Department of Defense (DoD) were utilized and showed to be conservative on the collapse identification of RC structures under fire conditions.

Seismic Performance of Precast Concrete Frame Beam-Column Connections with High-Strength Bars.

As the construction industry is striding towards the industrialization of green buildings, a precast concrete frame beam-column joint with high-strength reinforcement was proposed. Simulate reversed cyclic loading was carried out on two precast connections and one cast-in-place connection to examine the seismic behavior of the proposed new precast connection. The main test variables between the two precast connections were the strength of the reinforcement at the bottom of the beam. The failure shape, hysteresis curve, skeleton curve, strength, deformation ability, stiffness degradation, and energy dissipation were monitored and compared with the cast-in-place connection. The findings of this paper showed that the precast joints had good strength reserve, and the seismic performance in the later stage of loading even exceeds the cast-in-place joints. It was also found that the plastic hinge zone of the beam could be moved away from the column surface via reinforcement method. Additionally, based on the experiment, a detailed nonlinear finite element analysis (FEA) method was developed to reproduce the test response of specific types of bending moment-resistant precast concrete beam-column connections under a reversed loading test, which provided a theoretical reference for further research of the connections.

Experimental Study on Seismic Behavior of Precast Bolt-Connected Steel-Members End-Embedded Concrete (PBSEC) Beam-Column Connections

With the rapid development and research of precast concrete frame structures, it is not difficult to find that the structural form and seismic performance of dry-connected precast joints have always been the focus of research. Since this type of structural system is complex, the construction is inconvenient in practical application, and many additional parts need to be installed, this paper develops a kind of precast bolt-connected steel-members end-embedded concrete (PBSEC) beam-column connection to solve the shortcomings of the current dry-connected precast joints. There is no wet work in the assembly process, and all-dry construction and assembly methods are used. There is no need to pour concrete and support formwork, which significantly improves construction efficiency compared to wet and cast-in-situ connections. Low cyclic reversed loading tests were conducted to obtain test data, such as failure mode, hysteresis curve, skeleton curve, stiffness, ductility, and deformation capacity of the precast concrete joint. The failure mode of the PBSEC joints is the buckling failure of the connecting steel plate, leading to a perfect seismic capacity and collapse resistance of the structure. The hysteresis curves of the PBSEC joints are bow-shaped and full in shape, showing high energy dissipation capacity. The bearing capacity of the joints begins to rise rapidly at the initial loading stage and then decreases slowly after reaching the peak, which is an ideal shape. By summarizing the average peak load, strength degradation coefficient, loop energy per cycle, loop energy per level, and cumulative energy damping coefficient, it is found that the joint using 10 mm thick Q235 steel can obtain the most suitable failure mode and obtain the best energy dissipation performance. When the strength of the steel plate material increases, the energy dissipation performance of the joint drops.