Beam-column Joints Research Articles

Numerical Simulation Study on the Seismic Performance of Prefabricated Fiber-Reinforced Concrete Beam–Column Joints With Grouted Sleeve Connections

Based on the available experimental data, fiber models for four prefabricated fiber-reinforced concrete beam–column joint specimens with grouted sleeve connections are first developed in OpenSees software. Then, the simulated seismic performance of the specimens is compared with the experimental results. Finally, the effects of axial load ratio and shear-to-span ratio on the seismic performance of the specimens are further investigated numerically. The results indicate that Concrete02 material model and Reinforcing Steel material model can accurately simulate the constitutive relationship of concrete and reinforcing steel, respectively; the beam–column joint elements can accurately simulate different damage behaviors of the joint zone. Fiber-reinforced concrete can significantly improve the seismic performance of the specimens. The relative errors of the simulated seismic performance indexes are about 15%. It is recommended that the optimum value of shear-to-span ratio for prefabricated FRC BCJs is 2.0–2.5. The effect of axial load ratio on the seismic behavior of PBCJs-CM is very small, and can be negligible in the case that the prefabricated FRC BCJs has a moderate value of shear-to-span ratio. The fiber model developed in this article can provide a numerical simulation basis for subsequent studies of prefabricated fiber-reinforced concrete beam–column joint specimens with grouted sleeve connections.

Seismic Response of RC Beam-Column Joints Strengthened with FRP ROPES, Using 3D Finite Element: Verification with Real Scale Tests

A 3D-finite element analysis within the numerical program ABAQUS is adopted in order to simulate the seismic behavior of reinforced concrete beam-column joints and beam-column joints strengthened with CFRP ropes. The suitability of the adopted approach is investigated herein. For this purpose, experimental and numerical cyclic tests were performed. The experiments include four reinforced concrete (RC) joints with the same ratio of shear closed-stirrup reinforcement and two different volumetric ratios of longitudinal steel reinforcing bars. Two joints were tested as-built, and the other two were strengthened with CFRP ropes. The ropes were applied as Near Surface Mounted (NSM) reinforcement, forming an X-shape around the joint body and further as flexural reinforcement at the top and bottom of the beam. The purpose of the externally mounted CFRP ropes is to allow the development of higher values of concrete principal stresses inside the joint core, compared with the specimens without ropes, and also to reduce the developing shear deformation in the joint. From the results, it is concluded that X-shaped ropes reduced the shear deformation in the joint body remarkably, especially in high drifts. Further, as a result of the comparisons between the yielded outcome from the attempted nonlinear analysis and the observed response from the tests, it is deduced that the adopted method sufficiently describes the whole behavior of the RC beam-column connections. In particular, comparisons between experimental and numerical results of principal stresses developing in the joint body of all examined specimens, along with similar comparisons of force displacement envelopes and shear deformations of the joint body, confirmed the adequacy of the applied finite element approach for the investigation of the use of CFRP-ropes as an efficient and easy-to-apply strengthening technique. The findings also reveal that the connections that have been strengthened with the FRP ropes demonstrated improved performance, and the crack system preserved its load capacity during the reversal loading tests.

The action of heated RC joints strengthened with a novel strategy combined CFRP and SSEMSM under a quasi-static cyclic load

The current work presents the application of a novel strategy for strengthening heated beam column (B-C) joints under a quasi-static cyclic load. This technique involves utilizing a layer of carbon fiber-reinforced polymers (CFRP) sheets with a layer of stainless-steel expanded metal sheet mesh (SSEMSM). These two layers are installed on the steel reinforcement cage inside the joint before concrete casting. Then the reinforced concrete B-C joints, after being cast and cured, were subjected to heat (i.e., 400 °C and 600 °C). The joints were divided into three groups: three joints were kept as is (i.e., reference joints; no strengthening was applied), whereas three joints were strengthened with the previously mentioned strategy. With a view to investigating the seismic behavior of RC joints, a quasi-static cyclic load was applied to the joints to simulate a seismic load. Results showed that the average maximum load capacity for upgraded joints (strengthened) increased by 30%, 19%, and 1% at ambient (i.e., 23 °C), 400 °C, and 600 °C temperatures, respectively, with respect to the reference joint (JCTA). More importantly, the experimental results reveal a significant increase in the cyclic response of strengthened joints (i.e., higher load capacity, greater displacement, higher dissipated energy, higher ductility, and slower degradation in the secant stiffness).

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.

Numerical Investigation on the Seismic Behavior of Novel Precast Beam–Column Joints with Mechanical Connections

Traditional cast-in-place beam–column joints have the defects of high complexity and high construction difficulty, which seriously affect the efficiency and safety of the building construction line, and precast beam–column joints (PBCJs) can greatly improve the construction efficiency and quality. At present, the investigations on the seismic behavior of precast reinforced concrete structures are still mainly focused on experiments, while the numerical simulations for their own characteristics are still relatively lacking. In the present study, the seismic behavior of novel precast beam–column joints with mechanical connections (PBCJs-MCs) is investigated numerically. Based on the available experimental data, fiber models for four PBCJs-MCs are developed. Then, the simulated and experimental seismic behaviors of the prefabricated BCJs are compared and discussed. Finally, the factors influencing the seismic behavior of the PBCJs-MCs are further investigated numerically. The numerical results indicate that the fiber models can consider the effect of the bond–slip relationship of concrete and reinforcement under reciprocating loads. The relative errors of the simulated seismic behavior indexes are about 15%. The bearing capacity and displacement ductility coefficients of the PBCJs-MCs decrease rapidly as the shear-to-span ratio (λ) increases. It is recommended that the optimum λ for PBCJs-MCs is 2.0–2.5. The effect of the axial load ratio on the seismic behavior of PBCJs-MCs can be negligible in the case of the PBCJs-MCs with a moderate value of λ.

Seismic performance and skeleton curve model of prefabricated coral aggregate concrete-filled aluminum tube joint

Corrosion-resistant and high load-carrying capacity coral aggregate concrete-filled aluminum tube (CCFAT) structures show promising applications in island construction. However, research on CCFAT joints related to structural safety remains scarce. To advance the engineering application of this structure, a novel prefabricated CCFAT beam-column semi-rigid joint with bolt connections is designed in this study. The seismic performance of the joint is investigated through a pseudo-static method, analyzing the effects of each parameter on failure mode, hysteresis curve, deformation characteristics, and energy dissipation performance, considering the earthquake-prone nature of islands. The primary objective of this study is to explore the influence of different parameters on the seismic performance of the CCFAT joint and establish the moment-rotation relationship of this joint. It is observed that the ultimate moment relationship between the beam and connector significantly impacts the failure mode of the joint, thus affecting its seismic performance. Hence, prioritizing the ultimate moment relationship between the beam and connector in the design phase is crucial to avoid undesirable joint failures. The skeleton curve of CCFAT joints differs significantly from that of steel and reinforced concrete structures, rendering existing joint theories inapplicable to CCFAT joints. Considering joint material, structure, and failure mode, this paper proposes a theoretical calculation method for the initial stiffness and ultimate moment of the CCFAT joints. This method is based on the component method and mechanical model, establishing an exponential three-parameter skeleton curve model for the joint. This model enables an accurate prediction of the moment-rotation relationship of the CCFAT joint, aiding in its seismic performance evaluation.

Evaluation of various FRP strengthening configurations for RC beam-column joints

There are several methods for strengthening reinforced concrete joints. Due to the unique properties of FRP (Fiber Reinforced Polymer) composites, the use of FRP laminates is one of the most commonly used techniques. The high cost of preparing concrete surfaces and attaching FRP laminates is a restricting factor for its application in reinforced concrete joint retrofit. Therefore, determining proper configurations that reduce the needed FRP material, as well as the surface preparation required for attaching FRP is an important factor in decreasing the strengthening cost. The proper arrangements of FRP strips can improve their performance in the rehabilitation and retrofit of reinforced concrete joints. To determine the proper configuration of FRP strips, finite element modeling was employed. The connection specimens are modeled in ABAQUS general-purpose finite element software and are classified into 10 general groups. To improve the performance of FRP strip configuration, the determined arrangement is investigated for different thicknesses and different widths of the FRP strips, and their results are compared with those of the connection specimen strengthened with full FRP coverage. The analysis results indicated that the load-bearing capacity of the connection retrofitted by the combined configuration of X-shape and orthogonal strips of FRP is close to that of the specimen with full FRP coverage. In this suitable configuration, the required FRP strips are reduced by about 30% , which decreases the cost and construction works needed for concrete joint rehabilitation.

Experimental research on H-section beam-square steel column joints connected by self-tapping screws

This paper proposes a novel thin-walled steel beam-column joint entirely using self-tapping screws. Compared to bolted and welded connections, its advantages of easy construction, low precision requirements, and fast construction are suitable for low-rise steel structures. Four full-scale H-section beam-square steel column joints connected by self-tapping screws were tested and the force transfer mechanism was investigated. Three of the specimens were loaded monotonically at the beam ends. The effects of the L-shaped connecting plate thickness and the arrangement of stiffening ribs on the bending performance of the joints are analyzed. Monotonic loading tests have demonstrated that the increased thickness and the arrangement of stiffening ribs enhance the common forces in the clusters of self-tapping screws, thereby increasing the bending stiffness of the joints. One of the specimens was tested with cyclic loads. The cyclic loading test revealed that the hysteretic curve of the self-tapping screws connection is relatively full, with high energy dissipation capacity and low degradation of strength and stiffness. Finally, the improved component method proposed the calculation method of bending resistance of self-tapping connection joints. The calculation accuracy is within 10 %, which can be used as a reference for the design of bending resistance.

Cyclic behavior and shear strength of exterior reinforced concrete beam-column joints with inclined columns

The adoption of inclined columns results in inclined beam-column joints (BCJs). Although the behavior of regular BCJs have been widely investigated, researches on the cyclic behavior and shear strength of inclined BCJs are limited, and further investigations are required to ensure seismic safety of the frames adopting inclined columns. In this work, cyclic behavior of inclined BCJs was first experimentally studied by testing 3 exterior BCJ specimens. After that, a finite element model was developed and validated by the experimental results. The model was subsequently used for parametric study to reveal the effects of key parameters on the joint shear strength. In the end, a theoretical model based on the softened strut and tie model was proposed to estimate the joint shear strength of inclined BCJs. Results showed that the inclination caused an initial joint shear force under column axial load, leading to different joint behavior in positive and negative loading directions. The joint shear strength was increased in the inclination direction but declined in the other direction, while the ductility showed an opposite trend. Meanwhile, regardless of the inclination direction, energy dissipation and equivalent viscous damping of BCJs were reduced and stiffness degradation was slowed. The parametric study revealed that the inclination effect was amplified with higher inclinations. The overall joint shear strength can be effectively enhanced by adopting higher concrete strength and column axial load. Increasing the joint stirrup ratio was also beneficial for the shear strength, but its efficiency was relatively lower. Based on the comparison of the predicted joint shear strengths and those from experimental and numerical programs, it was proved that the modified strut and tie model was advantageous over the formulas in GB 50010 in capturing the shear strengths. This work contributes to understanding the cyclic behavior and shear strength of inclined BCJs to improve seismic safety of frames adopting inclined columns.

Experimental response of semi-rigid reinforced concrete beam-column joints with bolted angle dissipating connections

Accelerated building construction is a challenge and opportunity for modern construction techniques such as prefabricated building. However, insufficient connection detail for precast structures resulted in serious damages (even collapse) in past earthquake, which significantly hit the further development of prefabricated building. With satisfactory seismic performance and minimal residual displacement, self-centering joint is an excellent alternative with respect to traditional prefabricated joint. In self-centering system, bolted connections are sufficiently utilized as energy dissipation system. However, the information about connection details is quite limited. Thus, a comprehensive experimental study was conducted to characterize the seismic behavior of semi-rigid reinforced concrete (RC) beam-column joints with bolted angle dissipating connections, namely, semi-rigid joints. Ten full-scale semi-rigid joints were tested under cyclic loading, taking the connection detail as variable. The main configurations of semi-rigid joints based on Eurocode 3 were angle thickness, angle stiffener, bolt diameter, column bolt gauge, rows of beam bolts, and grouting of beam bolts. The test results showed that, by adopting the ductile connection concept, it was possible to produce high ductility and abundant energy dissipation, control damages within the connection zone, and even achieve equivalent monolithic behavior through mobilizing a sufficient rigidity. Feasibility of replacing the damaged connection with a new one with the identical or higher capacity thus obtaining the equivalent or better performance with respect to the original tested joint is also evaluated. Finally, a theoretical model was proposed to evaluate the initial stiffness and bearing capacity of the joints. A good correlation was achieved as comparing to the test results. This research provides significant insight into the performance of precast semi-rigid joints and offers essential data for further investigation of developing design-oriented procedures.

Seismic evaluation of post-tensioned precast concrete frames with non-grouted fuse-type dissipaters under successive excitations

In recent years, demands for mitigating structural damage and post-earthquake repair costs have spurred considerable research on self-centering seismic force-resisting systems. This study evaluates the Post-tensioned Precast concrete Frame with non-grouted fuse-type Dissipaters (PPFD) through experimental and numerical methods. Quasi-static tests were conducted on a one-bay, single-story PPFD to investigate its seismic response. The tested PPFD was shown to effectively controlling damage to concrete components and limit residual displacements; imperfections at the beam-column interface joint had a negative effect on the initial stiffness and self-centering performance of the PPFD. Parametric analyses were then performed to discuss the force and deformation responses of the beam-column joint in the PPFD with dissipaters solely beneath the beam. A design method for the PPFD was developed based on the formulas derived and verified from the parametric analyses. Nonlinear dynamic analyses were then employed to evaluate a prototype designed multi-story PPFDs subjected to individual earthquakes in addition to mainshock-aftershock sequences. The findings indicated that both configurations of PPFD, with dissipaters either symmetrically arranged on the beam or located exclusively below the beam, exhibited comparable maximum story drifts and significantly smaller residual story drifts than a comparable reinforced concrete frame. Moreover, the PPFD demonstrated only a minor increase in both the maximum and residual story drifts when subjected to aftershocks, compared to much larger increase for the reinforced concrete frame.

New reinforcements combining a steel plate and screws to enhance beam-column contact surfaces for prestressed timber joints

ABSTRACT The beam-column contact surface of joints in prestressed timber frames is one of the key factors determining structural performance. In this paper, a new reinforcement combining a steel plate and screws was proposed, and the effect of the reinforcements on the performance of joints was investigated by quasistatic tests for 5 beam-column edge joints. First, compared with the conventional joint, the joints reinforced by the steel plate and screws had an average increase in capacity of 25.8% and an average reduction in the degradation rate of the secant stiffness of 14.5%, which were beneficial for resisting repetitive loading. Then, the rate of the final prestressing loss and residual drift of the joint reinforced by the flat steel plate and screws were reduced by 20.5% and 85.7%, respectively, compared with those of the conventional joint. The enhancement effect of the reinforcement combining a U-shaped steel plate and screws was difficult to realize due to the susceptibility to the initial clearance. Finally, the mechanical mechanism of the new reinforcement was clarified, and a method for calculating the compression zone height of the beam in joints with the reinforcement was suggested, which improved the calculation accuracy by 13.7%.

Seismic Performance Evaluation of Exterior RC 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 BCJ using a perforated steel haunch system. This perforated steel haunch system is designed to mitigate damage in BCJs and improve seismic performance of the structure. Employing finite element modeling (FEM) techniques, the study investigates the impact of perforated steel haunches on BCJ behavior and performance. The investigation involved creating nine distinct models, each representing a BCJ with a steel haunch system. These models included 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 connection's performance, considering square, circular, hexagonal, and triangular shapes. The findings reveal that employing 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 joint failure and promote ductile behavior. These findings hold the potential to advance the design methodology for RC joints subjected to seismic loads, thereby enhancing structural resilience in earthquake-prone regions.

Static Behavior of UHPC Corner Beam–Column Joint Under Constant Axial and Increasing Bi-Directional Bending Loads

Static Behavior of UHPC Corner Beam–Column Joint Under Constant Axial and Increasing Bi-Directional Bending Loads

Welded beam-to-column steel joints: Assessment of European design rules

Properly validated high-quality Finite Element (FE) models with experimental tests permit an accurate description of the load-deformation path and stress state of steel joints and are nowadays accepted as “experimental results”. Changes to the design of welded joints in Eurocode 3 are currently proposed that affect the resistance and stiffness of the components associated with the column web panel. This paper presents an assessment of the design formulations included in the current Eurocode 3, part 1–8, and its forthcoming update in terms of stiffness and moment resistance, compared against a large parametric study of strong-axis beam-column welded joints for open sections carried out using validated sophisticated FE models. The results show that both the old and new Eurocode formulations provide a large scatter and no big differences between both methods. Additionally, the presence of axial force in the column shows a clear increase in the ratio between design resistance vs numerical resistance that, particularly in the case of transversally stiffened joints, may be unconservative.

Seismic behaviour of Exterior RC beam-column joints repaired and strengthened using post-tensioned metal straps

Exterior beam-column joints are the most vulnerable part of substandard reinforced concrete (RC) buildings and are often the first to be damaged during earthquakes. This article presents an experimental and numerical investigation into the behaviour of exterior RC beam-column joints repaired and strengthened using Post-Tensioned Metal Straps (PTMS) for active confinement. The study focused on full-scale beam-column joints with an inadequate core zone detailing, thus emulating the deficiencies found in existing substandard RC buildings. Initially, four “bare” joints were subjected to cyclic tests to induce substantial damage within the core zone. Subsequently, the damaged core of the joints was repaired and recast with new concrete, and PTMS were applied to strengthen the joints, followed by another round of cyclic testing. The experimental findings were compared with predictions generated through established models from existing literature. The results revealed that ASCE/SEI 41–17 guidelines accurately predict the shear capacity of the bare joints. It is shown that recasting the core with new concrete significantly increased the joint’s shear capacity by up to 42% compared their bare counterparts. The use of PTMS strengthening further enhanced the capacity by up to 25%. A “scissors model” was employed for numerical simulations of both bare and PTMS-strengthened joints using DRAIN-2DX, which proved effective at predicting their nonlinear load-displacement envelope response. This article contributes towards the development of new cost-effective post-earthquake strengthening techniques for beam-column joints, with the potential to reduce the vulnerability of substandard RC buildings in developing countries.

Experimental study on large deflections of beam–column joints with reinforced flange plates

Web openings facilitate the passage of pipes and enable plastic hinge transfer. However, because these openings reduce the ultimate load at certain values, reinforced flange plates are introduced into the beam–column connections with web openings. In this study, five experimental specimens were constructed and tested, including one base specimen with only web openings, one base specimen with only flange plates, and three specimens with both flange plates and web openings. The failure modes, load–displacement responses, deflection shapes, and deformation capacity were mainly considered. Subsequently, after experimental verification, the thickness and length of the flange plates, as well as the position and diameter of the web openings were studied by numerical simulation. The results indicate that the catenary contribution coefficients and internal energies of the specimens with reinforced flange plates were higher than those of the base specimens. We also concluded that the optimal thickness of the flange plate is equal to that of the beam flange, and the optimal diameter is the maximum web opening that meets the specification requirements. In addition, the mechanical properties gradually increased with an increase the distance a from the web opening to the beam end for a ≤ 190 mm and then decreased for a > 190 mm.

Design optimization of obstacle avoidance of intelligent building the steel bar by integrating reinforcement learning and BIM technology

In promoting the construction of prefabricated residential buildings in Yunnan villages and towns, the use of precast concrete elements is unstoppable. Due to the dense arrangement of steel bars at the joints of precast concrete elements, collisions are prone to occur, which can affect the stress of the components and even pose certain safety hazards for the entire construction project. Because the commonly used the steel bar obstacle avoidance method based on building information modeling has low adaptation rate and cannot change the trajectory of the steel bar to avoid collision, a multi-agent reinforcement learning-based model integrating building information modeling is proposed to solve the steel bar collision in reinforced concrete frame. The experimental results show that the probability of obstacle avoidance of the proposed model in three typical beam-column joints is 98.45%, 98.62% and 98.39% respectively, which is 5.16%, 12.81% and 17.50% higher than that of the building information modeling. In the collision-free path design of the same object, the research on the path design of different types of precast concrete elements takes about 3–4 minutes, which is far less than the time spent by experienced structural engineers on collision-free path modeling. The experimental results indicate that the model constructed by the research institute has good performance and has certain reference significance.

Mechanical property of bolted-assembled reinforced concrete column-steel composite joints

Herein, a new type of bolted-assembled reinforced-concrete column-steel (RCS) beam composite joint is proposed by analysing the force and force transmission process of RCS beam composite joints. The practicality and uniqueness of the structure apply to beam–column joints in large shopping malls, mid- to high-rise office buildings, factories, garages and other building structures. By the finite-element software modelling, a numerical simulation is established and used to analyse the variation of stress and equivalent plastic deformation, hysteresis curve, skeleton curve, stiffness degradation and energy dissipation coefficient under monotonic displacement–load and cyclic displacement–load. Results elaborate that the RCS composite connection has good ductility under monotonic displacement–load. Besides, under the cyclic displacement–load capacity, the hysteresis curve is full, the stiffness degradation is not obvious and the ductility and energy dissipation are good. This study is expected to promote the engineering application and guide follow-up research of the new nodes.

Shaking table test of a dry-connection fully precast frame structure system

In view of the construction difficulties and ecological environment sensitivity of building construction in extremely cold and high seismic intensity areas, a new type of dry-connection fully precast frame structure system was proposed. The connections of the structure are easy to assemble, which can greatly improve the construction efficiency and provide convenience for the upgrading and replacement of components during service. In order to provide essential insights into the seismic performance of the dry-connection precast structure, a three-story precast frame structure specimen with a scale ratio of 1/2 was designed, constructed, and tested on a shaking table subjected to a series of ground motions with increasing seismic intensities. The connections of the specimen structure include beam-column joint, beam-floor joint and column-foundation joint, precast components were processed in the factory and assembled in the laboratory. The vibration characteristics, damage development, acceleration response and displacement response of the structure were investigated. The experimental results illustrated the excellent seismic performance of the structure with sufficient strength and relatively confined damage. The gradually decreasing frequency and increasing damping ratio were attributed to the slippage and plastic deformation of the connectors and the cracking of beam concrete. And the maximum story drift under rare earthquake of intensity 8 was within the design limit, indicated that the precast frame structure could achieve the performance target of no collapse under severe earthquakes. The data of this test provided support for further study on the design methods and numerical modeling of dry-connection fully precast frame structure systems.