RC Beam-column Joints Research Articles

Proposal of a scissor-based model for the non-linear analysis of RC beam-column joints strengthened by FRP

The paper presents a new simple modeling approach for studying the monotonic response of RC beam-column joints externally strengthened by Fiber Reinforced Polymer (FRP) materials. The approach assumes a parallel combination of the behavior of the joint in the unstrengthened configuration and the contribution of strengthening system. To achieve this, the common scissor model, where the behavior of joint shear panel is modeled through a rotational spring, is here modified by introducing an additional spring, arranged parallel to the concrete spring, to account for the contribution of strengthening system. Regarding the behavior of the additional spring, the authors proposed a multilinear simplified constitutive law by appropriately combining analytical models available from the literature with specific guidelines provided by Italian technical standards. The proposed model, implemented in the computer code OpenSees and validated against experimental case studies from the literature, demonstrates its strong capability to capture the contribution of the strengthening system on both the strength and ductility of joints.

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.

Research on seismic performance of replaceable prefabricated RC beam-column joints

Based on the seismic design philosophy of recoverable functionality, this paper proposed a prefabricated concrete beam-column joint utilizing replaceable friction energy dissipation artificial plastic hinges (FAPH) as connecting devices. The connecting device comprised a pair of lugs and high-strength pins. This study analyzed the failure modes and hysteresis characteristics through cyclic loading tests performed on the precast beam-column joints. The results showed that the FAPH had a high peak capacity. However, the yield load was low, which reduced the energy-dissipation capacity of joints at the early stage. Therefore, lateral energy dissipation steel plates (EDPs) were added on both sides of the PAPH to improve bearing capacity. Then, utilizing ABAQUS finite element software, the mechanical behaviors of the optimized prefabricated joint such as the load-displacement curve, bearing capacity, ductility, and energy dissipation capacity were further analyzed. This paper also investigated the effect of the axial compression ratio, the friction coefficient, bolt preload, and connecting plate form of EDPs on the seismic capacity of the optimized joint. After optimization, the prefabricated joint exhibited a significant improvement in both yield capacity and cumulative energy dissipation, increasing by 47 % and 22 %, respectively. Additionally, there was a slight improvement in ductility. Increasing the axial compression ratio reduced the bearing capacity and ductility of prefabricated joints after the peak point. The specimen exhibited a significant increase in both peak capacity and cumulative energy dissipation as the friction coefficient increased. Additionally, the hysteresis curve of the joint became fuller with the increase in bolt preload. The connecting plates of EDPs mainly serve to transmit loads, and different forms of connecting plates had little effect on the bearing capacity and energy dissipation capacity of prefabricated joints.

Hysteresis Behavior of RC Beam–Column Joints of Existing Substandard RC Structures Subjected to Seismic Loading–Experimental and Analytical Investigation

Four exterior reinforced concrete beam–column joint subassemblages with poor reinforcement details and low-quality materials were constructed and subjected to cyclic lateral deformations under constant axial loading of the columns. The longitudinal rebars at the top of the beams were well-anchored in the joint region with a 90° hook and transversely welded to prevent premature slippage. The same was true for the longitudinal rebars at the bottom of the beam of the first specimen. Contrarily, the anchorage of the rebars at the bottom of the beam of the other three subassemblages was straight and of insufficient length. One of these specimens (the second) also had deficient lap splices of the column reinforcement, while the other three specimens had continuous column rebars. The third and the fourth subassemblage were designed with different joint aspect ratio and beam shear span/depth ratio values. The overall seismic performance of the specimens was evaluated and compared. The failure mode of the subassemblages was accurately predicted by the proposed analytical model. It was clearly demonstrated that the anchorage of the rebars, the length of the lap splices, the joint aspect ratio and the shear span/depth of the beam ratio value crucially affect the cyclic response of beam–column joints and, hence, may cause a severe detrimental impact to the overall structural integrity.

Bi–axially loaded RC beam–column joints and haunch retrofit

AbstractIn this study, seismic bi–axially loaded RC beam–column joints are investigated. An experimental campaign on shear–critical corner joints is presented, including two as–built specimens and one retrofitted using fully–fastened–haunches (FFHR). Bi–axial tests adopted hexagonal protocol which is essentially to apply load in one direction double with respect to the other. Results obtained for as–built condition were included in a database of corner joints tested bi–axially and discussed in the light of the impact of bi–axial load on joint’s shear strength. Further, non–linear finite elements were employed to thoroughly evaluate the bi–axial response. Haunch retrofit was capable to reduce both shear stresses and distortion at joint. Experimentally–derived internal forces were used to validate three–dimensional Strut-and-Tie model of the joints. Such design tool is recommended for practice cases adopting FFHR.

Retrofitting RC beam-column joint subassemblies using UHPC jackets reinforced with high-strength steel mesh

Outdated building codes in seismic zones often did not require seismic detailing on beam-column joints, leaving many existing structures vulnerable to earthquakes. To address this issue, three different ultra-high-performance concrete (UHPC) jackets were proposed for retrofitting seismically-deficient exterior beam-column joints, with variables including construction method (cast-in-place or precast) and inclusion of high-strength steel bar meshes. The effectiveness of these jackets was investigated using cyclic loading tests on beam-column joint subassemblages. The results demonstrated that all three UHPC jackets considerably improved the strength, stiffness, and energy dissipation of the beam-column joint subassemblage, as well as both repairable and collapse drifts. However, the cast-in-place UHPC jacket, when not reinforced with steel meshes, failed to effectively improve the ultimate drift capacity of the original beam-column joint subassemblage. Moreover, retrofitting with precast UHPC jackets using chemical anchors failed to generate sufficient composite action. Only the cast-in-place UHPC jacket, when reinforced with high-strength steel meshes, successfully delayed localized joint shear damage and allowed for effective utilization of beam flexural capacity. It improved the joint shear strength by 66%, initial stiffness by approximately 35%, and total energy dissipation by 140%. Finally, strength models were suggested for evaluating the joint shear strength and beam flexural capacity of UHPC-retrofitted beam-column joints.

Enhancement in performance of RC beam-column joint under cyclic loading by using various grades of engineered cementitious composites in the joint zone-a sustainable numerical study

In this research, the response of the RC Beam-Column Joint under the cyclic loads was analyzed with a FEM solver (Abaqus) by using various grades of Engineered Cementitious Composite (ECC) in the joint zone. The concrete damage plasticity model for concrete and ECC material under cyclic loading was proposed. Accordingly, the Finite Element Analysis (FEA) model was established with the consideration of different constitutive material models for concrete and Engineered Cementitious Composites. The accuracy of the proposed FEA model was validated with the experimental results. Failure mechanism, crack propagation, moment rotation relationship, and energy absorption under cyclic loading were investigated. Under controlled deformation, cyclic loads were applied to the samples at the end of the beam up to the failure point. It was found that the use of various grades of Engineered Cementitious Composites in the joint zone was effective in enhancing the ultimate moment capacity upto 38.50%, ductility upto 13.72%, and siffniness degradation upto 28.57% respectively of the joint up to the failure stage alongwith significant reduction in crack propagation.

Rehabilitation of seismically-damaged RC beam-column joints with UHPC and high-strength steel mesh reinforcement

In the aftermath of strong earthquakes, diagonal shear failure in RC beam-column joints is a prevalent damage pattern observed in older buildings lacking seismic detailing. This research investigated the efficacy of ultra-high-performance concrete (UHPC) jackets reinforced with high-strength steel mesh for rehabilitating such seismically-damaged exterior beam-column joints. The primary aim was to determine if this novel repair approach could both restore and enhance the seismic performance of the compromised joints. The conclusions drawn from this study were based on systematic experimental evaluations of four beam-column joint specimens and were further supported by strength models, encompassing both the joint shear strength model and a fiber-based cross-sectional analysis. The findings revealed that the UHPC jacket, fortified by high-strength steel mesh, demonstrated an exceptional capability to curtail extensive joint diagonal cracks and column splitting cracks, which were characteristic of the original, substandard beam-column joint specimens. This remedial measure enabled the beam's flexural yielding to predominantly govern the cyclic behavior of the rehabilitated specimens. Notably, the joint shear failure evident in the original specimens was effectively prevented post-repair, resulting in a surge of up to 93 % in peak strength. Furthermore, the tension-stiffening behavior manifested by the steel mesh-reinforced UHPC emerged as a pivotal factor in the structural rehabilitation, influencing aspects such as damage patterns, load-displacement hysteretic responses, stiffness, energy dissipation capacity, steel mesh strain demands, and thresholds for repairable and collapse drift ratios. Complementing the experimental findings, this study proposed appropriate strength models, namely the joint shear strength model and the fiber-based cross-sectional model, to evaluate the failure modes of the rehabilitated beam-column joint components. These models successfully captured the joint shear and beam flexural behaviors observed in the experiments with reasonable accuracy. The findings suggest that the proposed UHPC jacketing, reinforced with high-strength steel mesh, along with its analytical model, offer effective and viable solutions for seismic rehabilitation practices. These methods not only restore but also significantly enhance the seismic performance of damaged beam-column joints.

Machine learning-based shear strength prediction of exterior RC beam-column joints

Machine learning-based shear strength prediction of exterior RC beam-column joints

Assessment of the impact of column-to-beam strength ratio on seismic response of RC beam-column connections

Beam-column joints play an important role in the overall resistance of reinforced concrete frames during seismic events. The Earthquakes of Al Asnam on October 10, 1980, and Boumerdes on May 21, 2003 in Algeria, have highlighted the failure of beam-column joints as a cause of building collapse. 3D nonlinear finite element analysis with ANSYS software has been used in order to examine exterior RC beam-column joints under monotonic loading. The research has investigated the influence of the value of the column-to-beam strength ratio (CBSR) of these joints on shear strength and seismic performance of concrete structures by changing the height and longitudinal reinforcement of the beam while keeping column dimensions constant. It has been shown that the beam-column depth ratio and the beam longitudinal reinforcement ratio have a significant effect on the shear capacity and seismic behaviour of exterior beam-column joints. An appropriate value of the flexural strength ratio between the column and beam is crucial in order to establish a "strong column-weak beam" mechanism in reinforced concrete frames, because inadequate values can lead to premature failure or reduced shear capacity at the junction. The Algerian seismic code – RPA99/version2003 suggests a minimum value of column-to-beam strength ratio equal to 1.25 at joints for seismic design when building codes in other countries call for higher ratios. Nevertheless, this approach might not accurately represent the actual behaviour and could constrain the optimal performance of structures.

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.

Energy-based damage assessment of RC frames with non-seismic beam-column joint detailing using crack image processing techniques

Quantitative post-earthquake failure safety assessment of RC framed buildings with non-ductile joints, as one of the most vulnerable structures, is presented in this study utilizing crack image analysis. For this purpose, energy-based damage indices, as the representatives of the cyclic behavior of earthquakes, are considered to quantify seismic damage. The complexity and irregularity of the crack images are quantified through the generalized fractal dimensions of the crack maps for the damaged RC beam-column joints with non-seismic details. The presented method takes advantage of a collected databank by the authors, including 255 images of surface crack maps of 56 beam-column joint specimens under cyclic loading covering a wide range of energy-based damage indices. In this study, a basic damage index based on energy dissipation along with a combined damage index based on deformation and energy dissipation are used to estimate the extent of the damage. Five symbolic regression-based predictive equations for each of the damage indices are presented based on the after-event access of the structural details. Finally, the efficiency of the proposed method is evaluated for a sample seismically damaged RC beam-column joint specimen. The post-earthquake estimation of the presented damage indices can be used for quantitative failure safety assessment of seismically damaged buildings against aftershocks, secondary numerical seismic analysis, and providing strengthening solutions for damaged RC buildings with non-seismic detailing.

Rectification of Sabah Stilt House Using Shear Wall Subjected to Earthquake

A moderate earthquake with 6.0-magnitude hit Sabah in 2015 especially in Ranau, Sabah has been labelled as one of the most powerful earthquakes ever in Malaysia. Numerous buildings in Sabah have become defective with the severity level of damages as absolute (non-repairable) in the RC beam-column joints and soft-storey structures. Seismic design and construction requirements were not considered in most buildings in Sabah. Hence, this research is to investigate how to mitigate the effect of earthquake on the low-rise building using a more practical and economical method. A stilt house model is developed using ABAQUS software to determine the behaviour of the stilt, low-rise building subjected to earthquake by constructing shear wall at the short columns support. There are 4 models constructed namely, frame model without shear wall (W1), with shear wall of 100mm (W2), 300mm (W3) and 500mm (W4). The results of seismic response are evaluated and compared. Different length of shear wall affects the displacement and stress of the frame model. As shear wall length increases, the displacement, stress at columns and stress at walls decreases. Thus, adding a shear wall can be used to retrofit stilt houses and a credible way to mitigate damage due to earthquake load for new houses along hill slopes

Seismic performance of corroded non-seismically and seismically detailed RC beam-column joints rehabilitated with High Strength Fiber Reinforced Concrete

The experimental investigation was undertaken to restore the seismic performance of the corrosion-damaged beam-column joint (BCJ) rehabilitated with High Strength Fiber Reinforced Concrete (HSFRC). A total of eight exterior beam-column sub-assemblages were cast following two types of reinforcement detailing as per IS 456:2000 and IS 13920:2016, respectively. Three specimens from each reinforcement detailing regime were subjected to three different levels of corrosion and thereafter rehabilitated with HSFRC. The hysteresis behavior, energy dissipation, stiffness degradation, crack patterns, and damage index of all rehabilitated specimens are analyzed and compared with the conventional specimens. Test results indicate that the replacement of damaged concrete with HSFRC can recover the strength of corrosion-damaged BCJ when the corrosion ratio is within 10 %. The peak load-carrying capacity and initial stiffness of rehabilitated specimens showed a significant increase up to 36 % and 84 % respectively, when compared to control specimens. The ductile detailing rehabilitated specimens showed up to 90 % higher equivalent viscous damping ratio than the non-ductile ones, exhibiting close stirrups arrangement superiority. Despite recovering the load-carrying capacity at initial drifts, the seismic performance of non-ductile and ductile rehabilitated specimens having 17.76 % and 20.32 % corrosion ratio were not recovered at higher drifts.

Behaviour of Stainless-Steel Fibre-Reinforced Exterior Beam-Column Joints under Reverse Cyclic Loading

The objective of this study is to evaluate the flexural behaviour of stainless-steel fibre-reinforced concrete beam-column (BC) joints under reverse cyclic loading. Based on the properties of concrete with various percentages of fibre, the optimized volume fraction was obtained as 0.75% of stainless-steel fibre. In the present work, two sets of beam-column joints with and without fibres were cast and tested under reverse cyclic loading. The beam-column joints were loaded up to five cycles, to study their behaviour, and examine the failure pattern of the joint. Based on test results, parameters such as ductility and the energy absorption capacity characteristics were evaluated. It is concluded that the inclusion of stainless-steel fibre improves the overall seismic resistance of RC beam-column joints.

Shear capacities of reinforced concrete interior beam-column joints subjected to cyclic loading

The primary focus of this research is the experimental investigation of internal RC beam-column joints with cyclic loads. There were two interior RC beam-column joints test specimens made without shear reinforcement. The longitudinal reinforcement ratio of the beams served as the study’s test variable. The specimen test results were compared to the theoretical capacity given in SNI 2847-2019 after that. The test revealed the following: (a) shear and flexural beam capacities; (b) shear and flexural column capacities; and (c) shear capacities of joints. The results showed that there was a significant impact on the shear capacity of the beam-column joint as a result of the variation in the reinforcement bars of the beam. After the longitudinal reinforcement bars of the beam yielded in both instances, the degradation of the beam-column joint occurred. A sharp decline in the load value that the specimen can support serves as evidence.

Strengthening of RC Beam-Column Joints Using Steel Plates and Shear Connectors

Abstract: The role of a beam‐column joint is very vital in RCC framed structures. Most of the structural collapses due to earthquakes have been initiated by the failure of the beam‐column joints and therefore understanding the behavior of beam‐column joints is important. The beam column joint is a crucial area where loads from the beam and columns are transferred. It becomes the most critical part of the structure when poor detailing ,unsafe design adopted in the region ,overuse or lack of maintenence.

Structural Behavior of Steel Reinforced Concrete Joint Under Flexural Loads

This research investigates the behavior of RC beam column joints reinforced with steel sections. The study deals with the strengthening of RC joints by different steel sections. The investigation included a theoretical analysis through a performing of simulation of beam-column joints laced with steel sections by using FEA. Implementation of the parametric study included reinforcing the concrete beam with steel sections in many configurations. Shapes and length were the most variables in this study, and many shapes were used, such as I-section, box section, and plates, beside the concrete compressive strength variable. The most recent study revealed the possibility of the method to enhance the efficiency of the joint in resisting the loads while the offering many additional features such as higher ductility, stiffness, and energy absorption. The results showed that strengthening by the steel section enhanced the flexural strength of the joint, but these enhancements were to a certain limit due to the concrete strength limitation. The ultimate strength enhancement was 49%, which is considered a good index for the joint efficiency. The use of compressive strength in small amounts led to the enhancements being limited due to the weakness of the concrete. Strengthening the flexural side of the beam by adding a steel section requires stronger concrete to provide more contribution for the steel section to resist more flexural loads. The increase in the compressive strength of the concrete made the improvements reach their peaks. Strengthening by I-shaped and box steel sections showed that the enhancement due to the existence of the I section was greater than that of the box one. Doi: 10.28991/CEJ-2023-09-03-015 Full Text: PDF

Research on design and numerical simulation of self-centering prefabricated RC beam-column joint with pre-pressed disc spring devices

To improve the resilience performance of precast concrete frame structure, a novel self-centering prefabricated concrete beam-column joint with controllable plastic hinge (PJ-CPH) is proposed in this manuscript. Controllable plastic hinge is an innovative connection configuration composed by pin shaft, rotational friction damper and disc spring self-centering devices. The rotational friction damper is used for withstanding bending moment and dissipating seismic energy. The disc spring self-centering device is used for withstanding bending moment and providing restoring force, while the pin shaft is merely used for withstanding shear force. A detailed design procedure was presented by introducing self-centering ratio α and moment amplification factor β. A flag-shaped hysteretic model of PJ-CPH was proposed, simultaneously, a numerical model was developed based on the OpenSees computational platforms. The numerical simulation analysis was carried out for four PJ-CPH models with different parameters and one cast-in-situ beam-column joint model under low cyclic loading. Analysis results indicate that the hysteretic curve obtained by theoretical calculation are in good agreement with the numerical simulation results. Consequently, the effectiveness of the established hysteretic model was verified. Compared with the cast-in-situ beam-column joint, PJ-CPH achieves the damage-free connection and exhibits the superior resilience performance. The simulation results suggest that self-centering ratio α values should be assumed approximately in the range 1.00–1.30, moment amplification factor β values in 1.30–1.40, which can induce damage to concentrate in controllable plastic hinge, protect the main structure from damage and reduce repair costs.

RC Beam-Column joints, discussion of the provisions in the second generation Eurocode 8

This paper reviews the provisions given in the draft of the second-generation Eurocode 8 (EC8) for the design and assessment of RC beam-column joint against seismic conditions. The analytical bases were recently published by Michael Fardis. A critical discussion of the analytical models, supported by a numerical example, is given. Validation against an independent database of exterior joints is made. A final comparison with respect to (i) current EC8 provisions and (ii) other Building Codes is presented.