Exterior Beam-column Joints Research Articles

Shear Strength Estimation of Nonseismically Designed Exterior Beam–Column Joints Strengthened with Unsymmetrical Chamfers

Shear Strength Estimation of Nonseismically Designed Exterior Beam–Column Joints Strengthened with Unsymmetrical Chamfers

Image-based assessment of seismic damage in RC exterior beam-column joints

Seismic damage to reinforced concrete (RC) beam-column joints in reinforced concrete (RC) structures significantly impacts their stability and safety after an earthquake. Cracks caused by earthquakes weaken these joints, reducing their ductility, strength, and stiffness. Therefore, a systematic method for assessing damage in RC beam-column joints is crucial. This study introduces a new method that uses image analysis, along with ranking algorithms and machine learning, to assess seismic damage in RC exterior beam-column joints. The study identified three key indicators of severe damage in joints: drift ratio, strength, and stiffness. The method uses image analysis to extract features from preprocessed, binary images of cracks. These features capture both the texture and geometry of the cracks. The chosen features, including crack area, aspect ratio, and distribution of line widths, along with structural parameters like geometry and bond index, were selected using F-test and MRMR algorithms. Seismic damage assessments were conducted on 115 images from 37 specimens using four machine learning models (Regression Trees, Support Vector Machine, Gaussian Process Regression, and Gradient Boosting). The study achieved a high R-squared value of 0.80, indicating strong accuracy, for assessing seismic damage based on drift ratio using the image-based method. This demonstrates that image analysis techniques can effectively link surface crack patterns to quantifiable image features, leading to a more precise assessment of seismic damage.

Mechanics guided data-driven model for seismic shear strength of exterior beam-column joints

This study presents an enhanced predictive model for the seismic shear strength of exterior beam-column joints (BCJs). Initially, the principles of strut-and-tie mechanism and variable selection procedures were first utilized to identify the most influential parameters. Subsequently, an evolutionary algorithm, specifically multigene genetic programming (MGGP), was utilized to search for the near-optimal predictive model. The dataset used to develop, train, and test the proposed model was compiled from previously published tests, focusing specifically on cyclically loaded exterior BCJs that encountered shear and flexure -shear failures. The prediction performance of the developed model was assessed through various statistical measures, and then compared with that of other existing models. Additionally, sensitivity analyses were also performed to identify the influence and importance of each design parameter. The results demonstrated that the methodology employed in this study yielded an elegant model that adheres to the underlying mechanics and provides higher prediction accuracy compared to existing models. Furthermore, the sensitivity analyses showed that BCJ shear strength positively correlates with concrete compressive strength, beam reinforcement, joint transverse reinforcement, column intermediate vertical reinforcement, and axial load ratio, while it negatively correlates with the joint aspect ratio. Among these design parameters, beam reinforcement has the greatest influence on the model response, followed by concrete compressive strength. Conversely, column intermediate vertical reinforcement and axial load ratio have the least impact on the model response. The notable prediction capabilities and robustness demonstrated by the developed model render it an efficient design tool with promising potentials for adoption by practicing engineers and for consideration in design guidelines.

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

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

Experimental study on seismic behavior of reinforced concrete exterior beam-column joints under varying axial load

The majority of low-cycle loading tests on reinforced concrete (RC) beam-column joints were currently conducted under constant axial loads. During earthquake shaking, the axial load on the joints fluctuates due to the overturning moment and vertical ground vibration. Particularly in exterior beam-column joints, where beam shear occurs on only one side, the range of axial load variation is significantly larger. To elucidate the impact of varying axial loads on the seismic performance of exterior beam-column joints, low-cycle loading tests were conducted on four groups of full-size beam-column subassemblage specimens. Two identical specimens from each group underwent low-cycle loading tests with constant and varying axial loads, respectively. Based on the experimental findings, this paper examines the differences in cyclic behaviors among comparison specimens, focusing on damage characteristics, joint shear strength, stiffness degradation, displacement ductility, and longitudinal bar slip. The study suggests that compared to specimens subjected to constant axial loads, the comparison specimens exhibit variations in load-carrying capacity corresponding to the fluctuations in axial load. Furthermore, varying axial loads accelerate post-peak stiffness and strength degradation, leading to reduced ductility. Additionally, specimens in one of the comparison groups exhibited different failure models when subjected to varying axial loads and constant axial loads, specifically beam failure and joint failure, respectively. Numerical simulations of the corresponding beam-column subassemblages were conducted on the Opensees platform to elucidate how the two axial loading methods affect the transformation of failure modes. A subsequent parametric study focusing on the axial compression ratio was performed to further explore the impact of varying axial loads on the seismic behavior of beam-column joints.

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

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

Experimental Investigation on Self Curing High Performance Concrete

Proper curing of concrete structures is important to ensure that they meet their intended performance and ductility requirements. Therefore an effective in situ curing is necessary to maximize the degree of hydration and to minimize cracking problems due to drying shrinkage. Traditional external curing could not achieve a desired effect due to very low permeability and high chemical reaction in high-performance concrete. So some researches shifted their attention to self curing, a new curing method that may greatly enhance the curing effect on high performance concrete. Super Absorbent Polymers (SAP) are used as self curing agent. SAPs are a group of polymeric materials that have the ability to absorb and retain a significant amount of liquid from their surroundings and to retain the liquid within their structure without dissolving. In this study investigate experimentally and analytically the behavior of exterior beam-column joint and strength characteristics of Self Curing high performance Concrete (SCC) containing Super Absorbent Polymers (SAP) and Silica Fume. In this investigation SCHPC was made by replacement of cement by 10% of Silica fume and Super Absorbent Polymer (SAP) added at a various range of 0%, 0.2%, 0.3%, and 0.4% of cement. The experimental results were then compared with analytical results obtained from the FEM Analysis using ANSYS 14.0. Load Deflection characteristics, Stiffness, Ductility were studied and it is found that the SCHPC has shown good improvement in load caring capacity. Mechanical characteristics like Compressive strength, Split-tensile strength, Flexural strength and Modulus of Elasticity examined. A mathematical model was conducted using SPSS software for the mechanical characteristics of SCHPC.A comparative study between the results obtained from the laboratory and SPSS has been made. The predicted mathematical model for mechanical characteristics produced accurate results for the respective ages when compared with the experimental results. Also, the durability study for Self cuing concrete after 28 and 56 days curing was done by conducting the tests such as saturated water absorption, porosity, Acid resistance, Sea water resistance, Accelerated electrolytic corrosion and Modified sorptivity.

Behavior of Exterior Beam-Column Joints Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) Against Cyclic Lateral Loads

Behavior of Exterior Beam-Column Joints Steel Fiber Reinforced Self-Compacting Concrete (SFRSCC) Against Cyclic Lateral Loads

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.

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.

Investigation on effect of ECC coverage condition on seismic behavior of beam-column joint

There is a renewed interest around the world to do fundamental research on novel materials to enhance the overall response of structures under seismic loading. Engineered cementitious composite (ECC) is a special class of concrete with good ductility, which is widely adopted in engineering structures. In this paper, the seismic behavior of beam-column joints incorporated with ECC materials is numerically and experimentally investigated. A database containing available related test results in literature is collected and analyzed to investigate the relations between ECC coverage area and failure characteristics. An interior and an exterior beam-column joint with ECC adopted in the joint region are prepared and tested in this study. The effect of ECC coverage area on the overall joint seismic response is analyzed through a validated finite element model. A modified strength hierarchy analysis is proposed and conducted to consider the application of ECC on the joint. Based on the analytical investigation, the weakest structural element in the joint region is found. The strength hierarchy analysis results have a good correlation with the experimental failure pattern, which shows a potential application as a preliminary analysis to evaluate ECC joint failure mechanisms under seismic loading.

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.

Estimating the joint shear strength of exterior beam–column joints using artificial neural networks via experimental results

Estimating the joint shear strength of exterior beam–column joints using artificial neural networks via experimental results

Seismic Performance of Welded Exterior Beam-Column Joint without Stiffeners

Seismic Performance of Welded Exterior Beam-Column Joint without Stiffeners

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.

Beam-column joint modeling effects on the seismic response of a non-ductile reinforced concrete building

Seismic performance evaluation of existing reinforced concrete buildings requires numerical approaches that reflect the damage modes that may arise from deficiencies in beam-column joints. In this study, the seismic performance of an existing reinforced concrete building with four stories was investigated by applying elastic and deformable beam-column joint models. The deformable beam-column joint model was verified using an exterior non-ductile beam-column joint test. The model included a rotational spring located at the joint with two connected nodes in a zero-length with rigid elements in the vicinity of frame elements. Moment- rotation relationships represent the joint behavior, and they were defined based on shear stresses and strains. After effective modeling of beam-column joints, it was aimed to obtain the cyclic behavior of the building model using non-linear time history analysis. For this purpose, scaled earthquake records were applied to the three-dimensional numerical model, and the results were compared in terms of inter-storey drift ratios, column and beam chord rotations, and base shear. It was determined that the exterior beam-column joints reached their strength and deformation capacity, while the beam and columns remained below their section deformation limits according to the Turkish Earthquake Code.

Slab Reinforcement Contributions to Negative Moment Strength of Reinforced Concrete T-Beam with High Strength Steel at Exterior Beam-Column Joints

Previous studies have revealed that the contribution of slab reinforcement to the T-beam flexural strength in negative moment regions are not negligible for the seismic capacity design. An effective slab width (i.e., effective width of flanged section) has been proposed, within which the slab reinforcement needs to be included in the calculation of the beam nominal flexural strength in negative moment regions. These studies mainly focused on the cases using normal-strength steel in moment resisting frames. However, recently high-strength steel has been widely used in reinforced concrete moment resisting frames in high seismic regions to avoid congestion near beam-column joints. The use of high-strength steel may affect the beam stiffness due to the fact that it will require less amount of reinforcement, and result in a different normal stress distribution compared to the case with normal-strength steel. Therefore, this paper investigates the slab reinforcement contribution to the flexural strength of the reinforced concrete T-beam designed with high-strength steel in negative moment regions at exterior beam-column joints, for which nonlinear pushover analyses were conducted. Beam reinforcement grade was considered as a primary parameter with several other design variables including slab thickness, height, and span length of the beam. Analytical results show that the use of high-strength steel can result in a wider effective slab width than the case of normal-strength steel for calculating the beam nominal flexural strength under the negative moment. Based on these results, new design equations were proposed.

An experimental study for effectiveness of steel fibre reinforced exterior beam-column joints under cyclic resistance

An ability of the structure to sustain levels of inelastic deformation, implicit in ductility values, is dependent on the material and detailing used. In order to achieve this high percentage of lateral reinforcement in the core of the joint is needed; which lead to reinforcement congestion and construction difficulties. In this paper, the behaviour of beam-column joint was investigated for different variations in spacing of lateral reinforcement in critical region. This increased spacing of lateral hoops reduced the reinforcement conjunction and addition of steel fibre reinforced concrete (SFRC) for same region help to remove deficiency due to removal of lateral reinforcement. The steel fibre volume fraction of 2% was used in critical region. Test results of six one-third scaled beams-column joints of reinforce concrete frame are presented to study the influence of steel fibres for effective reduction of lateral hoops in joint region. The experimental investigations also incorporate the evaluation of parameters such as ultimate strength, energy dissipation, ductility, stiffness, specific damping capacity and crack patterns. An experimental result demonstrated that SFRC beam-column joint perform satisfactorily and showed enhancement in all above properties. The behaviour of beam-column joint also showed that the additions of fibre in critical region provided necessary confinement and ductility after reduction in lateral hoops.

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.

Seismic performance evaluation and strengthening of RC beam-column joints adopted in Nepal

Beam-column joints are a crucial component of the reinforced concrete (RC) moment-resisting frame (MRF) as the behavior of the joints significantly influences the strength and ductility of the overall framing system. This study is performed to explore the seismic behavior of interior and exterior beam-column joints designed based on NBC 205:1994 (NBC1), NBC 205:2012 (NBC2), and the revised seismic design standard NBC 105:2020, defined as a well-designed joint (NBC3) which are the building standards used for designing low-rise RC buildings in Nepal and compares the results from the numerical simulations quantitatively. Three possible retrofit options (CFRP, steel and RC jacketing) were explored. Finally, retrofitting options were suggested for the joint of NBC1 and NBC2 with consideration of a well-designed joint (NBC3) as the currently required capacity of the joint based on the demand of revised seismic design standard NBC 105:2020.