Full-scale Beam-column Joints Research Articles

Seismic performance of the ST-RC columns to RC beams exterior joint with assembled connection details

An innovative composite column type, the steel tube-reinforced concrete column (ST-RC), consists of a core of concrete-filled steel tube (CFST) and reinforced concrete (RC) encasement. This study aims to validate the reliability of two convenient and rapid assembly methods between RC beams and ST-RC columns. Four full-scale beam-column joint specimens were tested, comprising two prefabricated assembly joints of ST-RC column-RC beam frames, one integrally cast joint of ST-RC column-RC beam frames, and one traditional integrally cast joint of RC column-RC beam frames for comparison. The experiments were conducted based on the principles of a self-balanced system, and quasi-static tests under constant axial compression on the ST-RC columns were performed. Hysteresis curves, skeleton curves, failure modes, strength degradation, energy dissipation capacity, stiffness degradation, deformation capacity and the influence of connection method and joint form on mechanical performance were analyzed and obtained based on the test results. The results indicate that, compared to integral casting, the assembly surrounding method with steel sleeves reduces specimen energy dissipation by 19.8 % and damping ratio by 21 % at 4 % drift, with minimal impact on other mechanical properties. In contrast, reinforcement surrounded and connected by steel plates reduces initial stiffness and peak load-carrying capacity by 1.0 %, along with decreasing negative ductility. It also lowers total energy dissipation by 37.4 % and damping ratio by 45.4 % due to compressive effects from bottom steel plate connections. Despite these effects, its impact on negative ductility and load-carrying capacity remains minimal. Additionally, experimental observations and rebar strain data indicate higher stress on rebars at the base of steel plate connection beams, suggesting a need to strengthen transverse rebars at the beam’s base. The study confirms the feasibility of two convenient and rapid assembly methods for the joints of ST-RC column. Both methods meet current Chinese standards for MCE, with failure modes characterized by “strong columns and weak beams” in both cases.

Seismic behavior and resilience assessment of prefabricated beam–column joint with replaceable graded-yielding energy-dissipating connectors

Conventionally assembled monolithic concrete frame structures achieve structural ductility through beam-end failure, which results in structures that are difficult to repair after an earthquake. To improve the seismic and resilience performance, a prefabricated concrete beam–column joint with replaceable graded-yielding energy-dissipating connectors (RGECs) is introduced. The connectors assembled on the upper and lower sides of the beam end dissipate energy and transfer the beam-end load with the steel hinge device. By adjusting the design bearing-capacity coefficient of RGECs to precast beams, the plasticity and damage of the structure can be centered on the core energy-dissipation bending–shear components (BSCs) and buckling segment (BS) of the RGEC, and the structural function can be quickly recovered by replacing only the damaged RGECs after a seismic disaster. Moreover, compared to the conventional joints, the joint with RGEC can achieve target seismic-performance goals at different seismic-risk levels by designing BSCs and BS with graded yielding. Low-cyclic-loading tests were performed on seven full-scale beam–column joint specimens to investigate the effects of different core energy-dissipating member thicknesses, beam reinforcement ratios and loading protocols on the seismic behavior of the proposed joint. Subsequently, the damaged RGECs were replaced, and the structural-function resilience performance was evaluated in terms of the function-recovery efficiency and quality, indicated by the hysteresis response, strain development, and component energy dissipation. The experimental results proved that the beam–column joint exhibited excellent seismic performance and could realize graded-yielding energy dissipation. The damage to the specimens was concentrated in the RGECs, the key members (beams and columns) were in an elastic state, and the energy dissipation ratio of the RGEC was more than 97 %. This enables the rapid recovery of function after earthquakes. After replacing the RGEC, the hysteresis response, strain development, and component energy dissipation of the specimens were consistent with those of the initial specimens. Compared with the original specimen, the difference in each seismic index of the replaced specimen was less than 10 %. Additionally, the structural function recovered quickly, and the resilient performance was good.

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 evaluation on the seismic performance of high-strength reinforcement beam-column joints with different parameters

This paper reports the results of cyclic load tests and analysis of full-scale beam-column joints using 600 MPa high-strength reinforcement as beam longitudinal reinforcements. The focus was on evaluating the effect of the relative length of beam bars through the joint (hc/d) on the seismic performance of the high-strength reinforcement beam-column joints, while the effects of variables such as axial compression ratio, shear compression ratio, and transverse reinforcement ratio were also discussed. The failure pattern, strength, stiffness, ductility, energy dissipation, and bond performance of each specimen under reciprocal loading were analyzed. The test results showed that applying high-strength steel bars improved the failure pattern, load-bearing capacity, and energy dissipation of the joints. The increase in hc/d improved the bond degradation of the high-strength reinforcement, which positively influenced the seismic performance of the joint. Conversely, high axial compression ratios and high shear compression ratios had a clear negative effect on the bond degradation and failure patterns when high-strength reinforcement used. A proposed equation for adjusting the hc/d in a high-strength reinforcement joint was also presented, which considered the effect of concrete strength and reinforcement strength on the bond performance of beam reinforcement.

Seismic performance of precast column-beam joint with artificial plastic hinge

To improve the seismic performance and repairability of precast structures, an artificial plastic hinge (APH) was proposed for precast beam-column joint. The proposed APH was made from a combination of steel and high-strength-concrete (HSC), and the AHP will dissipates energy through metal plastic deformation when the earthquake occurs. To carry out the research, three full-scale beam-column joints were designed and fabricated, including one cast-in-place joint and two precast joints with APH. By using hysteretic loads, the seismic performance of joint was examined. For more systematic research, the finite element models were established and verified, and the parameter analysis was carried out. The findings demonstrate that the proposed joint performs well in terms of ductility and energy dissipation. It is recommended to use 12 mm steel plate thickness in the actual design, and to ensure the number of connecting bolts to avoid connection damage under earthquake. Through design optimization, the damage to the APH will be revealed at the location of the replaceable steel components, so as to achieve rapid repair after the earthquake.

Experimental study on seismic performance of prefabricated viscoelastic damping bolted joints

Aiming at the defect of insufficient bearing capacity of prefabricated concrete beam-column joint with bolted connection, a prefabricated viscoelastic damping bolted joint (VDBJ) is proposed with good seismic performance. The damping principle is based on that viscoelastic (VE) dampers can provide energy dissipation and additional stiffness for the structures. Three full-scale beam-column joint specimens were designed, including one cast-in-place joint specimen, one prefabricated bolted joint specimen without VE dampers and one prefabricated bolted joint specimen with VE dampers. Since the viscoelastic damper is a passive energy dissipation device with velocity correlation, comparison and analysis of three specimens under high-frequency cyclic loading are performed on the failure modes and seismic performance indexes such as hysteretic energy dissipation, displacement ductility, stiffness degradation and ultimate bearing capacity. The analysis of the test results indicate that the proposed prefabricated viscoelastic damping bolted joint has stronger ultimate bearing capacity and displacement ductility than the cast-in-place joint. The arrangement of VE dampers effectively controls the appearance and expansion of concrete cracks, which not only achieves the expected effect of shock absorption and energy dissipation, but also can realizes the rapid replacement of components after the earthquakes.

Joint strengthening by external bars on RC beam-column joints

Column strengthening is a very common practice for improving the seismic performance of reinforced concrete frame structures or repairing damage after a seismic event. Several methods are employed for column strengthening, which can improve column strength by preventing its shear, bending or compression failure. However, not all methods allow column strengthening connections between adjacent floors, thus the beam-column joint strength could be limited by the column-joint interface capacity. This work aimed to analyse two joint strengthening designs, for which an experimental campaign of eight full-scale beam-column joints strengthened with steel caging, and subjected to cyclic and gravity loads, was carried out. As access to joint panels is very complex in existing structures, joint strengthening consists of external solutions: vertical or diagonal bars and capitals connecting columns. The results showed that these techniques significantly increased beam-column joint strength and highlighted that failure can be undesirably transferred to the joint. Vertical bars prevented the bending failure of the column-joint interface, but failure occurred at the joint in this study. Diagonal bars can also prevent joint failure.

Effect of slab and transverse beam on the FRP retrofit effectiveness for existing reinforced concrete structures under seismic loading

The seismic behaviour of reinforced concrete (RC) structures is critically influenced by the complex mechanical interactions at beam-column joints. To ensure the desired hierarchy of failure is achieved when retrofitting existing structures, numerical and experimental assessments need to represent realistic structures. A review of published literature indicates that most experimental work on the seismic behaviour pre-1970′s RC beam-column connections considers sub-assemblies without slabs or transverse beams, which are unrepresentative of reality. To evaluate the effect of these elements on the failure mechanism, retrofit need and retrofit effectiveness, experiments on four full-scale beam-column joints are carried out. Two specimens with and without slab and transverse beams, are tested in their as-built and FRP strengthened configurations. As expected, the experimental results demonstrate that the progression of damage and failure mechanisms differ significantly when slabs and transverse beams are present, confirming previous numerical and experimental evidence on the strong contribution of these elements on the overall joint behaviour. Moreover, a significantly higher retrofit effectiveness is observed for the specimen without slab and transverse beam. This implies that experiments on retrofitted joints without slab and transverse beam can lead to a focus on joint shear strengthening alone as they inadequately represent the hierarchy of strengths of the framing members. They can also lead to an overestimation of retrofit effectiveness. These observations have implications when considering common simplifying assumptions made in the numerical modelling of RC moment resisting frames when assessing their seismic performance.

Composite steel beam is commonly used element in multistory steel buildings today. The composite action between the concrete deck and the steel beam reduces both steel weight and deflection, accordingly, enhance floor economy and serviceability. Many earlier researches were carried out to optimize the design of the composite steel beams under both static loading and dynamic behavior. None of these

In many situations, it is necessary to have a beam web opening in the plastic hinge location. However, very limited studies investigated the behavior of reinforced concrete (RC) beam-column joints with nearby beam web openings. A previous study was conducted for investigating the behavior of beam-column joints with unreinforced nearby web opening. In this study, the effect of adding additional reinforcing around a nearby web opening on the seismic behavior of RC exterior Beam-Column joints is being investigated. Nine full-scale beam-column joints were tested, four joints had an unreinforced opening, while five joints had reinforced opening. The behavior of the beam-column joints is described in terms of maximum resisting load, deflection, energy dissipated, and stiffness degradation. The behavior was significantly affected by the nearby opening. The increase in opening width and the reduction in the distance between the opening and the column resulted in decreasing the strength and ductility of the RC beam-column joint. However, adding additional reinforcement improved the behavior. Thus, it is recommended to provide additional reinforcement all around the opening.

In many situations, it is necessary to have a beam web opening in the plastic hinge location. However, very limited studies investigated the behavior of reinforced concrete (RC) beam-column joints with nearby beam web openings. A previous study was conducted for investigating the behavior of beam-column joints with unreinforced nearby web opening. In this study, the effect of adding additional

the paper presents an efficient scheme for a Nonlinear PID (NPID) controller to improve the dynamic response of the Electric Vehicle (EV). The objective of the proposed controller is to track accurately the reference speed selected by the driver of the EV. A MATLAB/Simulink model is established and validated for the considered EV to study the system performance. The proposed NPID controller has been investigated by comparing it with the traditional PID controller. The optimal parameters of Both the NPID and PID controllers were obtained using the Harmony Search (HS) optimization technique based on a cost function. The desired rise time, settling time, steady-state error, and overshoot have been taken into account in the cost function. Two tests were performed, the first test was implemented at fixed reference speed while the second one was carried out at a staircase command of reference speed. The simulation results can be summarized as follows: in the first test, the NPID controller reaches the steady-state speed at 38.12 seconds while the PID controller stabilizes at 44.68 seconds. Moreover, the NPID controller has a 0.5% steady-state error however, the PID controller has a 4% steady-state error. Besides, the second test shows that the NPID controller can decrease the root mean square of error by 30.1% compared to the PID controller. Lastly, the proposed NPID controller can enhance EV performance significantly.

Analysis of slab action on the seismic behavior of external RC beam-column joints

The correct evaluation of beam flexure capacity is of paramount importance in the capacity design process of reinforced concrete (RC) frame structures. Even though few experimental studies on beam-column joints have considered the presence of slab, its action as a tension flange in modifying beam-column strength hierarchy has been clearly found. This is mainly due to the increased hogging moment capacity of beams. Nevertheless, European and Italian seismic codes do not explicitly consider slab action as tension flange nor indicate proper values for effective slab width.To better understand this action, an accurate 3D finite element model has been calibrated based on the results of past experimental tests carried out on a full-scale beam-column joint. Afterwards, the calibrated model has been equipped with a portion of the adjacent spandrel beam and slab in order to evaluate their effect on the beam-column connection's behavior through numerical analyses. Alike previous studies, numerical results show that the tension flange effect of slab can significantly increase hogging (negative) moment in beams framing into beam-column joints. Additionally, it has been found that this effect is a function of slab steel amount, also highlighting the role of slab reinforcement orthogonal to the beam. Based on the above, practical indications have been provided for the evaluation of hogging moment in beams specifically concerning effective slab width to be considered in resisting moment calculations as a function of slab steel amount.

Bond strength of confined normal strength concrete beam-column joints

The article presents the results of a research study that was conducted at the American University of Beirut (AUB) on the effect of transverse reinforcement crossing the critical hooked bars region of normal strength concrete (NSC) beam-column joints on the bond strength and ductility of the mode of failure of the hooked bars. Nine full-scale beam-column joint specimens were tested. The specimen simulated the rigid connection of a cantilever vertical beam to a base column. The load was applied near the tip of the beam while the column was fixed to the strong floor. The tensile beam bars were anchored in the column using hooked-bar anchorages. In previous research, confinement to the joint was provided either by carbon fiber reinforced polymer (CFRP) sheets externally confining the joint or steel fibers incorporated in the concrete mix. Results revealed that the transverse reinforcement crossing the hooked bars region was effective in increasing the anchorage capacity and the ductility of the load-deflection history of the specimens. Correlation of the effects of the three different confinement modes is presented.

Cyclic response analysis of high-strength self-compacting concrete beam-column joints

In this paper, finite element analysis software “DIANA” is implemented to simulate quasi-static cyclic loading test results of three full-scale beam-column joints cast with high-strength self-compacting concrete (HSSCC). The specimens were designed according to the New Zealand concrete standard (NZS3101 2006). Material models for concrete and steel were calibrated based on the physical characteristics of the materials derived either from laboratory tests or using expressions available in literature. Two-dimensional curved-shell elements were used in modelling the specimens. As the specimens were designed following the code requirements for seismic actions, bond between the reinforcement and concrete was assumed as perfect. In order to obtain a more representative prediction, both the longitudinal and transverse reinforcement were modelled in their actual locations. Pushover analyses were first conducted to check the mesh sensitivity; after which the modelled specimens were subjected to reversed cyclic loading histories applied in the experimental tests. Seismically important response parameters such as damping, stiffness, concrete and steel contributions in the joint shear resistance, joint shear deformation, strain development in the joint stirrups, elongation of the plastic hinge zone, development of compressive stress, and cracking pattern were extracted from the analytical predictions and compared to the experimental results. It was found that the adopted modelling and analysis approach was capable of predicting cyclic performance of HSSCC beam-column subassemblies with reasonable accuracy.

Modelling beam-column joints and FRP strengthening in the seismic performance assessment of RC existing frames

The recent seismic events demonstrated that the high vulnerability of existing RC structures is often related to the joint subassemblies shear failure which may lead to the collapse of the entire structural system. However, most of the available computer programs do not properly account for this aspect. This paper deals with the numerical seismic assessment of RC structural systems designed without proper seismic details in the joint panel and the benefits of the FRP local strengthening. A new modelling strategy has been developed to account for the joint nonlinear behaviour and the fiber reinforced polymer (FRP) strengthening in the finite element method (FEM). Several case studies were selected for the model validation. At the subassembly level, the model predictions were compared with recent experimental tests on full-scale beam-column joints with and without FRP strengthening. At the structure level, a case study building damaged in the joints during the L’Aquila earthquake and then retrofitted with FRP systems was analyzed. The predicted structural performances and structural damages were compared with observational data. Furthermore, the benefits of the joint FRP strengthening on the global seismic performances were numerically assessed.

Influence of Axial Load on the Seismic Behavior of RC Beam-Column Joints with Wide Beam

Beam-column joints can play a key role on the seismic behavior of reinforced concrete buildings. Until now studies and experimental investigations on this topic have been mainly focused on beam-column joints with stiff beams, i.e. beams with height larger than the thickness of the adjacent floor slab. However, especially in the European residential building stock, frame structures are often equipped with wide - therefore rather flexible - beams. However, not many studies have been devoted so far to this type of connection, therefore an experimental investigation on full scale beam-column joints with wide beam was planned at the University of Basilicata and is currently in progress. In the present paper the main results of two cyclic tests are reported and discussed specifically analyzing the role of the axial load applied to the column on the joint performances and damage mechanisms. Test results highlights that the axial load value has a significant influence of on deformation capacity and ductility behavior.

Seismic Tests on RC Building Exterior Joints with Wide Beams

Reliable assessment procedures of existing RC buildings are currently available, and have been introduced in the Italian and European codes reporting new rules for seismic analysis. However, further studies are required in order to further improve such procedures and, specifically, obtain more accurate data on the behavior of beam-column joints, whose role on the global behavior of framed RC buildings can be crucial. Until now studies on this issue have been mainly devoted to joint specimens with stiff beams, however frame structures having wide (also called flexible or flat) beams are widely used in the European residential building stock. To this purpose, given the lack of knowledge, an experimental investigation on full scale beam-column joints with wide beam has been planned and is currently in progress. In the present paper the main results of three tests are reported and discussed. The role of different earthquake resistant design levels on joint performances is pointed out.

Nonlinear Analysis of Full-Scale Beam-Column Joints of RC Frames

In order to research on seismic performance of full-scale beam-column joints of RC frames under low cyclic loading, finite element software ABAQUS is used to nonlinear analysis. Analysis results show that: the process of load carrying and fracture development of beam-column joints are simulated using concrete damage plasticity model; nonlinear finite element method is easy to obtain stress-strain relationship; and can effective analyses the complex mechanical behavior of core areas of joints.

Nonlinear Analysis of Full-Scale Beam-Column Joints of RC Frames

In order to research on seismic performance of full-scale beam-column joints of RC frames under low cyclic loading, finite element software ABAQUS is used to nonlinear analysis. Analysis results show that: the process of load carrying and fracture development of beam-column joints are simulated using concrete damage plasticity model; nonlinear finite element method is easy to obtain stress-strain relationship; and can effective analyses the complex mechanical behavior of core areas of joints.

Análise comparativa do comportamento cíclico de nós viga-pilar com armadura lisa e nervurada

Da observação dos danos provocados por diversos sismos recentes, verifica-se que o escorregamento aço-betão é uma das principais causas de dano e colapso de edifícios existentes de betão armado. Em muitos países, este fenómeno assume particular importância nos edifícios construídos até aos anos 70, com armadura lisa e anteriormente à introdução dos primeiros regulamentos que contemplam a acção sísmica com maior detalhe. Este tipo de estruturas apresenta, geralmente, pormenorização deficiente da armadura, fracas condições de aderência e confinamento inadequado do betão. As ligações viga-pilar nas estruturas de betão armado são pontos onde ocorrem danos significativos quando as estruturas estão sujeitas a carregamentos cíclicos, uma vez que nestas zonas ocorre a maior concentração de esforços. O fenómeno do escorregamento assume particular relevância nas ligações viga-pilar, devido aos maiores esforços que aqui se desenvolvem mas também ao facto de nestas zonas se realizar tipicamente a ancoragem dos varões longitudinais dos pilares e/ou vigas. Neste artigo são apresentados os principais resultados dos ensaios cíclicos de dois nós viga-pilar à escala real com igual geometria e igual pormenorização da armadura, representativos de nós interiores de edifícios de betão armado construídos até meados dos anos 70 sem pormenorização adequada para fazer face à acção sísmica. Um dos nós foi construído com armadura lisa (com fracas condições de aderência) e o outro nó com armadura nervurada (com boas condições de aderência). Faz-se também a comparação dos resultados obtidos para compreender a influência das condições de aderência na resposta cíclica de nós interiores viga-pilar deste tipo de estruturas de betão armado. Dos resultados obtidos, conclui-se que o fenómeno do escorregamento condiciona significativamente o desempenho das estruturas com armadura lisa quando solicitadas por acções cíclicas.

Damage characterization of beam-column joints reinforced with GFRP under reversed cyclic loading

The use of fiber reinforced polymer (FRP) reinforcement in concrete structures has been on the rise due to its advantages over conventional steel reinforcement such as corrosion. Reinforcing steel corrosion has been the primary cause of deterioration of reinforced concrete (RC) structures, resulting in tremendous annual repair costs. One application of FRP reinforcement to be further explored is its use in RC frames. Nonetheless, due to FRP's inherently elastic behavior, FRP-reinforced (FRP-RC) members exhibit low ductility and energy dissipation as well as different damage mechanisms. Furthermore, current design standards for FRP-RC structures do not address seismic design in which the beam-column joint is a key issue. During an earthquake, the safety of beam-column joints is essential to the whole structure integrity. Thus, research is needed to gain better understanding of the behavior of FRP-RC structures and their damage mechanisms under seismic loading. In this study, two full-scale beam-column joint specimens reinforced with steel and GFRP configurations were tested under quasi-static loading. The control steel-reinforced specimen was detailed according to current design code provisions. The GFRP-RC specimen was detailed in a similar scheme. The damage in the two specimens is characterized to compare their performance under simulated seismic loading.