External Beam-column Joints Research Articles

Minimally Invasive FRP Strengthening of External Beam–Column Joints

Minimally Invasive FRP Strengthening of External Beam–Column Joints

Seismic performance of HECC/RC beam–column external joint with no stirrup and reduced anchorage length in core region

In this paper, steel–polyethylene hybrid fiber-reinforced strain-hardening cementitious composites (HECC) are applied in beam–column external joint core region to form a novel HECC/reinforced concrete (RC) composite beam–column joint with reduced anchorage length of beam longitudinal rebar and eliminated transverse rebar, and thus to alleviate rebar congestion and simplify the construction process efficiently especially for precast RC frame structures. Five external beam–column joint specimens are constructed and tested under cyclic loading to illustrate the influences of the anchorage length of beam longitudinal rebar and longitudinal rebar ratio on the seismic performance of beam–column joint. The effects of design parameters on seismic performance, including hysteresis behavior, degradation of strength, energy dissipation capacity, and cracking patterns are discussed in detail. Experimental results indicate that the replacement of normal concrete with HECC in beam–column joint core region could apparently reduce the amount of stirrups in the joint core area while maintaining reliable seismic behavior. Remarkably, specimen with no stirrups in the core area exhibits nearly equivalent seismic behavior to that of the control RC specimen. Furthermore, the application of HECC in joint core area allows for a substantial reduction of the required anchorage length for the beam longitudinal rebar to 9d, which further simplifies the construction process considerably.

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.

Effect of silica fume on Pullout capacity and corrosion resistance of hook bars in the external beam-column concrete joint

Purpose This study aims to determine the effect of replacing a portion of the cement in the concrete mixture with silica fume (SF) on the corrosion resistance of reinforcing bars, the compressive strength of concrete and the tensile strength of hook bars in both corroded and non-corroded external joints of structures. The external beam-column connection was studied because of its critical role in maintaining structural continuity in all three directions and providing resistance to rotation. Design/methodology/approach In external concrete joints, the bars at the end of the beams are often bent at 90° to form hooks that embed in columns. Owing to the importance of embedding distance and the need to understand its susceptibility to corrosion damage from chloride attack, a series of experiments were conducted on 12 specimens that accurately simulate real-site conditions in terms of dimensions, reinforcement and hook bars. SF was replaced with 10% and 15% of the weight of cement in the concrete mixture. To simulate corrosion, the specimens were subjected to accelerated corrosion in the laboratory by applying a low continuous current of 0.35 mA for 58 days. Findings The results revealed the effect of SF in improving the compressive strength of concrete, the pullout resistance of the hook bars and the corrosion resistance. In addition, it showed an apparent effect of the corrosion of reinforcing bars in reducing the bonding strength of hook bars with concrete and the effect of SF in improving this strength. Originality/value It was noted that the improvement of the results, achieved by replacing 10% of the weight of cement with SF, was significantly close to the results obtained by replacing 15% of the SF. It is recommended that an SF ratio of 10% be adopted to achieve the greatest economic savings.

Behaviour and design of monotonically loaded reinforced concrete external beam-column joints

This paper describes an experimental investigation into the influence of beam reinforcement detailing, column axial load and shear reinforcement on the joint shear strength of reinforced concrete external beam-column connections. A series of twelve external beam-column joint specimens were tested in three groups of four specimens. Series 1 investigated the influence of beam reinforcement anchorage type and bend radius. Series 2 studied the influence of column axial load on joint shear strength while series 3 studied the influence of intermediate column bars and joint shear reinforcement. The paper presents the experimental results and describes the influence of the considered variables on joint shear strength. Three existing empirical design equations for external beam-column are evaluated using data from this program and previously tested beam-column joint specimens. Finally, design recommendations are made.

Experimental Analysis of the Effectiveness of Pre-Stressed Steel Strips for the Strengthening of Beam-Column Joints in Existing RC Buildings

Beam-column joints in existing Reinforced Concrete (RC) buildings are usually characterized by the absence of transverse reinforcement. The observation of post-earthquake damage, as well as several numerical and experimental studies, have soundly demonstrated the possible impact of the response of unreinforced joints on the damage – up to collapse – of existing RC buildings under seismic action. In this study, a possible strengthening approach for these elements, based on CAM® technology, is investigated through experimental tests. The results of these tests are reported, along with the results of a previous experimental campaign carried out on the same topic. Full-scale external beam-column joint specimens are tested, with and without strengthening, and with different characteristics in terms of amount of beam longitudinal reinforcement and concrete compressive strength. Different failure modes are observed for the as-built specimens (joint failure without (J) or after (BJ) beam flexural yielding). The effectiveness of the adopted strengthening approach is demonstrated, observing an increase in joint shear strength and subassemblage ductility and – unless a joint failure in compression occurs – a possible modification of the failure mode into a ductile, flexure-controlled response of the subassemblage, as for code-compliant beam-column joints.

Seismic retrofit of severely damaged beam-column RC joints using HPFRCC

The purpose of this paper is to use high performance fiber reinforced cement composites materials (HPFRCC) in seismic repair and retrofit of the concrete exterior beams-column joints without special seismic details with severe damage, considering the effect of slab and transverse beam. For this purpose, four external beam-column joints with scale ½ have been subjected to cyclic loading. Initially, two original joints without special seismic details suffered severe damage, which led to shear failure due to unconfinement and slip of beam rebars in the core. Then the damaged joints were repaired using HPFRCC materials and a similar load history was applied to the repaired specimens. The cyclic behavior of repaired joints was evaluated with the behavior of original specimens and the results were presented in the form of load bearing capacity, stiffness degradation, ductility, and dissipated energy. The results show that the use of HPFRCC materials in the joint core area of the repaired specimens has resulted in better confinement and integrity of the longitudinal rebars of the beam and column and in addition, has caused the flexural plastic hinge in the beam. This mechanism has improved the cyclic behavior and significantly increased the bearing capacity, energy dissipation and ductility in the repaired specimens.

Retrofit of External Beam-Column Concrete Joints with Diagonally Crossed Reinforcement: Experimental and Analytical Investigations

AbstractExperimental research was carried out regarding the flexural behavior under cyclic reversal loading of six full-scale external beam-column concrete joints cast with plain concrete in the pr...

Novel Ductile Enhancement in the Structural Characteristics of External Beam Column Joint with Potassium-Activated Green Concrete Technology

Ductility and energy dissipation capacity of the beam column joints are the two prominent characteristics which govern the stability of the entire structure constructed in the seismic prone areas. In this paper, the effect of potassium-activated geopolymer concrete in the exterior beam column joint application is investigated under low frequency cyclic loading. Numerical analysis has been done by using the finite element software Abaqus and compared with the experimental work. From the load deformation relationship, parametric studies are carried out in the aspects of ductility, stiffness degradation, energy dissipation capacity, drift ratio and cracking pattern. The use of potassium-activated geopolymer technology in the exterior beam column joint application resulted in the improved ductility, energy dissipation capacity with superior ultimate load carrying capacity of 1.05% over conventional cement reinforced concrete beam column joints with special confining reinforcement confirmed by IS 13920 due to the enormous polymerization activated by high molecular potassium ions. There is an improved energy dissipation capacity of 2.78% of potassium-based geopolymer specimen resulting in lesser number of non-structural cracks and 11.26% more deformation under 11.96% enlarged drift ratio than the conventional reinforced concrete specimen. From the observed results, it is clearly noted that the implementation of potassium-activated green polymer technology in the beam column joints possessed enhanced ductility characteristics to protect the structure susceptible to seismic environment and resulted in innovative, economical and sustainable mode of seismic-resistant building construction.

Strengthening of RC beam-column joints using steel plate with shear connectors: Experimental investigation

This paper presents experimental analyses on beam-column joints strengthened with steel plate & steel plate with shear connectors subassemblies subjected to cyclic loading. For the investigation, a total of six reduced-scale external beam-column joints were cast. Two specimens with individual closed stirrups are used as the reference models. Among the remaining, two specimens were strengthened with steel plates and two specimens were retrofitted with steel plates and shear connectors. The reinforced beam-column subassemblies were subjected to cyclic tests to determine their crack propagation and resistance capability during seismic excitations. The primary objectives of the analyses have been to monitor the seismic performance of the joints in terms of load–displacement pattern, hysteresis behavior, failure pattern, and energy dissipation capability. In addition, some experiments were carried out to differentiate and evaluate the efficiency of conventionally closed stirrups. The results are inspiring as the steel plate with shear connectors outperformed the traditional stirrups in terms of lateral strength, stiffness, and accumulated energy dissipation. The results indicated that the proposed methodology can be used as a feasible and adequate technique to improve the seismic resilience of RC structures in regions of high seismicity.

Behaviour of steel fibers reinforced exterior beam-column joint using headed bars under reverse cyclic loading

Fiber-reinforced cementitious composites have been increasingly used during recent years on beam-column joints and the introduction of headed bars is a practical solution to eliminate the congestion problem caused by hooked bars in beam-column joints. The present study emphasizes the evaluation of the performance of steel fiber reinforced concrete (SFRC) external beam-column joints (BCJ) using headed bars as an anchorage mechanism and the comparison has been made with the conventional bars which have been detailed in accordance with ACI 318-19 and ACI 352R-02. The repository of previous BCJ work has been further expanded by researching the effect of structural parameters i.e. compressive strength (C20 and C40) and steel fibers (1 and 1.5%) on the hysteresis curve, ductility, stiffness, energy dissipation, and cracking on all specimens. The experimental results have revealed that the headed bars can be significantly replaced by the conventional bars for the areas vulnerable to earthquakes due to their higher load carrying capacity with better ductility and stiffness response and reducing congestion in BCJ.

Hysteretic performance of reinforced concrete external beam-column joint subassemblies using non-conventional diagonal bars

The performance of beam-column joints in reinforced concrete (RC) framed structures have long been recognized as a significant factor that affects the overall response of structure subjected to cyclic loads. The reversal of forces in beam-column joints during earthquakes may cause distress and often failure, when not designed and detailed properly. Thepresentworkaimstostudythe seismic performanceofexteriorbeam column joint with non-conventionalreinforcement detailing. Four one third scaled beam-column joint sub assemblages were tested under reverse cyclic loading applied at beam end.The specimens have been looked after into two groups based on the joint reinforcement detailing. The first group of two specimens (Group-I) comprises of joint assemblages having joint detailing as detailed in construction code of practice in India i.e. IS 456:2000. The second group (Group-II) consists of two specimens, one of the specimens having additional cross bracing reinforcements for the joint detailed as per IS 456:2000 and another specimen having diagonal bars in form of development length. Here comparison between conventional and non-conventional type reinforcement has been done to study its effect on strengthening of joint. The experimental results and findings indicate that additional cross bracing reinforcements improves the seismic performance.

Experimental investigation on rcc external beam-column joints retrofitted with basalt textile fabric under static loading

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. Large numbers of retrofitting techniques are being adopted worldwide to strengthen the beam-column joint. This paper presents the results of the first phase of experimental investigation on retrofitting of an external beam-column joint by externally bonded basalt fabrics. Eleven specimens of external beam-column joints using strong column-weak beam concept were prepared and tested under static loading conditions. Three specimens were tested and considered as control specimens. Remaining eight specimens were subjected to an induced damage by preloading them up to 50% of ultimate load recorded in control specimens. The damaged specimens were then retrofitted with basalt fiber fabric adopting four different configurations. The retrofitted specimens were tested for their ultimate capacity and the outputs were compared with that of the control specimens. The test results show that basalt textile reinforcement enhances the performance of the retrofitted specimens.

Anchorage strength development of headed bars in HSRC external beam-column joints considering side-face blowout failure under monotonic loading

As the use of headed bars in reinforced concrete (RC) beam or column members has increased in recent years, preventing their unexpected failure modes has become an increasingly important part of their design. Headed bars that are embedded in concrete under tensile loading have six potential failure mechanisms, one of the critical failure modes is side-face blowout failure (SBF). Since the selected existing models of anchorage strength related to SBF for a headed bar were developed based on specimens with normal-strength reinforced concrete, they should be experimentally verified to investigate their application to high-strength reinforced concrete (HSRC) members. Therefore, in this work, HSRC external beam-column joints are designed based on the results of a parametric study and ACI 318-14. Based on the experiment (12 full-scale specimens) and results of simulations using finite-element analysis (FEA), when the diameter of a headed bar that is embedded in HSRC external beam-column joints is ≤ 35 mm, its minimal clear concrete cover could be reduced to be the diameter multiplied by 1.5. Additionally, with the diameter or yield strength increasing, this work also provides the engineering graphs for designing headed bars in HSRC external beam-column joints to prevent SBF before the bar yielding.

Evaluation of efficacy of basalt textile fabric on retrofitting of damaged reinforced concrete external beam–column joints

Beam–column joints are crucial elements in reinforced concrete framed structures. These are prone to failure during seismic action and may result in structural collapse. In this context, retrofitting of joint demands a deep attention. This paper presents the results of numerical investigation of retrofitting of an external beam–column joint by externally bonded basalt fabrics using ANSYS along with experimental findings. An external beam–column joint using strong column-weak beam concept was modeled by using appropriate elements available in ANSYS. Three specimens of the joint were experimentally investigated and tested under simulated static loading condition. These were considered as control specimens. Based on the results, the deformations corresponding to a load level equivalent to 60% of average ultimate load were simulated to a new model which was considered as a damaged specimen. By using another suitable element available in ANSYS, the retrofitting using basalt fabric was simulated in the new model in four different configurations and their behavior was analyzed. Two specimens each were experimentally studied. The numerical investigation results show that basalt textile reinforcement enhances the performance of the retrofitted specimens and the results arrived from ANSYS showed good agreement with experimental results.

Application of HPFRCC in beam–column joints to reduce transverse reinforcements

In this paper, in order to prevent the congestion of transverse reinforcements in beam-column joints of reinforced concrete frames which meet special seismic regulations, high-performance fiber reinforced cement composites (HPFRCC) with a combination of double hooked-end steel fibers and steel microfibers were used.For this purpose, four external beam-column joints were constructed to a scale of 1/2 and the specimens were tested under cyclic loading.The tested specimens include a normal concrete one meeting special seismic regulations as the control specimen and three HPFRCC ones made by reducing the transverse reinforcement in the beam and column. Hysteresis behavior, load-carrying capacity, energy dissipation and cracking patterns were analyzed and compared with the cyclic response of the control specimen for all experimental specimens. The test results indicate that the HPFRCC specimens, in comparison with the control specimen, have higher stiffness, load-carrying capacity and energy dissipation. Moreover, HPFRCC joints show a better damage tolerance capacity than the control specimen at higher drifts. Furthermore, the results of this study indicate that the use of HPFRCC in joint can be a proper strategy for increasing shear capacity and reducing the amount of beam and column transverse reinforcements.

A Study on Behavior of Headed Bars Made of Fiber-Reinforced Polymers in Rcc Exterior Beam Column Joints

Seismic pressures on a reinforced concrete moment-resisting structure are known to create critical and essential regions at the reinforced beam-column joints. Beam-column junctions are a microcosm of the whole structure, therefore brittle behavior at these points predicts brittle action. Ductile behavior at beam-column joints predicts ductile action. Under the influence of seismic forces, the joints between RC beams and columns are exposed to high shear stresses. Learn more about the performance of fiber-reinforced polymer headed bars in rcc external beam column joints in this publication.

Experimental evaluation of external beam-column joints reinforced by deformed and plain bar

In this study, the behavior of external beam-column joints reinforced by plain and deformed bars with non-seismic reinforcement details is investigated and compared. The beam-column joints represented in this study include a benchmark specimen by seismic details in accordance with ACI 318M-11 requirements and four other deficient specimens. The main defects of the non-seismic beam–column joints included use of plain bar, absence of transverse steel hoops, and the anchorage condition of longitudinal reinforcements. The experimental results indicate that using of plain bars in non-seismic beam-column joints has significantly affected the failure modes. The main failure mode of the non-seismic beam-column joints reinforced by deformed bars was the accumulation of shear cracks in the joint region, while the failure mode of the non-seismic beam-column joints reinforced by plain bars was deep cracks at the joint face and intersection of beam and column and there was only miner diagonal shear cracking at the joint region. In the other way, use of plain bars for reinforcing concrete can cause the behavior of the substructure to be controlled by slip of the beam longitudinal bars. The experimental results show that the ductility of non-seismic beam-column joints reinforced by plain bars has not decreased compared to the beam-column joints reinforced by deformed bars due to lack of mechanical interlock between plain bars and concrete. Also it can be seen a little increase in ductility of substructure due to existence of hooks at the end of the development length of the bars.

Numerical Evaluation of the Steel Plate Energy Absorption Device (SPEAD) for Seismic Strengthening of RC Frame Structures

In this paper, a new strengthening technique is proposed: the Steel Plate Energy Absorption Device (SPEAD) system, which is intended to increase the flexural strength of beam and column members in RC frame structures. In this way, while permitting calibration of the strength increase in the beam to comply with the strength hierarchy criteria needed for a proper seismic behaviour it can provide additional energy absorption. A numerical evaluation of the SPEAD system is carried out by means of a refined 3D model built with an advanced nonlinear finite element program. The SPEAD system has been virtually applied (through finite element analyses) to an RC external beam–column joint, representative of typical existing RC buildings, and the numerical results are compared to those of a specimen that was not upgraded and subjected to the same experimental tests. The SPEAD upgraded model provided a strength increment of about 50% with also a strong reduction of bond-slip effects in the joint panel region. This latter, in turn, provided a beneficial increase of ductility. Based on the positive results from numerical simulations, a design method is also provided.

Behavior of Monotonic Loading for Glass Fibre based High Performance Concrete in External Beam-Column Joint using ANSYS. Analysis

Strength, ductility of structures differ primarily on appropriate detailing of. beam column joints need a vital role in the structural reliability of the structures given with appropriate stiffness and ultimate strength to maintain the loads transmitted from beam and column. Beam column joints defined as the reinforced concrete buildings, in which portion of columns and beams having their intersections. Although these forces greater than these are affected during earthquakes, joints are relentlessly damaged. As far as earthquake is affected, research on beam-column joint is essential. In HPC, these materials with admixtures are meticulously designated and proportioned to produce very high early, ultimate strengths and durability away from conventional concrete. The admixtures like flyash, silicafume, ground granulated blast furnace slag (GGBFS), which are combined with its strength and durability and boost its marketability as a natural friendly product. The most important purpose of the present study is to investigate the performance of high performance reinforced beam-column joints (replacement of cement with GGBFS). Ground granulated blast furnace GGBFS is employed as a partial replacement of cement with glass fibre and super plasticizer is applied to accomplish required workability. In this study, a evaluation of control specimen and specimen of beam column joint with 7.5% GGBFS and 0.3% glass fibre replacement intended as per IS 456:2000 and IS 13920:2016. Also, to ascertain the performance of beam-column joints subjected to monotonic loading for high performance concrete employing with Ground Granulated Blast Furnace Slag (GGBFS) and glass fibre.