Exterior Beam-column Joints Research Articles

A Review-Behavior of Reinforced Concrete Exterior Beam-Column Connections under Cyclic Loading

In many seismically active regions worldwide, massive reinforced concrete (RC) structures built before the 1970s existed. These older RC buildings, in countries having seismic history, were designed for gravity loads only. Anyway, the beam-column connections influence the structures where the functions of connection shortage by transport the forces like shear, moment, and torsion through the beam to the column. Also, it could behave in a ductile manner to help the structure resist the seismic, as simulate the seismic loading by high and low cyclic loading. Due to the failure of external joints more than the internal beam-column joints, this review focuses on the behavior of exterior beam-column joints under cyclic loading, consequently simulated the behavior under an earthquake and the reinforcement detailed.

Quasi-static cyclic performance of RC exterior beam-column joint assemblages strengthened with geosynthetic materials

The beam-column joints are the most critical and vulnerable part of the RC framed structures when subjected to earthquake load. The objective of the present study is to investigate the cyclic behaviour of seismic and non-seismic exterior reinforced concrete (RC) beam-column joints strengthened with innovative polymeric based geosynthetic materials. Two variants of geosynthetic material named geogrid and geotextile were used for strengthening the beam-column joints in the experimental program. In this strengthening protocol, two different types of strengthening patterns were used in which one was horizontal U-shaped pattern, and the other one was the diagonal cross (X-shaped) pattern. All the beam-column specimens were tested under the quasi-static cyclic loading with controlled amplitude to explore the cyclic performance on the parameters such as failure modes, hysteresis loops, load-deformation envelope curves, ductility, energy dissipation capacity, stiffness and strength degradation behaviour, pinching width ratio, damage index and joint distortion. The test results showed that the adopted strengthening schemes with geotextile and geogrid materials could successfully alter the failure of beam-column joints from shear to flexural and improved the ductile behaviour of the strengthened specimens. The load-carrying capacity and ductility-factor of the geosynthetic strengthened specimens significantly increased up to 48.4% and 37.8%, respectively when compared to the non-seismic control specimen, and it was highest in geogrid strengthened BCJs, especially in diagonal X-shape bonded specimen. The significant increment of energy dissipation capacity was also observed as 2.08 to 3.73 times for the strengthened specimens. Furthermore, the post-elastic performance and the joint shear strength of strengthened RC beam-column joints was also improved in comparison to the non-seismic control specimen. In addition, an analytical study was carried out to predict the shear strength contributions of externally bonded strengthening materials in the RC beam-column joint, which was compared with experimental findings. A good agreement was observed between the analytical and experimental results. Hence, the experimental and analytical study of the strengthened beam-column joints using geotextile and geogrid have confirmed that the appropriate bonding of these materials to the concrete can improve the seismic performance of the non-seismic exterior RC beam-column joints.

Seismic behavior of exterior RC beam-column joints without code-specified ties in the joint core

Beam-column joint design for reinforced concrete (RC) buildings is a critical issue for modern earthquake engineering, because for these structural elements, the current codes provide several geometrical constraints and reinforcement provisions, which may be very complex to implement during the construction phase. To investigate how a construction error might influence the joint behavior, two identical full-scale exterior beam-column joints specimens are built, according to Italian Building Code specifications for the high ductility class, but without the required horizontal ties inside the joint panel. This construction error could be plausible because, according to the design drawings, the panel was very crowded with reinforcement bars and the concrete casting and compaction was objectively difficult. The performance of the joints is tested under cyclic loads simulating seismic actions. Although the joints are designed for high ductility class, a 50% reduction of the horizontal reinforcement in the joint core, and 25% in the critical regions, led the specimens to shear failure, with crushing of the concrete in the joint core. A discussion of the failure mechanism is presented, in which shear strength obtained from the tests is compared to shear strengths calculated using the expressions provided for exterior joints by Eurocode 8, the ACI Code and the formula proposed by Pauletta et al.

Analytical Examination of Reinforced Concrete with Hybrid Fibres Exterior Beam Column Joint

This research paper pacts with the analytical examination of synthetic fibres (Polypropylene and Recycled polyethylene terephthalate RPET) and steel fibres in reinforced exterior beam column joint by using ANSYS. Based on IS 10262-2009, M40 grade of concrete was prepared along by volume fractions up to 0.5% of synthetic and steel fibre. 9 number of exterior beam column joint with various proportions of hybrid fibre incorporated reinforced concrete specimens were tested by means of monotonic loading. Their experimental results exhibited that reinforced concrete exterior beam column joint specimens with hybrid fibre specimens achieved superior performance along with high ductility, high strength and less crack patterns. The main aim of this research paper was based on the experimental input, analytical examination by ANSYS was carried out and related with the experimental results found. The comparison showed that both the experimental and numerical results similar.

Seismic performance of non-ductile detailing RC frames: An experimental investigation

Non-ductile detailing of Reinforced Concrete (RC) frames may lead to structural failure when the structure is subjected to earthquake response. These designs are generally encountered in older RC frames constructed prior to the introduction of the ductility aspect. The failure observed in the beam–column joints (BCJs) and accompanied by excessive column damage. This work examines the seismic performance and failure mode of non-ductile designed RC columns and exterior BCJs. The design was based on the actual building in Tainan City, Taiwan, that collapsed due to the 2016 Meinong earthquake. Hence, an experimental investigation using cyclic testing was performed on two columns and two BCJ specimens scaled down to 50%. The experiment resulted in a poor response in both specimens. Excessive cracks and their propagation due to the incursion of the lateral loads could be observed close to the top and bottom of the specimens. Joint shear failure appeared in the joints. The ductility of the member was below the desired value of 4. This is the minimum number required to survive an earthquake with a similar magnitude to that of El Centro. The evidence provides an understanding of the seismic failure of poorly detailed RC frame structures.

Plastic Hinge Model for Performance-Based Design of Beam-Column Joints

For performance-based design of reinforced concrete moment frames, the inelastic load-displacement relationship including strength degradation of beam-column joints should be accurately defined. In this study, a simplified design equation for joint shear strength was developed, addressing the effects of the target story drift ratio, beam rebar detail, joint configuration ratio, and joint hoops. Using the proposed method, a plastic hinge element was developed for nonlinear numerical analysis of beam-column connections. The proposed model was applied to existing interior and exterior beam-column joint specimens with or without joint hoops. The predicted lateral load-drift ratio relationships were compared with the test results and current design models. An existing cyclic behavior model was also implemented in the proposed plastic hinge model for time history analysis.

Energy dissipative beam-column connection for earthquake resistant moment frames

This study presents the details of experimental investigations on a novel energy dissipative beam-column connection. This work is in line with the current research focused on developing resilient structures by confining inelastic actions or damage within easily replaceable select number of elements in a structure at predetermined locations. Towards this, a novel connection consisting of two fuse links and a standard shear tab is developed such that the beam, column, shear tab and connecting bolts remain elastic, while sufficient energy dissipation is provided by the fuse links alone. The experimental programme entails component level tests on fuse plates and full-scale exterior beam-column joint sub-assemblage studies by using the novel connection to demonstrate its performance and to prove its efficacy. For this purpose, monotonic and standard pseudo-static reversed cyclic loading protocol is used. It is observed that the connection exhibits good energy dissipation characteristics by confining the damage within the fuse links keeping the primary structural members in elastic state. The same column and beam sections are used for all the experiments as no damage is observed, except bolt thread marks in beam. Also, a damaged connection could be easily dismantled within about 10–15 min and replaced with a new one.

Application of ultra-high performance fiber reinforced concrete for retrofitting the damaged exterior reinforced concrete beam-column joints

In the present research work, the effectiveness and the efficiency of a retrofitting approach using a layer of ultra-high performance fiber reinforced concrete (UHPFRC) jacket for damaged substandard exterior beam-column joints (BCJs) is experimentally investigated. The main objective of this study is to rehabilitate the already damaged BCJs to meet the serviceability requirements without compromising safety. According to the proposed strengthening technique, a chipped surface, lightly brushed with a dry condition was selected for making a successful bond between normal concrete substrate surface (NCSS) and UHPFRC. Then a fresh UHPFRC jacket with a thickness of 30 mm was cast around the damaged specimens. The entire test matrix was comprised of three 1/3 scale damaged exterior BCJs with a different column axial load (CAL). These specimens were repaired with UHPFRC and retested under monotonic loading. Based on the experimental results, repaired specimens showed an excellent performance in terms of their load-displacement response, maximum strength, displacement ductility, initial stiffness, secant stiffness and energy dissipation capacity when compared with the corresponding values registered when these specimens were tested in their virgin state. This rehabilitative intervention not only restored the strength, stiffness, ductility and energy dissipation capacity of severely damaged specimens but also improved their performance.

Study on Cyclic Response of Circular Spiral Confined Exterior Beam–Column Joints with Welded Wire Fabric

The experimental results of four exterior beam–column joints (CS, CS1, CS2 and CS3) with circular spiral confinement and various reinforcement detailing under reversed cyclic loading are presented. All the four specimens were detailed according to ductile detailing code for reinforced concrete structures IS 13920. CS1 was provided with additional reinforcement from column to beam. CS2 and CS3 were provided with welded wire mesh. CS2 had welded wire mesh in the joint region, and CS3 had welded wire mesh both in the joint and beam region. The intention of these detailing schemes was to relocate the plastic hinge and to explore the potential of welded wire mesh as additional joint confinement (CS2 & CS3) and means to relocate plastic hinge (CS1& CS3). The seismic behaviour was evaluated in terms of load–displacement relation, ductility, stiffness, energy dissipation, viscous damping ratio, load ratio, beam rotation and crack pattern. Out of the four test specimens, seismic performance of CS1 was better than that of CS, CS2 and CS3 in terms of all parameters.

Structural performance of exterior beam-column joint using biochar impregnated pond ash concrete

RC Structures when exposed to seismic waves Beam-Column joints are an important part of the construction and play a significant role in the overall behavior. The most significant explanation behind the failure and abrupt breakdown during the seismic tremors is the insufficient provision of shear reinforcement in joints RC Structures. In reinforced concrete frames beam-column joint is the critical zone that should be designed to provide sufficient deformation capacity and ultimate strength. More vulnerable failures of joints around the exterior border of the structure occur than interior joints. In the static load analysis, the priority is strength and ductility So, in ordinary structures joints are designed by considering strength to resist wind and gravity loads. Experimental research is the most significant way to know the parameters which influence both joint performance and those that should be improved to upgrade joint performance. In the present study, two Specimens of Beam-Column joints were prepared one is with conventional concrete and other with concrete using 5% binder replaced with Biochar and 20% fine aggregate replaced with pond ash and the test results showed that the energy absorption and ductility were increased but stiffness was reduced in pond ash concrete when compared to conventional concrete and there is no much difference in deflections within yield stage but deflections were reduced in Ultimate stage in pond ash concrete compared to traditional.

외부 보-기둥 접합부에 정착된 보 주철근의 압축 정착길이

압축정착에 관한 현행설계기준은 매우 제한적인 실험결과를 바탕으로 제정되어 정밀한 압축정착강도를 예측할 수 없다. 콘크리트구조 학회기준에서 압축정착이 인장정착보다 유리하다고 명시하였으나, 압축정착길이가 인장정착길이보다 긴 정착길이로 산정된다. 이로 인해 불필요하게 긴 정착길이가 요구되고, 기둥 단면 치수를 증가시킬 수 있다. 이 연구에서는 압축정착에 관한 선행 연구의 실험결과를 바탕으로 압축정착강도 평가식을 도출하고, 평가식에 5 % 분위수 안전율을 고려하여 압축을 받는 직선철근 및 갈고리철근의 압축정착길이 설계식을 제안하였다. 제안식의 효용성을 검증하기 위하여 제안식과 기존의 압축을 받는 이형철근의 정착길이 설계식 및 인장을 받는 표준갈고리 정착길이 설계식을 비교하였다. 결과 동일한 조건에서 기존식 보다 제안식으로 산정된 정착길이가 짧은 길이로 산정되었다. 제안식을 이용하여 압축정착길이가 인장정착길이보다 길어지는 설계의 오류를 해소할 수 있고, 압축정착에 관한 현행설계기준보다 경제적인 압축정착길이 설계가 가능할 것으로 판단된다.

Experimental investigation into the failure process of exterior beam-column joints with high-strength reinforcements

Although using high-strength reinforcements (HSRs) have economical and execution benefits, their possible negative effects on the performance of structures such as ductility, energy dissipation, and damage process caused them to be restricted by building codes in seismic areas. In this research, the HSR effects on the cyclic behavior, cracking process, and damage indices of exterior beam-column joints were experimentally investigated under cyclic loading. Three exterior beam-column joints with HSRs (with the yield strengths of 500 and 580 MPa) were designed based on the special seismic provisions of ACI 318-19. These specimens were subjected to cyclic loading and their responses were obtained. The results showed that using HSRs led to increasing the width and depth of the cracks. Then, two methods of calculating damage indices (introduced by Promis et al., 2009) were applied based on the experimental results. Considering the damage indices, it was observed that using HSRs increased the damage indices of the specimens and the damage distribution in them.

Seismic behavior of exteriorbeam–column joints with high-performance steel rebar: Experimental and numerical investigations

Three full-scale exterior beam–column joints with anti-seismic steel reinforcement were tested under quasi-static cyclic loading and column axial compressive loading. The test variables were column axial load ratio and joint core hoop reinforcement ratio. Experimental results, including failure mode, hysteretic curve, ductility, energy dissipation, stiffness degradation, and decoupling of deformations, were presented and analyzed. The tests revealed that the anti-seismic rebar resulted in good joint seismic performance and that column axial load ratio and joint core hoop reinforcement ratio impose limited influence of joint performance when the joint failed in beam flexural failure. The calibrated finite element models developed based on OpenSees were then used to simulate the behavior of joint specimens. Parametric studies via finite element modeling were performed to study the influence of various parameters on the performance of beam–column joints.

Cyclic Response of Steel Fiber Reinforced Normal Strength Concrete Exterior Beam-Column Joint Under Reversed Cyclic Load

Failure investigation studies on a large number of buildings exposed to earthquake loads revealed that Beam-Column Joint (BCJ) is the most critical structural regions in any moment resisting RC structure. The structural response of RC moment resting frame system under the earthquake loads mainly depends on the behavior and performance of the BCJ. It should be designed and detailed properly to ensure safety and serviceability of the structure under various earthquake loads. In the present Experimental work, Normal Strength Concrete (NSC) Fiber Reinforced Beam-Column Joint specimens are cast and are subjected to Cyclic loading. Proportions of steel fibers used are 0%, 0.5% and 1%. Load response curves have been plotted to demonstrate change in the Energy absorption, Stiffness Degradation and Ductility factors.

3D RC beam–column joints retrofitted by joint enlargement using steel angles and post-tensioned bolts

The performance of moment frames in concrete structures is influenced by the behavior of beam-column joints. Experience in past earthquakes has shown that beam-column joints with non-seismic details are highly vulnerable due to the lack of details and transverse reinforcement intervals in the joint core; furthermore, the brittle failure in joints of such type causes overall structural destruction. The present paper focuses on the seismic retrofitting of 3D exterior beam-column joints with no seismic details and considering the effect of slab and transverse beam. For this purpose, four exterior 3D concrete beam-column joint specimens with a scale of 1/2 were constructed and subjected to cyclic loading. The tested specimens comprised two control specimens with and without special seismic details; the two other specimens were retrofitted using angles and post-tensioned bolts. Noteworthy, the effect of initial damage on the cyclic behavior of one of the specimens with retrofit system was further taken into account. All specimens were compared in terms of hysteresis curves and other such parameters as strength, energy dissipation, stiffness reduction, equivalent hysteretic damping, and cracking pattern. The results indicated the efficiency of the retrofit system in enhancing the cyclic behavior of the joints, due to the relocation of shear hinge from the joint core and the formation of flexural plastic hinge in the beam.

Experimental and analytical investigations of reinforced concrete beam-column joints retrofitted by single haunch

Recently, the single haunch with specifications such as less invasive and architectural consistency, and easy to practice have been adopted as one of the considered retrofitting options for deficient reinforced concrete beam-column joints. In this article, by analytical evaluation, the influence parameters such as haunch to beam stiffness ratio, haunch inclination angles, and mounted position were investigated. Analytical equations were also proposed for haunch to beam stiffness ratio in terms of both shear interaction between haunch and beam-column members and reduction of joint shear demand. Moreover, five exterior beam-column joint sub-assemblies were fabricated afterwards four of those retrofitted by various cross-sectional area of single steel haunch. Then, all of these beam-column joints and remaining one (as-built joint) were experimentally subjected to cyclic loading. To validate the analytical results, the experimental responses in four limit states including first diagonal core crack in as-built joint, drift ratio 2%, the first diagonal core crack in all the joints, and ultimate state (peak load) were provided for comparison. Also, by definition of an index as vulnerability index in fraction ratio of available joint shear force to joint shear strength predicted by international codes, the obtained vulnerability index of experimental responses were compared to analytical results.

The effect of high-performance fiber-reinforced cementitious composites on the lateral behavior of reinforced concrete frames without seismic details

In areas with high seismicity, the construction of reinforced concrete structures with high ductility requires observance of the special seismic specifications of the ACI 318 regulations. This will increase the congestion of transverse reinforcement in the beam-column joints, and this reinforcement congestion in the joints in turn will bring along problems in the construction and concreting. In this study, the use of high-performance fiber-reinforced cementitious composites (HPFRCC) in the joints of frames has been investigated in order to prevent the congestion of the transverse reinforcement in beam-column joints. First, four half-scale exterior beam-column joints were tested under incremental cyclic lateral loading. The tested specimens consisted of two conventional concrete control specimens with and without seismic details and two HPFRCC specimens. Second, physical models for conventional concrete and HPFRCC joints were proposed. Third, verification was performed using experimental results. Then, 5 and 10-story frames including two conventional control frames with and without seismic details and two HPFRCC frames without seismic details are developed by assembling these physical models with OpenSees software. Using nonlinear analyses, the ductility ratio, energy dissipation capacity as well as the cyclic behavior of the frames are examined and compared. The results show that the use of HPFRCC in beam-column joints of frames without seismic details increases the shear strength of joints, the relocation of plastic hinge to the outside of the joint core and the improvement of lateral behavior. The proposed method also shows a significant improvement in seismic parameters such as strength, stiffness, energy dissipation and ductility capacity.

Light FRP Strengthening of Poorly Detailed Reinforced Concrete Exterior Beam–Column Joints

Abstract Experiments have demonstrated the effectiveness of fiber-reinforced polymer (FRP) materials for the seismic strengthening of deficient reinforced concrete (RC) beam–column joints. However,...

Seismic Design of Precast Component Beam-Column Joints using Headed Anchors

Precast construction system ensures high degree of quality, safety, and accelerated construction practice in R.C structures. It is well established in non-seismic conditions where gravity loads are predominated. But it is hesitated to implement during seismic conditions by the effect of lateral loads. Most of structural failures in precast framed structures are associated with beam-column joints as the integrated joint system experience high shear, and moments by cyclic action of seismic loads. In this context, researchers found that the joint distortions in precast system is well associated with its location of beam-column sub-assemblage. In beam-column joints the connections are attributed to locate in D-regions (D:Discrete) and B-regions (B:Beam) where the force transfer mechanism follows by strut - tie method (STM) or flexure beam theory(FBT) respectively. This paper analyzed the seismic performance of “Component Based Precast Joints”[CBPJ] located in D& B regions. To meet the convergence requirements, the connection systems are detailed by mechanical couplers and headed anchors. Five numerical models of exterior beam-column joints representing two models (BM1,BM2) of B-region and three models (DM1,DM2,DM3) of D-region are developed and verified their seismic performance with monolithic joint system by non-linear finite element analysis using ABAQUS software .The results indicated that the use of headed anchors in precast joints are effectively contributed to seismic requirements of shear, ductility, stiffness and energy dissipation. Also the precast joints located in D & B regions resembling good performance of joint sustainability during moderate seismic conditions as monolithic system.

Implications of impact experiments on honeycomb shielded exterior beam-column joint

The response of building structures under impact loads is a challenging subject for both numerical and analytical studies, as the available experimental data is limited. In the current research, an attempt was made to study the experimental investigation on the exterior beam-column joint against accidental and intentional impact loading. The velocity regime of the projectile was considered in the range 30–34 m/s. The response of the structural member shielded with the Aluminum honeycomb sandwich panel was compared with the unshielded beam-column joint. The target damage, failure modes, energy absorption, and evolution of cracks were examined in terms of both analytically and experimentally. Results obtained from high-speed imaging were used to obtain the projectiles incident, residual, and re-bound velocities. The application of honeycomb shielding on the seismic group specimens shows that the ballistic limit was increased by its energy absorption characteristics. It was found that they have a 22% higher ballistic limit than that of the seismic group specimens without honeycomb shielding. The shielded honeycomb sandwich panel specimens show promising results as they absorbed 49% higher impact energy than that of seismic specimens without honeycomb shielding. The current study provides a valuable reference for designing of honeycomb panels as a sacrificial material to safeguard the engineering structures against impact loads in the intermediate velocity regime.