Joint Transverse Reinforcement Research Articles

Seismic shear and flexural performance of new RCS joints with W-FDP, W-FBP, and small hoops

New through-beam joint details were developed for New high-strength Reinforced Concrete and Steel beam (New RCS) special moment frames. The columns hadfy = 690 MPa andfc′ = 84 MPa. The new joint details enhanced the joint strength for the large force demand seen in high-rise buildings in regions of high seismicity and minimized the construction difficulty associated with conventional joint transverse reinforcement. The new joint details included Wide Flange Doubler Plates (W-FDPs), Wide Face Bearing Plates (W-FBPs), and small rectilinear hoops. Three large-scale beam-column joint specimens with the proposed design details were tested using lateral cyclic loading to examine their seismic shear and flexural performance. Test results showed that the W-FDPs were effective in preventing joint bearing failure. Using W-FDPs, FBPs, or W-FBPs, and small hoops effectively mobilized the joint shear strength. The 2015 ASCE model modified to consider the proposed details provided a conservative estimation of the joint shear strength of the specimen that failed in joint shear. Moreover, the model was successfully used to design specimens to prevent joint shear failure and to produce desired beam-hinging behavior that met the requirement of AISC 341 for beam-column connections of special moment frames. The beam eccentricity did not significantly affect the hysteretic behavior of the specimen up to the 4% drift ratio.

Seismic shear behavior of new high-strength reinforced concrete column and steel beam (New RCS) joints

New high-strength reinforced concrete column and steel beam (New RCS) joints were developed in this research. Two-way, through-beam New RCS joint details with beams concentrically or eccentrically connected to the joint were proposed. The beam in one direction was continuous through the joint (continuous beam). The beam in the other direction was connected to the continuous beam by complete joint penetration (CJP) groove welds. Five-spiral reinforcement was used for joint transverse reinforcement. A method to calculate the amount of five-spiral reinforcement was proposed considering the confinement effect from the face-bearing plates (FBPs). Doubler plates were used to strengthen the eccentric beam flanges with predrilled holes to allow the passage of column longitudinal reinforcement. A method was proposed for the design of the doubler plates. Large-scale New RCS joint specimens designed to fail in joint shear were tested. Test results showed that the proposed joint details and design methods effectively avoided failure in undesirable locations. All the specimens failed in joint shear but still reached high drift ratios. The eccentric joint specimens (IDEHS and ISEHS) exhibited peak joint shears higher than the concentric beam specimen (IHS). The 1994 ASCE and 2015 ASCE shear strength models produced conservative predictions of the peak joint shear and the joint shear at 0.5% joint shear deformation for all the specimens. The predictions by the 2015 ASCE method were more reasonable with less scatter than the 1994 ASCE method because the former recognizes the shear strength contribution from the outer joint panel even without the use of shear keys and allows a longer steel web in shear strength calculation.

Cyclic behavior of high-performance fiber-reinforced cementitious composite corner joints

In moment frames, beam-column joints are critical elements that ensure the structural integrity of the frames. During earthquakes, beam-column joints can withstand large shear forces transmitted from nearby columns and beams. In old reinforced-concrete (RC) moment frame buildings, beam-column joints had little joint transverse reinforcement, which are susceptible to significant damage during large earthquakes. Their corner joints could experience a more severe seismic loading environment than other joints because they are subjected to bidirectional lateral loadings during earthquakes. The objective of this study was to improve the cyclic behavior of corner joints by using high-performance fiber-reinforced cementitious composite (HPFRCC). For this purpose, seven corner joint specimens were made and tested under unidirectional and bidirectional cyclic loadings. The application of HPFRCC improved the cyclic behavior of corner joint specimens. The contribution of HPFRCC outweighed that of the minimum joint transverse reinforcement. The minimum joint transverse reinforcement moderately affected the cyclic behavior of the specimens. The shear strength and drift capacity of unidirectional HPFRCC specimen without the joint transverse reinforcement had 13% and 24% larger than those of unidirectional RC specimens with the joint transverse reinforcement, respectively. Similar observations were made for bidirectional specimens. Particularly, the failure mode of the specimens was changed by using HPFRCC from brittle joint shear failure and axial failure to beam flexural failure followed by joint shear failure.

Seismic retrofit of deficient exterior RC beam-column joints using steel plates and angles

This paper proposes a simple and practical method for retrofitting deficient (non-seismic detailed) exterior beam-column joints based on fixing steel plates and angles around the joint with different configurations. Six half-scale exterior RC beam-column joints were tested under quasi-static cyclic loading with a constant axial load on the column. The experimental program included two control specimens representing code-detailed and deficient joints in addition to four retrofitted specimens. The proposed retrofit methods were designed to compensate the lack of joint transverse reinforcement using different steel arrangements (X-shape, horizontal plates) and the short development length of beam bars using angles tied by external or internal anchors. One of the retrofit methods is applicable in the presence of a transverse beam. The test results showed that the deficient joint exhibited brittle joint shear failure, unlike the code-detailed joint which failed by flexure in the beam. The proposed retrofitting methods effectively prevented the brittle joint shear failure and increased the joint strength, ductility, stiffness, and energy dissipation. A softened strut and tie model was applied and modified to predict the joint shear strength of control and retrofitted joints and it showed a good agreement when compared with the experimental results.

Seismic performance of exterior r/c beam-column joint under varying axial force

Previous studies have suggested the maximum experimental story shear force of beam-column joint frame does not reach its theoretical value due to beam-column joint failure when the column-to-beam moment capacity ratio was close to 1.0. It was also pointed out that under a certain amount of axial force, an axial collapse and a sudden decrease of lateral load-carrying capacity may occur at the joint. Although increasing joint transverse reinforcement could improve the lateral load-carrying capacity and axial load-carrying capacity of beam-column joint frame, the conditions considering varying axial force were still not well investigated. For this purpose, 7 full-scale specimens with no-axial force and 14 half-scale specimens with varying axial force are designed and subjected to static loading tests. Comparing the experimental results of the two types of specimens, it has indicated that introducing the varying axial force leads to a reduction of the required joint transverse reinforcement ratio which can avoid the beam-column joint failure. For specimens with varying axial force, to prevent beam-column joint failure and axial collapse, the lower limit of joint transverse reinforcement ratio is acquired when given a column-to-beam moment capacity ratio.

Seismic vulnerability of reinforced concrete knee joints under reversed cyclic loading

Reinforced concrete beam–column knee joints are generally located at the roof level of moment-resisting frame structures. Knee joints undergo significantly different closing and opening actions under seismic excitations. The complex and vulnerable behaviour of knee joints makes them considerably different from conventional exterior and interior joints. To understand this complexity, three full-scale knee joint specimens were subjected to varying closing and opening joint shear stresses produced from the variation of relative closing and opening moment capacities. Peak opening-to-closing joint shear stress ratios of 0·5, 0·6 and 0·8 were achieved for the three specimens. In addition, the effect of anchorage of longitudinal and joint transverse reinforcement was studied in terms of the enhancement of peak joint closing and opening shear stresses. This paper presents a detailed discussion on the effect of closing and opening actions on the overall joint performance of knee joints subjected to reversed cyclic loading.

Cyclic behavior of RC OMF beam-corner column joints under unidirectional and bidirectional loadings

Reinforced concrete (RC) ordinary moment frames (OMFs) are commonly used for building construction in low-to-moderate seismic regions. Unlike those in special moment frames (SMFs), beam-column joints in RC OMFs are susceptible to damage during earthquakes because the joints are not designed to resist the large shear forces transferred from adjoined members in the elastic range. For this reason, they are more vulnerable when subjected to bidirectional seismic loading. Beam-corner column joints (corner joints) especially are exposed to bidirectional seismic loading. The aim of this study was to explore the cyclic behavior of RC OMF corner joints. Three full-scale corner joint specimens with slabs were built and tested under unidirectional and bidirectional loadings. It was observed that minimal joint transverse reinforcement placed in the OMF joints played an important role on the cyclic performance of the joints, particularly under bidirectional loading. Noticeable difference existed between measured and ASCE 41-17 force-deformation curves, particularly in bidirectionally loaded specimens and in the specimen without joint transverse reinforcement.

Interior Reinforced Concrete Beam-to-Column Joints Subjected to Cyclic Loading: Shear Strength Prediction using Gene Expression Programming

An empirical model, which predicts the shear strength of interior reinforced concrete (RC) joints exposed to cyclic loading, is developed using gene expression programming (GEP). Five main parameters are used to develop the GEP model including concrete compressive strength, joint transverse reinforcement, beam reinforcement ratio, joint aspect ratio, and joint width. A large database including 160 data test points is used to test and train the GEP model. The GEP model is then evaluated using the coefficient of determination (R2). The formulation proposed by ACI-352 is used to predict the shear strength of RC joints. The R-squared values of the ACI and the GEP model are 66% and 87% respectively which indicates that the joint shear strength predicted using the GEP model is closer to the experimental results than that predicted using the ACI-352 formulation.

Exterior RC joints subjected to monotonic and cyclic loading

PurposeThe purpose of this study is to develop two empirical models that predict the shear strength of exterior beam-column joints exposed to monotonic and cyclic loading using Gene expression programming (GEP).Design/methodology/approachThe GEP model developed for the monotonic loading case is trained and validated using 81 data test points and that for cyclic loading case is trained and validated using 159 data test points that collected from different 9 and 39 experimental programs, respectively. The parameters that are selected to develop the cyclic GEP model are concrete compressive strength, joint aspect ratio, column axial load and joint transverse reinforcement. The monotonic GEP model is developed using concrete compressive strength, column depth, joint width and column axial load.FindingsGEP models are proposed in this paper to predict the joint shear strength of beam-column joints under cyclic and monotonic loading. The predicted results obtained using the GEP models are compared to those calculated using the ACI-352 code formulations. A sensitivity analysis is also performed to further validate the GEP models.Originality/valueThe proposed GEP models provide an accurate prediction for joint shear strength of beam-column joints under cyclic and monotonic loading that is more fitting to the experimental database than the ACI-352 predictions where the GEP models have higher R2 value than the code formulations.

Seismic behavior and strength capacity of steel coupling beam-to-SRC wall joints

A hybrid coupled wall system, where steel coupling beams couple steel reinforced concrete (SRC) walls in series, has been recognized as an alternative to reinforced concrete (RC) coupled wall systems for enhanced seismic performance of high-rise buildings. A key issue of this system is seismic design of steel coupling beam-to-SRC wall joints. This paper presents a series of full-scale tests to investigate the cyclic behavior and strength capacity of the steel coupling beam-to-SRC wall joints, where a steel beam was rigidly connected to an encased steel column in wall boundary using a fully welded connection detail. The steel beam-to-SRC wall joints failed in panel shear mode, characterized by yielding of the steel web panel and joint transverse reinforcement, and crisscrossed-diagonal cracking and crushing of joint panel concrete. A design model for calculating the nominal strength of the steel beam-to-SRC wall joint is presented. The accuracy of the design model was verified against the collected test data and additional finite element (FE) analysis. The experimental tests and FE analysis also identified that severe vertical cracks might develop along the inner side of wall boundary element, due to horizontally tensile forces induced by the steel beam flange. Increased amount of horizontally distributed rebar is recommended to be assigned in around the join region, in order to control such unwanted damage. In addition, the test results of one specimen demonstrated that properly designed beam-to-wall joint remained slightly damaged when the steel coupling beam fully developed its plastic rotation.

Probabilistic Model for Shear Strength of RC Interior Beam Column Joints

ABSTRACT This paper proposes a stochastic model to predict the joint shear capacity of reinforced concrete interior beam column joint specimens. A database of the test results obtained from experiments on interior beam column joints was compiled for analysis. The parameters affecting the joint shear strength were identified, and a multiple log-linear regression model for predicting shear capacity was developed. Concrete compressive strength, joint transverse reinforcement, and column axial load were identified as the variables that positively affect the joint shear strength. The model identified concrete compressive strength as the most significant variable that contributed to the shear strength. Bond deterioration of beam bars and the joint aspect ratio were observed to have adverse effects on the shear strength. The developed model was validated by testing 12 interior joint specimens loaded to failure under quasi-static cyclic loading. The model provided consistent results between the estimated and measured joint shear strengths. The calibrated model can be implemented for effectively predicting the interior joint shear strength under seismic lateral loading.

Shear strength of interior beam–column joints with lightweight aggregate concrete

Lightweight aggregate concrete (LWAC) elements can effectively reduce dead load and improve the seismic resistance capacity of building structures. However, the shear performance of LWAC remains questionable due to its specific brittle failure mechanism. In this work, four one-third-scale LWAC interior beam–column joints were prepared and tested under reversed quasi-static cyclic loading. Two levels of axial compressive forces and joint transverse reinforcement ratios were considered for each specimen to quantify and analyse the shear performance of LWAC joints. The test results indicate that all LWAC specimens experienced shear failure at the joint core and presented satisfactory shear resistance capacity in terms of shear strength, displacement ductility, stiffness degradation and energy dissipation compared to normal-weight concrete (NWC) specimens. The test results were used to examine the applicability and accuracy of six shear design models based on the behaviour of NWC elements for LWAC beam–column joints. A comparison of the results indicated that there is no apparent difference between the ultimate shear strengths of LWAC and NWC specimens, and all six previously proposed shear equations examined can accurately predict the ultimate shear strength of LWAC interior beam–column joints.

Anchorage performance of headed deformed bars in exterior beam-column joints under cyclic loading

The anchorage performance of headed deformed bars anchored in inter-story exterior beam-column joints under cyclic load was examined based on a test database with 118 test data. A proposed performance index based on the ACI 318 development length equation was used to evaluate the anchorage performance of the headed deformed bars of the specimens in the database. The results of the evaluation showed that the anchorage performance was positively correlated with the axial load, amount of joint transverse reinforcement parallel to the direction of applied shear, and head bearing area ratio, and was negatively correlated with the clear bar spacing and column moment ratio. Based on the evaluation, limits on design parameters (i.e., the minimum clear bar spacing, head bearing area ratio, concrete and steel strengths) were proposed. It was found that all the specimens in the test database showed satisfactory seismic performance if they satisfied the development length equation of the ACI 318 code and the proposed limits on design parameters.

Behavior of Damaged Exterior RC Beam-Column Joints Strengthened by CFRP Composites

This paper presents an experimental investigation on the behavior of retrofitted beam-column joints subjected to reversed cyclic loading. The experimental program comprises 8 external beam-column joint connection subassemblages tested in 2 phases; one was the damaging phase and second was the repairing phase. The Beam-column joints were designed only for gravity loads. The joints had no beam-column joint transverse reinforcement and special stirrups in beam and column critical zones. These Non-Seismically designed (NS) joints were damaged with different levels at the first phase of the experiment. In the second phase, the damaged joints were strengthened with externally bonded carbon-fibre-reinforced polymers (C-FRP) sheets. From the observed responses of the examined specimens it can be deduced that the technique of externally bonded retrofitting (EBR) using C-FRP sheets is appropriate for the rehabilitation of the joints seismic capacity. This technique had a significant improvement of the energy dissipation and the performance level and finally it leads to improved type of damages compared with the damage modes of the specimens during the initial loading. Shortcomings of the application of C-FRP sheets for practical use are also pointed out.

Seismic Response of Strengthened RC Beam Column Joints with Haunch Effects

From the study of a large number of buildings, it has been recognized that beam column joint is one of the critical elements of a building system. This element should be designed and detailed properly, especially when the frame is subjected to earthquake loading. Beam column joints are brittle in nature. The breakdown of beam column joint during earthquake is controlled by bond and shear failure mechanism. The main reinforcement of columns just above the joint region, discontinuous bottom beam reinforcement and little or no joint transverse reinforcement are the most critical details of beam column joints in buildings. Therefore, current international code of practices gives more importance to provision of adequate anchorage to longitudinal bars and confinement of core concrete so as to resist shear. Modern codes propose for reduction of seismic forces through provision of special ductility requirements. Details for achieving ductility in reinforced concrete structures are given in IS 13920-1993. In the present study, a two-bay five-storey reinforced cement concrete moment resisting frame for a general building has been analyzed and designed by using STAAD Pro as per IS 1893–2002 code procedures and detailed as per IS 13920-1993 recommendations. An exterior beam column joint has been modelled to 1/5th scale of the prototype and the specimen has been subjected to cyclic loading to study its behaviour during earthquake loading. The experimental programme consists of two interior beam-column joint specimens, one is RC haunch and other one is strengthened RC haunch. The specimens are designated as RC and RCH respectively. In this study key structural issues such as load carrying capacity, load deflection behavior, stiffness degradation, energy dissipation capacity, ductility factor and cracking pattern have also been examined.

Analytical Evaluation of the Vulnerability of RC Frames for Progressive Collapse Caused by the Loss of a Corner Column

AbstractIn the past decades, several guidelines have been developed for designs against progressive collapse based on a number of experimental and numerical studies that have been conducted. However, the majority of the previous experimental and numerical investigations focused on the response of buildings under the scenarios of loss of interior or exterior columns. However, the loss of a corner column in the event of a terrorist attack is more likely to trigger progressive collapse given the paucity of surrounding elements that could help to redistribute the axial force initially resisted by the lost corner column. In order to investigate the progressive collapse of RC frames under the loss of a corner column scenario, an analytical model was proposed and subsequently validated through comparison with the experimental results. The influences of the beam longitudinal reinforcement ratio, beam depth, beam width, column width, and joint transverse reinforcement ratio on the progressive collapse performance ...

Seismic behavior of reinforced concrete interior beam-column joints with beams of different depths

Current Design Codes for Reinforced Concrete (RC) interior beam-column joints are based on limited experimental studies on the seismic behavior of eccentric joints. To supplement existing information, an experimental study was conducted that focused on the effect of eccentricity of the deeper beams with respect to the shallow beams. A total of eight one-third scale interior joints with beams of different depths were subjected to reverse cyclic loading. The primary variables in the test specimens were the amount of joint transverse reinforcement and the cross section of the shallow beams. The overall performance of each test assembly was found to be unsatisfactory in terms of joint shear strength, stiffness, energy dissipation and shear deformation. The results indicated that the vertical eccentricity of spandrel beams in this type of joint led to lower capacity in joint shear strength and severe damage of concrete in the joint core. Increasing the joint shear reinforcement was not effective to alter the failure mode from joint shear failure to beam yielding which is favorable for earthquake resistance design, whereas it was effective to reduce the crack width at the small loading stages. Based on the observed behavior, the shear stress of the joint core was suggested to be kept as low as possible for a safe and practical design of this type of joint.

Seismic Performance of Lightly Reinforced Concrete Exterior Beam-Column Joints

This paper presents the experimental results of four lightly Reinforced Concrete (RC) exterior beam-column joints with and without beam stubs under cyclic loading with constant column axial force applied at the top of the column. The parameter investigated was the type of reinforcement used in the beam, i.e. plain and deformed bars. Test results showed that when the hooks anchored down in the column increased the tensile stress in the diagonal concrete strut in the joint core, this led to diagonal crack of the concrete and a decrease in the joint shear strength. The seismic performance of the exterior RC joints without beam stub was also observed to be much improved when the hook tail of beam reinforcements was bent inside the joint core. The strut-and-tie model based on the recorded strain in the joint transverse reinforcement could be used to determine the force flow in the joint core.

Joint shear strength prediction for reinforced concrete beam-to-column connections

In this analytical study numerous prior experimental studies on reinforced concrete beam-to-column connections subjected to cyclic loading are investigated and a database of geometric properties, material strengths, configuration details and test results of subassemblies is established. Considering previous experimental research and employing statistical correlation method, parameters affecting joint shear capacity are determined. Afterwards, an equation to predict the joint shear strength is formed based on the most influential parameters. The developed equation includes parameters that take into account the effect of eccentricity, column axial load, wide beams and transverse beams on the seismic behavior of the beam-to-column connections, besides the key parameters such as concrete compressive strength, reinforcement yield strength, effective joint width and joint transverse reinforcement ratio.

반복하중을 받는 강섬유 보강 철근콘크리트 외부 접합부의 거동 특성

횡보강근이 적게 포함된 보통강도 철근콘크리트 보-기둥 접합부에서 강섬유의 보강효과에 관한 실험적 연구를 진행하였다. 이를 규명하기 위해 총 10개의 접합부 실험체를 제작하였으며, 접합부 횡보강근량과 강섬유 혼입률(Vf = 0%, 1%, 1.5%)을 주요변수로 실험하였다. 실험은 총 19싸이클의 반복주기하중의 형태로 가력되었으며 각 싸이클의 반복회수는 2싸이클씩 준정적 지진하중의 형태로 적용되었다. 실험 결과를 통해 보통 강도 철근콘크리트 보-기둥 접합부에 강섬유를 보강함으로써 횡보강근 감소에 따른 피해정도를 어느 정도 줄일 수 있다는 결론을 얻었고, 또한 강섬유 보강으로 접합부 전단강도를 증가시킬 수 있고 동시에 에너지소산능력을 향상시킬 수 있다는 결론을 도출하였다. 보다 정량적인 평가를 위해 이 연구의 시험체들과 기존의 보-기둥 접합부 RC 시험체들에서 측정된 최대 접합부 전단강도값과 ACI 352R-02의 설계기준식, Jiuru et al.의 제안식, 그리고 Kim et al.의 제안식을 비교·분석하였다. 이러한 분석 결과 Jiuru et al.의 전단강도 제안식이 실험 결과를 과대평가하는데 반해 Kim et al.의 전단강도 제안식은 모든 시험체에 대해 안정적인 결과와 적은 오차범위를 나타내었다. 따라서, 이 연구를 바탕으로 해서 적절한 접합부 배근상세와 함께 강섬유 보강 철근콘크리트 보-기둥 접합부에 대한 추가적인 연구가 진행된다면, 횡보강근의 감소를 통한 시공의 어려움 해소 및 내진성능의 향상이 가능할 것으로 판단된다.