ACI 352R-02 Research Articles

Modelling Studies of Retrofitted Anchorage System in Exterior Beam Column Joint by Supplementary Steel

A Nonlinear finite element based ABAQUS modeling studies were conducted to evaluate the performance of exterior Beam Column Joint (BCJ) under quasi-static test loads. Six integrated BCJ models representing different configurations of beam reinforcement anchored in joint are verified by using a novel retrofitting technique called "Post Installation of Supplementary Anchorage" (PISA) by using headed bar as supplementary steel. The configuration of beam reinforcement anchored in column are described by straight bar,90 degree bend ,180 degree hook (confirming to design code IS456:2000) and single head, double head bars (confirming to ACI 318-19, ACI 352R-02 ) and 90 degree long bend of ductile detailing (as per IS 13920-2016). Two series (A&B) of integrated joint specimens representing conventional (series-A) and retrofitted anchorage (series-B) systems are modeled and tested by using ABAQUS software. The test parameters considered are configuration of anchorage system and presence of supplementary anchorage. The test variables representing nonlinear performance of retrofitted joint system are Von Mises stress conditions, Principal tensile stress, Moment-Rotation, Degraded stiffness, Crack mechanics and Damage index. The results shows good improvement of post failure conditions of exterior beam-column joint such as relocation of plastic hinge mechanism and failure mechanics of retrofitted joint system. Also the results validated with experimental program on typical specimens casted and tested. This study imparts useful information on implicit retrofitting methods applied by external means in exterior beam-column joint. It also promotes performance based design principles with viable construction practice.

Performance of exterior beam-column connections with innovative bar anchorage schemes: Numerical investigation

Proper detailing of the joint reinforcement is essential for achieving an optimum framing action of the connected members. The ACI 352R-02, ACI 318–19 and EC-8 codes specify minimum requirements for the components of the standard 90-degrees hook; horizontal part, bend, and vertical tail as a reliable detailing alternative for achieving satisfactory performance of the joint. This numerical study aims to investigate the optimum tail length needed for ensuring adequate performance of the exterior joint and to develop a measure for the joint shear strength under various vertical tail length conditions, utilizing two experimentally tested joints with different reinforcement details as reference. The impact of a wide range of vertical tail lengths on the joint’s ultimate strength has been evaluated. It has been found that the provided tail length governs the joint's ultimate shear strength, where providing a vertical tail length of thirty times the bar diameter or greater achieves the superior performance, which is attributed to the improved confinement to the joint and the better bond condition in the joint region. However, the available column depth determines how the vertical tail length affects the joint strength, where the influence is more significant for joints with narrow depth columns. Thus, this study reveals that the dependence on increased vertical tail length, as a non-conventional alternative, can be safely considered to ensure sufficient joint shear strength, especially in joints with narrow depth columns. Hence, the limits of tail length given by several international codes; e.g., ACI 352R-02, ACI 318–19, and EC-8, are inadequate. Furthermore, an accurate equation for predicting the joint shear strength has been developed based on an extensive parametric study on various sets of exterior joints, taking into account the tail length under various conditions of column depths, joint aspect ratio, column axial stress, and the concrete strength.

Numerical investigation of RC exterior beam-column connection with different joint reinforcement detailing

The proper detailing of joint reinforcement plays an essential role in ensuring adequate performance of reinforced concrete frames in terms of strength and ductility. The influence of various options of joint reinforcement detailing on joint performance has been numerically investigated using the nonlinear finite element analysis software, ABAQUS. Two sets of beam-column connections of various joint reinforcement detailing with greater spacing between the stirrups at two different locations have been modeled for achieving this purpose, considering validated experimentally tested specimen as reference. This study reveals that achieving the minimum requirments of joint reinforcement ratio according to the ACI 318-19 and ACI 352R-02 codes utilizing both internal cross ties and outer stirrups with greater spacing between the stirrups rather than closely spaced outside stirrups only is more efficient in terms of joint strength and deformation capacity. This implies that the contribution of the inner cross ties considering their configuration and location in the shear strength resistance should be considered. Therefore, the joint stirrups' main role should be considered as tension ties and a crack-control reinforcement that requires less steel and wider spacing for the joint details rather than the confinement of the concrete. Furthermore, it has been observed that both the joint strength and deformation capacity have been significantly improved with the use of three layers of stirrups with two closed rectangular cross ties or one polygon cross tie. However, the employment of only two layers of stirrups with two crossed rectangular cross ties located at the middle third of the joint as well as diagonal bars at the corners between the beam and column of the joint core successfully controlled the joint cracks and improved the performance of the connection.

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.

Experimental cyclic behavior of code-conforming exterior wide beam-column connections

Reinforced concrete (RC) frames with wide beams are efficient systems for resisting against lateral and gravity loads. However, there are limited experimental studies on the performance of wide beams under cyclic lateral loading. This paper presents the results of an experimental investigation on seismic behavior of RC exterior wide beam-column connections. Four 3:5 scale wide beam-column connections were tested under combined constant axial and quasi-static cyclic lateral loads. Different spandrel beam types including conventional and wide beam and three column geometries (square, rectangular and circular) were used in the specimens. The specimens all were designed in accordance with ACI 318-14 and ACI 352R-02 provisions. Special attention was given to reinforcement detailing of wide beam and spandrel beam at the joint area. The test results showed that although all specimens were code conforming and similarly designed for interaction of bending, shear and torsion, more torsional cracks developed in the cases that transverse beam was wide. The performance of all the specimens was satisfactory in terms of strength, ductility and energy dissipation capacity. It was observed that the load transfer mechanism from wide spandrel beam to column is a combination of torsion and bending. In the specimen with circular column, higher displacement ductility and lower energy dissipation were observed compared with the similar specimen containing square column. Besides, the importance of fine reinforcement detailing for wide and spandrel beam at the joint zone was confirmed by the test results.

Experimental and numerical study of reinforced concrete interior wide beam-column joints subjected to lateral load

Past researches showed that the energy dissipation capacity of the wide beam-column joints was not sufficient. So, two full-scale reinforced concrete interior wide beam-column joints were tested under quasi-static cyclic loads and the performance of the specimens was studied experimentally and numerically. Effect of using wide beams in two directions was investigated and it became clear that the longitudinal reinforcement of transverse wide beam had significant effect on the seismic behavior of the joints. Flexural hinging mechanism in the wide beams occurred instead of torsion brittle mode of failure. Effect of eccentric beams on joints is one of the areas needing research in ACI 352R-02. In the numerical study, it was seen that damage of the joints was concentrated to one side of the joints that the beams shifted to. Besides, concrete grade did not have much effect on behavior of the joint.

Exterior RC wide beam-column connections: Effect of beam width ratio on seismic behaviour

Abstract Design recommendations stipulated in international standards for seismic design of reinforced concrete (RC) wide beam-column connections are based on limited experimental studies. To supplement the existing information, an experimental study was conducted that focused on the effect of beam width to column width ratio (or beam width ratio) on the seismic behaviour of exterior beam-column connections. Four specimens were designed, constructed and tested under reversed cyclic loading conditions. The primary test variables were the beam width ratio and the joint shear stress ratio ( γ d ). The specimens were designed in conformance with ACI 318-14 and ACI 352R-02. They had beam width ratios of 1, 1.5, 2 and 2.5 and γ d , of 0.74, 1.12, 1.63, and 2.03. According to ACI 352R-02, the γ d value should be lower than γ n = 1.25 for joints confined on three faces. The results indicated that specimens with beam width ratios of 1 and 1.5 and γ d of 0.74 and 1.12 were capable of supporting the complete formation of beam plastic hinges with no major cracks in the joint region. In contrast, specimens with beam width ratios of 2 and 2.5 and γ d of 1.63 and 2.03 exhibited significant damage at the joint core. Torsional failure of the spandrel beam was also observed in specimen with beam width ratio of 2.5.

Behavior of interior RC wide and conventional beam-column roof joints under cyclic load

Performance of RC interior beam-column joints at roof level is defined as the area needing research by ACI 352R-02. Because of a lack of research data on performance of this type of joints, two half scale interior beam-column connections with discontinuous column were designed in accordance with ACI 318-11 and ACI 352R-02 provisions. One of the specimens had wide beams and the other had conventional beams to compare their behavior. These specimens were tested under quasi-static cyclic loading. It became clear by the experiments that roof wide beam-column joint had lower strength compared to that of roof conventional beam-column joint. Both of the specimens had almost equal energy dissipation capacity. The conventional beam-column joint reached its expected capacity but wide beam-column joint did not reach its capacity. Moreover, wide beam-column joint had sufficient joint shear strength unlike conventional one. Therefore, joint shear requirements could be relaxed for roof wide beam-column joint. This relaxation must be reapproved by more tests to be advisable for design purposes.

Reinforced concrete roof exterior wide and conventional beam-column joints under lateral load

Summary Performance of beam–column joints at roof level is one of the areas needing research in ACI 352R-02. Thus, behavior of roof exterior beam–column joints was evaluated by testing two half-scale roof wide and conventional beam–column joints effectively confined on three vertical faces under lateral quasi-static cyclic loading. Both of the specimens had conventional transverse beams. They were designed in accordance with ACI 318-11 and ACI 352R-02 provisions. It became clear by the tests that roof exterior wide beam–column joint was more ductile compared with roof exterior conventional beam–column joint. But there was not considerable difference between strength and energy dissipation capacity of the specimens. Moreover, joint shear strength was sufficient in wide beam–column joint. Therefore, joint shear requirements can be relaxed for roof exterior wide beam–column connection. Copyright © 2015 John Wiley & Sons, Ltd.

고강도 콘크리트를 사용한 철근콘크리트 외부 보-기둥 접합부의 거동 평가

이 논문은 고강도 콘크리트를 사용한 철근콘크리트 외부 보-기둥 접합부의 실험결과를 보고한 것이다. 실험체의 주요 실험변수는 접합부 파괴모드, 콘크리트 압축강도, 철근의 정착 방법이다. 모든 실험체는 ACI 352R-02 기준에 바탕을 두어 J파괴와 BJ파괴가 되도록 계획하였다. 주철근은 90도 표준갈고리로 하거나 확대머리철근으로 하였다. 실험결과는 콘크리트 압축강도에 제한되는 현행 ACI 설계 기준식이 고강도 콘크리트를 사용한 보-기둥 접합부의 강도를 다소 과소평가하고 있음을 보여준다. 또한 확대머리철근을 가진 J파괴형 보-기둥 접합부의 강도는 표준갈고리를 가진 접합부보다 약 10% 이상 높게 평가되었다. This paper reports the test results of reinforced concrete exterior beam-column joints with high-strength concrete. The main parameters of eight specimens were joint failure modes, the compressive strength of concrete, and the head shapes of steel bars. All specimens were designed according to ACI 352R-02 design recommendations. Two types of failure modes were considered; J-failure and BJ-failure. The longitudinal steel bars were anchored by 90 degree standard hooks or headed reinforcement. Experimental results indicated that the current ACI design recommendation limited by the compressive strength of concrete somewhat underestimated the strength of beam-column joints with high-strength concrete. In the specimens showed joint shear failure, the strength of beam-column joints with headed bars was approximately 10 percent higher than that of joints with 90 degree standard hooks.

Effects of joint aspect ratio on required transverse reinforcement of exterior joints subjected to cyclic loading

This paper presents an analytical model for determining the transverse reinforcement required for reinforced concrete exterior beam-column joints subjected to reversed cyclic loading. Although the joint aspect ratio can affect joint shear strength, current design codes do not consider its effects in calculating joint shear strength and the necessary amount of transverse reinforcement. This study re-evaluated previous exterior beam-column joint tests collected from 11 references and showed that the joint shear strength decreases as the joint aspect ratio increases. An analytical model was developed, to quantify the transverse reinforcement required to secure safe load flows in exterior beam-column joints. Comparisons with a database of exterior beam-column joint tests from published literature validated the model. The required sectional ratios of horizontal transverse reinforcement calculated by the proposed model were compared with those specified in ACI 352R-02. More transverse reinforcement is required as the joint aspect ratio increases, or as the ratio of vertical reinforcement decreases; however, ACI 352R-02 specifies a constant transverse reinforcement, regardless of the joint aspect ratio. This reevaluation of test data and the results of the analytical model demonstrate a need for new criteria that take the effects of joint aspect ratio into account in exterior joint design.

Reinforced concrete wide and conventional beam–column connections subjected to lateral load

In order to illustrate the structural performance of reinforced concrete wide beam–column connection, an experimental research was carried out to compare the behavior of two RC wide beam–column connections and two conventional beam–column connections when subjected to quasi-static cyclic loading. The specimens were full-scale connections and they were composed of two sets of interior and exterior joints. These specimens were designed in accordance with Syrian code of practice version 2006 (dependent on ACI 318 and ACI 352-R02 codes). Transverse beams in the wide beam–column joints, were also wider than the columns. Experimental results indicated that the hysteresis response of the wide beams was likely exhibited remarkable enhancement compared to that of conventional beams and the total energy dissipating capacity of a wide beam–column connection was higher than the conventional joint. Also it was found that by presence of the longitudinal reinforcement of the spandrel beam which was also a wide beam in the wide beam–column joints, flexural hinging mechanism in the wide beam was occurred instead of torsion brittle mode of failure. The experimental behavior of the sub-assemblages is reported within this paper.

Performance of an Interior Beam-Column Joint with and without a Slab under Cyclic Load

The beam-column joint is a crucial zone in a reinforced concrete moment resisting frame. It is subjected to large forces during severe ground shaking, and its behaviour has a significant influence on the response of the structure. In the present study, two half-scaled cast-in-situ beam-column subassemblies (i) without slab and (ii) with slab, with reinforcement detailing as per ACI 318-63 (1963) provisions are constructed. The beam-column joints are comprehensively instrumented and tested under static displacement controlled cyclic loading. This paper explains the contribution of the floor slab, especially in “Tension flange” on the overall cyclic behaviour of the subassembly, and the experimental results of horizontal joint shear stress are discussed, and compared with the ACI 352R-02 provisions.

Behavior of Reinforced Concrete Wide Concealed-Beam/Narrow-Column Joints under Lateral Earthquake Loading

This study discusses an experimental program carried out for evaluating the behavior of reinforced concrete wide concealed-beam/narrow-column joints when subjected to lateral earthquake loading. The first part of the study focuses on as-built joints, designed and constructed without taking earthquake loads into account. The second part of the study concentrates on the seismic performance of the same joints tested in the first part, except that the reinforcement details are improved in part in accordance with ACI 318-08 provisions for earthquake-resistant structures. Four full-scale interior and exterior beam-column subassemblages were tested under quasi-static cyclic lateral loads. The joints satisfied some of the ACI 318-08 design and steel detailing requirements but still violated the dimension limitations specified in the same code or recommended by ACI 352R-02. All joint specimens developed considerably improved seismic performance, manifested by preventing or delaying joint shear failure, higher lateral load capacities, lower stiffness degradation, larger energy dissipation capacities, and a stable overall hysteretic response when compared with the as-built joints.

Probabilistic Joint Shear Strength Models for Design of RC Beam-Column Connections

This paper constructs an extensive experimental database that includes all the types of reinforced concrete (RC) beam-column connections found in the literature to have experimental joint shear failure. Three kinds of RC joint shear strength models are developed using this database in conjunction with a Bayesian parameter estimation method. The improved performance of the developed joint shear strength models is evaluated by comparison with other deterministic RC joint shear strength models from the literature and codes. A modified ACI 352R-02 joint shear strength definition for design, with adjusted joint shear strength factors for greater consistency, is suggested.

A new statistical approach for joint shear strength determination of RC beam-column connections subjected to lateral earthquake loading

Reinforced concrete (RC) joint shear strength models are constructed using an experimental database in conjunction with a Bayesian parameter estimation method. The experimental database consists of RC beam-column connection test subassemblies that maintained proper confinement within the joint panel. All included test subassemblies were subjected to quasi-static cyclic lateral loading and eventually experienced joint shear failure (either in conjunction with or without yielding of beam reinforcement); subassemblies with out-of-plane members and/or eccentricity between the beam(s) and the column are not included in this study. Three types of joint shear strength models are developed. The first model considers all possible influence parameters on joint shear strength. The second model contains those parameters left after a step-wise process that systematically identifies and removes the least important parameters affecting RC joint shear strength. The third model simplifies the second model for convenient application in practical design. All three models are unbiased and show similar levels of scatter. Finally, the improved performance of the simplified model for design is identified by comparison with the current ACI 352R-02 RC joint shear strength model.

Key influence parameters for the joint shear behaviour of reinforced concrete (RC) beam–column connections

An extensive database of reinforced concrete (RC) beam–column connection test specimens exhibiting joint shear failure has been constructed. All test specimens included (with at least a minimum amount of joint transverse reinforcement necessary for proper joint confinement) were subjected to cyclic lateral loading, and had no out-of-plane members (transverse beams or slabs). Major categories within the database include the type of joint shear failure (in conjunction with, and also without, yielding of longitudinal beam reinforcement), as well as connection type (interior, exterior, and knee joint). Influence parameters for joint shear stress and/or strain behaviour at identified key points (displaying the most distinct stiffness changes) have been assessed. Concrete cracking and yielding of joint transverse or longitudinal beam reinforcement triggered the most distinct changes in stiffness, for both overall and local behaviour up to the point of initiation of joint shear failure (maximum experimental storey shear). Examined parameters for joint shear behaviour were grouped by material property, joint panel geometry, reinforcement confinement, column axial load, and reinforcement bond condition. The most important influence parameters on joint shear behaviour were found to be somewhat different by connection type and failure mode sequence. However, concrete compressive strength was the most common governing parameter on joint shear behaviour for all groups in the constructed database. In addition, joint shear cracking stresses and strains (for the point displaying the first distinct stiffness change) were investigated by simple equations. Finally, the design checks recommended by ACI 352R-02 were also examined for the specimens within the constructed database.