Wide Beam Column Connections Research Articles

Seismic performance of precast wide beam-column connections with asymmetrical anchorage reinforcement details

This study aims to investigate the seismic performances of precast concrete (PC) wide beam-column connections under reversed cyclic loading, in which the precast beam width is 1.5 times larger than that of column. Experimental program consists of a monolithic reinforced concrete (RC) specimen and two PC specimens with unique connection details. To avoid reinforcement congestions and also to secure emulative connecting performances, the PC specimens were integrated by asymmetrically placed connecting bars anchored into the column panel zone, and their anchorage end details were chosen as a key testing variable. Detailed numerical models were developed to identify the failure mechanisms and key influencing factors of the cyclic responses of PC wide beam-column connections. It appeared that the precast wide beam-column connections with asymmetrical anchorage details can also provide the so-called emulative seismic performance as a monolithic connection. Significant effects of bond-slip behaviors of the anchorage connecting reinforcements in the joint and axial compression level of the column on the seismic performance of PC wide beam-column connections were also identified by the nonlinear numerical simulations.

Seismic Upgrading of RC Wide Beam–Column Joints Using Steel Jackets

This study is devoted to experimentally investigate the seismic behaviour of reinforced concrete (RC) wide beam–column joints equipped with a steel jacketing seismic strengthening solution. To this end, three identical full-scale specimens have been tested under cyclic loading, one in the as-built condition and two after the application of the strengthening solutions. Details of selected solutions are described in the paper along with the experimental results which confirm how the application of simple and feasible steel interventions can effectively improve the seismic capacity of wide beam–column connections in RC frames, especially in terms of lateral load carrying capacity and energy dissipation.

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.

Parametric finite element analysis of RC wide beam-column connections

This paper presents the finite element analysis (FEA) of reinforced concrete wide beam-column connections using the theoretical context of the concrete damaged plasticity (CDP) model. The predictive capability of the model was verified by simulating the behaviour of four full-scale, exterior wide beam-column connections that were tested under reversed cyclic loading conditions. A brief description of the test program is reported. The finite element predictions showed excellent agreement with the test results, in particular, the lateral load-displacement response, reinforcement yielding, crack patterns and failure modes. In addition, the sensitivity of the results to various model parameters, including the viscosity parameter, mesh size, dilation angle, yield surface variables, damage parameter, fracture energy, and the type of analysis was discussed. The key parameters of the model and their distinct characteristics were identified. Finally, the parametric numerical study was conducted to explore the effects of several parameters including the column axial load, column and beam dimensions, beam bar anchorage ratio, and spandrel beam reinforcement, on the performance of exterior wide beam-column connections.

FE Modelling of the Seismic Behavior of Wide Beam-Column Joints Strengthened with CFRP Systems

A large share of reinforced concrete (RC) framed buildings is provided with wide beams being a type of beam allowing greater freedom in the architectural arrangement of interiors, beyond further advantage due to fewer formworks needed during the construction. Nevertheless, little attention has been devoted to the seismic vulnerability of this kind of framed RC buildings as well as to the study of strengthening systems purposely developed for wide beams and wide beam-column connections. Under these premises, this paper proposes simple strengthening solutions made by Fibre Reinforced Polymers (FRP) systems able to effectively improve seismic capacity through feasible arrangement suitable in case a wide beam is present. On the basis of wide beam-column joints previously tested without strengthening system, detailed nonlinear finite element models were calibrated. Then, an FRP strengthening intervention based on a brand new arrangement was modeled in order to perform additional simulations under seismic actions. This way, the effectiveness of the strengthening intervention was assessed finding out that significant strength and ductility increments were achieved with a relatively simple and cheap strengthening arrangement. Additional research would be desirable in the form of experimental tests on the simulated wide beam-column joints.

Exterior RC Wide Beam–Column Connections: Effect of Spandrel Beam on Seismic Behavior

AbstractThis paper presents the results of a set of experiments performed on four large-scale exterior wide beam–column connections. The beam and column geometry and reinforcement detailing are ide...

Effect of post-tensioned spandrel beam on wide beam–column connections

Reinforced concrete wide beam flooring systems are used increasingly in seismic regions, despite little information being available on their performance under seismic actions. This paper presents the results of a set of experiments performed on two full-scale exterior wide beam–column connections, which were tested under lateral quasi-static reversed cyclic loading. The control specimen had both longitudinal and transverse reinforcement in its spandrel beam. The second specimen was built in the same way but provided with post-tensioning force. The specimens were tested under a combination of axial force and quasi-static reversed cyclic lateral displacements. Results show that the control specimen reached its expected beam flexural capacity at a drift ratio of 3%, and then the joint shear failure and spandrel beam torsional failure controlled the behaviour. The seismic performance of the specimen with a post-tensioned spandrel beam was considerably improved compared to the control specimens. The specimen sustained a 5% drift without any significant drop in strength. No signs of joint shear failure or spandrel beam torsional failure were observed in this specimen. The results indicate that adopting a post-tensioned spandrel beam can not only prevent torsional failure, but can also improve the joint shear capacity and displacement ductility.

Analysis of laterally loaded exterior wide beam–column connections

Most of the current design codes of practice allow the use of reinforced-concrete moment frames with wide beams in regions of high seismicity. These design codes prescribe beam-width limitations and special reinforcement details to minimise the lag in the formation of full-width plastic hinges. However, due to insufficient experimental and analytical studies, empirical design formulas for beam-width limitation, with remarkable differences, have been implemented in these codes. In this paper, an effective beam-width model of exterior wide beam–column connections is analytically developed using the equivalent-frame model representation, where the effect of torsion of transverse beams and flexure around the joint core is considered. The validity of the model is verified using flexural strength predictions of previously published tests in the literature, covering a wide range of design parameters. Combining the proposed effective beam-width model and the rational, analytical approach, a formula is presented for determining the beam-width limitation of exterior wide beam–column connections. For convenient application in practical design, the proposed beam-width limitations of both exterior (derived in this paper) and interior connections (previously derived by the authors) are further simplified, and the relevant design curves and charts are presented.

Seismic performance and force transfer of wide beam–column joints in concrete buildings

Various experimental investigations have been conducted on wide beam–column connections in reinforced concrete buildings in the past decade. However, the cyclic behaviour and failure modes of such connections under seismic loading are not clearly understood due to the complexity of force-transfer mechanisms in joint cores. In this paper, an investigation is conducted on the cyclic behaviour and force-transfer mechanisms of reinforced concrete exterior wide beam–column joints using computational simulation. Exterior wide beam specimens with different beam widths and reinforcement details are simulated under reversed cyclic loading using well-calibrated finite-element models with appropriate material constitutive laws and boundary conditions. It is shown that wide beam–column joints have good post-peak behaviour compared with conventional beam–column joints, which show severe pinching behaviour and low inherent ductility, although having higher strength and stiffness. Two load-transfer paths in wide beam–column connections have been identified, which are characterised by two struts with different inclined angles in the connecting wide beams and transverse beams. On the basis of research findings, reinforcement details and width limitation of wide beams are addressed in connection with the design of exterior wide beam–column connections.

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.

Effective beam width of reinforced-concrete wide beam–column connections

The reinforced-concrete wide-beam floor system is recognised as one of the most efficient beam-and-slab floor systems in buildings. However, potential advantages of the system as a lateral load-resisting structure are often ignored due to a lack of understanding of the seismic behaviour of wide beam–column connections. Design codes prescribe beam width limitations to minimise the shear lag effect on the formation of full-width plastic hinges and achieving the expected capacity. However, owing to insufficient experimental and analytical studies, empirical design formulas for the beam width limitation, with remarkably different results, have been implemented in different design codes. In this paper, parametric studies of the influence of key parameters on the behaviour of wide beam–column connections are conducted based on available test results. An effective beam-width model is analytically developed using the equivalent-frame representation, where the effects of torsion of transverse beams and flexure around the joint core are considered. The validity of the model is verified using flexural strengths of test specimens, covering a wide range of design parameters. Combining the proposed effective beam-width model and the rational analytical approach, a simple and efficient, yet accurate, design formula is presented for determining the beam width limitation of wide beam–column connections.

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.

A seismic index method for vulnerability assessment of existing frames: application to RC structures with wide beams in spain

A method for assessing the vulnerability of existing frames in terms of an energy-based seismic index is proposed. The ground motion is characterized by the so-called Seismic Hazard Energy Factor AEI, and the susceptibility of the frame to damage is a function of two counterpart energy factors, AEIS and AEIU. AEIS represents the level of the “maximum earthquake” that the frame can sustain within the elastic range. AEIU characterizes the level of the “ultimate earthquake” associated with the collapse of the structure. The procedure takes into account the relation between the dynamic properties of the existing frame and the spectral shape of the ground motion expected at the site. The seismic index used by the method has a transparent and direct physical meaning; thus, it is useful not only for screening existing buildings but also to design a seismic retrofit solution, if needed. The method is applied to reinforced concrete frames with wide beam-column connections built in the southern part of Spain during the 1970’s, 1980’s and 1990’s.

An energy-based procedure for the assessment of seismic capacity of existing frames: Application to RC wide beam systems in Spain

Abstract A methodology for assessing the seismic capacity of existing frames in terms of energy is proposed. It estimates the global amount of input energy—in form of a factor AE IU —and hysteretic energy that the overall structure can dissipate until collapse under earthquake-type loadings. The method requires static pushover analyses to determine the ductility factor and energy shape of an equivalent single-degree-of-freedom system for the first—two or more—modes. The procedure accounts for the relation between the frequency content of the earthquake expected at the site and the dynamic properties of the existing structure. It can be useful for evaluating the possible deficit on energy dissipation capacity of existing structures, and for designing seismic retrofit solutions. Finally, the methodology is applied to reinforced concrete frames with wide beam-column connections representative of existing post-1970 buildings located in the earthquake-prone southern part of Spain.

Interior wide beam-column connections in existing RC frames subjected to lateral earthquake loading

The seismic performance of two RC interior wide beam-column connections representative of existing frames designed and detailed according to past construction practices in the moderate-seismicity Mediterranean area was investigated experimentally. The specimens were subjected to axial loads, moderate levels of gravity loading and cyclic displacements up to failure. The specimens exhibited a “strong column-weak beam” type of flexural yielding mechanism. The wide beams did not reach the expected capacities corresponding to the formation of a full-width plastic hinge. The wide-beam longitudinal bars exhibited significant slippage, and the transverse beams underwent severe torsion cracking and even failure; this caused severe pinching in the load versus displacement hysteretic loops and exacerbated the intrinsic flexibility of this type of connection. The average drift ratios at first yielding of the wide beam longitudinal reinforcement and at failure were 2.7 and 4.5%, respectively. The displacement ductility ratio was about 2.8. The ultimate energy dissipation capacity of each specimen—obtained by dividing the total plastic strain energy by the product of the yield load and yield displacement—was approximately 9, which is about one fourth of the value recommended for providing adequate seismic performance. Finally, a simple approach is suggested for prediction of the bending capacity of existing connections.

Exterior wide beam–column connections in existing RC frames subjected to lateral earthquake loads

In this paper, the seismic performance of reinforced concrete exterior wide beam–column connections with shallow spandrel beams lightly reinforced for torsion and moderate levels of gravity loads was investigated experimentally. The study focuses on existing frames designed and detailed according to construction practices used over ten years ago in the moderate-seismicity Mediterranean area. The results can be useful for assessing the seismic vulnerability of older structures and orienting seismic retrofit alternatives. Two 3/5 scale test models representative of exterior sub-assemblages in a prototype six-story building were subjected to gravity-load levels typical of those acting during an earthquake, and quasi-static cyclic lateral loads until failure. The performance was studied in terms of strength, displacement, ductility and energy dissipation capacity. The data are analyzed in conjunction with the results of previous tests. The specimens exhibited a “strong column–weak beam” type of flexural yielding mechanism. The average drift ratios at first yielding of the wide beam longitudinal reinforcement, δ y o , and at failure, δ u , were 2.2% and 4.5% respectively; the displacement ductility ratio μ was approximately 2.2. Comparison to similar connections without added gravity loads showed that moderate levels of gravity loading increased δ y o by about 40%, and decreased by a similar percentage the value of μ and the energy dissipated in each half cycle of displacement expressed in terms of an equivalent viscous damping ratio. Finally, two approaches for estimating the wide-beam flexural capacity are examined.

AE Monitoring for Damage Assessment of RC Exterior Beam-column Subassemblages Subjected to Cyclic Loading

This paper ascertains that Acoustic Emission (AE) monitoring is very effective for assessing the damage of reinforced concrete wide beam-column connections subjected to earthquake-type loadings. A cyclic test is conducted on an exterior connection until its failure. The experimental results show a strong correlation between the hysteretic strain energy and the AE energy histories. For this reason, a tentative formula is proposed, to predict the level of damage and the closeness to failure of the connection on the basis of the AE recorded by one piezoelectric sensor located near the critical zone (i.e., the beam-end and beam-column joint).

Inelastic behaviour of exterior wide beam–column connections with U-shaped precast shell beam stressed by post-tensioning

The post-tensioned precast concrete system (PPS) consists of U-shaped precast wide beams and a concrete column. The continuity of the beam–column joint is provided with the topping concrete on the precast concrete shell beam and post-tensioning. The purpose of the current paper is to evaluate the response of a PPS exterior beam–column joint subjected to cyclic lateral loading. To this end, the experimental investigation was performed with three half-scale specimens of the exterior connection. The design parameters are the beam-width-to-column-width ratio and the amount of beam reinforcement placed inside the column core. The test results showed that specimen cracks were distributed well and plastic hinges spread towards midspan without any significant degradation of strength and ductility. Furthermore, the specimens sufficiently resist up to a limiting drift ratio of 0·035 in accordance with the the provisions given by the American Concrete Institute in their ‘Acceptance criteria for moment frames based on structural testing’.

Post-Tensioned Interior Precast Wide Beam—Column Connections Subjected to Lateral Loading

The post-tensioned precast concrete system (PPS) developed in this study consists of U-shaped precast wide beams and concrete columns, where the continuity of wide beam-column joint is provided with the cast-in-place concrete on the U-shaped precast wide beam and the post-tensioning to the beam after casting of slab. The PPS structure can overcome the defect of discontinuity in the connections of precast members using cast-in-place concrete on precast members, and complement the low sectional efficiency of wide beam by applying the post-tensioning. In this study, an experimental investigation was performed with three half-scale specimens of interior connection fabricated employing PPS structure. Specifically, this paper presents the response of PPS interior beam-column joint subjected to cyclic lateral loading and evaluates the relevance of the beam-to-column width ratio criteria specified in ACI 318–05. The test results indicate that the PPS specimens can resist properly seismic loads maintaining overall structural integrity.

Modeling of cyclic bond deterioration in RC beam-column connections

This paper presents an analytical model for RC beam-column connections that takes into account bond deterioration between reinforcing steel and concrete. The model is based on the Lumped Damage Mechanics (LDM) theory which allows for the characterization of cracking, degradation and yielding, and is extended in this paper by the inclusion of the effect as observed in those connections. Slip is assumed to be lumped at inelastic hinges. Thus, the concept of slip hinge, based on the Coulomb friction plasticity theory, is formulated. The influence of cracking on the behavior is taken into account by using two concepts of LDM: the effective moment on an inelastic hinge and the strain equivalence hypothesis. The model is particularly suitable for wide beam-column connections for which bond deterioration dominates the hysteretic response. The model was evaluated by the numerical simulation of five tests reported in the literature. It is found that the model reproduces closely the observed behavior.