Beam Bars Research Articles

Experimental assessment of unreinforced exterior beam–column joints with deformed bars

In the performance assessment of typical existing buildings, seismic collapse safety might be significantly affected by non-linear behavior of joints that are involved in the failure mechanism, especially if they are characterized by poor structural detailing such as the lack of an adequate transverse reinforcement in the joint panel.Unfortunately, commonly accepted tools to assess existing joints capacity are not available. Few reliable approaches for modeling all sources of nonlinearity are proposed in literature for poorly designed beam–column joints because of relatively poor information from experimental tests.The present study aims at improving the understanding of seismic performance of exterior joints without transverse reinforcement in existing RC buildings through experimental tests.Two full-scale exterior unreinforced beam–column joint sub-assemblages are tested under cyclic loading. The specimens are reinforced with deformed bars but they are different for beam longitudinal reinforcement ratio. Two different kinds of joint failure are expected, with or without the yielding of the adjacent beam. Strain gauges located on beam bars and displacement transducers on the joint panel allow the complete definition of both the main deformability contributions, namely fixed-end-rotation and shear strain of joint panel, highlighting the differences between failure modes.Design criteria, adopted setup and experimental results are described and discussed. Finally, experimental results are compared with proposals from literature in terms of shear strength.

Influence Factors for the Shear Strength of Exterior and Interior Reinforced Concrete Beam-column Joints

This paper investigates the key influence factors for the shear strength of both exterior and interior reinforced concrete (RC) beam-column joints. A database of totally 172 experimental RC beam-column connections constructed using the published literature was used in the analysis. Based on the database, the correlation coefficient (CC) between the considered parameters and the tested joint shear strength was computed, and the important level of these parameters was quantified. Results of the analysis showed that five key parameters for the joint shear strength included (1) the concrete compressive strength, (2) the vertical joint shear reinforcement, (3) the beam bars detail index, (4) the horizontal joint shear reinforcement and (5) the column axial stress. Among the influence factors, the concrete compressive strength had the most significant correlation to the joint shear strength and interestingly its correlation was higher for the interior connections with CC = 0.8 compared to CC = 0.69 for the exterior connections. For the remaining factors, the analysis conversely showed that their correlations to the joint shear strength of exterior joint were stronger than that of the interior joint.

鋼繊維補強コンクリートを用いた省人化型接合部工法の実用化

著者らは，鉄筋コンクリート（RC）造のPCa工法を用いた施工において，柱と梁の接合作業を省力化した鋼繊維補強コンクリートを用いた省人化型接合部工法を開発し，2015年6月に実用化に至った。本工法では，3つの画期的な特長を有している。1）梁主筋を通し定着せずに，接合部内で梁主筋を機械式定着させる点，2）梁主筋間の接合部せん断補強筋を配筋しない点，3）接合部せん断強度および，梁主筋の定着強度を割り増すために繊維補強コンクリートを使用し，日本（建築分野）で初めて繊維補強コンクリートの効果を構造設計に取り入れた点である。本稿では，工法の概要から実用化に至った事例の概要について示す。

Structural Behaviour and Design of Geopolymer Concrete Members

The worldwide production of concrete is on the increase in order to meet the increasing rate of construction. Since cement production contributes to the greenhouse gas emission, it is vital to develop alternative low-emission binders to reduce the carbon footprint of concrete. Fly ash based geopolymer is an alternative binder that has potential to reduce the CO2 emission of concrete production. It has been shown in different studies that the mechanical properties of geopolymer concrete are comparable to those of ordinary Portland cement (OPC) concrete. This paper describes the behaviour and design aspects of geopolymer concrete structural members. The design aspects presented in this paper are bond of reinforcing steel in pull-out and spliced bars in beams, beams in shear and flexure, and columns in uniaxial and biaxial bending. It is shown that the current provisions for OPC concrete can be conservatively used for design of reinforced geopolymer concrete members.

Bond performance of basalt fiber-reinforced polymer bars in conventional Portland cement concrete: a relative comparison with steel rebar using the hinged beam approach

Abstract This paper reports the results of an experimental investigation carried out to evaluate the bond stress behavior of basalt fiber-reinforced polymer (BFRP) bar and steel rebar (SR) in conventional C30-type concrete. The experimental program was conducted on testing 16 hinged beam specimens that were prepared according to BS 4449:2005+A2:2009 standard. Conventional C30-type concrete was used to produce hinged beams. In beam tests, bar diameter and embedment length were used as experimental variables. The bond performances of BFRP bar and SR were compared with the help of the load-slip results of hinged beam bending tests conducted on produced beam samples after 28 days of curing. Results showed that much higher bond stress values were obtained from BFRP bars compared to SR for both 12 and 8 mm bar diameters. Besides, the maximum bond stress values decreased with increasing bar diameter and embedment length for both BFRP bar and SR.

Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors

This study presents an experimental effort for the damage assessment of concrete reinforcing bars using bonded piezoelectric transducers and the implementation of an integration analytical approach based on the electromechanical admittance method. Tests are performed in (i) single steel reinforcing bars with predefined and artificially induced damages corresponding to two different damage states and (ii) steel reinforcing bars embedded in typical large scale reinforced concrete beams subjected to flexural load at two different loading levels (before and after yielding) that inevitably cause two different damage levels. The damage of the embedded steel bars in the concrete beams after yielding is the result of excessive elongation of the bars due to yielding caused by flexural deformation of the beams. Test measurements of healthy and damaged steel bars and reinforced concrete beams have been conducted using the developed monitoring system. The experimental program comprises data acquisition of current intensity curves for healthy and damaged bars as detected by the test instrumentation and implementation of the adopted admittance-based procedure to evaluate damages at different levels. It can be concluded that the sensitivity of the piezoelectric transducers greatly depends on the selection of the excitation frequencies. Admittance signatures showed a clear gradation of the examined damage levels. The experimental results provide cogent evidence that piezoelectric lead zirconate titanate transducers are sensitive to damage detection in concrete and in steel reinforcing bars from an early stage of the performed tests. Thus, the use of these sensors for monitoring and detecting concrete cracking and steel yielding by employing the electromechanical admittance approach can be considered as a highly promising non-destructive structural health monitoring method.

Seismic Behavior of RC Beam-Column Exterior Joints with Unbonded Tendons and High Strength Concrete

In the moment frame subjected to earthquake loads, beam-column joint is structurally important for ductile behavior of a system. ACI Committee 352 proposed guidelines for designing beam-column joint details. The guidelines, however, need to be updated because of the lack of data regarding several factors that may improve the performance of joints. The purpose of this study is to investigate the seismic performance of reinforced concrete exterior joints with high-strength materials and unbonded tendons. Three specimens with different joint shear demand-to-strength ratios were constructed and tested, where headed bars were used to anchor the beam bars into the joint. All specimens showed satisfactory seismic behavior including moment strength of 1.3 times the nominal moment, ductile performance (ductility factor = at least 2.4), and sufficiently large dissipated energy.

Monitoring corrosion of reinforced concrete beams in a chloride containing environment under different loading levels

Corrosion has significant adverse effects on the durability of reinforced concrete (RC) structures, especially those exposed to a marine environment and subjected to mechanical stress, such as bridges, jetties, piers and wharfs. Previous studies have been carried out to investigate the corrosion behaviour of steel rebar in various concrete structures, however, few studies have focused on the corrosion monitoring of RC structures that are subjected to both mechanical stress and environmental effects. This paper presents an exploratory study on the development of corrosion monitoring and detection techniques for RC structures under the combined effects of external loadings and corrosive media. Four RC beams were tested in 3% NaCl solutions under different levels of point loads. Corrosion processes occurring on steel bars under different loads and under alternative wetting - drying cycle conditions were monitored. Electrochemical and microscopic methods were utilised to measure corrosion potentials of steel bars; to monitor galvanic currents flowing between different steel bars in each beam; and to observe corrosion patterns, respectively. The results indicated that steel corrosion in RC beams was affected by local stress. The point load caused the increase of galvanic currents, corrosion rates and corrosion areas. Pitting corrosion was found to be the main form of corrosion on the surface of the steel bars for most of the beams, probably due to the local concentration of chloride ions. In addition, visual observation of the samples confirmed that the localities of corrosion were related to the locations of steel bars in beams. It was also demonstrated that electrochemical devices are useful for the detection of RC beam corrosion.

Plastic Hinge Relocation Methods for Emulative PC Beam–Column Connections

AbstractVarious plastic hinge relocation methods were studied to improve the earthquake resistance of emulative precast concrete (PC) beam-column connections using PC U-shell beams. The present study used two strengthening methods (hooked bars and headed bars) and a weakening method (reduced beam bar section), to relocate the plastic hinge zone of beams away from the weak beam-column joint. Five full-scale test specimens including a conventional reinforced concrete (RC) specimen were tested to evaluate the earthquake resistance. The test results showed that the used relocation methods significantly decreased that bond-slip of beam flexural bars and joint shear cracking. As a result, the energy dissipation capacity significantly increased, compared to those of the conventional RC specimens and PC specimens without relocation methods. On the basis of the test results, design recommendations are suggested for plastic hinge relocation design of emulative PC beam-column connections.

RESEARCH OF STABILITY NONCENTRAL COMPRESSED OF COMPOSITE BAR

In a publication the decision of task of stability of the compressed bar is resulted with the use of model as the stratified system. The bars of the stratified beam are connected by resilient discrete supports (by slats) or resilient layer

Embedded Through-Section shear strengthening technique using steel and CFRP bars in RC beams of different percentage of existing stirrups

The Embedded Through-Section (ETS) technique is a promising technique for the shear strengthening of existing (RC) elements. According to this technique, holes are drilled through the beam section, and bars of steel or FRP material are introduced into these holes and bonded to the concrete with adhesive materials. An experimental program was carried out with RC T-cross section beams strengthened in shear using the ETS steel bars and ETS CFRP rods. The research is focused on the evaluation of the ETS efficiency on beams with different percentage of existing internal transverse reinforcement (ρsw=0.0%, ρsw=0.1% and ρsw=0.17%). The effectiveness of different ETS strengthening configurations was also investigated. The good bond between the strengthening ETS bars and the surrounding concrete allowed the yield initiation of the ETS steel bars and the attainment of high tensile strains in the ETS CFRP rods, leading to significant increase of shear capacity, whose level was strongly influenced by the inclination of the ETS bars and the percentage of internal transverse reinforcement.

The Strength and Ductility of Lapped Splices of Reinforcing Bars in Tension

When designing a reinforced concrete member for strength, ductility and robustness, it is essential that the tensile reinforcement at the critical section can not only develop the yield strength of the steel f sy, but that it can sustain this level of stress as deformation increases. At a lapped splice, each bar must be fully anchored beyond the lap length. The minimum lap lengths of deformed reinforcing bars in tension specified in the Australian Standard for Concrete Structures AS3600-2009 were recently revised and a procedure similar to, but less conservative than, the provisions in Eurocode 2 was adopted. The new provisions require longer lap lengths for small diameter bars in slabs, but considerably shorter lap lengths for larger diameter bars in beams and columns. This paper reports on several series of tests that examine the efficacy of the AS 3600-2009 provisions from the perspectives of adequate strength and ductility. Over 50 specimens containing both contact and non-contact lapped splices have been tested. The aim was to assess the current Australian provisions and to examine the reliability and consistency of the factors of safety associated with lapped splices. It is concluded that the strength requirements of AS3600-2009 are adequate for small diameter bars in slabs but may not provide an adequate factor of safety for large diameter bars in beams. Also, the AS3600 provisions may not ensure sufficient ductility of a lapped splice in members that use high strength concrete. Further tests are required to investigate these aspects.

On the strength and ductility of lapped splices of reinforcing bars in tension

AbstractWhen designing a reinforced concrete member for strength, ductility and robustness, it is essential that the tensile reinforcement at the critical section can not only develop the yield strength of the steel f sy, but that it can sustain this level of stress as deformation increases. At a lapped splice, each bar must be fully anchored beyond the lap length. The minimum lap lengths of deformed reinforcing bars in tension specified in the Australian Standard for Concrete Structures AS3600-2009 were recently revised and a procedure similar to, but less conservative than, the provisions in Eurocode 2 was adopted. The new provisions require longer lap lengths for small diameter bars in slabs, but considerably shorter lap lengths for larger diameter bars in beams and columns. This paper reports on several series of tests that examine the efficacy of the AS 3600-2009 provisions from the perspectives of adequate strength and ductility. Over 50 specimens containing both contact and non-contact lapped splic...

연성 강봉을 사용한 프리캐스트 콘크리트 보-기둥 접합부의 내진성능

Precast concrete (PC) beam-column connections using ductile rods are proposed for earthquake zone. An existing beam-column connection, two PC specimens designed by considering failure modes and a conventional RC specimen were tested under cyclic loading to evaluate the seismic performance. The specimens were designed to satisfy the requirements of current design code. The variables are the yield strength of longitudinal reinforcing bars of PC beams. The test results showed that the proposed system applying smaller yield strength of the longitudinal reinforcing bars at the PC beams than the ductile rods was satisfied with seismic criteria. The deformation capacity and energy dissipation capacity of the proposed PC beam-column connections were greater than those of the existing DDC system.

Cyclic behaviour of interior beam–column joints reinforced with plain bars

SummaryThe seismic damages commonly observed on beam–column joints of old reinforced concrete structures, built with plain bars and without proper detailing, justifies the need to further study the behaviour of this type of structures. The response of these structures when loaded cyclically, as occurs during the earthquakes, is partially controlled by the bond properties between the reinforcing bars and the surrounding concrete. This paper presents the results of an experimental campaign of unidirectional cyclic tests carried out on six full‐scale beam–column joints built with plain bars. These joint specimens are representative of existing reinforced concrete structures, that is, built without adequate reinforcement detailing for seismic demands. For comparison, an additional specimen is built with deformed bars and tested. The seven specimens are designed and detailed to allow the investigation of the influence of bond properties, lapping of the longitudinal bars in columns and beams, bent‐up bars in the beams, slab contribution and concrete strength. The lateral force–drift relationships, global dissipated energy evolution, contribution of the joint, beams and columns to the global dissipated energy, ductility, equivalent damping, final damage observed, homogenized reinforced concrete damage index, displacement components, curvature evolutions and Eurocode requirements are presented and discussed. Copyright © 2014 John Wiley & Sons, Ltd.

A Effective Solution Method Based on Bayesian Rule for Prediction of Long-Term Tensile Strength of GFRP Bars in Concrete Beams

It is necessary to research on the long term structural behavior of GFRP bars in concrete by limited samples. The two models, Arrhenius Equation and Fick’s Law were compared to form a long-term durability prediction thinking. Based on the work and ideas of the prior researchers, a detailed derivation of the iterative equation on the Bayesian prediction was conducted. Especially, a new likelihood function was set up to solve the long term behavior prediction of GFRP bars in concrete with less information. Then a new and effective solution method was developed. The residual strength behavior of GFRP bars in concrete beams after seven years’ environmental exposure was analyzed. The results showed that the theoretical predictions and experimental data were very close and theoretical prediction model was reasonable.

Numerical simulation of performance of near-surface mounted FRP-upgraded beam–column sub-assemblages under cyclic loading

This study deals with the performance of the upgrading schemes for the existing gravity load designed (GLD) reinforced concrete (RC) beam–column sub-assemblages using near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars. In this study, exterior beam–column sub-assemblage of a general RC-framed structure has been considered. Numerical investigations of the sub-assemblages have been carried out under cyclic loading using nonlinear finite element analysis. Experimentally validated numerical models have been used for evaluating the performance of various upgrading schemes using NSM bars. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond–slip relations between concrete and steel reinforcement have been incorporated. The study also includes numerical investigation of crack and failure patterns, ultimate load-carrying capacity, strain comparisons and formation of plastic hinges, load–displacement hysteresis, energy dissipation and ductility. Seismic performance in terms of energy dissipation and development of strain in beam bar shows that some of the upgraded schemes are found to be comparable to the seismically designed ductile specimens. The findings of this study would be helpful to the practising and design engineers for developing detailing criteria for newly designed – or strengthening of deficient – reinforced concrete structure.

A new empirical model for shear strength of reinforced concrete beam–column connections

A new empirical model to estimate the joint shear strength of both exterior and interior beam–column connections is proposed. In the model, four parameters that have the most influence on joint shear strength are considered. Among these four, a new parameter is introduced to consider the bond condition and the possibility of beam bars transferring joint shear force into the columns. Consideration of this parameter in the model significantly improves the accuracy of the predicted joint shear strength. To calibrate the model, a large database of 98 reinforced concrete (RC) exterior and 73 RC interior beam–column connections displaying joint failure mode was compiled from the literature. A parametric study was also carried out to evaluate the dependence of the predicted to tested joint shear strength ratio on the four influence parameters using the database. The proposed model showed superior performance over existing models. Moreover, comparisons of the predicted joint shear strength with experimental results and with four existing models showed the accuracy of the proposed model.

Effect of tension lap splice on the behavior of high strength self-compacted concrete beams

Construction using concrete is spreading widely and there is a need for concrete that is capable of flowing under its own weight without mechanical vibration or compaction and fill the places between reinforcement and the complicated form shapes. From here, Self-Compacted Concrete (SCC) appears for the first time. Limited attention has been directed toward the bond between High Strength Self-Compacted Concrete (HSSCC) and spliced bars in beams [1–8].This research studies the bond between HSSCC and spliced tension bars in beams. It is focused on observing the effect of some factors such as; reinforcement bar diameter and ratio, splice length and casting position on the beam flexural behavior. An experimental program consisting of sixteen simply supported beams divided into four groups is considered. All beams are of 1800mm span and 200×400mm cross-section cast with HSSCC. In twelve beams, the tensile steel was spliced in the constant moment zone, and four control beams without splice for comparison purpose. During testing; ultimate capacity, deflection, crack pattern and mode of failure have been recorded. Test results had been compared with proposed values in the Egyptian code of practice, other international design codes and recorded values of other researchers.

Fatigue Behavior of GFRP Reinforcing Bars in Air and in Concrete

Although the use of glass fiber-reinforced polymer (GFRP) reinforcing bars is gaining acceptance as an alternative to conventional steel reinforcement in concrete structures, little empirical data exist on the long-term fatigue performance of GFRP bars in concrete. Abrasion at the bar-concrete interface is known to have an adverse effect on bonds and on the overall member response under cyclic loading, although this effect was not adequately quantified until now. This paper presents the results of an experimental study comparing the fatigue performance of GFRP bars in air with the behavior of similar bars embedded in concrete. The experimental findings showed that the GFRP bars tested in air survived fatigue lives that were approximately a full order of magnitude longer than similar bars in concrete beams. The results were used to calibrate a statistical fatigue life model and a residual stiffness model for GFRP bars in reinforced concrete flexural members.