Behavior Of Reinforced Concrete Columns Research Articles

A lumped plasticity model for corrosion-damaged reinforced concrete columns

Chloride-induced corrosion is one of the most important causes of the strength degradation of reinforced concrete (RC) bridges. As the piers of RC bridges are important elements for sustaining lateral loads, corrosion of pier columns may lead to significant degradation of the structure. It is thus necessary to have an appropriate evaluation technique to assess the effect of corrosion on the behaviour of RC columns. Numerical modelling approaches based on a concentrated plastic hinge can predict structural behaviour rapidly and with acceptable accuracy, and are highly regarded by engineers. In this study, a numerical approach was conducted to develop an empirical lumped plasticity model (LPM) for corroded RC column elements. In this study, 13 440 RC column specimens, including corroded and uncorroded columns of both rectangular and circular cross-section, were analysed under monotonic and cyclic loading. The LPM was extracted based on regression of the results of cyclic and monotonic analyses. The calibrated model, valid for corroded and uncorroded columns, was assessed using experimental results and numerical models with data out of the range of those used in the parametric study and was found to have high accuracy. The newly developed plastic hinge model can be used to model and analyse corroded bridge columns rapidly. The results are appropriate for use in further assessments such as fragility or rehabilitation analyses.

Dynamic Behavior of RC Columns Confined with Micro-Expansive Concrete-Filled Steel Tubes Subjected to Lateral Low-Velocity Impact: Experimental and Numerical Study

In order to improve the anti-collision capacity of existing reinforced concrete (RC) columns under vehicle impact load, an experimental study on the anti-collision performance of RC columns strengthened with micro-expansive concrete filled steel tube was carried out. By combining an experiment and finite element calculation, the influence of steel tube strength, micro-expansive concrete strength and steel tube wall thickness on the anti-collision performance of strengthened RC columns were studied. The results showed that the peak displacement of an SM-RC column is 25.9% lower than that of an RC column, due to the increased stiffness, the peak impact force increased by 138.2%. The micro-expansive concrete filled steel tube reinforcement method can significantly improve the anti-collision performance of RC columns and reduce the lateral deformation. Increasing the strength grade of steel tube and thickness of steel tube can greatly improve the impact resistance of strengthened RC columns and reduce the lateral deflection deformation of short columns, compared with steel tube strength Q235, the displacement of Q690 is reduced 47.4%. the displacement of the 8-mm thick steel tube is reduced by 48.1% compared with the 4-mm one. while the strength grade of micro-expansive concrete has little effect on the impact resistance and lateral deflection deformation of strengthened RC columns.

Residual Axial Behavior of Restrained Reinforced Concrete Columns Damaged by a Standard Fire

A simplified procedure to predict the residual axial capacity and stiffness of both rectangular and circular reinforced concrete (RC) columns after exposure to a standard fire provides the means to replace the current descriptive methods. The availability of such a procedure during the design phase provides engineers with the flexibility to come up with better designs that ensure safety. In this paper, finite difference heat transfer and sectional analysis models are combined to determine the axial behavior of RC columns with various end-restraint conditions at different standard fire durations. The influence of cooling phase on temperature distribution and residual mechanical properties is considered in the analysis. The ability of the model to predict the axial behavior of the damaged columns is validated in view of related experimental studies and shown to be in very good agreement. A parametric study is then conducted to assess the axial performance of fire-damaged RC columns. A procedure is proposed to determine the residual strength and stiffness of fire-damaged RC columns in typical frame structures.

Effect of Internal Stirrups on the Eccentric Compression Behavior of FRP-Confined RC Columns Based on Finite-Element Analysis

Fiber-reinforced polymers (FRPs) have been widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can provide substantial lateral confinement to concrete. Conventionally, the presence of internal stirrups is neglected in the retrofitting design due to a lack of understanding on the effect of internal hoops when both external FRP and internal steel confinement exist, particularly under eccentric loading. In this study, a finite-element (FE) method is developed to investigate the eccentric compression behavior of FRP-confined RC columns. A reliable concrete plastic-damage model that accurately considers the confining stiffness ratio between the FRP and steel is proposed for the first time, which facilitates the study of a difficult problem: the behavior of RC columns with the dual confinement system under eccentric loading. The accuracy of the model is verified by test results. An extensive parametric study of various affecting factors is carried out to investigate the confinement mechanisms of the concrete columns in terms of the axial stress and confining pressure distributions, lateral principal stress ratio, local stress–strain response, and interaction between the FRP/steel hoops and concrete. It is found that the nonuniform confining pressures under eccentric compression are significantly affected by the internal stirrups. With the existence of discrete transverse steel reinforcement, the axial resistance of the concrete core is increased, thereby improving the ultimate load capacity of the columns. An ultimate axial load model for RC columns that considered combined FRP–steel confinement is subsequently proposed. More accurate results are obtained using the proposed model compared with those calculated from existing design codes.

Numerical Investigation of Bundled RC Column under Impact Load

Dynamic impact load has an extensive application area in civil engineering, including highway, military, and marine structures. Many researchers have studied the performance of reinforced concrete (RC) columns under impact load. However, very limited work has been conducted on the effect of bundle reinforced concrete (BRC) columns subjected to lateral impact load. In this study, to examine the behavior of RC columns under impact load, numerical simulations of one with normal reinforcement distribution and three different bundles of reinforced concrete column specimens have been conducted using an explicit finite element (FE) analysis. In addition to the bundle reinforcement distribution, the parameters considered in the study are impact scenarios, impact velocity, pure axial load, and impact locations. From the numerical analysis, it has been found that bundling of longitudinal reinforcement does not only improve the impact capacity but also stabilizes the fluctuating response of impacted reinforced concrete columns. Both peak impact force and maximum lateral displacements of impacted BRC columns increase with increasing initial impact velocity. The numerical results also show that pure axial load slightly improved the impact capacity of the BRC columns. Finally, while the global failure of the RC column governs the response of repeatedly impacted BRC columns, failure characteristics of the single impacted columns are associated with local concrete damage at the impact zone.

Behavior of RC columns and those strengthened with FRP composite under an innovative reversing cyclic eccentric axial loading

The fundamental role of columns in structural stability calls for an in-depth understanding of their behavior under different loadings. In this study, an innovative test was designed and the required apparatus was manufactured to apply axial eccentric cyclic loading in two opposite directions as an effort to create more realistic conditions for eccentric axial loading of columns in the structures under cyclic loads. For this purpose, six reinforced concrete (RC) columns were tested. The columns included non-strengthened specimens, those strengthened with longitudinal FRP strips installed using the externally bonded reinforcement on groove (EBROG) technique, and those strengthened with full FRP wraps. All the specimens subjected to axial loading with an eccentricity of 90 mm in both monotonic and reversing cyclic method (the innovative method developed herein) to compare the effects of both cyclic and monotonic loadings. The specimens exhibited reduced bearing capacity and ductility under cyclic loading when compared with those subjected to monotonic. Moreover, the trend of the load-deformation relationship of RC columns and those strengthened with FRP wraps were almost the same under monotonic and cyclic loads, while strengthened specimens with longitudinal FRP exhibited different load-deformation trends. Comparison of the specimens strengthened via the two methods used in this study revealed that using longitudinal FRP sheets via the EBROG technique caused a significant (about 60%) increase in bearing capacity under high eccentric loads through a reduction in ductility. Application of FRP wraps, however, exhibited almost no effect on bearing capacity under the same loads but led to the columns’ enhanced ductility.

Longitudinal axial strain in plastic hinge regions of reinforced-concrete columns

Energy dissipation of columns in the post-yielding range of deformation plays a significant role in preventing the total collapse of reinforced-concrete (RC) structures. However, such plastic deformations cause elongation in plastic hinge regions of RC columns if the axial force ratio is low. This study investigated the elongation behaviour of RC columns by testing five groups of 20 specimens subjected to three different loading patterns. Experimental results showed that the longitudinal axial strain of RC columns was quite different from that of RC beams because of the presence of axial force. The longitudinal axial strain of RC columns reduced with increasing axial force. Axial strain was also a function of loading pattern and lateral reinforcement ratio. Based on these observations, an analytical model was developed to predict the axial strain behaviour of RC columns. The proposed model includes four path types: a loading region, an unloading region, a slip region and a repeated loading region. The model was verified against 32 test results, including specimens tested in this study and reported in the literature. The longitudinal axial strain predicted using the proposed model agreed reasonably well with the experimental axial strains results.

Seismic behavior of strengthened square reinforced concrete columns under combined loadings

This paper presents an experimental study examining the seismic behavior of square reinforced concrete (RC) columns subjected to combined loadings. In this study, nine full-scale square RC columns were made with the same structural properties. Five of them were strengthened with high-performance ferrocement laminate and bonded steel plates in order to investigate the effects of strengthening on the seismic behavior of RC columns under combined loadings. Finally, the failure mode, hysteretic load-displacement response, bearing capacity, energy dissipation, ductility and plastic hinge characteristics were recorded and analyzed. The results show that combined loadings reduced the bearing capacity and changed the failure modes and deformation characteristics. Strengthened RC columns had significantly improved bearing capacity and different failure modes under the same combined loadings in contrast to the non-strengthened RC columns. The vertical eccentricity had little effect on the mechanical properties of columns, while the horizontal eccentricity significantly weakened the mechanical properties of columns. The mechanical properties of uniaxial compression-bending-shear-torsion columns were the worst. The tri-linear model calculation parameters under different failure modes and combined loadings were fixed and validated by experimental results.

Numerical model to simulate shear behaviour of RC joints and columns

In this paper, a new numerical model for the evaluation of the seismic behaviour of existing reinforced concrete (RC) structure with considering the effect of variation of applied axial load on columns is presented. Focus is given on developing accurate and practical models for simulating nonlinearities in joint core as well as column under varying axial load. For exterior as well as interior joints, according to experimental and finite element results, principal tensile stresses versus shear deformation relations in joint core are recommended. Moreover, to consider the effects of stirrup on the principal tensile stress-shear deformation relation, an incremental procedure is proposed based on the Mohr theory. According to the proposed numerical model, complex nonlinear behaviour of joint core is simulated by two diagonal axial springs so that the effect of variation of axial load is also considered. The properties of these springs are determined based on the proposed principal tensile stress-shear deformation relation in the joint core. Moreover, the shear and flexural nonlinear behaviour of RC beams and columns is also simulated by rotational springs. A simplified methodology is developed to consider the effects of axial load variation on shear and flexural nonlinear behaviour of RC columns. To demonstrate the capability of the proposed numerical model at structural level, two RC frames with various failure modes are investigated. The results confirm the ability of the model in predicting the nonlinear behaviour of the frame, which can provide an alternative method for engineers in practice.

Nonlinear numerical simulation of RC columns subjected to cyclic oriented lateral force and axial loading

A nonlinear Finite Element (FE) algorithm is proposed to analyze the Reinforced Concrete (RC) columns subjected to Cyclic Loading (CL), Cyclic Oriented Lateral Force and Axial Loading (COLFAL), Monotonic Loading (ML) or Oriented Pushover Force and Axial Loading (OPFAL) in any direction. In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of RC columns. In the proposed numerical simulation, the column is discretized into two Macro-Elements (ME) located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into Fixed Rectangular Finite Elements (FRFE) in general cases of CL, COLFAL or ML and are discretized into Variable Oblique Finite Elements (VOFE) in the particular cases of ML or OPFAL. For pushover particular case, a fairly fast converging and properly accurate nonlinear simulation method is proposed to assess the behavior of RC columns. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns.

Near-Field Explosion Effects on the Behaviour of Reinforced Concrete Columns: A Numerical Investigation

The high incidence of global terrorism and accidental explosions have highlighted the vulnerability of built infrastructure to blast loading. Thus, owners of iconic structures are looking for ways to protect their critical assets from the effects of explosions. Many of the research efforts, in this light, have been devoted to the effects of far-field explosions on structural elements. The effects of near-field explosions on structural elements, especially columns, have not been as widely investigated.This paper presents the results of a comprehensive research program designed to investigate the effects of near-field explosions on the behaviour of reinforced concrete columns designed and detailed for regions of different levels of seismicity. The numerical study shows that reinforced concrete columns subjected to blast loading from higher explosive charge masses have higher deflections than those subjected to blast loading from lower charge masses, but at the same scaled distance. Also, the effect of closely spaced transverse reinforcement is significant at smaller scaled distances. Thus, reinforced concrete columns designed and detailed for areas of high seismicity have an inherently high blast resistance.

Effects of circular openings on the compressive behaviour of R.C. columns

Core-drilling technique is nowadays always more frequently performed in existing reinforced concrete (RC) structures in order to investigate on the mechanical properties of concrete and for structural health monitoring purposes. Even if the engineering practice discourages to drill columns, this can be often unavoidable. In this last case the presence of the circular opening influences the compressive behavior of the column in terms of load-carrying capacity and axial deformability. The goal of this investigation was the experimental evaluation of the effects induced by circular openings on the behavior of RC columns. Twenty-four reinforced and plain concrete prisms in presence of circular openings were tested in compression. The effects of concrete strength, hole diameter and repairing were taken into account. Axial loads and strains were recorded during the tests in order to evaluate the effects of key parameters. Finally, analytical predictions of the load-carrying capacity were made with a strut-and-tie model available in the literature, which was also used to estimate the load-shortening curves showing good agreement with experimental data.

Behavior of reinforced concrete columns under combined effects of axial and blast-induced transverse loads

The results of numerical studies on the dynamic response of reinforced concrete (RC) columns subjected to axial and blast-induced transverse loads utilizing an advanced single-degree-of-freedom (SDOF) model are presented in this paper. The main variables considered in this study were the level of axial force and longitudinal reinforcement ratio. This work addressed the effect of various levels of axial compressive load on the resistance function, time-history response, and load–impulse diagram when the columns were subjected to transverse loads due to blast. The blast loads were idealized as triangular pulses and the effects of flexural, diagonal shear, and tension membrane behaviors were included in the RC column response. The results from the SDOF analyses were validated using the commercial finite element (FE) program ABAQUS. The results of the parametric study indicated that the level of axial compressive load has a significant influence on the behavior of RC columns when subjected to transverse blast-induced loads.

Shear Resistant Behavior of RC Columns Subjected to Axial Pulse-Like Ground Motions

The shear-resistant behavior of reinforced concrete (RC) columns subjected to axial velocity pulse-like ground motions was studied. Single RC columns with the constant vertical and horizontal fundamental period were used to investigate the influences of fault-distance of earthquake records, vertical to horizontal acceleration spectral ratio of earthquake records, initial axial load ratio and shear span ratio of RC column, on the shear-resistant behavior of RC columns. a suite of 18 strong ground motion records from Chi-chi earthquake divided into three fault-distance groups were taken as excitations to execute nonlinear dynamic time history analysis. The results demonstrated that axial velocity pulse-like earthquake action (fault-distance) had significant influences on the shear resistant-resistant of RC columns. Shear-resistant behavior (shear capacity/shear demand) increases with the increasing of fault-distance. Fault-distance and shear span ratio had a certain coupling influences on the shear-resistant behavior of RC columns.

Seismic Behaviour of RC Columns Strengthened with Steel Bar/Wire Mesh Mortar

In order to enhance the seismic behavior of reinforced concrete (RC) columns more efficiently, a thought to strengthen concrete columns by using steel bar/wire mesh mortar （FS）was proposed. An experimental study including five RC square columns strengthened with FS and steel bar mat mortar (S), respectively, under constant axial loading and lateral cyclic loading was carried out. Seismic bearing capacity, ductility, failure modes and hysteretic characteristics of all columns were tested, and the effect of reinforcement ratio and strengthening method to the tested columns was analyzed. The results showed that the energy dissipation capacity of FS strengthened columns was 73% higher than that of the S strengthened column, though the reinforcement ratio of the former was only 3.02% higher than that of the latter.

Axially loaded RC columns strengthened by steel cages

Steel caging is routinely used to strengthen reinforced concrete (RC) columns in many countries. This paper studies the behaviour of RC columns strengthened by this technique. Following the results obtained from an experimental study, all the specimens are modelled by the finite-element (FE) method. After verifying the FE models, a parametric study is carried out, determining how variations in the parameters affect the behaviour of the strengthened column. FE models are used to compare the ultimate load of RC columns strengthened by steel cages with that obtained from two design rules, showing one of them very conservative and in good agreement with the other. This proposal can be used with confidence for design, since the results obtained are slightly conservative.

Effect of axial load on flexural behaviour of cyclically loaded RC columns

The flexural behaviour of symmetrically reinforced concrete (RC) columns cast of normal- and high-strength concrete under both monotonic and cyclic loading is studied based on an analytical procedure, which employs the actual stress-strain curves and takes into account the stress-path dependence of concrete and steel reinforcement. The analysis is particularly extended into the post-peak stage with large inelastic deformation at various applied axial load level. The effect of axial load on their complete flexural behaviour is then identified based on the results obtained. The axial load is found to have fairly large effect on the flexural behaviour of RC columns under both monotonic and cyclic loading. Such effects are discussed through examination of various aspects including the moment-curvature relationship, moment capacity, flexural ductility, variation of neutral axis depth and steel stress.

Behaviour of RC column to iTECH composite beam joint

Since the end of twentieth century, the number of high-rise buildings in Korea has greatly increased. Due to the limited city area, storey height is a significant factor for tall residential structures. To occupy less storey height, the use of wide reinforced concrete (RC) beams was adopted in some projects such as Trump World and Galleria Palace in Seoul. However, the space for joints between the wide beams and the core walls was too narrow for the reinforcement. In this paper, an alternative composite beam is proposed. The joint with the RC column was experimentally explored through cyclic loading tests. The proposed composite beam is named iTECH (Innovative, Technical, Economical and Convenient Hybrid). It has an asymmetric steel assembly with web openings, where the top plate is welded on top of an inverted structural T-cut ‘honeycomb’ style. The joint of the RC column–iTECH beam behaved well and may be suitable for field applications.

Cyclically and Biaxially Loaded Reinforced Concrete Slender Columns

This study explored and examined the behavior of various cyclic compressive load levels on the ultimate strength, deflection, and moment-curvature characteristics of reinforced concrete (RC) slender columns with bidirectional eccentricities. Furthermore, a part of the research developed a numerical analysis that can simulate the behavior of RC columns under combined biaxial bending and cyclic axial compression. For the study, 4-ft (1.2-m) RC columns were tested under cyclic axial compression with bidirectional eccentricities. The main parameters of the column tests were the bidirectional eccentricities and its angle to the reference axis. The load pattern considered in the study was cyclical, and the applied load was a full loading of cycles that was loading up to the envelope curve and then unloading down to nearly zero stress level. The cyclic axial compressive load with bidirectional eccentricities considered was in the longitudinal direction, but not in the transverse direction, with respect to the column axis. The experimental ultimate load, load-deflection, and moment-curvature curves were compared with predictions from a computer model developed in the study. Results should provide guidance for structural engineers when they rehabilitate RC columns in building and bridge projects.

Behavior of RC Columns under Nonproportionally Varying Axial Load

The effect of nonproportionally fluctuating axial load on the inelastic cyclic behavior of reinforced concrete (RC) columns is investigated. For this purpose, a uniaxial flexural model is developed where columns are represented with an assemblage of plane‐stress and bar elements to model the concrete and the reinforcing steel, respectively. The results indicate that under uncoupled variations in axial and lateral forces, the hysteresis curve is not of the Masing type. Furthermore, the shear force versus lateral displacement relationships demonstrate “negative energy” regions. The cause of such a phenomenon is explained in light of axial deformations. It is also shown that the phasing of the axial force has a significant effect on the response. Those properties of RC columns that are affected by this type of loading are important factors in the seismic design of RC structures. The importance of varying vertical loads on the response of bridges is demonstrated through two practical examples.