Reinforced Concrete Columns Research Articles

Cyclic performance of non‐ductile reinforced concrete columns retrofitted by partial steel plate jacketing: Experiment and numerical analysis

AbstractThis paper investigates the strengthening of non‐ductile reinforced concrete (RC) columns using partial steel‐plate jacketing to enhance ductile capacity. Quasi‐static cyclic loading tests were conducted on three rectangular RC columns with varying shear‐span‐to‐depth ratios, evaluating the effectiveness of steel‐plate jacketing. Results show improved ductile flexural response, high drift capacity, and maintained gravity‐loading capacity under high lateral displacements. A numerical investigation, adopting a multi‐spring fiber section model, predicted cyclic lateral strength, drift ratio, and failure mode, accurately simulating reinforcement behavior and capturing the shear‐strength enhancement due to steel‐plate jacketing. Numerical results demonstrated good agreement with experimental findings. Based on these outcomes, a simple design procedure for retrofitted concrete columns, applicable to design engineers, has been developed and reported in this paper. This study contributes valuable insights into the practical applications of steel‐plate jacketing for non‐ductile RC column retrofitting, offering a comprehensive approach to predicting their seismic performance.

Study on Axial Compression Performance of Corroded Reinforced Concrete Columns Strengthened by Concrete Canvas and Carbon Fiber Reinforced Plastic under Secondary Corrosion

To investigate the effects of concrete canvas (CC) and carbon fiber reinforced plastic (CFRP) reinforcement on the mechanical properties of corroded reinforced concrete columns (compressive strength, flexure strength, strength of extension, and so on), 42 columns in four groups were designed and axial compression experiments were carried out. For the corroded reinforced concrete columns reinforced with CC and CFRP, the effects of initial corrosion rate (5%, 10%), secondary corrosion time (15 d, 30 d), number of CC layers (0, 1), and number of CFRP layers (1, 2, 3) on the failure morphology, load carrying capacity, and ductility of concrete columns were analyzed. The test results show that the properties of the single layer CC confined specimens are improved to a certain extent, and the ductility properties are enhanced. The properties of the CC–CFRP composite constrained specimens are greatly improved, the plastic deformation ability is enhanced, and the typical ductile damage characteristics are shown. The corrosion inhibition of CC for specimens with a theoretical corrosion rate lower than 20% showed an increasing trend, and the corrosion inhibition rate ranged from 23.0% to 31.2%. CC and CFRP restrain the concrete jointly, hindering the expansion inside the concrete, and the peak strain of the joint restraint specimen itself changes greatly, while the overall peak strain of the corrosion specimen is very small under the action of the joint steel bar. Finally, according to the existing peak stress–strain model and the experimental data in this paper, a peak stress–strain model suitable for corroded reinforced concrete columns is established. The established calculation model has a high accuracy, which provides a certain theoretical basis for subsequent research.

Post-damage recovery of substandard RC columns by CFRPs

Cyclic response of substandard reinforced concrete (RC) columns and structural repair of pre-damaged columns by carbon-fiber-reinforced polymers (CFRPs) were investigated through combination of experimental and advanced numerical modeling methods. The specimens, representing typical RC columns in substandard buildings, were constructed from low-strength concrete, plain round bars, and nonconforming reinforcement details. The key parameters under investigation included the lap-splice, hook detail in the longitudinal reinforcement, and axial load ratio. First, the RC columns were subjected to cyclic loading until the attainment of their heavy damage state. The failure mode was dominated by the flexural response alongside significant reinforcement slip and axial damage, involving concrete crushing and reinforcement buckling. Subsequently, the severe cracks and concrete damage were repaired by the externally wrapped CFRP sheets. The former load-carrying capacities of the repaired RC columns were recovered. The damage formation in the concrete and reinforcement was transferred to CFRP sheets. The final failure mode was characterized by local deformations in the CFRP, with minimal damage observed in the concrete and reinforcement bars. Furthermore, the numerical solution effectively reproduced the nonlinear behavior of the as-built specimens. The crack patterns and capacities observed in the numerical solutions align with the responses observed in the experimental tests.

Axial compressive behavior of predamaged RC columns retrofitted with precast steel-reinforced grout jackets

Steel jacketing and concrete jacketing are popular retrofitting techniques to strengthen the axial compressive behavior of reinforced concrete (RC) columns. However, these retrofitting methods lack efficiency in practical application due to intensive labor and time-consuming installation. In order to improve the retrofit efficiency of damaged RC columns, this study proposed a novel precast steel-reinforced grout jacket (PSRGJ) consisting of early-strength cementitious grout and a steel frame. Ten columns were tested to investigate the axial compressive behavior of predamaged RC columns retrofitted with PSRGJ. The tested parameters were the stirrup reinforcement ratio, the transverse reinforcement ratio of PSRGJ, and the predamage level. The results indicated that the columns’ peak load and ductility index I10 were significantly improved by PSRGJ retrofitting and increased with the increase of transverse reinforcement ratio of PSRGJ. Besides, the peak load and the initial stiffness of PSRGJ-retrofitted RC columns decreased with the predamage level, while the ductility index I10 increased. In addition to the confinement effect, PSRGJ carried 11%−17% of the peak load through the interfacial bonding effect. Based on the test results, the actual confinement pressure model and interfacial bonding strength model were proposed. Further, peak load models considering the size effect were developed for PSRGJ-retrofitted intact and predamaged RC columns. The predictions of the proposed models agreed well with the test results from this study and the literature.

Predictive Behaviour from Finite Element Analysis on PVC-Ducted Reinforced Concrete Column

This research investigated the behaviour of square reinforced concrete columns with embedded PVC pipes, aiming to comprehensively analyze their performance. The study addressed the lack of significant research on the contributions and effects of embedded PVC pipes on structural performance compared to hollow columns. The objectives of the study sought to evaluate the contributions and effects of embedded PVC pipes on the structural performance of columns under loading conditions, determine how the presence of PVC pipes influenced the columns' ability to deform and dissipate energy, and identify the optimal size of PVC pipes to enhance column performance while maintaining stability and safety. Numerical analysis using ABAQUS CEA 2020 software was employed to simulate the behavior of reinforced concrete columns with embedded PVC pipes. The computational model used the same cross-sections with varying diameters of PVC pipes (50mm, 75mm and 100mm). The analysis focused on assessing load-bearing capacities, deformation characteristics, and energy dissipation patterns under axial vertical displacement loading scenario. Findings indicated that PVC-embedded columns exhibit, on average, approximately 0.5% higher load-bearing capacities than Perforated columns. With a composite average of 0.00543 for plastic strains (LE) in PVC-Embedded columns compared to 0.00673 in Perforated columns, a composite average of 5.87E-03 for Equivalent Plastic Strains (PEEQ) in PVC-Embedded columns compared to 7.41E-03 in Perforated columns, and a composite average of 0.0091 for Magnetic Potential Energy (PEMag) in PVC-Embedded columns compared to 0.012 in Perforated columns, collectively suggested that PVC pipes positively impact controlled deformation and energy dissipation. The observed trend is particularly evident in specific instances, with PVC-Embedded-50mm exhibiting a marginal load-bearing increase of approximately 0.2%, PVC-Embedded-75mm indicating an improvement of about 0.5%, and PVC-Embedded-100mm manifesting a load-bearing capacity increase of roughly 0.7%. Overall, these findings highlight that smaller sizes of embedded PVC pipes result in better load-bearing performance. The study recommended meticulous attention to material composition and structural design during PVC-embedded column implementation, careful selection of PVC pipe sizes based on structural requirements and project specifications, further research on dynamic loading conditions to comprehensively understand column behavior, and implementation of stringent quality control measures during manufacturing and construction processes.

Influence of Variation in Tie Reinforcement Diameter on the Ductility of Reinforced Concrete Columns

Reinforced concrete columns are crucial structural elements in ensuring the strength and stability of buildings. Column ductility, which is the ability to absorb energy and undergo deformation before failure, is a primary concern in structural engineering, especially in extreme external loading situations such as earthquakes. This study aims to evaluate the influence of variation in Tie reinforcement diameter on the ductility of reinforced concrete columns using Xtract software. The research method involves creating column structure models with specified dimensions and specifications, followed by the gradual application of axial loads to each model. Three models were created with varying Tie reinforcement diameters, namely 10 mm, 12 mm, and 14 mm. Structural analysis was conducted to examine the structure's response to the applied axial and moment loads, including evaluation of stresses, deformations, and column capacities. The analysis results show differences in ductility levels among the models. The model with a 10 mm Tie reinforcement diameter achieves higher ductility levels at low axial loads but fails to meet the requirements at higher axial loads according to the SNI 1726:2019 standard. However, models with Tie reinforcement diameters of 12 mm and 14 mm also exhibit a similar pattern, with good ductility at low axial loads but failing to meet the requirements at higher axial loads. In conclusion, variations in Tie reinforcement diameter affect the ductility of reinforced concrete columns. To ensure full ductility under various axial load conditions, adjustments to the design or specifications of the reinforced concrete column structure are necessary. This research contributes to understanding the factors influencing the ductility of reinforced concrete columns and can serve as a basis for the development of more effective design methods in the future.

A prediction model for plastic hinge length of rectangular RC columns using gene expression programming

In the reinforced concrete (RC) columns which are exposed extreme loads such as earthquake effects, the plastic hinge length can be defined as the length of the region where flexural moments exceed the yielding capacity, and the plastic deformations are concentrated. More accurate estimation of plastic hinge length increases the reliability of the seismic design. However, a sensitivity prediction of plastic hinge length is difficult due to a large number of model parameters. Therefore, this study aims to predict the plastic hinge length using the gene expression programming (GEP). An experimental database of 133 RC columns gathered from the literature was utilized for prediction with GEP. The results of GEP model are statistically compared with those of 13 models existing in the literature proposed by various researchers. The comparison results reveal that the proposed GEP-based formulation has the best efficiency among all models. Furthermore, a sensitivity analysis and parametric study are conducted to identify the most influential parameters affecting the GEP formulation.

PROBABILISTIC ANALYSIS OF FLEXURAL OVERSTRENGTH FACTOR FOR SEISMICALLY DESIGNED REINFORCED CONCRETE BEAMS AND COLUMNS

The study presented here aims to address some issues related to seismic design of structures, with special focus on the probabilistic modeling of reinforced concrete (RC) cross-sections capacity. It aims to validate the overstrength factors provided in Eurocode 8 for the design RC beams and columns. A statistical analysis is carried out to determine the uncertainty in the reinforcing steel properties. Uncertainties in concrete properties, geometry of cross-sections and mechanical model are also considered. Assessing the flexural overstrength of RC beams and columns designed according to Eurocode 8 involves ensuring that the structural members meet the capacity design specifications. This research studied 128 cross-sections of beams and columns with different geometry and reinforcement areas by performing Monte Carlo simulation. The code provisions are evaluated through a comparison with the simulation results. In particular, the analyses suggest using an overstrength factor of 1.5 for beams and columns with 95% probability of exceedance (or 1.3 with 50% probability of exceedance). Eurocode 8 provisions, adopting an overstrength factor of 1.3, does not seem conservative enough.

Shear Strength of Reinforced Concrete Columns with External Post-Tensioned Clamps

Shear Strength of Reinforced Concrete Columns with External Post-Tensioned Clamps

Numerical Analysis of Reinforced Concrete Columns Strengthened With Steel Jacket

Numerical Analysis of Reinforced Concrete Columns Strengthened With Steel Jacket

A Quantitative Investigation on the Effects of Flexure-Dominated Reinforced Concrete Column Characteristics on the Dissipated Energy

This paper presents the effects of fundamental member and loading parameters on total dissipated energy capacity of RC columns in quantitative way by using an experimental database. Specifically, concrete compressive strength, yield strength of reinforcing bars; shear span-to-depth ratio, reinforcement ratios; peak drift ratio, and axial load ratio, are considered as influencing factors. Pearson’s correlation coefficients are utilized as dependency indicators to construct a correlation matrix where the effect of each factor on dissipated energy level is quantified. Results show that the effective factors among selected features are peak drift ratio, transverse reinforcement volumetric ratios of a member, and yield strength of rebars whereas the most influencing factors are the first two.

Cyclic Behavior of Reinforced Concrete Columns with L-Shaped Ties

Cyclic Behavior of Reinforced Concrete Columns with L-Shaped Ties

Strengthening damaged columns on the soft first story of reinforced concrete building using ultra-high-strength fiber-reinforced concrete panels

In this study, ultra-high-strength fiber-reinforced concrete (UFC) panels were used as a quick and effective measure for seismic strengthening of damaged reinforced concrete (RC) columns. Four 1/3-scale specimens, which replicated RC columns of the soft-first-story of a 10-story condominium building that was heavily damaged in the 2016 Kumamoto Earthquake, were constructed and tested. The specimens were strengthened using UFC panels after being preloaded to the drift ratio, at which the maximum load capacity of the target column was measured, and then subjected to the main loading until the ultimate state was reached. The UFC panels were installed on the two faces of the column in a direction parallel to the assumed loading direction. Two of the specimens had a UFC or RC wing wall attached to one side of the column, which was also aligned with the assumed loading direction. During the preloading and main loading, the specimens were subjected to a cyclic lateral load and varying axial load that simulated an earthquake load. The proposed method improved the maximum strength and ultimate drift ratio, and helped restore the initial stiffness of specimens with UFC panels and a wing wall to that of a column specimen during preloading. The test results of a previous study, wherein the target column, loading method, and strengthening method were the same but the specimens were not damaged before strengthening, were compared to study the impact of the damage on the RC column before strengthening.

Shear capacity model of rectangular RC columns based on Bayesian update

Reinforced concrete (RC) columns are function as structural member resisting vertical loading. The combined effects of vertical loading and transverse loading might induce shear failure of RC columns, posing a significant threat to the structure's integrity. While the accuracy of existing models to determine the shear strength of RC column is crucial for design, there is a need for further refinement. In this context, a study introduces a probabilistic shear capacity model based on the truss-arch theory and incorporating the Bayesian theory Monte Carlo Markov Chain (MCMC) method. This model delineates the shear contribution into four distinct components: concrete, stirrup, axial compression force and longitudinal reinforcement longitudinal reinforcement in the middle of the section parallel to the loading direction. A database, comprising 233 RC column specimen sets, facilitates the model's regression analysis. Calibration is achieved against the density distribution and confidence intervals of the posterior parameters. When set against four established models, the new proposal offers a mean value closely aligned with experimental data and showcases reduced variance. To substantiate the shear mechanism of the proposed model, a thorough contribution of each shear component's contribution is made with those in four existing models: Sezen, ACI 318, Priestley, and GB50010. While the Sezen and ACI 318 models recognize the shear contributions of concrete and stirrup, the Priestley and GB50010 models extend to factor in the beneficial impact of the axial compression force component. Comparative analysis underscores the superior predictive capability of the newly proposed model.

Experimental Study and Bearing Capacity Calculation of Compression-Reinforced Concrete Columns Strengthened with Ultra-High-Performance Concrete

A total of five ultra-high-performance concrete (UHPC)-strengthened reinforced concrete (RC) columns and one RC column were built and subjected to eccentric compression testing to examine the force performance of UHPC-strengthened eccentrically compressed plain RC columns. This experimental study examined the crack progression, the damage morphology, the deformation ability, the maximum load-carrying capacity, and the ductile properties of the eccentrically compressed columns. It also investigated the impacts of eccentricity, the reinforcement thickness, and the addition of steel fibers on the effectiveness of reinforcement. The cracking load, peak load, and ductility coefficient of the UHPC-reinforced specimens were increased by 100.28%, 172.30%, and 56.30%, respectively, compared with the RC column at an initial eccentricity of 50 mm. As the eccentricity distance increased, the bearing capacity of the UHPC eccentrically compressed specimens decreased, and the deformation capacity increased. Increasing the steel fiber dosage within the appropriate range decreased the crack width of the specimen. The addition of 2% steel fiber resulted in a 24.8% increase in cracking load, an 8.96% increase in peak load, and a 2.60% increase in ductility coefficient compared to the addition of 1% steel fiber. However, the reinforcing effect of UHPC was weakened under high eccentric pressures. Based on the theory of concrete structure and mechanical principles, the formula for calculating the compressive bearing capacity of RC columns strengthened with high-performance concrete was proposed. The results of calculating the positive section bearing capacity of eccentrically compressed RC columns reinforced with high-performance concrete are in good agreement with the test values. The results of this paper provide an experimental basis and theoretical foundation for the cross-sectional design of UHPC eccentrically compressed columns.

Data-based equations for damage evaluation of reinforced concrete columns with square cross sections

This study aims to develop simple equations for assessing the damage of reinforced concrete (RC) columns subjected to seismic loading. A fiber element model in OpenSees, validated against experimental data, was used to generate a large dataset of 56548 data values for various RC columns. The Monte Carlo Hierarchical Adaptive Random Partitioning (MC-HARP) strategy was then applied to evaluate the sufficiency of the dataset and propose reliable equations for estimating the residual displacement ratio (RDR), damage index (DI), and residual curvature of RC columns under given displacement demands. A relationship between these parameters and the structural performance levels was also established. Residual displacement is a practical measure that can be observed in the field after an earthquake. The proposed equations facilitate the determination of the performance level of the structure after an earthquake event. The findings of this paper can also be used in designing new structures within a performance-based seismic design (PBSD) context.

Influence of GFRP Confinement of Reinforced Concrete Columns Exposed to Sodium Chloride on Microstructure and Hydration Products

This paper explores the effect of sodium chloride (NaCl) on microstructure and hydration products of cylindrical column concrete and compares the results after covering it with Glass Fiber Reinforced Polymer (GFRP). 20 short RC columns were prepared with a single concrete mixture. The specimens have cured in different concentration of NaCl (0, 5%, 10%, 15%), some specimens cured directly in solution and other specimens exposed to wet and dry cycle. These specimens were tested, a first group after 28 days of curing, second group after 56 days, while the third group was repaired by GFRP after 28 day then returned to the cured environment and tested after56 day. In order to determine the main crystalline phase composition of concrete specimens and for phase identification of a crystalline material, scanning electron microscopy (SEM) morphology of microstructure concrete and X-ray diffraction (XRD) have been used. The results revealed denser microstructure with the concentration of NaCl crystalline, existence of binding chloride as free halite, chemical pound as a Friedel’s salt or Physical binding held to the surface of hydration products. In addition, the corrosive compounds were observed, and the hydration product phase decreased due to concentration of curing environment. Furthermore, the results from the samples that were covered with GFRP showed that the value of the hydration products didn't change when compared with the samples that were tested after 28 days, moreover, the voids were found in them when compared with the samples exposed to the environment damage without covering it with GFRP.

Residual axial strength of reinforced concrete columns after exposure to standard and non-standard fires

This study investigated the residual axial strength of reinforced concrete (RC) columns after exposure to standard and non-standard fires. Experiments and theoretical analyses were performed on 30 RC columns, which were divided into five groups: one group (the control group) was not exposed to fire; two groups were exposed to 30-min and 45-min ISO 834 standard fires; and the other two groups were exposed to 60-min and 75-min non-standard fires. These postfire specimens were axially loaded until they failed. The experimental results showed that 30-min and 45-min ISO 834 fires decreased the residual strength by 11.6% and 17.4%, respectively. 60-min and 75-min non-ISO 834 fires caused similar reductions in the residual axial strength of postfire RC columns, although the durations of these non-standard fires were considerably longer. This experimental result confirmed that the maximum temperature, rather than the fire durations, of non-standard fires governed the reduction in the residual axial strength. In theoretical analysis, the axial strength of postfire RC columns can be calculated using the proposed model, which combines the confinement model, the 500°C isotherm method, and the distribution model of temperature. The proposed model can appropriately predict the residual axial strength of postfire columns when the fire closely follows the ISO 834 fire. The inaccuracy of the model significantly increases when the fires are non-ISO 834 fires. Two concepts, namely equivalent area and maximum temperature, were introduced to address the issue. The concept of maximum temperature successfully addressed the above-mentioned issue and exhibited superiority over the concept of equivalent area. This result reaffirmed the superior governing characteristic of the maximum temperature compared with the duration of non-standard fires, as evidenced in the experimental results. The proposed models would be useful for engineers in practice when evaluating the residual axial strength of both standard and non-standard postfire RC columns.

Analiza sloma hibridno ojačanog AB kvadratnog stupa

This paper presents an analytical and experimental examination of reinforced concrete (RC) columns strengthened with a combined system of fibre-reinforced cementitious material (FRCM) and externally bonded fibre-reinforced plastics (EB-FRP). The proposed technique makes use of these advantages in enhancing the strength and minimising the premature failure of RC columns. Seven square RC columns were cast: one control column, four FRCM-strengthened columns, and two hybrid-strengthened columns. Two fibres, namely, carbon and glass fibres, were used. The columns were tested under an axial compression load in a loading frame. The ultimate strength, load vs. deformation, failure, and ductility were discussed to examine the failure and strengthening behaviour. The proposed method provided a higher confinement effect and increased capacity with fewer FRCM with EB-FRP than the other methods. Analytical predictions of the peak load were made and correlated with the experimental results.

Influence of Confinement Interaction on the Compressive Behavior of Steel Tube–Reinforced Concrete Columns

Influence of Confinement Interaction on the Compressive Behavior of Steel Tube–Reinforced Concrete Columns