Slender Reinforced Concrete Columns Research Articles

Enhancing slender reinforced concrete columns with G-FRCM jackets: Experimental and numerical analysis of confinement effects and cross-sectional shape impact

This research investigates the use of Glass Fabric Reinforced Cementitious Matrix (G-FRCM) as a confinement material for slender reinforced concrete (RC) columns with slenderness ratios greater than the slenderness criterion for isolated members. An experimental program was conducted on six slender RC columns, including two control and four G-FRCM-confined specimens. The results demonstrated that the G-FRCM strengthening strategy was highly effective, with the compression resistance of the columns increasing by 22.1% and 55.5% for one and two layers of G-FRCM, respectively, compared to the control samples. The experimental results were used to implement and validate the non-linear behaviour of G-FRCM-confined RC columns, employing the Finite Element Method (FEM) through the ABAQUS software. The results, in terms of compression strength, were consistent compared to the experiments, with a difference of less than 5%. Additionally, a parametric investigation has also been conducted to analyse the influence of the slenderness ratio on the response of confined columns. The findings of this study contribute to the understanding of the use of G-FRCM as a highly effective confinement material for RC columns.

Novel approach to the stability assessment of reinforced concrete columns

Geometric and material nonlinearities inherent in slender reinforced concrete (RC) columns have often limited the accuracy of stability models in determining the deformational response under axial and lateral loading. Design codes for slender RC columns in code provisions employ a factor of safety to compensate for the complex interactions associated with the nonlinearities which results in large discrepancies and magnified for increasing column slenderness. The present study introduces a novel approach in quantifying the moment- rotation relationship of RC column sections parallel to a partial-interaction tension-stiffening model. The moment-rotation model is used to determine axial and lateral load–deflection relationships in addition to stability curves to assess buckling capacities of RC columns for various loading conditions. Extensive experimental studies on the structural behaviour of slender RC columns are used to validate models developed in the study. Results show the effectiveness of the moment-rotation model in predicting column behaviour, and the accuracy of the stability model in determining failure behaviour.

A new Distinct Element meso‐model for simulating the rocking‐dominated seismic response of RC columns

AbstractThe rocking‐dominated seismic response of reinforced concrete (RC) columns is a complex mechanism that entails P‐Δ effects, concrete crushing and spalling, rupture and dislocation of steel bars and stirrups, as well as combined localized failures causing splitting and shear‐flexure cracking. In this paper, we present a new meso‐scale numerical modeling strategy for the detailed simulation of the rocking response of slender RC columns under seismic actions. This work advances the current state‐of‐the‐art by exploring the unprecedented use of the Distinct Element Method (DEM), originally conceived for geotechnical studies and whose applicability in earthquake engineering has been primarily limited to the assessment of unreinforced masonry sub‐structures. To decrease analysis time and enable the use of DEM for RC problems, concrete is herein idealized as an assembly of solid macro‐block layers of size directly proportional to their distance from expected plastic hinges. These layers are connected by nonlinear interface springs to simulate tensile and shear cracking via a simplified Mohr‐Coulomb criterion. Crushing of concrete in deformable blocks is modeled using the Feenstra and De Borst strain‐softening linearized compression law, while confinement and combined failures are accounted for numerically through the explicit representation of longitudinal and transversal reinforcement bars, idealized as link elements. Previous experimental static and dynamic tests on full‐scale RC column specimens and results from fiber‐based Finite Element and sectional analysis models are used to evaluate DEM results and quantify the influence of key modeling parameters, including block number and deformability, as well as the amount of damping. The agreement between simulated failure modes and force and displacement capacities and their experimental counterparts demonstrate the applicability of the proposed approach, while demonstrating the pros and cons of simplified numerical methods.

Finite Element Analysis of Slender Reinforced Concrete Columns Subjected to Eccentric Axial Loads and Elevated Temperature

Finite Element Analysis of Slender Reinforced Concrete Columns Subjected to Eccentric Axial Loads and Elevated Temperature

Nonlinear Analysis of Hollow Slender Reinforced Concrete Columns Subjected to Concentric and Eccentric Loads

Abstract This paper investigates the load capacity and failure modes of slender hollow RC column under axial and eccentric loads. For the slender hollow columns, different load eccentricities and hole shapes are used. The finite element software ABAQUS is used to model and analyze the columns. The experimental test result is used to conduct a verification investigation of the nonlinear finite element modeling. All specifications of the experimentally tested columns are taken into consideration in the modeling to establish the verification of the model. When the modeling and test results are compared, it is noticeable that they are in good agreement. As a result, the modeling’s accuracy is proved. Then, a parametric study included different slenderness ratio, section shape, concrete strength and SFR strengthened has been done with the same modeling method. The effects of these variables on the column load capacity are investigated. It is found that increasing slenderness ratio led to smaller peak load. Increasing of moment of inertia of square and circular section decreased the peak load capacity. The maximum bearing capacity increased with higher concrete strength. Also, SFR distribution through the length of columns effected on load bearing capacity.

Evaluation of square slender RC columns subjected to eccentric loading strengthened with longitudinal FRP sheets based on PIV analysis

In this study, the behavior of square slender reinforced concrete (RC) columns strengthened with carbon fiber-reinforced polymer (CFRP) sheets was investigated. The externally bonded reinforcement on grooves (EBROG) method as a new technique was employed to strengthen the specimens compared to the externally bonded reinforcement (EBR) method as the conventional strengthening technique. Twelve small-scale slender square RC columns (i.e., 125 × 125 × 900 mm) with a slenderness ratio of 25 were loaded under eccentricity-to-cross-section ratios (e/h) of 0, 0.24, 0.48, and 0.72. The results showed the EBROG's superiority over EBR in load-carrying capacity enhancement of the strengthened RC column specimens in various eccentricities; i.e., the loading enhancements were 10.6 to 99.3% for the EBROG specimens and 1.2 to 41.7% for the EBR specimens at varying eccentricities of 0 to 90 mm, compared to those of un-strengthened specimens. Furthermore, the moment capacity enhancement of the EBROG specimens was higher than that of the EBR columns; i.e., it was 100.0% for the EBROG specimens and 42.2% for EBR specimens in the eccentricity of 90 mm, compared with the un-strengthened specimen. Using particle image velocimetry (PIV) analyses, the results of flexural stiffness, strain distribution, ductility, and energy absorption were presented and discussed. Results revealed that by increasing the eccentricity, flexural stiffness decreases; this reduction was more intense for EBR specimens (42%) than the EBROG specimen (36%). An analytical procedure was conducted to compare the experimental and theoretical results. The analysis demonstrated good agreement between the results and the superiority of the EBROG method over the EBR.

Analytical Study on Behaviour of Slender Reinforced Concrete Columns with Gfrp Bars and Discrete Fibres

Analytical Study on Behaviour of Slender Reinforced Concrete Columns with Gfrp Bars and Discrete Fibres

Analytical Review on Eccentric Axial Compression Behavior of Short and Slender Circular RC Columns Strengthened Using CFRP.

Although reinforced concrete (RC) columns subjected to combined axial compression and flexural loads (i.e., eccentric load) are the most common structural members used in practice, research on FRP-confined circular RC columns subjected to eccentric axial compression has been very limited. More specifically, the available eccentric-loading models were mainly based on existing concentric stress–strain models of FRP-confined unreinforced concrete columns of small scale. The strength and ductility of FRP-strengthened slender circular RC columns predicted using these models showed significant errors. In light of such demand to date, this paper presents a stress–strain model for FRP-confined circular reinforced concrete (RC) columns under eccentric axial compression. The model is mainly based on observations of tests and results reported in the technical literature, in which 207 results of FRP-confined circular unreinforced and reinforced concrete columns were carefully studied and analyzed. A model for the axial-flexural interaction of FRP-confined concrete is also provided. Based on a full parametric analysis, a simple formula of the slenderness limit for FRP-strengthened RC columns is further provided. The proposed model considers the effects of key parameters such as longitudinal and hoop steel reinforcement, level of FRP hoop confinement, slenderness ratio, presence of longitudinal FRP wraps, and varying eccentricity ratio. The accuracy of the proposed model is finally validated through comparisons made between the predictions and the compiled test results.

Experimental Verification of Slender Reinforced Concrete Columns Design

The columns have been part of the constructions since the beginning of the buildings and have retained their design and construction importance to the present. The advantage of using more slender elements are less material consumption and more usable space in the interiors. The continuous improvement of the building materials and the use of hybrid structural elements leads to the downsizing of the structural elements. The aim of this article is the nonlinear analysis of the slender rein-forced concrete columns and the loss of stability verified by the experimental tests. Nonlinear calculations can be considered as the most accurate calculation option for the load bearing structural elements. On the other hand, the effect of the “black box” has been, and will be the cause of a large number of building defects. In the Eurocode 2 in chapter 5.8.6 of the European Concrete Design Standard, there is a possibility of using the general nonlinear method in practice, even for the com-pressed elements. In the design of the slender structures, the influence of second-order theory is a very important part of the design. In this publication are described theoretical and experimental analyses of the slender columns, that failed due to loss of stability inside of their design interaction diagram - much sooner than the critical cross-sections reached its resistance. As a part of the experimental preparations, reinforced concrete columns were designed, based on numerous numerical analyses. Later, the chosen columns were tested in the laboratories of TU Wien in Vienna. Experimental verification is one of the main parts of my dissertation thesis.

Analytical study on the effectiveness of hybrid FRP strengthening on behaviour of slender reinforced concrete square columns

Strengthening of reinforced concrete (RC) columns using external bonded (EB) fibre-reinforced polymer (FRP) composites has become popular since last three decades. The effectiveness of EB confinement reduces for slender columns due to the secondary moment arising from applied axial loads. The effectiveness of the hybrid FRP strengthening system for enhancing the performance of RC slender square columns is analytically investigated. Hybrid FRP strengthening uses a combination of EB FRP wrapping for confinement and longitudinal near-surface mounted (NSM) FRP laminates for bending. Hybrid FRP strengthening aims to reduce the second-order lateral displacement of the slender RC column and increase its axial capacity and flexural stiffness. A numerical modelling approach is presented to capture second-order effects in hybrid FRP strengthened slender RC square column based on Newmark's central difference scheme. Both material and geometric nonlinearities are accounted for in the calculations. The predictions are validated with test results available in the literature. After validation, a parametric study is carried out to evaluate the influence of slenderness ratio, the number of EB FRP layers, NSM laminate ratio, modulus of NSM laminate, and buckling of FRP composites. Results show that hybrid FRP strengthening is effective in improving the performance of slender RC columns.

Experimental Study of Hollow Slender Reinforced Concrete Columns Subjected to Eccentric Loads

Abstract This paper was focused on the investigating on the behavior of hollow slender reinforced concrete columns subjected to the axial loads. A total of seven specimens were designed as slender reinforced columns and these were divided into two groups. Each column is symmetrical and had a rectangular cross section of 140 × 80 mm and 2000 mm in length. The column was reinforced by 6Ø6mm for longitudinal reinforcement and Ø6@6 mm bars were used for transverse reinforcement ties. The effect of strengthening by CFRP sheet on the buckling of column, eccentricity 20, 40 and 120 mm and opening shape were studied. The results showed that the strengthened columns by CFRP caused an in the ultimate load CFRP were 26.3 % and 76.3 % for strengthened lengths of L/4 and L respectively compared with the un-strengthened column. The ultimate load of columns is reduced with existing the load eccentricity and amount of losses in strength increased with increasing the eccentricity. Also, it was found the hollow columns having circular holes had better performance compared to hollow columns having rectangular hole

The Proposition of an EI Equation of Square and L–Shaped Slender Reinforced Concrete Columns under Combined Loading

The stability and strength of slender Reinforced Concrete (RC) columns depend directly on the flexural stiffness EI, which is a major parameter in strain calculations including those with bending and axial load. Due to the non-linearity of the stress-strain curve of concrete, the effective bending stiffness EI always remains variable. Numerical simulations were performed for square and L-shaped reinforced concrete sections of slender columns subjected to an eccentric axial force to estimate the variation of El resulting from the actual behavior of the column, based on the moment-curvature relationship. Seventy thousand (70000) hypothetical slender columns, each with a different combination of variables, were used to investigate the main variables that affect the EI of RC slender columns. Using linear regression analysis, a new simple and linear expression of EI was developed. Slenderness, axial load level, and concrete strength have been identified as the most important factors affecting effective stiffness. Finally, the comparison between the results of the new equation and the methods proposed by ACI-318 and Euro Code-2 was carried out in connection with the experimental results of the literature. A good agreement of the results was found.

Experimental Study on Slender CFRP-Confined Circular RC Columns under Axial Compression

The test results on the performance of carbon fiber-reinforced polymer (CFRP)-confined reinforced concrete (RC) columns under axial compression load are presented in this study. Twelve slender CFRP-confined circular RC columns with a diameter of 200 mm were divided into two groups. Six specimens with different slenderness ratios of 12, 20, 32, 40, 48, and 56 were contained in each group. The experimental results demonstrated the circumferential CFRP wrap was effective in enhancing the ultimate axial load of slender CFRP-confined circular RC columns compared with unwrapped RC columns. The experimental investigation also showed that the slenderness of the specimens had important influences on the axial compressive behavior, and the axial bearing capacity of slender CFRP-confined circular RC columns decreased as the slenderness ratio increased. In order to predict the load-carrying capacities of slender CFRP-confined circular RC columns, a formula was proposed and the prediction agreed with the experiments. The slenderness of slender CFRP-confined circular RC columns was recommended to be less than 26.5 in practical engineering.

Behavior of Square Slender RC Columns Strengthened with Longitudinal FRP Sheets Subjected to Eccentric Loading

Abstract In this study, the grooving method was employed to strengthen reinforced concrete (RC) columns with longitudinal fiber-reinforced polymer (FRP) sheets, and the performance of columns was i...

Model uncertainty in non‐linear numerical analyses of slender reinforced concrete members

AbstractThe present study aims to characterize the epistemic uncertainty within the use of global non‐linear numerical analyses (i.e., NLNAs) for design and assessment purposes of slender reinforced concrete (RC) members. The epistemic uncertainty associated to NLNAs may be represented by approximations and choices performed during the definition of a structural numerical model. In order to quantify epistemic uncertainty associated to a non‐linear numerical simulation, the resistance model uncertainty random variable has to be characterized by means of the comparison between experimental and numerical results. With this aim, a set of experimental tests on slender RC columns known from the literature is considered. Then, the experimental results in terms of maximum axial load are compared to the outcomes achieved from NLNAs. Nine different modeling hypotheses are herein considered to characterize the resistance model uncertainty random variable. The probabilistic analysis of the results has been performed according to Bayesian approach accounting also for both the previous knowledge from the scientific literature and the influence of the experimental uncertainty on the estimation of the statistics of the resistance model uncertainty random variable. Finally, the resistance model uncertainty partial safety factor is evaluated in line with the global resistance format of fib Model Code for Concrete Structures 2010 with reference to new and existing RC structures.

Behavior of Slender RC Columns Bent in Single and Double Curvature at Elevated Temperatures

In this study, a numerical model for tracing the behavior of eccentrically loaded slender reinforced concrete (RC) columns bent in single and double curvature, and subjected to elevated temperatures is presented. The developed model incorporates the high-temperature material properties, the nonlinear behavior of concrete sections, time dependent effects, and the nonlinear responses of slender RC columns. Based on Newton–Raphson method, an iterative technique, wherein strain and curvature are concurrently iterated, is used to find the strain distribution on the cross-section. By proposing a simple and reliable calculation procedure, the lateral deflection is calculated using numerical and searching techniques. The compatibility between forces and deformations at a joint in the column is established by another iterative technique, which involves the analysis of the whole column. The validity of the analytical model is established by comparing its predictions with results obtained from laboratory tests found in literature. A parametric study is conducted to investigate the effect of end eccentricity conditions on columns bent in single and double curvatures. It was found that lateral deflection plays an important role on column responses when subjected to fire. This finding confirms the usefulness of lateral deflection as a powerful tool in validating eccentrically loaded slender RC columns. It was also found that unwinding at elevated temperature has detrimental effect on columns bent in double curvature. It was observed that for all columns, there exists a critical eccentricity after which column responses to fire change.

Reliability of Slender Reinforced Concrete Columns in Second Generation of Eurocodes

Design of slender reinforced concrete columns based on currently valid series of codes has its blank spaces. Authors of this articles are systematically working on filling these blank spaces with theoretical and experimental verifications, with focus on upcoming series of Eurocodes. They are attending the meetings of work group TC250-SC2-WG1, which is preparing changes in the new series. In this article we are presenting our suggested changes based on calculations and series of slender reinforced concrete columns experiments.

Numerical Study of Specially Shaped Slender RC Columns under Compressive Load

In most Reinforced Concrete (RC) buildings, the cross-section size of rectangular columns that conventionally used in these structures is larger than the thickness of their partitions. Consequently, a part of the column is protruded out of the wall which has some architectural disadvantages. Reducing the column size by using high strength concrete will result in slender column, thus the stability problem may be occurred. The stability problem is difficult to be overcome with rectangular columns. This paper study the effectiveness of using new types of columns called Specially Shaped Reinforced Concrete (SSRC) columns. Besides, the use of SSRC columns provides many structural advantages when compared with traditional rectangular columns. This research was conducted to study the structural behavior of slender SSRC columns via nonlinear finite element analysis using Abaqus program. The study based on twenty-four RC column specimens of the same cross-sectional area and different shapes and Slenderness Ratios (SR). The results showed that the use of SSRC columns led to improve the strength by about 12% and reduce deformations as compared with the square-shaped specimen. However, the columns individually exhibited almost the same trend of decreasing the strength with increasing in SR. In general, a maximum loss in strength of about 10% was found when the SR increased to 40 and 35% for columns with SR of 80. Two design approaches were proposed to evaluate the strength of SSRC columns under concentric loading. The results obtained show a good structural response of SSRC columns as compared with square-shaped columns.

Structural Performance of Slender RC Columns with Cross and Square-Shaped under Compression Load

The idea of using slender Reinforced Concrete (RC) columns with cross-shaped (+-shaped) instead of columns with square-shaped was discussed in this paper. The use of +-shaped columns provides many architectural and structural advantages, such as avoiding prominent columns edges and improved the structural response of member. Therefore, this study explores the structural response of slender +-shaped columns experimentally and numerically by nonlinear finite element analysis using Abaqus simulation tools. The results showed an excellent convergence in strength between numerical and test results with an average standard deviation of 0.05 and 0.07. Besides that, the use of +-shaped columns led to improve the ultimate strength and reduce deflections in all stages of loading, especially with the slenderness ratio more than 40, as compared with square-shaped column. Two design approaches were suggested to evaluate the ultimate strength of +-shaped columns with different slenderness ratios. Briefly, the results showed good structural response of +-shaped columns as compared with square-shaped columns, but further studies are needed to establish the behavior of this type of column, particularly with varying states of loading.

A Comparative Study of the Performance of Slender Reinforced Concrete Columns with Different Cross-Sectional Shapes

Most reinforced concrete (RC) structures are constructed with square/rectangular columns. The cross-section size of these types of columns is much larger than the thickness of their partitions. Therefore, parts of these columns are protruded out of the partitions. The emergence of columns edges out of the walls has some disadvantages. This limitation is difficult to be overcome with square or rectangular columns. To solve this problem, new types of RC columns called specially shaped reinforced concrete (SSRC) columns have been used as hidden columns. Besides, the use of SSRC columns provides many structural and architectural advantages as compared with rectangular columns. Therefore, this study was conducted to explain the structural performance of slender SSRC columns experimentally and numerically via nonlinear finite element analysis. The study is based on nine RC specimens tested up to failure, as well as eighteen finite element (FE) models analyzed by Abaqus soft wear program. The use of SSRC columns led to increase strength by about 12% and reduce deformations, especially with slenderness ratio more than 40 as compared with equivalent square-shaped columns. Two design formulas were proposed to determine the compressive strength of SSRC columns under concentric loading. The results obtained indicate a good structural performance of SSRC columns when compared with equivalent square-shaped columns.