Circular Reinforced Concrete Columns Research Articles

Combined nomograms for calculating the bearing capacity and reinforcement of high-strength and normal concrete RC columns

PurposeThis paper aims to obtain a calculation method by hand without iteration.Design/methodology/approachThis paper adopts strains as known quantities to solve the internal forces and deformations of the section, simplifies the deflection curve of the column and obtains nomograms that can calculate the bearing capacity and reinforcement of circular reinforced concrete (RC) columns by hand.FindingsNomograms include five variables: mechanical reinforcement ratio, relative normal force, dimensionless bending moment, slenderness ratio and ultimate dimensionless curvature. Nomograms corresponding to all classes of concrete have been drawn, and their dimensionless form makes them widely applicable. The calculation results of nomograms are compared and analysed with numerical calculation results, and the difference is within 5%, meeting the engineering requirements.Originality/valueCalculating the bearing capacity of compression bending components requires considering second-order effects. Therefore, the calculation of the bearing capacity of circular RC columns requires iterative calculation, as it includes dual nonlinearity of material and geometry, and the two are coupled with each other. To calculate the bearing capacity of the section adopting ordinary concrete, it is necessary to solve the transcendental equation iteratively. For high-strength concrete, it can only be solved by numerical integration. A fast calculation method by hand is proposed in this paper.

Reliability-Based Code Development for Carbon Fiber- Reinforced Polymer-Strengthened Circular Reinforced Concrete Columns

Reliability-Based Code Development for Carbon Fiber- Reinforced Polymer-Strengthened Circular Reinforced Concrete Columns

Experimental investigation of transition composite connections in historic style buildings

Historic timber buildings possess immense historical, artistic, and scientific value, but a few of them have survived after thousands of years of natural disasters and wars. Historic style buildings with modern construction material, imitating historic timber buildings forms, have emerged to inherit and promote traditional culture. To investigate the seismic performance of transition columns commonly used in historic style buildings, two full-scaled composite column transition (CCT) connections between steel reinforced concrete (SRC) square column and reinforced concrete (RC) circular column were designed and tested under invariable axial load and cyclic lateral load. Both failure patterns and force mechanism were studied based on the test process of the CCT connections. Then, the influence of axial compressive ratio on the mechanical behaviour of the CCT connections was assessed by looking at the hysteretic curves, backbone curves, characteristic loads, ductility, energy dissipation capacity and strength degradation. The results demonstrated that the failure patterns of the CCT connections were typical flexural failure, with the failure zone occurring at the upper column-root. The CCT connections exhibited excellent capacities of deformation and energy dissipation. As axial compression ratio increases, the failure of the CCT connection becomes more severe, leading to enhanced energy dissipation capacity. However, the strength and ductility of the CCT connection decrease. Based on the experimental results, an equation for calculating the lateral stiffness of CCT connections between SRC square column and RC circular column in historic style buildings was proposed, and verified to be accurate. The findings can provide necessary basis for the rational design and widespread application of historic style buildings.

Axial compressive behavior and model analysis of BFRP-jacketed corroded and pre-damaged circular reinforced concrete columns

Corrosion of steel reinforcements degrades the structural performance of reinforced concrete (RC) columns under static and seismic loads. Such corroded RC columns are usually retrofitted with fiber-reinforced polymer (FRP). However, existing studies on the retrofitting of RC columns with corrosion and load-induced damage are limited. To confirm the effectiveness of basalt FRP (BFRP) jacketing on the compressive behavior of corroded and pre-damaged RC columns, this study performed axial compression tests on eleven circular RC columns. The columns were fabricated, corroded, pre-damaged, and then jacketed with BFRP composites and reloaded to investigate the effects of BFRP layer number, corrosion ratio, and pre-damage degree. When jacketed by BFRP, the ultimate strength and ultimate strain of RC columns increased with BFRP layer numbers, ranging from 5% to 98% and 448% to 926%, respectively. Further, the ultimate strength and elastic modulus of the jacketed RC columns decreased with the increase in pre-damage degrees and corrosion ratios, while the ultimate strain was little affected. Buckling and corrosion of longitudinal bars significantly reduced the bar stresses at the ultimate state of BFRP-jacketed RC columns and resulted in local rupture of BFRP. This adverse effect became more pronounced as the corrosion ratio increased, but was alleviated by BFRP jacketing. On the other hand, a refined rebar stress-strain model was developed by addressing the effects of buckling, corrosion, and lateral confinement. Further, a feasible constitutive model for corroded hoop-confined columns was determined by validating the existing test results. Finally, models for the ultimate strength, ultimate strain, and stress-strain response of BFRP-jacketed corroded and pre-damaged RC columns were developed.

Predicting the Maximum Load Capacity of Circular RC Columns Confined with Fibre-Reinforced Polymer (FRP) Using Machine Learning Model

This article conducts an exhaustive investigation into the utilization of machine learning (ML) methods for forecasting the maximum load capacity (MLC) of circular reinforced concrete columns (CRCC) using Fiber-Reinforced Polymer (FRP). Extreme Gradient Boosting (XGB) algorithm is combined with novel metaheuristic algorithms, namely Sailfish Optimizer and Aquila Optimizer, to fine-tune its hyperparameters. The robustness and generalizability of these optimized hyperparameters are ensured through 200 Monte Carlo simulations (MCS). The model is constructed based on a database of 207 experimental results. Its performance is evaluated using three criteria: root mean squared error, mean absolute error, and the coefficient of determination. This study includes a performance comparison of the XGB4 model with eight other ML models, namely CatBoost (CAT), Gradient Boosting (GB), Hist Gradient Boosting (HGB), default XGB, Light Gradient Boosting (LGB), Linear Regression (LR), and Random Forest (RF). This comparison identifies the most effective model for predicting the MLC of columns. Additionally, this study explores the interpretability of the XGB model by SHAP values. This analysis illuminates the significance and interactions of various input features in predicting the FRP-confined CRCC's MLC. It offers insights into the primary elements influencing structural behavior by displaying a graphical depiction of the impact of specific characteristics on the model's output. This study culminates in developing an interactive Graphical User Interface (GUI) based on the XGB model. This tool allows users to investigate the influence of input parameters on the predicted MLC values, thereby enhancing their understanding and application of the model.

Random Forests Machine Learning Applied to PEER Structural Performance Experimental Columns Database

Columns play a very important role in structural performance and, therefore, this paper contributes to the critical need for failure mode prediction of reinforced concrete (RC) columns by exploring the capabilities of random forest machine learning (ML) based on a well-known experimental column database. Known as the PEER structural performance database, it assembles the results of over 400 cyclic, lateral-load tests of reinforced concrete columns. The database describes tests of spiral or circular hoop-confined columns, rectangular tied columns and columns with or without lap splices of longitudinal reinforcement at the critical sections. The efficiency towards the aforementioned goal of supervised ML methods such as random forests using a randomly assigned test set from the Pacific Earthquake Engineering Research Center (PEER) database is examined here. The overall accuracy score for rectangular RC columns is 94% and for circular RC columns is 86%. The latter performances are influenced by the size of the testing and training sets of data and are independent of the number of decision trees in the forest employed in the random forest algorithm. The performances of random forests in postdicting the failure mode of RC columns prove that ML has great promise in revolutionizing the profession of earthquake engineering.

Cyclic load behaviour of reinforced concrete columns with SMA and ECC in the critical regions

Design techniques that can reduce the residual deformation are necessary to ensure that reinforced concrete (RC) structures function properly after earthquakes. The use of superelastic materials in the plastic hinge region permits the structure to undergo large displacements with less residual displacement upon load removal. The present study deals with the incorporation of two innovative materials, super-elastic shape memory alloy (SMA) and engineered cementitious composites (ECC), in the critical region or plastic hinge zone of the column. This numerical study focused on the seismic performance evaluation of full-scale RC circular cantilever columns reinforced with two types of nickel-based and two iron-based SMA and ECC in the critical region. The specimens were subjected to a reverse cyclic lateral loading with a constant axial load at the top. The performance of these hybrid columns was compared with those of conventional steel-reinforced columns and steel-reinforced columns with ECC in the critical region. The results of the study revealed that the columns reinforced with SMA and ECC in the critical region showed negligible residual displacement compared to the normal and ECC columns. The column reinforced with the FeNCATB SMA and ECC in the critical region showed better behaviour in terms of a higher load-carrying capacity and ultimate displacement/rotation under a higher drift ratio. From the longitudinal rebar strain profile, it is evident that this hybrid column specimen did not reach the elastic strain limit at a higher drift ratio than the other specimens.

Numerical Study on Discrete Confinement of Circular RC Column Subjected to Eccentric Load

Background: The performance of concrete-filled steel-tube (CFST) columns under axial compression is excellent. However, the steel-tube wall's instability due to insufficient outward restraint from the concrete made the steel tube lose its lateral support, thereby making it more susceptible to buckling. Objective: This study aims to propose and investigate a confinement mechanism that can remove the possibility of buckling of the steel tube by introducing gaps and pre-tension to prevent tube detachment from concrete. The investigation was carried out using both experimental tests and numerical simulation. Methods: The proposed confinement mechanism consists of thin steel sheets with gaps between them and is pre-tensioned in a staggered scheme. The performance of the proposed confinement mechanism is evaluated through experimental tests and numerical simulations using an in-house 3D-NLFEA package. The observed behaviors are the axial stress-strain, strength index, initial confining pressure, and ductility. Results: Experimental works found that the primary failure mode in the compression zone of the strengthened column was due to lateral expansion of concrete which may be attributed to strain localization, longitudinal tensile cracking, and severe concrete crushing. On the other hand, at the tensile region, pure tensile forces occurred, followed by crack opening displacement at the outer tensile fiber region. With the proposed confinement mechanism, the extreme failure event can be reduced. The axial capacity and ductility of the strengthened column were enhanced. The numerical model presented the initial confining pressure by the pre-tensioned steel sheet (a clamping mechanism), which successfully increased the axial load capacity of the slender reinforced concrete (RC) column and reduced the possibility of cover spalling. Conclusion: The proposed confinement mechanism to strengthen an RC column was found to successfully enhance the load-carrying capacity and ductility of a slender circular reinforced concrete column.

Soft computing approach on estimating the lateral confinement coefficient of CFRP veiled circular columns

For any structures, Reinforced concrete (RC) columns are the utmost carping members. RC columns jacketed with CFRP membrane enhance resistance, deformation aptitude, and the auspicious confining impacts. Sundry scrutiny has been implemented about circular columns wrapping or veiled with CFRP layers. This scrutiny will manifest about Genetic Programming (GP) and Artificial Neural Networks (ANN) as soft computing models, mobbing exploited to ascertain the lateral confinement coefficient (Ks) valuate of RC circular columns jacketed with CFRP membrane. For the purpose to ascertain Ks value, manipulate the corresponding ambit such as the diameter of the column (b), column length (L), thickness layer of CFRP (tw), the elastic modulus of CFRP membrane (Ef) along with the compressive strength of unconfined concrete (fcc). Total collection of 142 datasets for the RC circular column was employed to decipher the prediction of Ks. Various statistical metrics (R2 = 0.933; RMSE = 0.054; NMBE = -0.001) compared with the ANN model and exhibits the superiority of GP in predicting the Ks. Taylor diagram and Rank analysis were also carried out in this article for justification. The lucidity of the GP machine enlightenment model overtures a greater sensible and exact prediction of Ks value for RC circular columns in accordance with versatile loading conditions.

Numerical Study on Slender Circular Reinforced Concrete Column Clamped with Steel Sheet

Various methods to enhance the performance of circular reinforced concrete column have been widely investigated. However, most researches used internal strengthening method such as intensifying steel reinforcement. Others utilized carbon fiber reinforced polymer (CFRP), glass fiber and aramid to retrofit either reinforcement or concrete surface. Few studies incorporated steel to cover concrete surface but neglecting clamp pressure between steel and concrete surface. This study proposes a steel sheet strap strengthening method by initial clamping stress on steel sheets as an external confining technique through experimental works and in-depth numerical analysis. The experimental investigation includes nine steel sheet strengthened reinforced concrete specimens of 20 MPa subjected to axial concentric and axial eccentric. Retrofitting devices will be fabricated from BJ37 steel. Steel sheet straps in each specimen will be subjected to varying initial clamp pressure by fastening bolts. Applied load, lateral displacement and vertical and horizontal deformation will be measured by the instrumentation. Experimental works will observe failure mode, force displacement, stress and ductility. Section analysis based on experimental results will define compatibility equations for numerical stage. Strengthening model from experimental stage will also be analyzed in numerical study with inhouse software 3DNLFEA. F-D curve and moment-curvature loading behavior and ductility will be obtained from numerical analysis. It is believed that the proposed strengthening mechanism with its geometrical and stress variations could enhance the section, member and structural ductility of circular reinforced column against vertical and lateral load. Furthermore, the developed analytical model could well predict the behavior of the proposed clamp mechanism for practical applications.

Experimental and numerical study of PEN FRP-strengthened circular RC columns under lateral cyclic loading with high axial compression ratio

This paper presents experimental studies and numerical simulations of circular reinforced concrete (RC) columns wrapped with Polyethylene Naphthalate fiber reinforced polymer (PEN FRP, a kind of large-rupture-strain FRP) and conventional CFRP. A total of seven columns were designed and fabricated, including a control column, three columns strengthened with CFRP, and three columns strengthened with PEN FRP. All columns were subjected to cyclic lateral load and a constant high axial load. The effectiveness of PEN FRP strengthening was systematically analyzed and discussed regarding the failure mode, displacement ductility, lateral cyclic load–displacement curve, stiffness degradation and energy dissipation capacity. The test results indicated that the control column exhibited inferior ductility and peak lateral strength, while FRP-strengthened columns possess better energy dissipation capacity and ductility. Further study found that PEN FRP was preferred to CFRP with similar tensile stiffness in seismic strengthening. Finally, based on the cyclic compression model of LRS FRP-strengthened concrete, the improved tensile model of FRP-strengthened concrete, and the cyclic stress–strain model of reinforcing steel, numerical simulations for seismic performance were carried out in OpenSees. It was found that the numerical simulation results of all FRP-strengthened RC columns were in excellent agreement with the test results. To better understand the effect of FRP confinement stiffness on the seismic performance of circular columns, parametric analysis was performed. Results showed that the numerical simulations need to consider the buckling of longitudinal reinforcement for accurately predicting the seismic behavior of FRP-strengthened columns of lower confinement stiffness.

Sustainable Design of Circular Reinforced Concrete Column Sections via Multi-Objective Optimization

An optimization model for reinforced concrete circular columns based on the Eurocodes is presented. With the developed optimization model, which takes into account the exact distribution of the steel reinforcement, which is not the case when designing with conventional column design charts, an optimal design for the reinforced concrete cross section is determined. The optimization model uses discrete variables, which makes the results more suitable for actual construction practice and fully exploits the structural capacity of the structure. A parametric study of the applied axial load and bending moment was performed for material cost and CO2 emissions. The results based on a single objective function show that the optimal design of the reinforced concrete column cross section obtained for the material cost objective function contains a larger cross-sectional area of concrete and a smaller area of steel compared with the optimization results when CO2 emissions are determined as the objective function. However, the optimal solution in the case where the material cost was assigned as the objective function has much more reserve in axial load capacity than in the optimal design where CO2 was chosen as the objective function. In addition, the multi-objective optimization was performed to find a set of solutions that provide the best trade-offs between the material cost and CO2 emission objectives.

Blast-resistant design approach for RC bridge piers

Piers are the critical components to support the superstructure of bridge, but susceptible to the intentional and accidental explosions due to its easy accessibility. The blast-induced damage to the pier may cause the entire bridge to collapse, resulting in huge casualties and economy loss, and thus it is necessary to perform the blast-resistant design for the bridge pier. At present, the analytical model and blast-resistant design approach for blast-loaded reinforced concrete (RC) pier considering both the direct shear and flexural responses were studied. Firstly, six shots of field ground explosion test on 1/5-scale circular and square RC columns were carried out, in which the TNT charges with the scaled distances of 0.86–1.22 m/kg1/3 were adopted. Then, the corresponding numerical simulations incorporating the newly developed Structured Arbitrary Lagrangian Eulerian (SALE) solver were conducted, and the validity of finite element (FE) analysis approach was verified by comparing the experimental incident and reflected overpressure-time histories acting on the periphery of pier with deviations for most measuring points less than 20%. Afterwards, total 176 explosion scenarios were numerically simulated, and a blast loading distribution model on the pier for ground explosions was proposed, which considers the pier cross-section shapes (circular and square) and pier diameter/edge length (0.2–1.6 m), the scaled distances of explosive charge (0.3–2.3 m/kg1/3), as well as the blast wave reflection and diffraction by the pier. Furthermore, a Timoshenko beam-based multi-degree of freedom (MDOF) analytical model was established, and validated by both the existing explosion tests on RC columns and refined numerical simulations of blast-loaded bridge piers with corresponding deviations no more than 5%. Finally, a blast-resistant design procedure incorporating the above-proposed blast loading distribution and MDOF models was given, providing a reliable and efficient blast-resistant evaluation and design tool for bridge piers.

Experimental and Numerical Study on Seismic Performance of PEN FRP-Jacketed Circular RC Columns

This paper presents an experimental study on the seismic behavior of polyethylene naphthalate (PEN) fiber–reinforced polymer (FRP)-jacketed circular reinforced-concrete (RC) columns. A total of seven specimens were tested under constant axial load and cyclic lateral load. The key parameters studied were the thickness (one, two, and three layers) and type (PEN FRP and CFRP) of FRP jacket. Test results indicated that the control column failed by buckling of the longitudinal reinforcement and shortage of ductility, while concrete spalling and bar buckling were effectively inhibited by the application of external FRP jacket. It is also observed that PEN FRP-jacketed specimens had more additional strain capacity compared with CFRP-jacketed specimens at the final condition. The additional strain capacity can serve as a safety reserve for structures and make PEN FRP more suitable for strengthening large or noncircular columns. Furthermore, it is found that 1-ply PEN FRP and 1-ply CFRP had a similar strengthening effect and thus the design of PEN FRP-strengthened column can simply refer to the design method of CFRP-strengthened columns in current codes. Different FRP thickness and types had marginal impact on the hysteretic curves of the specimens, which was attributed to the low axial load ratio (0.15) and high slenderness ratio (5.25) adopted in this paper. Finally, based on a cyclic stress–strain model for longitudinal reinforcement, including buckling effect, developed by the authors in a previous study, the test columns were simulated by the Open System for Earthquake Engineering Simulation (OpenSee)s to achieve an in-depth understanding of the experimental findings and associated strengthening mechanisms. Further parametric analyses showed that considering bar buckling played a significant role in accurately predicting the hysteretic response of FRP-jacketed columns.

Performance-Based Seismic Design of Hybrid GFRP–Steel Reinforced Concrete Bridge Columns

Damage quantification in terms of engineering demand parameters (EDPs) is a critical element of the performance-based design (PBD) approach. A widely used EDP for reinforced-concrete (RC) bridge columns is the drift ratio. This study establishes drift ratio limit states, and corresponding strengths for hybrid GFRP–steel RC circular bridge columns. The adopted reinforcement layout in this study consists of two layers of reinforcement, exterior with GFRP and interior with steel. Such coupling between the two materials in concrete bridge columns improves their corrosion resistance while maintaining their stiffness and ductility. Here, a validated fiber-based model is utilized to predict global as well as local responses of hybrid RC columns under monotonic displacement-controlled loading. A full factorial analysis was first adopted to screen parameters potentially influencing drift ratio limit states and corresponding strengths for their significance. The resulting data were then fitted to mathematical expressions using machine learning-based symbolic regression. Lateral load–deformation responses predicted based on the proposed expressions were validated against existing data from the literature. A complete example demonstrating how the proposed expressions could be utilized to design a hybrid bridge column within the context of PBD is also presented.

Rebar Replacement in Severely Damaged RC Bridge Column Plastic Hinges: Design Criteria and Experimental Investigation

This paper presents a procedure for rehabilitating plastic hinges with damaged/fractured weldable longitudinal rebars in severely damaged reinforced concrete (RC) bridge columns and possible improvements regarding connection protection and plastic hinge development. Damaged/fractured longitudinal rebars are replaced with new rebar segments, and the basis of this approach involves connecting intermediate machined parts to the original longitudinal rebars by welding with an off-the-shelf steel equal angle. The proposed rehabilitation design procedure is based on capacity design principles, with equations that define the new geometries and required ductility, and it is validated experimentally on three 1∶6-scale RC circular column specimens. Compared with the original columns, the ductility capacity of the rehabilitated columns increased from 39% to 58%, and the energy dissipation (equivalent viscous damping ratio) increased from approximately 50% to 250%. The base shears of the rehabilitated columns were smaller than those of the original columns owing to the reduction in the rebar area; thus, shear failure was avoided, and the demand on the foundation was reduced. The rehabilitation procedure, by adopting a welding connection that is easily performed on site and concentrates the damage in the new rebar segments, promises to be a quick, simple, reliable, and effective means to improve the ductility and shear capacity of RC bridge columns without using mechanical couplers or changing the column dimensions.

Size effect tests on axial compressive behavior of BFRP-reinforced concrete columns

To explore the compressive behavior and corresponding size effect of concrete columns internally reinforced with basalt fiber‐reinforced polymer (BFRP) bars and stirrups, twelve geometrically similar columns were tested under axial compression. The test parameters included cross-sectional shapes, cross-sectional diameters/widths and stirrup ratios. The test results indicated that both the circular and square BFRP reinforced concrete (RC) columns presented a notable size effect on nominal compressive strength and ductility. As the cross-sectional size varied from 200 mm to 600 mm, the nominal compressive strength of circular and square columns exhibited maximum decreases of 11.0 % and 19.1 %, respectively, while the maximum decreases of ductility index were 66.2 % and 16.7 %, respectively. Moreover, increasing the stirrup ratio could effectively improve the confinement efficiency and ductility as well as weaken the size effect on nominal compressive strength of BFRP RC circular columns. The accuracy of available design equations was significantly influenced by the confinement effect of BFRP spirals in circular columns, while for square columns the specimen size was the most important factor. Finally, new equations were derived by considering the confinement effect of stirrups or size effect of concrete, and these equations showed satisfactory accuracy in predicting the axial load-carrying capacity of BFRP RC columns.

Analysis of eccentrically loaded FRP partially wrapped reinforced concrete columns subjected to combined environmental erosion

The behavior of eccentrically loaded fiber reinforced polymer (FRP) partially wrapped reinforced concrete (RC) columns under combined environmental erosion was investigated in this paper. Circular RC columns were firstly subjected to chloride erosion where the target corrosion degree (0, 10 %, and 20 %) is obtained with externally applied current. This was then followed by partially strengthening with 2-ply of glass fiber reinforced polymer (GFRP) strips as well as 50 freeze–thaw cycles. Series of eccentric compression tests were conducted with ranging eccentricities of 0, 5 mm, 10 mm, and 15 mm. For comparison, the carbon fiber reinforced polymer (CFRP) partially strengthened columns with the corrosion degree of 10 % and subjected to 50 freeze–thaw cycles were also eccentrically loaded with an eccentricity of 10 mm. Results showed that with increasing corrosion degree, the bearing capacity of GFRP strengthened column showed a 2-stage behavior (firstly increased and then decreased), which may be caused by the confinement reduction of FRP on columns due to severe environmental erosion. Under small eccentric loading, The CFRP strengthened RC columns showed better compressive behavior than that of GFRP strengthened RC columns. Based on the stress–strain relationship of constituent materials, a simplified analytical model considered the effects of chloride and freeze–thaw erosion was put forward to predict the bearing capacity of FRP partially wrapped RC column under eccentric loading.

Numerical Analysis of Reinforced Concrete Circular Columns Strengthening With CFRP under Concentric and Eccentric Loadings

The purpose of this study is to explore the numerical behavior of circular RC short columns with different degrees of confinement with CFRP (0%, 25%, 50%, and 100%) wraps under concentric and eccentric loading. The numerical analysis carried out by using an improved concrete plastic-damage model (CDPM) implemented in ABAQUS software for finite element (FE) analysis. The FE model simulated a total of twenty-four numerical specimens. The findings were matched to published experimental test results in the literature. The findings of the FE model and the experimental data were good similar. As a consequence, the model was found to be valid. The numerical results shows that as load eccentricity increased, the load carrying capacity of columns decreased for unconfined specimens, whereas the decline in strength for confined specimens becomes limited as the degrees of confinement ratio increased. In addition, increasing the CFRP confinement ratio improves the column's load-bearing capability at the same load eccentricity.

Analysis-oriented model for partially FRP-and-steel-confined circular RC columns under compression

Even though analysis-oriented models exist to simulate the axial and dilation behavior of reinforced concrete (RC) columns strengthened with fiber-reinforced-polymer (FRP) full confinement arrangements, a reliable model developed/calibrated for FRP partially imposed confinements is not yet available, identified as a research gap. Therefore, this paper is dedicated to the development of a new analysis-oriented model generalized for fully and partially confined RC columns under compression. In addition to vertical arching action phenomenon, the influence of the concrete expansion distribution along the column height on confining stress is considered in the establishment of the combined confinement from FRP strips and steel transverse reinforcements. A new unified dilation model is proposed, where the substantial effect of additional axial deformations induced by damage evolution in unwrapped zones is formulated by considering available experimental results. This model is coupled with an axial stress-strain formulation that includes a new failure surface function for simulating the dual confinement-induced enhancements, which are strongly dependent on the confinement stiffness. The developed model considers the influence of partially imposed confinement strategy on the axial and dilation behavior of RC columns, whose validation is demonstrated by simulating several experimental tests. Lastly, a parametric study is performed to evidence the dependence of FRP-steel confinement-induced enhancements on steel hoop and FRP spacing, and on the concrete compressive strength.