Steel Confinement Research Articles

Design-oriented stress–strain model for RC columns with dual FRP- steel confinement mechanism

Many research studies have been conducted to evaluate confinement-induced enhancements on the mechanical properties of FRP (fiber-reinforced polymers)-confined plain concrete elements subjected to axial compressive loading, leading to the development of extensive predictive models. Nevertheless, experimental stress–strain results for FRP-confined RC columns (FCRC) have demonstrated some behavioural features that cannot be simulated accurately through this kind of model, developed exclusively for FRP-confined concrete columns (FCC). In this paper, a new design-oriented stress–strain model is proposed for the prediction of load-carrying capacity versus axial strain relationship of FCRC. For this purpose, a new parabolic stress–strain expression is developed for calculating the first branch of FCRC’s response up to the transition zone, followed by a linear function. New formulations are proposed to determine the first branch’s stress–strain gradient, transition zone-related information and the second branch’s slope, calibrated using a large test database of FCRC. The proposed design-oriented model is capable of simulating accurately the combined influence of the dual FRP and steel confinement on load-carrying capacity versus axial strain relationship of FCRC. Lastly, the capability of this model is validated by comparison to existing experimental data of FCRC and those obtained from some of existing models in the literature.

Seismic rehabilitation of URM heritage-listed Namazi school building using multiple retrofitting techniques

When dealing with retrofitting historical URM buildings, two prime aspects of their weakness against seismic action should be considered. These include: (i) the capacity of structural elements, such as foundations, masonry walls and floors, to resist earthquake forces and (ii) the integrity of the building as a whole under ground shaking. In this paper, different retrofitting techniques adopted to counter the above weaknesses in rehabilitation of the heritage-listed Namazi high school buildings are discussed. Extensive field investigations were first carried out to determine the detailed architectural and structural forms of the buildings, as well as, their material types and properties. It was found that in constructing the historic school buildings, traditional Iranian construction techniques and materials were used alongside some more modern elements such as reinforced concrete and masonry jack arch slab systems. This made the buildings unique in form, hence more challenging to retrofit. Seismic vulnerability studies were then carried out to evaluate the weaknesses of structural elements and the buildings as a whole. Different retrofitting techniques were then selected and applied to overcome the weaknesses. Effectiveness, cost and architectural constraints were the main considerations in selecting the retrofitting techniques for different parts of the historical buildings from a pool of different available methods. The techniques used in enhancing the seismic capacity of structural elements included: reinforced shotcrete overlay for masonry walls, FRP overlay for RC floors and beams, steel confinement and bracing of masonry jack arch floor systems and RC ground-beam confinement of brick and stone masonry foundations. To enhance the overall integrity of the buildings through confinement, vertical and horizontal steel tie elements and reinforced concrete tie elements were used.

Experimental and Analytical Study on the Axial Behavior of Circular High-Strength Concrete Columns with Hybrid Carbon Fibers and Steel Confinement System

This paper describes a work that examines a new solution to the problem that arises from the relatively high amount of transverse reinforcement required in HSC columns. It presents an alternative to common transverse steel reinforcement, a dual system comprising steel ties and a carbon-fiber mesh (CFM) applied internally together with steel ties. The behavior of the proposed system was examined in this work in a series of twelve laboratory tests of circular stub column specimens. The experiments performed in this work focused on the columns’ load and displacement capacities. The tests were planned with the aid of an analytical model that was originally developed for a hybrid system of external fiber-reinforced polymer (FRP) sheets and internal steel, and was adapted for the current system. An analysis of the results shows that for a given amount of conventional transverse steel, the application of the carbon-fiber meshes adds efficiency to the rebar confinement system, in terms of both the load bearing capacity and the ductility, and for specimens with the hybrid confinement system, the higher the carbon fiber amount the larger the ductility improvement. Furthermore, fair to good agreement was observed between the model and the measured stress–strain curves, especially those of the peak stresses. Based on the above findings and the added benefit of fire resistance, the hybrid method appears to be promising for confining HSC columns.

Loading performance of reinforced and recycled aggregate concrete-filled circular steel tube short column with different steel ratios

Experimental and numerical studies were conducted to clarify the influencing law of steel ratio on the mechanical properties of reinforced and recycled aggregate concrete (RAC)-filled circular steel tube short columns (R-RACFST) with 100% recycled coarse aggregate (RCA) replacement. Concrete-filled steel tube (CFST), RAC-filled steel tube (RACFST) and R-RACFST test series were designed using five different wall-thicknesses of steel tube with two replicates for each wall-thickness. Based on the test, the influencing law of steel ratio on the failure, loading performances and ductility was analyzed, and the improving effect of reinforcement on the behavior of R-RACFSTs was confirmed, and the finite element (FE) model was developed, and the FE simulations were then performed considering the coupling effect between the wall-thickness of steel tube, reinforcement and strength of RAC. The strength prediction equations of CFSTs from codes such as T/CECS 625, GBT51446-2021, GB50936-2014, ANSI/AISC A360-16, AIJ, Eurocode 4 and AS/NZS 5100.6 were studied and their applicability to RACFSTs was confirmed. Meanwhile, novel equations for predicting the strength of R-RACFSTs were proposed and verified. The results demonstrate that: R-RACFST makes it possible to fill RAC with 100% RCA; when combined with an appropriate amount of reinforcement, R-RACFSTs with thinner steel tube performs as well or better than RACFSTs with thicker steel tube; reasonable ranges of steel ratio and confinement index for R-RACFSTs are recommended as 6.2%∼12.8% and 0.78 ∼ 1.53, respectively; the proposed equations are accurate and reliable, and can be applied to design the load bearing capacity of axially loaded R-RACFSTs.

Compressive performance of SWSSC-filled CFRP-stainless steel composite tube columns

The structure of concrete confined by carbon fiber-reinforced polymer (CFRP) and stainless steel tubes was investigated. The columns, which take advantage of the ductility and corrosion resistance of stainless steel, are composed of stainless steel tube, core seawater and sea sand concrete (SWSSC) and outer FRP. Forty circular SWSSC-filled FRP-stainless steel composite tube columns (SCFSSCTs) were manufactured and subjected to axial compression tests. After fracturing of the FRP, the failure modes of the specimens mainly showed extrusion expansion, with a small amount of shear failure. The increase in the thickness of the stainless steel and the number of FRP layers resulted in a significant improvement in the load capacity and deformation capacity of the structure, which was more evident in the specimens with higher steel contents. With the increase in the number of FRP layers, the increases in ultimate stress and ultimate strain were 40.4% − 130.0% and 118.6% − 282.4%, respectively, compared with the column with single stainless steel confinement. The stress–strain curves for the SCFSSCTs were similar to those of structures reinforced by FRP and carbon steel and were divided into four stages. Models were proposed to predict the full axial stress–strain curves of SCFSSCTs, including the ultimate point and the peak point.

Experimental study on self-compacting concrete-filled steel tube samples containing shrinkage-controlling admixtures

Once again, the earthquake disaster in Turkey and Syria indicates the significance of aseismic structures. Concrete-filled steel tube (CFT) columns are key components in such structures. In this study, the effect of shrinkage control admixtures on the performance of self-compacting mixes that are often used in CFT column construction was evaluated. They were confined to a 3 mm thick cylindrical hollow steel tube and the infilled concrete shrinkage was monitored with the embedment of a vibrating wire strain gauge. The concrete length of this compound was found to be reduced as the length of the confining tube expanded. However, this change in concrete length was reduced by 70% with the use of a commercial grade liquid mixture that reduces shrinkage in the early stages. A substantial reduction in concrete shrinkage was observed with the use of limestone powder and a compensating admixture for shrinkage. The use of limestone also improved the resistance of concrete to water permeation and chloride ion transport by pore filling effects. Although steel confinement reduced concrete shrinkage by 50% at 28 days, the addition of specialty admixtures is still highly recommended to avoid the effect of debonding, induced by the shrinkage discrepancy between confining steel and the inner concrete mass.

Numerical Investigation of Axial Force–Bending Moment Interaction for FRP-Confined Reinforced Concrete Columns with Internal Steel Transverse Reinforcement

Externally bonded fiber-reinforced polymer (FRP) laminates are widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can increase the axial and bending moment capacities of these columns through a confinement mechanism. The confinement produced by FRP laminates acts in addition to that exerted by the internal transverse steel, although the latter is often neglected in current design standards and guidelines. In this study, a recently developed FRP-and-steel-confined concrete constitutive model was employed to numerically investigate the axial force–bending moment interaction for FRP-confined RC columns modeled using finite-element (FE) analysis. The proposed model was first validated against experimental data available in the literature and then used to quantify, through an extensive parametric study, the effects of transverse steel confinement, FRP strength, FRP stiffness, FRP reinforcement ratio, column diameter, concrete compressive strength, and load eccentricity ratio on the strength of FRP-confined RC columns subject to combined axial compression and bending moment. It was found that the internal steel confinement can substantially enhance the strength of these columns, especially for low concrete compressive strengths, large cross sections, and small eccentricities. When design code provisions limiting concrete and FRP deformations were considered for eccentrically loaded columns, the contribution of the steel confinement increased for increasing FRP reinforcement ratio. Based on the parametric study results, this investigation proposed an extension to eccentric axial compression of two relative confinement coefficients, which were previously developed to describe the contribution of transverse steel confinement to the peak strength of FRP-confined RC columns subject to pure compression.

Confinement mechanism and compressive stress-strain behaviours of FRP-interlayer-steel confined concrete tubes

A fiber-reinforced polymer (FRP)-interlayer-steel confined concrete (FISC) column is formed by bonding the FRP material and a concrete-filled steel tube (CFST) with the grouting material, and it can improve the corrosion resistance and bearing capacity of CFST columns and avoid the early cracking of the epoxy resin in FRP confined concrete-filled steel tubes (CCFT). However, there are few researches on the compressive behaviours of FISC columns and the dual confinement on core concrete from the FRP tube and steel tube has not been expounded clearly. In this paper, twelve FISC specimens were tested under axial compression. The ratio of FRP and steel confining indexes and the concrete strength were the main parameters and the loading conditions (core CFST loading and whole section loading) were included. Failure patterns, load–axial shortening curves, and the strain development were analysed. In addition, the confining stresses of the FRP tube and steel tube were obtained, and it was found that the confinement on concrete could be divided into three stages of the non-confinement stage, the steel-controlling stage, and the FRP-controlling stage. In the FRP-controlling stage, the FRP confining pressure increased at a constant growth rate while the steel confinement was gradually weakened owning to the restraints of the interlayer grouting material. Furthermore, by regarding the concrete and grouting material as a whole unity, the axial stress-strain model of the confined concrete-grouting was developed, and the proposed model can predict the compressive stress-strain behaviours of an FISC column with good accuracy and simplicity.

A nonlinear fibre beam-column model for partially encased composite columns incorporating local buckling effect

Partially encased composite (PEC) columns are being widely used as vertical load carrying members in high-rise building structures. The complex structural behaviour of PEC columns at ultimate and failure states, related to local buckling of steel section and confinement effect of concrete, has posed significant difficulties and computational costs for accurate analysis of these members. To address this issue, this paper presents a nonlinear fibre beam-column (FBC) model for efficient and accurate analysis of PEC columns. A 2D Euler-Bernoulli beam element based on geometrically exact beam theory is employed, which has fibre cross sections accounting for the material nonlinearity of steel and concrete. A generalised effective width method (GEWM) is developed and integrated in the FBC model to simulate the stress redistribution in the steel section due to the progression of local and post-local buckling. Numerical examples demonstrate that the proposed FBC model can reasonably predict the behaviour of short PEC columns under concentric and eccentric compression, as well as the global buckling behaviour of long PEC columns. The computational cost of the proposed FBC model is considerably lower than that of 3D finite element analysis. The numerical examples also show that the incorporation of the local buckling effect (GEWM) leads to decreases in the ultimate and post-peak loads predicted by the FBC model. The effect of local buckling becomes insignificant for long PEC columns with length-to-depth ratios greater than 15.

Peridynamic modeling of damage and non-shock ignition behavior of confined polymer bonded explosives under impact loading

A mechanical-thermal-chemical coupled peridynamic (PD) modeling for analyzing the damage and non-shock ignition behavior of polymer bonded explosives (PBXs) subject to impact loading has been presented. The friction and heat conduction and Arrenhenius law are embedded into the PD theory, ensuring that the simulation model is capable of capturing major features of dynamic damage response of PBX. A PD material model considering plasticity and the asymmetric behaviors of PBX under tensile and compressive loadings is proposed in this study. For a ring-shaped PBX 9501 sample confined by the steel structures, the simulation results indicate that the PBX 9501 in the regions towards the impact face and support face suffers from the serious damage. Meanwhile, the corresponding average temperatures in these two regions are also higher than their counterparts in other regions due to the more intense interaction between PBX 9501 and the steel confinement structures. The ignition time decreases with the increasing impact velocity within the range of 40–120 m s−1. The internal steel shell response is analyzed according to its velocity history within a representative box. It is found that the deformation process of internal steel shell is closely related to the complicated flow behaviors of PBX 9501.

Experimental characterization and analytical assessment of compressive behavior of carbon nanofibers enhanced UHPC

With superior mechanical and durability properties, ultra-high performance concrete (UHPC) is making strides towards revolutionizing concrete structures and the construction industry. Even though UHPC is widely known, it is still used only in small-scale elements. Recently, more advanced commercial and non-proprietary UHPC mixtures, e.g., nano-enhanced UHPC, have emerged timely to support a rapidly growing market and increased interest in expanding UHPC applications to full structural components. Thus, there is a need to comprehensively characterize the mechanical properties of such emerging mixtures using more experimental data and assess how such mixtures compare to traditional UHPC. This paper focuses on the uniaxial compression behavior of carbon nanofibers (CNF) enhanced UHPC. The literature is currently lacking any data on the combined effects of steel fibers and traditional reinforcement confinement in CNF-enhanced UHPC. The objective of this study is to experimentally characterize and analytically assess the uniaxial compressive behavior of CNF-enhanced UHPC at different ages and with varying steel fibers content and confinement reinforcement. In this study, more than 230 cylinders with 0–4 % varying steel fiber ratio and 0–4 % varying steel spiral confinement ratio were tested. Experimental results of the CNF-enhanced UHPC cylinders were assessed using established analytical models for traditional UHPC for Young's modulus and confinement effects on both stress and strain. The study first demonstrates that using accelerator in UHPC mixtures can help achieve about 80 % of the 28-day-strength only in three days after casting. Overall, the results suggest that the combined effect of steel fibers and steel spirals increases the ductility of CNF-enhanced UHPC relative to traditional UHPC. The study also concludes that current analytical models do not precisely capture the compressive and confinement behavior of this emerging type of UHPC.

Axial behavior of square and circular concrete columns confined with CFRP sheets under elevated temperatures: Comparison with welded-wire mesh steel confinement

The main goal of this study was to carry out an experimental investigation of the effectiveness and the efficiency of using carbon fiber-reinforced polymer (CFRP) strips and welded wire mesh jackets for retrofitting square and circular columns exposed to highly elevated temperatures. The investigated variables included the geometry of the column, strengthening scheme, and heating temperature. The samples were divided into three groups. The first group contains column samples not exposed to elevated temperatures and had no strengthening applied. The second category contains un-strengthened column samples subjected to elevated temperatures; the third category comprises strengthened column samples exposed to elevated temperatures. The elevated temperature exposure consisted of heating the specimens to 600 °C for 3 h. The column samples were subjected to axial compression testing till failure. The test results showed that both the circular and square columns exhibited reductions in axial capacity and initial stiffness when exposed to elevated temperatures. The use of welded wire mesh confinement around the circular and square columns exposed to elevated temperatures provided a more significant increase in strength as well as stiffness compared to strengthening the columns with unidirectional CFRP strips. In contrast, the CFRP repaired heated columns exhibited a significant increase in ductility and deformation capability without any reduction in strength than the WWM jacketed heated columns. Furthermore, the confinement effectiveness of CFRP jacketing provides considerable confinement to micro-cracked concrete compared to the WWM jacketed RC circular columns. However, in square columns the confining effectiveness for WWM was better compared to CFRP strips. Moreover, the use of CFRP strips were ineffective for recovering the stiffness of columns exposed to elevated temperatures. In addition, the results demonstrated that the use of welded wire mesh confinement and CFRP strips are cost-effective retrofitting techniques that could be used for circular and square RC columns.

Performance and modeling of FRP-steel dually confined reinforced concrete under cyclic axial loading

Fiber-reinforced polymer (FRP)-steel tubed reinforced concrete (FSTRC) columns present promising engineering applications due to the reasonable integration of three constituent materials. Compared with the numerous studies on their performance under monotonic loading, relatively few studies have focused on their cyclic axial behavior. Moreover, the available models for plain concrete solely confined by FRP might be incapable of estimating the confined concrete behavior in cyclically loaded FSTRC due to the possible effect induced by the steel reinforcement in concrete, the additional steel tube confinement, and the girth gaps at column ends. To this end, this paper investigated circular FSTRC stub columns under monotonic and cyclic axial loading. The test results confirmed that the inclusion of reinforcement had noticeable effects on the unloading path since the tensile axial stresses in longitudinal steel bars slowed down the stiffness degradation of the inner concrete during unloading. For envelope cycles, the increase of the additional steel confinement level had a negligible impact on the plastic strain and the stress deterioration of the inner concrete. A confinement model was developed to estimate the full-range behavior of the FRP-steel dually confined reinforced concrete under cyclic axial loading with favorable accuracy.

Axial Compression Performance of Concrete-Filled Steel Tubular Columns with Different D/t Ratios

The impacts of three diameter/thickness (D/t) ratios (21.22, 25.46, and 31.83) and concrete strengths (40 N/mm2, 50 N/mm2, and 60 N/mm2) on the strength capabilities of concrete-filled steel tubular (CFST) columns are investigated in this study. The central composite design (CCD) of the response surface methodology (RSM) was used to design the trials in order to complete the tests in a cost-effective manner. 13 (9 distinct tests) columns were evaluated according to the CCD experimental design, and the failure mode of the specimens, load–deformation behavior, and ultimate strength capacity were investigated. Concrete strength improves, resulting in a decrease in steel tube confinement on the core. Because the steel tube longitudinal compressive stress (fsl) increases as the D/t ratio lowers, the confinement is reduced by inhibiting the circumferential tensile stress (fsc). The Reynolds stress model’s, analysis of variance (ANOVA), Pareto chart, and contour plot demonstrated that the column D/t ratio, rather than the in-filled concrete strength, has a considerable impact on the CFST column’s strength capability. The proposed design models in different international codes and literature were evaluated for their effectiveness in predicting the strength capacities of CFST columns subjected to axial compression load. Using regression analysis, a simple design model was suggested to predict the axial strength capacities of CFST short columns, taking into account material strength and column shape. In comparison to other existing and suggested design models, the proposed design model of the present study delivers a more accurate and stable forecast.

Minimum weight design of reinforced concrete beams utilizing grey wolf and backtracking search optimization algorithms

In this study, optimal weight design of a reinforced concrete beam subjected to various loading conditions is investigated. The purpose of the optimization is to attain the minimum weight design of the reinforced concrete beam under distributed and two-point loads. The design problem is handled under three different design load cases. The two-point loads are affected on beam-to-beam connection nodes of reinforced concrete beams. Thus, while the magnitudes of distributed load and two-points load are remained constant, the distances between two-points loads are taken as 2m, 3m and 4m, respectively. The width and height of the rectangular cross-section of the concrete beam, and the diameters of the longitudinal and confinement steel rebars are treated as design variables of the optimum design problem. The design constraints of the optimization problem consist of the geometric constraints and necessities of the Turkish Requirements for Design and Construction of Reinforced Concrete Structures (TS500), and Turkish Building Earthquake Code (TBEC). As two novel metaheuristics, grey wolf (GW) and backtracking search (BS) optimization algorithms are selected as optimizers. Both algorithms are independently operated five times for three different design problems. Thus, the obtained results are examined statistically to compare in accordance with algorithmic performances. The optimal findings from optimization algorithms show that the GW algorithm is a little bit more robust on the exploitation phase, while the BS algorithm is stronger on the exploration phase. Moreover, it can be deducted from optimal beam designs that the GW algorithm is more viable to minimize reinforced concrete beam design.

Compressive behavior and stress-strain model of square confined ambient-cured fly ash and slag-based geopolymer concrete

Although a great deal of work has been completed towards the study on geopolymer concrete (GC), most of the efforts have focused on the material mechanical behavior. The objective of this paper is to present the results of an experimental study aimed to investigate the stress-strain behavior of confined fly ash and slag-based GC (FASGC) through the compression testing of a total of fourteen square ambient-cured short columns. The experimental results indicated that the increase in the slag content resulted in higher unconfined compressive strength but more obvious brittle property of confined FASGC. The effectiveness of lateral steel confinement was higher for FASGC than that for ordinary Portland cement-based concrete (OPCC), despite the lateral confinement index Kn of the former one was a little smaller compared to the latter one, the maximum differences in both fcc/fc0 and εcc/εc0 between them were 20.8% and 59.3%, respectively. Both fcc/fc0 and εcc/εc0 were not strongly related to the variation of the spacing of transverse reinforcement. The increase in the diameter of transverse reinforcement was not obviously improve the fcc/fc0 but resulted in the increase in the εcc/εc0, nonetheless, the εcc/εc0 was only increased by 70.9% as the Kn increased 3 times. The models were proposed to predict both ultimate stress and strain and to describe the stress-strain behavior of FASGC with good accuracy, more test data is further need to refine the proposed models. In light of the results, it is recommended to further investigate the effect of the fibers such as steel fiber, FRP fiber on the improvement of the brittle behavior of FASGC.

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.

Development of analytical model for predicting compressive behavior of engineered cementitious composites‐concrete encased steel composite columns

AbstractAnalytical models which can reliably predict the load–deformation behaviors and the ultimate strength of columns are indispensable tools for the practical design. In this paper, an analytical model is developed to predict the compressive load–deformation behavior and the ultimate capacity of engineered cementitious composite confined concrete encased steel (ECC‐CES) composite columns. The proposed analytical model employs the effective material stress and strain compatibility approaches for the predictions of compressive load–deformation response of ECC‐CES columns. The material constitutive models for ECC, concrete, and steel are first established, and then used in the analytical model. The effect of ECC and steel confinement on the concrete core and the softening behavior of steel column due to compression buckling are also considered. Based on the experimental results, appropriate strength reduction factors are proposed so that the effective material stresses can be calculated. The strength predictions from the proposed analytical methods and different design codes are compared with the experimental and numerical results. It was found that the proposed analytical models using effective material stresses gave better predictions than many commonly used design codes.

Numerička analiza cikličnog jednoosnog i dvoosnog bočnog opterećenja AB stupova

A numerical finite element study is conducted in this paper to examine structural behaviour of high strength RC columns exposed to biaxial and uniaxial lateral displacement histories with constant axial load. The numerical analysis of 24 models was made using ABAQUS / CAE. The comparison between numerical analysis and experimental results shows good agreement through validations. The considered parametric study involves determination of the longitudinal reinforcement ratio, total cross-sectional area of confinement steel (Ash), and uniaxial and biaxial cyclic shear load. Numerical analysis results show that an increase of longitudinal reinforcement for a uniaxial and biaxial lateral historic load will significantly increase maximum and ultimate load of columns, corresponding deflections, number of cycles at maximum and ultimate loads, and initial stiffness Ki, while the effect of transverse reinforcement is less pronounced. The columns load and deformation capacity decreases significantly with application of biaxial cyclic shear load, compared with uniaxial load. Also, this effect reduces with an increase in longitudinal reinforcement ratio (%ρl) and Ash.

Data-oriented analysis of axial capacity of externally CFRP-confined concrete columns transversely reinforced with steel hoops or spirals

Limited research is available in the literature for exploring the axial compressive behavior of circular concrete columns confined by both external CFRP wraps and internal transverse steel reinforcement (SCC columns). The main objective of the present work is to develop an empirical model and an analytical model for predicting the axial compressive strength of SCC columns by considering the interaction between the CFRP composite and steel reinforcement confinement action. An extensive experimental database of 76 SCC columns has been developed from the literature work. A general regression analysis method and curve-fitting techniques on the experimental test results of SCC columns are used for developing the new empirical model. The confinement mechanics-based analytical model has also been suggested by considering the influence of CFRP and transverse steel confinement. The comparative study solidly substantiated the superiority of the proposed empirical model over the proposed analytical model and the previous models with =0.892, =12.83, and =9.78. A parametric study is also performed using the proposed empirical strength model to examine the effect of different parameters of SCC columns confined by both CFRP and transverse steel.