Non-uniform Confinement Research Articles

Experimental investigation on the compression-bending performance of rubberized concrete columns confined by galvanized corrugated steel tubes

In the construction of building structures, numerous components simultaneously experience axial pressure and lateral bending moments. This concurrent influence plays a pivotal role in structural design considerations. This paper presents an experimental investigation of the compression-bending performance of rubberized concrete-filled corrugated steel tubes (RuCFCST). Twenty-two specimens were tested to evaluate the effect of eccentricity, length-diameter ratio, and confinement factor on the failure mode, load-displacement response, stiffness, compression-bending capacity, and ductility of the columns. The study also conducted a stress analysis on the corrugated steel tube to understand its confinement effect on the core rubberized concrete. The results demonstrate that the confinement factor emerges as a pivotal and sensitive parameter that impacts the compression-bending bearing capacity of RuCFCST columns. The study further elucidated the non-uniform confinement and failure mechanisms of the RuCFCST column, and subsequently assessed the applicability of the specimen's compression-bending bearing capacity as calculated by current specifications. The proposed RuCFCST columns offer new insights and serve as a reference for developing composite member systems with large hoop stiffness, small wall thickness, and environmental sustainability.

Circular concrete-filled double-skin steel tubular short columns under axial compression: An improved theoretical model and design

Existing theoretical analysis methods for concrete-filled double-skin steel tubular (CFDST) short columns generally ignore the reduction of concrete strength due to brittleness. As a result, these methods cannot accurately capture full range behavior for CFDST columns containing high-strength concrete. By focusing on the reduction effect of concrete strength in CFDST columns due to concrete brittleness, this paper proposes a reduction factor for use in design, for the first time. Based on this reduction factor, a theoretical model for axially compressed circular CFDST short columns considering non-uniform confinement effect of the sandwiched concrete is established. A substantial experimental database of 168 CFDST columns with carbon circular steel tubes is then compiled. By comparing with this database, the proposed theoretical model is shown to achieve greater accuracy than existing approaches. Utilizing this model, the influence of column parameters on the performance of the studied CFDST members are investigated and the results are discussed. It is shown that concrete strength, hollow ratio, yield strength of the outer tube, and the diameter-to-thickness ratio of the outer and inner tubes are influential to the ultimate strength and ductility of CFDST columns. However, the yield strength of the inner tube only affects the ultimate strength of CFDST columns but has a negligible influence on the ductility. Finally, utilizing the experimental and theoretical data presented, the accuracy of existing design codes for concrete-filled steel tubes for the design of CFDST members with or without considering the reduction effect of concrete strength is assessed. The results indicate that Eurocode 4 provides a more reasonable prediction result.

Tunable sequential pathways through spatial partitioning and frustration tuning in soft metamaterials.

Elastic instabilities have been leveraged in soft metamaterials to attain novel functionalities such as mechanical memory and sequential pathways. Pathways have been realized in complex media or within a collection of hysteretic elements. However, much less has been explored in frustrated and partitioned soft metamaterials. In this work, we introduce spatial partitioning as a method to localize deformation in sub-regions of a large and soft metamaterial. The partitioning is achieved through the strategic arrangement of soft inclusions in a soft lattice, which form distinct regions behaving as mechanical units. We examine two partitions: an equally spaced layer partition with mechanical units connected in series, and a cross partition, represented by interconnected series of mechanical units in parallel. Sequential pathways are obtained by frustrating the partitioned metamaterial post-manufacture and are characterized by tracking the polarization change in each partition region. Through a combination of experiments and simulations, we demonstrate that partitioning enables tuning the pathway from longitudinal with weak interactions to a pathway exhibiting strong interactions rising from geometric incompatibility and central domain rotation. We show that tuning the level of uniform lateral pre-strain provides a wide range of tunability from disabling to modifying the sequential pathway. We also show that imposing a nonuniform confinement and altering the tilting of one or two of the domain edges enables to program the pathway, access a larger set of states, and tune the level of interaction between the regions.

Analytical model for axially compressed circular concrete-filled double skin steel tubes (CFDSTs): Insights from concrete non-uniformly confined states

Concrete-filled double skin steel tube (CFDST) is becoming a competitive structural concept in deep-sea and deep-ground engineering structures. However, the passive non-uniform confinement of the sandwiched concrete needs to be further clarified and quantitatively described to achieve better design efficiency of CFDSTs in sophisticated application scenarios. This investigation suggests a development approach for the analytical model of the axially compressed circular CFDSTs considering the non-uniform confinement effect. The strength and deformation characteristics of the concrete subjected to constant lateral stresses have been first systematically analyzed through the extensively collected experimental database, and the corresponding constitutive models have been formulated accordingly. The stress distributions of the sandwiched concrete and the influence of the cross-sectional geometric properties have been discussed, and then the calculation method for the non-uniform confining factor has been developed. An efficient analytical model has been established on the basis of an incremental-iterative procedure, with the steel tube-concrete interaction and bonding behavior appropriately considered. The proposed analytical model has been verified through the widely collected experimental data of axially compressed CFDSTs, and the results show that it could effectively simulate the full-range axial load–strain curves and improve the prediction accuracy of ultimate loads by about 5% to 16% compared with the existing design formulas.

Confinement mechanism of rectangular CFST components using double horizontally-corrugated steel plates

This paper presents experimental and analytical investigations on the confinement mechanism of a novel rectangular concrete-filled steel tube (CFST) component for use in composite shear walls. The CFST component consists of a steel tube made by welding double horizontally corrugated steel plates and double flat steel plates, and infilled with concrete. Tests of eight components and finite element analysis of twenty-three components under uniform compression were conducted to explore confinement mechanism of the novel tube to core concrete. The impacts of several factors such as steel plate thickness, nominal sectional aspect ratios, slenderness ratios, and the strength of the steel and concrete on the confinement mechanism were analyzed. The non-uniform confinement mechanism of horizontally corrugated steel plates was investigated based on their vertical and horizontal strain responses at the wave crests, middles, and troughs. The test results and numerical simulations demonstrate that the proposed CFST components exhibited desirable axial compressive behavior with ductile failure modes. The tested specimens with nominal sectional aspect ratios ranging from 1.2 to 2.39 had strength indexes greater than 1.17. Even with a width-thickness ratio of 325.33, the horizontally corrugated steel plates effectively confined the core concrete. Furthermore, this research proposed a design strength model that considered the confinement effects of corrugated plates. The model accurately predicted the experimental and numerical results.

Axial compressive property of square and rectangular UHPC-filled duplex stainless steel tube stub columns

This study presents experimental and numerical investigations of the axial compression performance of square and rectangular ultrahigh performance concrete (UHPC)-filled duplex stainless steel tube (UFSST) stub columns. A total of twelve UFSST stub columns, six ordinary concrete filled duplex stainless steel tube (CFSST) stub columns, and six hollow duplex stainless steel tube (HSST) stub columns were tested under axial compression. The test parameters include the section type, three kinds of concrete strength grades, and three kinds of duplex stainless steel tube thicknesses. The test results showed that UFSST stub columns behaved with high bearing capacity and favourable ductility. In the UFSST stub columns with ξ ≥ 1.87, the square and rectangular duplex stainless steel tubes could well confine the shear failure of UHPC. The developed finite element model could effectively reflect the compressive behavior of the HSST, CFSST and UFSST stub columns. The available experimental database was employed to evaluate the feasibility of current design codes and existing calculation models in the literature to design UFSST stub columns. Finally, a modified computational model was proposed that takes into account the nonuniform confinement effect induced by square and rectangular section tubes on concrete and showed a higher prediction accuracy.

Damage evolution and full-field 3D strain distribution in passively confined concrete

The damage evolution of concrete under multiple stress states is complicated because the triaxial stress on the heterogeneous concrete affects mesoscale interactions between aggregates and mortar, which further alters the internal cracking of concrete and its load bearing mechanism. Hence, probing the internal cracking evolution of concrete under a complex stress state is the key to better understanding the characteristics and failure mechanism of concrete material. This study conducted a series of X-ray computed tomography (X-CT) tests on fiber-reinforced polymer (FRP) confined concrete with varied in situ axial load levels. Different cross-sections of concrete specimens—circular, square with round corners, and square with sharp corners—were designed to achieve uniform or nonuniform passive confinement conditions. The obtained volumetric images from X-CT clearly exhibited the internal damage evolution of concrete, where crack growth, shear banding, and failure localization were displayed for the concrete under varying triaxial stress states. The development of damage to concrete due to cracking with increasing load was also quantified by image segmentation. In addition, the digital volumetric correlation technique (DVC) was employed to produce the volumetric displacement field and strain distribution in the confined concrete according to the image variation of natural speckles. A three-dimensional internal strain analysis revealed that strain localization was mainly caused by mesoscale concrete heterogeneity and nonuniform confinement. More importantly, this study provides the first database of full-field strain tensors for FRP-confined concrete under different axial load levels. These data are valuable for the development of concrete mechanics, failure criteria of materials, and computational modeling of concrete materials and their structures, especially for concrete under complex stress states.

Mechanical analysis and finite element modeling of FRP-ECC-HSC composite stub column under axial compression

A novel composite column, consisting of an outer fiber-reinforced polymer (FRP) tube, an inner high strength concrete (HSC) core and an engineered cementitious composite (ECC) ring, has been proposed and investigated. Compared with normal FRP-confined HSC column, the FRP-ECC-HSC composite column could exhibit superior deformability performance. In this study, mechanical analysis was firstly conducted on the composite column to investigate the interaction behavior among different components, i.e. HSC core, ECC ring and FRP tube. Modified analysis-oriented models were proposed for HSC and ECC under uniform FRP confinement. Furthermore, finite element (FE) models were also established with the use of accurate concrete damaged plasticity (CDP) model to simulate the behavior of the composite column, especially the ECC ring which is under non-uniform confinement. The material property data used in the FE models were generated by the modified analysis-oriented models. It is shown that the FE models can provide close predictions on the axial load-axial strain behavior and hoop strain-axial strain behavior compared with test results. Meanwhile, stress distribution over the composite column section as well as the influence of ECC ratio were discussed with the validated FE model.

Experimental and numerical investigations on the behavior of a novel multilayer spirals reinforced square composite column under axial load

Existing studies have shown that under severe ground motion the column-end damage can be significant in rectangular (including square) RC columns due to the arch effect and the consequent insufficient lateral confinement by tie reinforcement. Improving the non-uniform confinement of tie reinforcement is necessary to enhance ductility and load bearing capacity of rectangular RC column. Against this background, the author proposed a novel multilayer spirals reinforced square composite column (MLSRSCC) consisting of one layer of outer square stirrup and two layers of spirals aligned with the centroid of the specimen section. Five MLSRSCC specimens and one conventional single spiral reinforced composite column (SSRSCC) for comparison were tested. The test results showed that the ultimate load and deformation capacity of MLSRSCC were greatly enhanced even with a slightly less amount of steel compared to reference SSRSCC. Moreover, a finite-element (FE) model is established to investigate the confinement mechanisms of MLSRSCC in relation to the distributions of axial stress, confining stress and principal stress ratio. An extensive parametric study containing 1,024 FE results is carried out to explore the effects of various key design parameters on the improvement of ultimate bearing load of MLSRSCC. Furthermore, a calculation method for the ultimate bearing capacity of MLSRSCC was subsequently developed, by which higher accuracy was obtained compared with those calculated from existing design specification.

Axial compressive behaviour of high-strength steel spiral-confined square concrete-filled steel tubular columns

The ductility of concrete-filled steel tubular (CFST) columns with square cross-sections is significantly lower than circular ones when subjected to large axial forces or when thin-walled steel tubes and high-strength concrete are employed. The additional confinement contribution of the internal steel spiral compensates for the shortcomings of the rapid reduction of the ductility and strength of square CFST columns. The axial compressive performance of high-strength steel (HSS) spiral-confined square CFST (HSS-CFST) columns was experimentally investigated to enhance this advantage. 20 HSS-CFST columns, five normal-strength steel spiral-confined CFST (NSS-CFST) columns, and four CFST columns without an internal steel spiral were tested under axial compression. It was found that the high strength characteristic of the internal HSS spiral was fully utilized, thereby alleviating the non-uniform confinement of the square steel tube and significantly enhancing the ductility and strength of CFST columns. The ultimate strength improvement induced by increasing the volume of HSS spiral is more pronounced than that caused by increasing the same volume in the outer steel tube. A strong interaction exists between the confinement contribution made by the internal steel spiral and that provided by the outer steel tube. A new ultimate axial load model was subsequently proposed based on the experimental findings of the author's own and those collected from the literature, which significantly extends the range of the parameter space and clearly illustrates the interaction between the steel tube and internal steel spiral.

Experimental Study on the Behavior of a Novel Stiffened Hexagonal CFDST Stub Column under Axial Load

A concrete-filled double skin tube (CFDST) consists of an outer steel tube, an inner steel tube, and the space between them filled with concrete. Existing studies have shown that the buckling of steel tubes can be significant in noncircular CFDST for nonuniform confinement or a large width-thickness ratio. Stiffening of the steel tubes is necessary to fully utilize the strength and improve the load-carrying capacity of CFDST. Against this background, the author proposed a novel stiffened hexagonal CFDST column with steel strips welded on both the inner tube and outer tube to form several closed cavities. This paper presents an experimental study on the axial compressive behavior of this new type of CFDST column. The experimental program consisted of five stiffened hexagonal CFDST specimens and two reference specimens for comparison, and the test variables were the hollow ratio and rib width. The test results showed that the ultimate bearing capacity and ductility of the CFDST specimens were greatly enhanced by the steel strips and ribs. Moreover, the finite-element (FE) method was used to develop a three-dimensional model of the CFDST column subjected to axial loading and validated against the experiment. The average error of the FE analysis when predicting the column bearing capacity was 0.029 compared with experimental results. Based on the FE model, a parametric study was conducted to analyze further the effect of each parameter on the axial behavior. Furthermore, a strength design formula was developed to estimate the compressive strength of the novel hexagonal CFDST column.

Mechanical behavior of square composite columns with four interlocking spirals under compression

The compressive capacity of square composite columns confined by four interlocking spirals and outer square stirrups are experimentally and analytically investigated. The proposed innovative transverse reinforcement configuration used for square columns can improve the non-uniform confinement of outer square stirrup and thus enhance the confinement effect for the core concrete. Eight square composite columns for axial compression and ten eccentric compression specimens were tested. The study demonstrated that the newly developed interlocking multi-spiral reinforced square composite column (IMSRSCC) with the same volumetric confinement ratio outperformed conventional single-spiral reinforced square composite columns (SSRSCC) both in terms of ultimate load, bending stiffness and ductility under eccentric compression, while in axial compression test, the proposed new square composite column obtained similar ultimate load and deformation capacity. In addition, a comprehensive parametric study is presented using finite element analysis to explore the confinement working mechanism and key design parameters of IMSRSCC. Moreover, an analytical model is developed considering the composite confinement due to outer square stirrups and interlocking spirals and the formulas for calculating the bearing capacity of IMSRSCC are proposed. The analytical results are found consistent with experimental and numerical data.

A plasticity constitutive model for concrete under multiaxial compression

Structural members with confined concrete are becoming increasingly popular in civil engineering applications because of their superior strength and ductility. In these structural members, the concrete is subjected to dilation-induced (passive) lateral compressive stresses from the confining device (e.g., a steel tube). Existing research has led to theoretical models that predict closely the stress–strain behavior of concrete under uniform confinement (e.g., concrete in circular steel tubes under concentric axial compression), but theoretical models with a similar capability have not been achieved for the more common situation of concrete under non-uniform confinement (e.g., concrete in rectangular steel tubes). This paper presents a three-dimensional (3D) plasticity constitutive model that is accurate in predicting the stress–strain behavior of concrete in various scenarios of confinement. In the proposed model, a well-established open strength surface with associated open yield surfaces is combined with a hardening/softening rule compatible with both plastic volumetric compaction and dilation. In addition, a novel potential surface with a triangle-like deviatoric trace is proposed and calibrated with available experimental data of non-uniformly confined concrete. The implementation of the constitutive model in finite element analysis with an enhanced stress-return algorithm suitable for the novel potential surface is explained. While the focus of the present work is on monotonic compression-dominated loading, the model can be combined with fracture and damage theories to depict the behavior of concrete under tension-dominated and cyclic loading conditions. The performance of the proposed model is evaluated by comparing its predictions with a wide range of experimental data covering uniform active, uniform passive, and non-uniform passive confinement conditions, which demonstrates the capability and high accuracy of the proposed model.

Behavior and modeling of CFRP nonuniformly wrapped circular seawater sea-sand concrete (SSC) columns under axial compression

An experimental study was performed in this paper to investigate the compressive behavior of carbon fiber-reinforced polymer (CFRP) nonuniformly wrapped seawater sea-sand concrete (SSC) cylinders. The effect of test variables on the mechanical performance was comprehensively discussed, including the clear spacing and thickness of external CFRP strips. The test results indicate that the failure process of tested specimens is less brittle compared with that of the fully or partially FRP-confined columns. Besides, the average ultimate stresses and strains of the specimens nonuniformly wrapped with two-layer external CFRP strips increase by 6.7%-27.4% and 5.9–41.6% respectively with the reduction of clear spacing ratio. Moreover, when the thickness of external CFRP strips double increases, the maximum increment of strength and strain at ultimate condition becomes 42.8% and 63.8% respectively. It is also shown that the FRP efficiency factor of confined specimens with nonuniform wrapping scheme is the highest among various strengthening strategies under the same FRP volumetric ratio. Finally, a new nonuniform confinement effective coefficient, as well as a analytical stress–strain model, is developed based on the available test results. Compared with several existing predicted models, the proposed model can provide more accurate and reliable predictions.

Axial compression tests on elliptical high strength steel tubes filled with self-compacting concrete of different mix proportions

The compaction state and the paste volume of concrete may significantly influence the compressive behaviour of concrete-filled steel tube (CFST) columns, while limited studies have been conducted to understand the compressive behaviour of CFST columns with different mix proportions. This study presents an experimental investigation to the axial compressive behaviour of elliptical CFST (ECFST) column consisting of a high-strength steel (HSS) tube and a self-compacting concrete (SCC) core with different mix proportions. Eighteen ECFST column specimens, fabricated with high-strength elliptical steel tubes in three different cross-sections and three batches of concrete with different mix proportions, were tested under axial compression. The parameters under investigation are the concrete paste volumes (41%, 37% and 32.5%), the cross-sectional aspect ratios (1, 1.5 and 2) and the compaction conditions (with and without mechanical compaction). The standard cylinder tests reveal that SCC without mechanical compaction has a better filling ability and thus a better self-compaction capability when the paste volume is larger than 37%, while SCC with mechanical compaction has the highest strength when the paste volume is the lowest. The axial compression tests show that the peak axial load capacities of ECFST columns are dependent on the paste and aggregate contents in concrete. The compaction state also affects the performance ECFST columns because compaction usually increases concrete strength especially when the aggregate content is high. In addition, it is found that key performance parameters (e.g., strain enhancement ratio, ductility and strength index) all decrease with the increase of cross-sectional aspect ratio due to the non-uniform confinement provided by elliptical steel tubes.

Compressive behavior of FRP-confined elliptical concrete-filled high-strength steel tube columns

Elliptical concrete-filled steel tube (ECFST) columns have been widely used, while they suffer deterioration due to various reasons. On the other hand, the concrete in ECFST columns is ineffectively confined due to the non-uniform confinement and the elliptical steel tube in ECFSTs is easy to experience buckling failure. To this end, fiber-reinforced polymer (FRP) jackets are proposed to strengthen the ECFST columns. In this study, axial compression tests on FRP-confined elliptical CFST (FCECFST) columns with a high-strength steel tube are carried out and the effects of the FRP jacket thickness (0, 1, 2, 3 layers) and the cross-sectional aspect ratio (1, 1.5 and 2) are investigated. The experimental results show that the elastic stifness, the ultimate axial load and ultimate axial strain of FCECFST columns increase with the FRP thickness at a given cross-sectional aspect ratio, while decrease with the cross-sectional aspect ratio at a given FRP jacket thickness. Also, FCECFST columns generally exhibit monotonic ascending load-strain behavior, implying that the performance of ECFST columns, which generally have a post peak descending load-strain behavior, is substantially enhanced. Given that the existing strength model is inaccurate and incapable to predict the ultimate condition of confined concrete in FCECFST, a new model of ultimate axial stress and ultimate axial strain is proposed and the verification demonstrates that the proposed model is of good accuracy.

Experimental behavior of concrete-filled corrugated steel tubular short columns under eccentric compression and non-uniform confinement

Concrete-filled galvanized corrugated steel tubular (CFGCST) column is potentially an economic member to overcome the corrosion of outdoor structures, of which the anticorrosive corrugated steel pipe (CSP) can be used conveniently as the corrosion protection and permanent concrete formwork. The confinement effect provided by CSP essentially contributes to the structural advantages of CFGCST, whilst it, brings about complexities in corresponding load-resisting mechanism. Apart from the non-uniform distribution of stresses of CSP through thickness and height due to its curved shape, the confinement also varies across cross-sectional depth due to eccentric compression. The in-depth understanding and accurate quantification of the confinement effect of such member become a key issue that needs to be addressed. To investigate the impact of confinement on cross-sectional behavior, 24 specimens were tested with 5 load eccentricity ratios and 2 confinement factors. The non-uniformities of confinement along with height and cross-sectional depth were studied based on finite element modelling, validated via measured strains and load bearing capacities. A theoretical derivation was then conducted to characterize the non-uniform confining stress by fully considering the bidirectional curvatures of CSP, as well as the influence of debonding failure on the confinement. In each period of corrugation, the calculation method of equivalent confining stress was proposed based on the uniformization of stresses and geometry.

Rheology of Water Flows Confined between Multilayer Graphene Walls.

Water confined by hydrophilic materials shows unique transport properties compared to bulk water, thereby offering new opportunities for the development of nanofluidic devices. Recent experimental and numerical studies showed that nanoconfined water undergoes liquid- to solid-phase-like transitions depending on the degree of confinement. In the case of water confined by graphene layers, the van der Waals forces are known to deform the graphene layers, whose bending leads to further nonuniform confinement effects. Despite the extensive studies of nanoconfined water under equilibrium conditions, the interplay between the confinement and rheological water properties, such as viscosity, slip length, and normal stress differences under shear flow conditions, is poorly understood. The current investigation uses a validated all-atom nonequilibrium molecular dynamics model to simultaneously analyze the continuum transport and atomistic structural properties of water in a slit between two moving graphene walls under Couette flow conditions. A range of different slit widths and velocity strain rates are considered. It is shown that under subnanometer confinement, water loses the rotational symmetry of a Newtonian fluid. Under such conditions, water transforms into ice, where the atomistic structure is completely insensitive to the applied shear force and behaves like a frozen slab sliding between the graphene walls. This leads to the shear viscosity increase, although it is not as dramatic as the normal force increase that contributes to the increased friction force reported in previous experimental studies. On the other end of the spectrum, for flows at large velocity strain rates in moderate to large slits between the graphene walls, water is in the liquid state and reveals shear thinning behavior. In this case, water exhibits a constant slip length on the wall, which is typical of liquids in the vicinity of hydrophobic surfaces.

Cold-formed elliptical concrete-filled steel tubular columns subjected to monotonic and cyclic axial compression

Concrete-filled steel tubular columns are widely used in structural systems, and elliptical concrete-filled steel tubular columns are receiving more and more attention. An experimental study on cold-formed elliptical concrete-filled steel tubular stub columns was carried out under monotonic and cyclic axial compression. The failure modes, axial load–displacement curves, ultimate loads, hoop strain–axial strain behavior, strength deterioration, and residual deformation were obtained and discussed. Complementary finite element models considering the complex non-uniform confinement between steel tube and concrete were developed and validated by experimental results. Then, the validated FE model was used to study the influence of aspect ratio, yield strength of steel, and compressive strength of concrete on the axial capacity of elliptical concrete-filled steel tubular stub columns. Finally, a relatively simple superposition method was put forward to predict the axial bearing capacity of elliptical concrete-filled steel tubular stub columns. Compared with the test data, both the numerical method and superposition method can generate accurate predictions.

Development of extended Drucker–Prager model for non-uniform FRP-confined concrete based on triaxial tests

Extended linear Drucker–Prager (DP) model has been a proper choice to capture the stress-strain of cylindrical concrete columns confined by fiber reinforced polymers (FRPs). However, most existing DP models calibrated by uniform active/passive tests are unsuitable for concrete under non-uniform passive confinement. This paper aims to calibrate the key parameters i.e., friction angle, plastic dilation angle and hardening needed for the DP model based on tri-axial test results on concrete cube subjected to non-uniform confinement. The effect of friction angle parameter is isolated from the hardening parameter within the yield function while the friction angle is defined as a function of concrete grade and hardening as a function of lateral confinement stiffness ratio. Here, the plastic lateral strains of non-uniform confined concrete, which could be obtained in cyclic tests but were usually left aside, are used to define a function for plastic dilation angle which works compatibly with the yield parameters. The resultant extended DP model could capture the stress-strain behaviour of concrete under both uniform or non-uniform passive pressure as well as the variable flow rules and different load paths occurring across the section of FRP-confined non-circular concrete.