Filled Fiber Reinforced Polymer Research Articles

Compressive behavior of seawater and sea sand concrete-filled FRP-steel composite multi-tube hollow columns

To further explore sustainable development in high-performance marine engineering structures, this study introduced a new approach - a hybrid structural member called the seawater and sea sand concrete (SWSSC)-filled fiber-reinforced polymer (FRP)-steel composite multi-tube hollow column (S-MTHC). The S-MTHC consists of double-walled FRP-steel composite tubes filled with SWSSC, along with several small-diameter SWSSC-filled FRP tubes (known as SSFFTs). Monotonic axial compression tests were conducted on the S-MTHCs, and a bearing capacity model was established. The test results demonstrated that the presence of FRP-steel composite tubes and SSFFTs significantly improved the axial compressive behavior of S-MTHCs. Increasing the number of external FRP layers or SSFFTs enhanced the strength and ductility of the hybrid column. The influence of increasing concrete strength or FRP tube thickness in SSFFTs, however, was relatively negligible. Additionally, specimens with carbon FRP (CFRP) tubes in SSFFTs exhibited higher bearing capacity while maintaining similar ductility.

Axial strength prediction of seawater sea sand concrete-filled circular FRP tubes under alkaline environment based on ensemble learning algorithms

The rapid development of marine and urban infrastructure led to the extensive studies on seawater sea sand concrete (SWSSC) filled fiber reinforced polymer (FRP) / steel tubes. The material property of FRP is a function of fiber orientations, and the confinement of SWSSC by FRP tubes enhances its axial load carrying capacity. And therefore, its strength prediction is very challenging because of various FRP layouts, surrounding harsh environment and complicated failure modes. The existing empirical models do not consider effects of surrounding seawater environment under elevated temperature. Therefore, this study concentrates on evaluating the axial capacity of two types of physical models: (1) SWSSC filled circular FRP tubes immersed in seawater environment (Pu1), and (2) SWSSC filled FRP-steel-FRP circular tubes (Pu2), with the help of machine learning (ML) algorithms namely extreme gradient boosting (XGBoost), support vector machine (SVM) and artificial neural networks (ANN). The experimental results of 138 and 120 tested specimens were used for the training and testing of ML models. The models were trained with the best hyperparameters based on grid search and cross validation approach. The models were evaluated with number of statistical indices i.e., R2, MAE and RMSE accompanied with visual comparison of trend line between experimental and predicted values and predicted to experimental ratios. The ML models were graded on the basis of performance as XGBoost > ANN > SVM for the Model 1, whereas for the Model 2, the order was observed as ANN > XGBoost > SVM. Further, SHAP analysis was conducted based on XGBoost to see the influence of input attributes on ML models.

Axial compressive behaviour of GPC filled FRP Tubes: Experimental and analytical investigations

The production of Ordinary Portland Cement (OPC) releases carbon dioxide (CO2), which is one of the main contributors in the rising level of Greenhouse Gases (GHG) into the atmosphere and adversely effecting the environment and subsequently causing the climate change. In this study, the fly ash (FA) an alternative of OPC is used to produce environmental friendly cementless geopolymer concrete (GPC). This study investigates the axial compressive behavior of GPC filled fiber reinforced polymer (FRP) tubes. Two types of FRP tubes, i.e., carbon FRP (CFRP) tubes and glass FRP (GFRP) tubes were prepared by the wet lay-up procedure using CFRP and GFRP sheets, respectively. A total of forty-five GPC specimens of 150 mm diameter and 300 mm height were prepared with five different molarity of NaOH (8–16 M) with Na2SiO3 to NaOH ratio of 1.5. The unconfined GPC (Control), GPC filled CFRP tube (GCT) and GPC filled GFRP tube (GGT) specimens exhibited a significant increase in the peak axial stress (fc) with the increase in the molarity of NaOH. The scanning electron microscopic investigation also exhibited a reduced number of unreacted fly ash particles in the GPC with increasing the molarity of NaOH. The fc and corresponding axial strains (∊c) of GCT and GGT specimens were significantly higher than those of unconfined GPC specimens. The GCT specimens exhibited higher fc and corresponding ∊c than the GGT specimens. The analytical axial stress–strain (fc-∊c) curves of GCT and GGT specimens developed using available fc-∊c models of FRP confined ordinary Portland cement (OPC) concrete matched well with the experimental fc-∊c curves of GCT and GGT specimens.

Compressive performance of concrete-filled steel tube columns with in-built seawater and sea sand concrete-filled FRP tubes

A structure termed as concrete-filled steel tube (CFST) columns with in-built seawater and sea sand concrete (SWSSC)-filled fiber reinforced polymer (FRP) tubes was investigated. The new composite columns are comprised of outer steel tubes, sandwich ordinary concrete, inner FRP tubes and core SWSSC. Thirty-six CFST columns with in-built SWSSC filled FRP tube and four CFST columns were manufactured, and the influences of the diameter of the FRP tube, FRP layers and the thickness of steel tube on compressive performance of the specimens were studied. The results indicated that the ultimate strength of the specimens was positively related to the FRP layers, diameter of the FRP tube and thickness of the steel tube. The stress–strain curve of new structure consists of four stages, and columns with larger FRP tube diameter and more FRP layers obviously underwent more stress-drop after the ultimate point. The installation of the FRP tube has a more significant strengthening effect on the columns with a thinner steel tube. Models to predict the ultimate stress, ultimate strain, peak stress and peak strain of new structure were proposed. Moreover, a simple model to predict the axial stress–strain response curve of CFST columns with in-built SWSSC-filled FRP tubes was suggested.

Experimental Study on Axial Compressive Behavior of Gangue Aggregate Concrete Filled FRP and Thin-Walled Steel Double Tubular Columns

In the present paper, the monotonic axial compression test of gangue aggregate concrete filled Fiber reinforced polymer (FRP) and thin-walled steel double tubular columns (DTCC) was carried out, and the gangue aggregate concrete filled FRP tubular columns (CFFT) were designed as a comparison. The main experimental factors were the confinement level of the FRP jacket, the relative diameter ratio (the ratio of the outer diameter of the steel tube to the inner diameter of the FRP jacket), and the different strengths of gangue aggregate concrete. The test results show that the bearing capacity and ductility of gangue aggregate concrete in CFFT were significantly improved. As the local buckling of thin-walled steel tube was effectively inhibited, the load bearing capacity of DTCC was further improved compared with CFFT, but the change of dilation behavior and ductility was insignificant. By analyzing the bi-directional stress state of the steel tube, the confinement level of the external FRP jacket was the most sensitive factor affecting the hoop stress of the steel tube, and the axial stress was obviously weakened under the bi-directional stress state. In addition, with the increase of steel tube diameter, the confinement effect of steel tube in DTCC became more obvious.

Analytical investigation on the load-moment interaction behavior of the FRP reinforced geopolymer concrete filled FRP tube circular columns

In this study, the load moment (P-M) interaction behavior of geopolymer concrete (GPC) filled fiber reinforced polymer (FRP) tube circular columns internally reinforced with FRP bars was analytically investigated. An analytical model for the P-M interaction behavior of the column was developed and validated against the experimental investigation results. The analytical model incorporates the confined GPC strength and the contribution of FRP bars in the load and moment capacities. In addition, a parametric study was conducted to investigate the influence of the compressive strength of the GPC, longitudinal reinforcement ratio and confinement ratio on the P-M interaction behavior of the column. The developed analytical model conservatively predicted the P-M interaction behavior of the column. It was found that the compressive strength of the GPC, the longitudinal reinforcement ratio and the confinement ratio significantly influenced the P-M interaction behavior of the column. All the tested parameters resulted in the linear increase of load and moment capacities with the increase in the tested parameter.

Design equation for concrete-filled FRP tubes in flexure including damage effects

Nonlinear finite element models are developed to investigate the effect of tube damage on flexural strength of concrete filled fiber reinforced polymer (FRP) tubes (CFFTs). The tube, being essentially an external reinforcement, is vulnerable to accidental damage or vandalism. The tube damage is induced at the outermost tension side of the CFFT in the form of a linear narrow cut with a variable length. The model is verified using experimental results from the literature. A comprehensive parametric study, comprising 140 new models, was then performed to study the damage effects in tubes with diameter-to-thickness (D/t) ratios of 30 to 100, [±θ] angle-ply tubes with (θ) varying from 15° to 75° and cross-ply tubes with 25–75% longitudinal fiber fraction. Additionally, the effects of damage were examined for hollow FRP tubes and compared to CFFTs with the same damage. It was shown that for angle-ply tubes and cross-ply tubes with 25–50% longitudinal fiber fraction, a sharp decrease (30–50%) in flexural strength occurs at circumferential cuts of length-to-perimeter (α) ratio of 5%, at all (D/t) ratios. For larger cuts, the decrease in capacity continuous but at a reduced rate so the reduction increases to (60–75%) as α increases to 30%. For hollow tubes, the damage affects moment capacity, only when material failure governs (at small D/t), not when local buckling governs (at large D/t). Statistical analysis was used to assess results of the comprehensive parametric study. A simple empirical equation was then deduced for condition assessment purposes. It enables engineers to predict flexural strength of both intact and damaged CFFTs for any given α, D and t, for a wide range of FRP tube laminate structures.

Cyclic behavior of FRP - crumb rubber concrete - steel double skintubular columns and beams

This paper presents experimental and analytical studies to understand the behavior of crumb rubber concrete (CRC)-filled fiber reinforced polymer (FRP) and steel tube double skin column (DSC) and beam (DSB) members under cyclic loading. The main test variable was the percentage of rubber which ranged from 0 to 40%. For column members, different heights corresponding to different aspect ratios were examined to understand the to understand the effect of DSCs' slenderness on the cyclic response of the columns. the. The behavior of the specimens in terms of failure mode, strain development, energy dissipation, load-displacement response were presented and compared. The ability of the current provisions of the Australian codes to predict the capacity of such double skin members was also evaluated based on the test results. This study concluded that the reduction in the concrete strength was more severe at the material level compared to structural level. Also, as the load changed from axial compression in columns to pure moment in beams the negative effect of rubber percentage on the strength became less significant.

Flexural Performance of Unbonded Posttensioned Rectangular Concrete Filled FRP Tube Beams

Abstract This paper experimentally investigates the effect of using the posttensioning (PT) steel strands on the flexural performance of rectangular concrete filled fiber-reinforced polymer (FRP) t...

Behavior and Modeling of Ultra-High Performance Concrete-Filled FRP Tubes Under Cyclic Axial Compression

Abstract This paper presents an experimental investigation and a stress–strain model for ultra-high performance concrete (UHPC)-filled fiber reinforced polymer (FRP) tubes under cyclic axial compre...

Behavior of high strength concrete – filled hybrid large – small rupture strains FRP tubes

This paper experimentally investigates the behavior of concrete filled fiber reinforced polymer (FRP) tubes (CFFTs) under cyclic axial compression. The FRP used in this study was either small rupture strain FRP (SRS-FRP), large rupture strain FRP (LRS-FRP), or hybrid LRS-FRP and SRS-FRP. LRS-FRPs are manufactured out of polyethylene naphthalate (PEN) and polyethylene terephthalate (PET). LRS-FRP has a high tensile rupture strain (usually greater than 5%) compared to 1–2% for SRS-FRP. The behavior of the investigated cylinders is presented in terms of ductility, ultimate strain, strength improvement, and energy dissipation. The results showed that using LRS-FRP significantly improved the ductility and ultimate strength of the confined concrete compared to SRS-FRP confined concrete. This study also carried out a comparison between the attained strengths, as well as the ultimate axial strain and the existing analytical models. A critical assessment of recent models has been made to suggest two models be implemented for predicting the ultimate stress–strain behavior of hybrid LRS-FRP.

Composite Action Assessment of Concrete-Filled FRP Tubes Subjected to Flexural Cyclic Load

Concrete filled fiber-reinforced polymer (FRP) tubes (CFFT) is a principal competitor to replace the conventional reinforced concrete (RC) members in severe environmental conditions. This paper investigates the composite action (interfacial bond) between the FRP tube and its concrete core. Four full-scale CFFT columns associated with RC footings were tested under lateral cyclic load without axial load. Two different diameters of CFFT columns were tested to study the size effect on the bond performance then consequently on the flexural behavior of the CFFT column. The interior surface of two FRP tubes have been covered by sand coating to improve the interfacial bond between the FRP tube and the concrete core. A new approach was proposed to evaluate the composite action between the FRP tube and the concrete core based on measuring strains inside the concrete core by using embedded concrete strain gauges. The assessment of the composite action between the FRP tube and the concrete core was implemented by comparing the interior concrete strains and the corresponding strains on the external tube skin. The experimental results illustrated that the bond significantly influences the flexural strength and stiffness of the CFFT column. Increasing the tube diameter leads to reduce the interfacial bond between the FRP tube and its concrete core. Using sand-coating as a bond enhancer improved the bond between the FRP tube and the concrete core, minimize the adverse effect of increasing the tube diameter, and increased the flexural capacity and stiffness of tested CFFT columns. An analytical model was developed to estimate the flexural capacity of the fully bonded CFFT member.

Experimental investigation on axial compressive behavior of ultra-high performance concrete (UHPC) filled glass FRP tubes

To investigate the axial compressive behavior of ultra-high-performance concrete (UHPC)-filled fiber-reinforced polymer (FRP) tubes, a total of 54 specimens, including 42 UHPC-filled glass FRP (GFRP) tubes and 12 unconfined UHPC specimens, were prepared and tested under axial compression. The effects of curing regime, steel fiber in the UHPC core, fiber orientation of the outer FRP tube, and specimen end condition during loading were examined. The test results indicate that UHPC-filled FRP tubes can exhibit highly ductile behavior and a significant enhancement in compressive strength, compared to the unconfined specimens. However, the axial compressive behavior of UHPC-filled FRP tubes is influenced by numerous factors. Hot-water curing can improve the performance of specimens unless the contribution from the enhancement of the UHPC core exceeds that from the damage of the outer FRP tube. Specimens without steel fibers experience a sudden strength loss in the transition region of the axial stress–strain relationship, and exhibit lower ultimate strength and strain than the steel-fiber-reinforced specimens. The test results indicate that aligning fibers in the hoop direction is the most effective way of improving the compressive performance of the specimens. Regarding specimens with thicker FRP tubes, loading the FRP tube can lead to a clear decrease in specimen ultimate strain; however, the influence of specimen end condition can be ignored for specimens with thinner FRP tubes.

Analytical modeling of moment-curvature behavior of steel and CFRP RC circular confined columns

This paper reports on the results of an experimental investigations and theoretical models of concrete filled fiber-reinforced polymer (FRP) tube (CFFT) columns reinforced with steel and carbon-FRP (CFRP) bars under concentric and eccentric compressive loads. The experimental test parameters were the type of the internal reinforcement (CFRP versus steel) and eccentricity to diameter ratios. It was found that the CFRP reinforced CFFT columns successfully maintained the axial load capacities under different eccentricities as compared with the steel reinforced CFFT columns. However, the strength and behavior of the steel and CFRP CFFT test specimens were mainly affected by the eccentric loading. The average compressive strength of CFFT columns was reduced by 42–75% with increasing the e/D ratio from 10 to 40%. Theoretical models using two approaches to predict the axial-moment interaction diagrams and moment curvature relationships were developed and validated through comparison with the experimental results. A nonlinear moment-curvature (M-φ) response was observed regardless the type of reinforcement and the applied eccentricity ratio. Furthermore, a comprehensive parametric study was performed to investigate the influence of different design variables on the moment capacity by creating numerous moment curvature relationships.

Compressive Behavior of Concrete Filled Glass Fiber Reinforced Polymer (GFRP) Box Profiles

The use of concrete filled fiber reinforced polymer (FRP) profiles for beams and columns has been studied extensively in recent years. Glass Fiber Reinforced polymers (GFRP) profiles are one of these materials. GFRP box profiles serve as formwork, and provide shear and flexural reinforcement in novel hybrid GFRP–concrete structural system. GFRP box profiles also protect the concrete and increase the strength of hybrid materials. This study presents results of an experimental study using concrete filled pultruded GFRP profiles. A series of compression tests were carried out to study the compression behavior of the proposed hybrid GFRP-concrete materials. Hybrid compression samples were fabricated and tested in three different strength classes. The results showed that compressive strength of hybrid material significantly increased when compared to reference samples.

Axial and flexural behavior of unreinforced and FRP bar reinforced circular concrete filled FRP tube columns

Fiber Reinforced Polymer (FRP) composites have emerged as a viable alternative of steel reinforcement due to higher ultimate tensile strength to weight ratio and corrosion resistance of FRP composites. Concrete Filled Fiber Reinforced Polymer Tube (CFFT) technique for new column construction has attracted significant research attention. This paper investigated the axial and flexural behavior of Concrete Filled Carbon FRP Tube (CFRP CFFT) columns with and without CFRP bar and concrete filled Glass FRP (GFRP) tube columns with and without GFRP bar. The test results of 16 circular CFFT and four steel Reinforced Concrete (RC) specimens of 203–205mm diameter and 800–812mm height have been reported in this paper. The test results showed a larger reduction in the confinement effectiveness of FRP tube than steel helices under increasing applied load eccentricity. FRP bar reinforced CFFT specimens exhibited higher axial loads, flexural loads, and deformations at peak loads than unreinforced CFFT and steel RC specimens. Experimental axial load-bending moment interaction curves of tested specimens also showed the improved performance of FRP bar reinforced CFFT specimens.

Numerical Modeling of Concrete-Filled FRP Tubes’ Dynamic Behavior under Blast and Impact Loading

AbstractA major difficulty of the analysis of and design for close-in blasts is the high variability of the blast shock waves and the complex interactions between these waves and structures. Close-in blasts also tend to be severe loads that may cause extensive damage to a structural member. If the member in question is a load bearing column, its destruction may lead to a catastrophic progressive collapse of the structure. Thus any improvement on the performance of columns under close-in blast loading is a valuable addition to knowledge. This paper outlines a numerical model built using commercially available software to predict the response of concrete filled fiber reinforced polymer (FRP) tubes (CFFTs) and regular round reinforced concrete members to impacts and close-in blasts and determine the factors influencing their response. The models were verified against drop weight impact test lab measurements and single degree of freedom blast analyses. A parametric study was conducted using the verified model...

Influence of Fiber Type on Behavior of High-Strength Concrete-Filled FRP Tubes under Concentric Compression

This paper presents results from an experimental study on the behavior of circular high-strength concrete (HSC)-filled fiber reinforced polymer (FRP) tubes (HSCFFTs). Concrete-filled FRP tubes (CFFTs) have received significant research attention over the last two decades and experimental investigations into the axial behavior are abundant for normal-strength concretes (NSC) confined by either carbon FRP (CFRP) or class FRP (GFRP). However, the same cannot be said for CFFTs filled with HSC or manufactured with other fiber types such as aramid or high-modulus carbon FRP (AFRP and HMCFRP), where experimental testing is very limited. To address this research gap, this study examined the compressive behavior of 24 test specimens prepared with three different fiber types (CFRP, HMCFRP and AFRP) and manufactured with HSC. The experimentally recorded stress-strain relationships are presented graphically and the influence of fiber type and other key experimental outcomes are discussed. The results indicate that fiber type has a significant influence on the axial compressive behavior of HSCFFTs.

Ultra-High-Strength Concrete-Filled FRP Tubes: Compression Tests on Square and Rectangular Columns

This paper presents the partial results of an experimental program undertaken to investigate the behavior of square and rectangular ultra-high-strength concrete (UHSC)-filled fiber reinforced polymer (FRP) tubes (UHSCFFTs) under axial compression. The effects of the amount of confinement, cross-sectional aspect ratio and corner radius were investigated experimentally through the tests of 24 concrete-filled FRP tubes (CFFTs) that were manufactured using unidirectional carbon fiber sheets and UHSC with 108 MPa average compressive strength. Test results indicate that sufficiently confined square and rectangular UHSCFFTs can exhibit highly ductile behavior. The results also indicate that HSCFFTs having tubes of low confinement effectiveness may experience a significant strength loss at the point of transition on their stress-strain curves. Examination of the test results have led to a number of important observations on the influence of corner radius and sectional aspect ratio, which are presented and discussed in the paper.

Behavior of High-Strength Concrete-Filled FRP Tube Columns under Simulated Seismic Loading: An Experimental Study

This paper reports on part of an ongoing experimental program at The University of Adelaide on the seismic behavior of high-strength concrete (HSC)-filled fiber reinforced polymer (FRP) tubes (HSCFFTs). The results from three square concrete-filled FRP tube (CFFT) columns that were tested under combined constant axial compression and reversed-cyclic lateral loading are presented. The main parameters of the experimental study included the axial load level, concrete strength, and FRP tube corner radius. The results indicate that square HSCFFT columns are capable of developing very high inelastic deformation capacities under simulated seismic loading. The results also indicate that increasing the corner radius beyond a certain threshold value provides no increase in column lateral drift capacities. It was observed that column deformability decreased with an increase in axial load level (P/Po) and concrete compressive strength (fc). The results of the experimental program are presented together with a discussion on the influence of the main parameters on the seismic behavior of CFFT columns.