Filled Fiber Reinforced Polymer Tubes 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.

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.

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...

FRP confinement of SCC incorporating expansive agent and saturated lightweight sand

Abstract This study investigated the effect of shrinkage, the use of lightweight sand (LWS) as internal curing and an expansive agent (EA) as shrinkage-reducing admixture on the confinement of self-consolidating concrete. Sixty-three concrete filled fiber reinforced polymer tube specimens were tested under axial compression. Using high EA content resulted in reduction in the unconfined compressive strength of concrete while using LWS resulted in up to 30% increase in the unconfined compressive strength at late ages. The coupled effect of LWS and EA increased the confinement effectiveness by 83%. The use of temporary confinement, in the form of rigid formwork, in conjunction with EA increased the confined strength by up to 23%.

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 and Computational Parametric Analysis of CFST and CFFT Columns

‘Concrete Filled Steel Tubes (CFST)’/ ‘Concrete Filled FRP Tubes (CFFT)’ comprises of a steel/ ‘Fiber Reinforced Polymer (FRP)’ hollow pipe of circular or rectangular shape filled with plain or reinforced concrete. Need of such composite columns in the field of building construction is due to advancements in technology, need of bigger space in smaller land area, ease in construction workability, and a lot of other modern time requirements. This paper defines an experimental and computational project carried out by testing a total of 49 CFST columns and 60 CFFT columns. Three Finite Element models were also made using the software pack ABAQUS. Variables for the study were aspect ratio of columns, Shape of columns (i.e. square, circular or rectangular) and material (i.e. steel or FRP). Basic aim of the project was to find structural parameters like load-deflection behaviour, deflection pattern, maximum load carrying capacity etc. The Steel reinforced concrete-filled fiber reinforced polymer (FRP)tubular column is proposed as a new form of composite column to obtain higher mechanical performance. A comparative analysis was also carried out using three main resulting indices like Ductility Index (DI), Strength Index (SI) and Concrete Contribution Ratio (CCR). Comparative observations between CFST/CFFT columns of different shapes and sizes is carried out, also experimental results were compared with analytical results obtained from ABAQUS software.

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.

Experimental and analytical investigation of new concrete filled FRP tube beam-column connections

Researchers have extensively investigated the behavior of concrete-filled fiber reinforced polymer (FRP) tubes (CFFTs) as beams or columns individually, while the beam-column connections of such elements remain to be investigated. The current study is focused at developing and investigating a simple and practical CFFT beam-column connection. The proposed connection is made of a steel connection to connect the CFFT beam to the CFFT column. The steel connection is attached to the CFFT beam using a high-performance epoxy cement-grout between the HSS tubing and the CFFT beam. The steel connection is fixed to the CFFT columns using eight high-strength bolts. Four different lengths of the steel connection are tested to study the required embedment length of the CFFT beams inside the HSS tubing. The experimental results show that the optimal embedment length required to induce flexural failure of the CFFT beam is two times the depth of the CFFT beam (i.e. FRP tube depth). Analytical equations are developed to calculate the flexural capacity of the CFFT beam and estimate the optimal embedment length required to achieve its nominal flexural capacity.

Experimental and analytical investigations of CFFT columns with and without FRP bars under concentric compression

This research study investigates experimentally and analytically the axial compressive behaviour of Concrete Filled Fiber Reinforced Polymer Tube (CFFT) columns with and without Fiber Reinforced Polymer (FRP) bars. The experimental program comprises five circular columns of 204-206 mm outer diameter and 800-812 mm height. All columns were tested under concentric axial compressive loads. It was found that CFFT columns with and without FRP bars achieved higher peak axial compressive loads and corresponding axial deformations than conventional steel reinforced concrete (RC) column. The contribution of FRP bars was about 12.1% of the axial compressive loads carried by CFFT columns reinforced with FRP bars. Axial load-axial deformation (P –

Experimental and numerical studies of CFRP tube and steel spiral dual-confined concrete composite columns under axial impact loading

Abstract Compared with conventional steel spiral reinforced concrete (SRC) or concrete filled fiber reinforced polymer tube (CFFT) columns, the fiber reinforced polymer (FRP) tube and inner steel spiral reinforcement (SR) dual-confined concrete hybrid columns (shortened as FRP-SR-concrete) showed higher load-bearing capacity and ductility in static compressive loading. In literature, very few studies have considered the dynamic behavior of FRP-SR-concrete columns under impact loading when using such hybrid structures under seismic-induced axial dynamic loading. This study investigated the axial impact behavior of carbon FRP-SR-concrete (CFRP-SR-concrete) columns subjected to a drop-weight impact test. The experimental parameters considered were CFRP tube thickness, the SR volumetric ratio, height and the weight of the impact hammer of the drop-weight test. The axial impact resistance of conventional CFFT and SRC columns was further used for a comparison. The test results showed that the CFRP-SR-concrete had higher dynamic impact load and better cracking resistance compared with the SRC or CFFT counterparts. The impact resistance of the CFRP-SR-concrete columns was enhanced with an increase in the CFRP tube thickness and the volumetric ratio of the SR. Additionally, numerical simulation was performed to predict the failure process and the impact resistance of the CFRP-SR-concrete columns.

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...

Compressive Behavior of Prestressed High-Strength Concrete-Filled Aramid FRP Tube Columns: Experimental Observations

AbstractThis paper presents an experimental investigation on the influence of prestressing fiber reinforced polymer (FRP) confining shell on the axial compressive behavior of high-strength concrete (HSC)-filled FRP tube columns. A total of 24 aramid FRP (AFRP)-confined concrete specimens with circular cross-sections were manufactured in the form of concrete-filled FRP tubes (CFFTs). The influence of the amount of prestress was examined by preparing the specimens with three different levels of lateral prestress ranging from 4.1 to 7.3 MPa. In addition to the prestressed specimens, companion specimens with no applied prestress were manufactured and tested to establish reference values. Results of the experimental study indicate that the influence of prestress on compressive strength is significant, with an increase in ultimate strength observed in all prestressed specimens compared to that of nonprestressed specimens. On the other hand, the influence of prestress on axial strain was found to be dependent on...

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.