Concrete-filled Glass Fiber-reinforced Polymer Research Articles

Experimental and Numerical Simulation of Reinforced Concrete-Filled Square GFRP Tubular Columns under Axial Compression.

To investigate the axial compressive behavior of reinforced concrete-filled square glass-fiber-reinforced polymer(GFRP) tubular (RCFSGT) columns, 17 specimens were designed with variations in GFRP tube wall thickness, spiral reinforcement yield strength, and spiral reinforcement ratio. A detailed model was developed using the finite element software ABAQUS, enabling in-depth mechanistic analysis and expanded parameter studies. The results indicate that the failure types of the specimens are all manifested as GFRP square tube cracking, and the core concrete is subjected to crushing or shear failure. The inclusion of a reinforcement cage can significantly enhance the load-bearing capacity and ductility of the specimen. Furthermore, as the yield strength and reinforcement ratio of the spiral reinforcement increase, so does the load-bearing capacity of the specimen. The finite element simulation results align well with the experimental findings. As the wall thickness of the GFRP square tube increases from 2 mm to 6 mm, the load-bearing capacity improves by approximately 19.69%. With the yield strength of the spiral reinforcement rising from 200 MPa to 400 MPa, the specimen's load-bearing capacity shows an increase of approximately 7.55%. However, as its yield strength continues to increase, there is minimal change in the load-bearing capacity. When the stirrup ratio of spiral reinforcement rises from 0.33% to 2.26%, the specimen's load-bearing capacity experiences an increase of approximately 56.90%.

Influence of GFRP Confining Tube Parameters in Double-Skin Tubular Short Columns under Axial Loading

Abstract Composite construction with steel and concrete has become a widespread solution in modern construction practices because of its inherent properties such as high strength-to-weight ratio, good corrosion resistance, and high stiffness. Concrete-filled fiber-reinforced polymer (FRP) steel double-skin tubular compression members as vertical load–carrying members in buildings helps in optimizing the advantages of three materials: steel, concrete, and FRP. This study investigates the axial compressive behavior of short, concrete-filled glass fiber–reinforced polymer (GFRP) steel double-skin tubular (GSDST) columns and concrete-filled GFRP tubular (CFFT) columns. Parameters such as the number of FRP layers, hollow section ratio (HSR), variation of diameter of the inner steel tube, and the angle of orientation of the fibers have been examined in this investigation. The experimental study was carried out by performing a monotonic axial compressive loading condition. Three different angles of fiber orientation, 0° along the hoop direction, 45°, and 0°/90° with respect to the axis of the column, were adopted in this study. The ultimate load-carrying capacity, axial displacement, axial and horizontal strains, and failure modes were observed. The experimental results indicate that the structural performance of GSDST columns is significantly influenced by GFRP tube thickness, inner steel-tube diameter, and fiber-orientation angle. Maximum displacement was observed in the specimens with high HSR, thus showing a ductile characteristic in the axial load-displacement behavior. The load-carrying ability of the specimens decreased as the HSR increased. The load-carrying capacity of the specimens increased with the increase in outer GFRP tube thickness. This study demonstrates that GFRP tubes can be used efficiently in the construction field as vertical load–carrying components by enhancing the axial behavior of FRP steel double-skin tubular columns.

Compressive Behavior of GFRP Tubes Filled with Self-Compacting Concrete

Self-compacting concrete (SCC) features excellent flow ability without the need of vibration for compaction during casting. This makes it particularly suitable for application in hybrid fiber-reinforced polymer (FRP)-concrete–steel double-skin tubular columns (DSTCs), a high-performance structural form evolved from concrete-filled FRP tubes (CFFTs). In a DSTC, the space between the inner steel tube and the outer FRP tube for filling concrete may be narrow and the application of vibration may be difficult. However, because of the large shrinkage of SCC compared to traditional concrete of normal flow ability, the integrity and composite action of DSTCs with SCC become a major concern. To clarify this issue, an understanding of the behavior of CFFTs filled with SCC is an essential prerequisite. While a large number of studies have been published on CFFTs with normal concrete (NC), only limited studies have been carried out on CFFTs with SCC. This paper presents a comprehensive investigation on the effect of SCC on the behavior of large-scale CFFTs. Axial compression tests were carried out on concrete-filled glass FRP (GFRP) tubes with diameters of 150, 200, 300, and 400 mm. The compressive behavior of the CFFT specimens filled with NC, a nonexpansive SCC, and an expansive SCC (ESCC) was compared and discussed. The results showed that the specimens with nonexpansive SCC behaved differently compared to those with NC as a result of larger shrinkage, especially for large specimens for which the confinement level was lower. This situation, however, improved in specimens where ESCC was used. Finally, the test results were further analyzed using a theoretical model recently proposed by the authors’ group.

Durability of discrete BFRP needle-reinforced seawater sea-sand concrete-filled GFRP tubular columns in the ocean environment

In this paper, a long-term durability test on a new type of seawater sea-sand concrete (SWSSC)-filled glass fiber-reinforced polymer (GFRP) tubular column, which was previously proposed by the authors, was conducted. The adopted inner-filled concrete included seawater sea-sand gravel aggregate concrete (SSGC), discrete basalt fiber reinforced polymer (BFRP) needle-reinforced SSGC (BNSSGC), seawater sea-sand coral aggregate concrete (SSCC), and discrete BFRP needle-reinforced SSCC (BNSSCC). The naked concrete columns and GFRP tube-confined columns were immersed in artificial seawater under ambient temperature for up to 22 months. The variation laws of the axial compressive properties of the short columns were tested and compared, and the performance degradation mechanisms were microscopically analyzed by scanning electron microscopy (SEM). In addition, a long-term prediction model was adopted to predict the degradation of the load-bearing capacity of the environmentally conditioned concrete-filled GFRP tubular columns. The test results showed that for the SWSSC-filled GFRP tubular columns, the strength degradation of the specimens with gravel aggregates was not obvious, while the strength of the columns with coral aggregates all showed a stable degradation trend. Pits and resin shedding were observed on the surfaces of the BFRP needles and GFRP tubes, and fiber/resin debonding was the internal mechanism of the degradation of mechanical properties. The predicted stable axial compression strength retention of the FRP-SSGC columns, FRP-SSCC columns, and FRP-BNSSCC columns was 0.944, 0.917, and 0.823, respectively.

Structural Performance of Concrete-Filled GFRP Tube Slender Columns in Ambient and Standard Fire Conditions

Abstract Concrete-filled glass fiber-reinforced polymer (GFRP) tube (CFFT) columns benefit from significant concrete confinement effects that enhance its structural performance compared to conventi...

The effects of elevated temperatures on the performance of concrete-filled pultruded GFRP tubular columns

Usage of concrete-filled pultruded glass fiber-reinforced polymer (GFRP) tubes (CFPGT) as columns can increase the service life of structures. However, marine structures such as oil platforms are always prone to fire because of the low resistance to the elevated temperatures. The purpose of this investigation is to evaluate the effects of concrete core strength (30 and 60 MPa), and exposure temperature (25, 100, 200, 300, and 400 °C) and time (60 and 120 min) on the compressive and bond behavior of CFPGTs. The properties of unexposed and exposed concrete core, pultruded GFRP hollow tubes, and CFPGTs were determined via compressive and disk-split tests. Also, the push-out test was used to measure bond–slip strength of partially-filled samples. The results showed that the maximum load-bearing capacity of the exposed stub columns at temperatures 100, 200, 300, and 400 °C was 8%, 22%, 34%, and 51% lower than that of the unexposed columns, respectively. Regardless of exposure conditions and the core strength, the pultruded GFRP tubes resisted about one fourth of the total load-bearing capacity. Moreover, it was observed that the ultimate axial strain (the strain corresponding to tube rupture) of column specimens was reduced with increase in concrete core strength and exposure temperature; however, the exposure time had insignificant effect on the ultimate axial strain. Dilation and load-bearing capacity of CFPGTs were considered to propose new models for predicting the experimental results. Concerning the bond strength tests, it was concluded that the exposure temperature increment led to the interlocking and coefficient of kinetic friction increase, resulting in higher bond strength. Finally, expressions were presented to estimate the bond strength of CFPGTs after exposure to elevated temperatures.

Axial Compressive Performance of a Composite Concrete-Filled GFRP Tube Square Column

A composite concrete-filled glass fiber reinforced polymer (GFRP) tube square column is a new type of composite column, where GFRP is externally wrapped over several GFRP square tubes to form a multicavity GFRP tube, and then concrete is poured inside. External GFRP wrapping methods can be divided into two types: entirely wrapped and strip-type wrapped methods. The former is superior to the latter in terms of performance under stress. However, difficulties are introduced in the construction process of the former, and substantial materials are required to wrap the entire structure. To examine the axial compressive performance for this new type of composite column and the impact of the wrapping method, we designed and fabricated one type of entirely wrapped composite column and two types of strip-type wrapped composite columns with clear spacings of 85 mm and 40 mm, respectively, and performed static axial compression tests. Through tests and numerical simulations, we obtained the failure mode, load–displacement curve, and load–strain curve of the specimen, and analyzed the impact of the externally wrapped GFRP on the mechanical behavior of the composite column. The results show that the composite column reached the peak load before the fracture of the GFRP tube fiber occurred, and the bearing capacity declined sharply to approximately 75% of the peak load after the fiber fractured, then entered a platform section, thereby displaying ductile failure. As the wrapped layers of GFRP strips increased, the load capacity of the specimen exhibited a linear growth tendency. Compared with the performance of the entirely wrapped method, the load capacity of the specimens in the W5040 group declined 9.8% on average, and the peak efficiency of the GFRP strips increased by 50%, thereby indicating that the use of appropriate GFRP layers and strip distance intervals can ensure the appropriate bearing capacity of composite columns and full utilization of GFRP material properties.

Experimental Study on Damage Identification of Nano-SiO2 Concrete Filled GFRP Tube Column Using Piezoceramic Transducers.

This paper proposes a new approach to damage detection of nano-SiO2 concrete-filled glass fiber reinforced polymer (GFRP) tube column using piezoceramic transducers. Stress waves are emitted and received by a pair of piezoceramic transducers embedded in the concrete-filled GFRP tube, and the energy and damage indices at different levels of loading in the tube are obtained by wavelet packet to evaluate the damage degree of GFRP tube nano-SiO2 concrete column. Through the experimental studies, the effects of different nano-SiO2 contents, concrete grades, and superplasticizer on the damage were analyzed to gain load–displacement curves, load–energy index curves, and load–damage index curves. The results show that the wave method can be adopted to monitor the damage of GFRP tube nano-SiO2 concrete column. The specimens with 3% nano-SiO2 content have the smallest energy change rate, indicating that adding 3% nano-SiO2 content into concrete can effectively delay the development of damage. After the addition of superplasticizer, with the increase in the strength grade of concrete, the cracks in the specimen tend to develop slowly, and therefore the specimens have a stronger resistance to damage. The damage of the specimens with the nano-SiO2 content of 1% appeared the latest, while the damage without the nano-SiO2 specimen appeared the fastest. The experimental results show that this method can better monitor the damage of the Nano-SiO2 concrete in the glass fiber reinforced polymer (GFRP) tube.

Experimental Studies of Concrete-Filled Composite Tubes under Axial Short- and Long-Term Loads.

The paper presents experimental studies on axially compressed columns made of concrete-filled glass fiber reinforced polymer (GFRP) tubes. The infill concrete was C30/37 according to Eurocode 2. The investigated composite pipes were characterized by different angles of fiber winding in relation to the longitudinal axis of the element: 20, 55 and 85 degrees. Columns of two lengths, 0.4 m and 2.0 m, were studied. The internal diameter and wall thickness of all the pipes were identical and amounted to 200 mm and 6 mm, respectively. The mean values of two mechanical properties, elasticity modulus and compression strength, were determined. These properties were determined for longitudinal compression and for circumferential tension. The graphs of longitudinal and peripheral deformations of polymer shells as a function of load level are presented both for empty tubes and for concrete-filled ones. The results of long-term investigations of three identically made 0.4 m high concrete-filled GFRP tubes are also presented.

Axial mechanical properties of concrete-filled GFRP tubular hollow composite columns

In this paper, a new type of concrete-filled Glass Fiber Reinforced Polymer (GFRP) tubular hollow composite column is tested and analyzed by finite element analysis. The axial pressure test of 27 concrete-filled GFRP tubular hollow composite columns is made to investigate the compressive properties of the specimens, including the failure mode, ultimate bearing capacity under axial compression, load-strain relationship and load-displacement relationship. The effects of the three parameters of hollow ratio, diameter-to-thickness ratio of GFRP tube and concrete strength grade on the axial compressive properties of concrete-filled GFRP tubular hollow composite columns are studied, and some key principles of designing concrete-filled GFRP tubular hollow composite columns are presented. The parameters of hollow ratio, diameter-to-thickness ratio of GFRP tube, and concrete strength grade are analyzed by using the verified finite element model. An ultimate bearing capacity adjustment coefficient is proposed, which takes into consideration the influence of hollow sections. A recommended formula is given for the axial bearing capacity of concrete-filled GFRP tubular hollow composite columns.

Mechanical properties of discrete BFRP needles reinforced seawater sea-sand concrete-filled GFRP tubular stub columns

This paper proposes a new type of tubular column, which is composed of glass fiber-reinforced polymer (GFRP) tube and discrete basalt fiber-reinforced polymer (BFRP) needles reinforced seawater sea-sand concrete (SWSSC). The discrete BFRP needles, with an aspect ratio of 10.0, were cut from BFRP bar production scrap and mixed into fresh concrete to replace 20% of the coarse aggregates by volume. The axial compression properties and lateral bending properties of the tubular columns were tested. The test variables included the wall thickness of the GFRP tubes (i.e., 3 mm and 4 mm), the type of coarse aggregates (i.e., gravel or coral), and the incorporation of BFRP needles or not. Additionally, unconfined bare columns were tested for comparison. The test results showed that the inclusion of BFRP needles had moderate adverse effects on the peak compressive strength of bare columns: the peak axial stress reduced slightly by 2.5% for gravel concrete and 7.2% for coral concrete, respectively. Besides, for the four types of concrete in this paper, the 3- and 4-mm GFRP tube-confinement increased the peak axial compressive strengths by 23 ~ 52% and 65 ~ 83%, respectively. In addition, the adoption of GFRP tubes was able to improve the bending performance of columns significantly, especially for energy consumption.

Early Age Concrete Strength Monitoring Using Power Spectral Density and Wavelet Packet Analysis

Concrete is a complex building material. Under normal curing conditions, concrete strength shows a nonlinear development process at an early age (1∼28 d). In the first few days after the completion of pouring, the strength of concrete increases slowly. Subsequently, the strength of concrete increases rapidly, reaching about 90% of its age strength. Finally, its strength gradually stabilizes. This paper introduces the experiment of 28‐day concrete age strength monitoring based on embedded piezoelectric smart aggregate (SA). Two piezoelectric SAs were embedded in a concrete‐filled GFRP (glass fiber reinforced polymer) tube column, one of which emitted a sinusoidal sweep signal and the other SA received the signal. With the hydration reaction of concrete, the stress wave would be significantly different when passing through concrete, and the received signal is changing constantly. Through power spectral density and wavelet packet energy analysis, the monitoring signal of concrete age within 28 days was analyzed. The experimental results show that the wavelet packet energy and power spectral density of the sensor monitoring signal show a nonlinear growth trend with time during the concrete target age. It can be divided into three stages, and the fifth day and the fourteenth day are the demarcation point of energy growth. And the trend of energy change corresponds well with the change of actual concrete strength and age. Comparing and analyzing the received signal energy of the sensor and the power spectral density function of the stress wave signal of the concrete specimen, the trend of the amplitude in the natural frequency domain is found to be the same in the three stages.

Behavior of Cross Arms Inserted in Concrete-Filled Circular GFRP Tubular Columns.

Fiber-reinforced polymer (FRP) materials nowadays have attracted much attention in both retrofitting of aged infrastructure and developing of new structural systems attributed to the outstanding mechanical properties. Extensive studies have been performed on concrete-filled glass FRP (GFRP) tubes for the potential application in piling, poles, highways overhead sign structures and bridge components. The new hybrid member also provides an alternative solution for traditional transmission structures. However, the connection between concrete-filled GFRP tubes and cross arms has not been fully understood. In this paper, an experimental study and theoretical analysis were conducted on the behavior of cross arms inserted in concrete-filled circular GFRP tubular columns. Steel bars with a larger stiffness in comparison with GFRP tubes were selected here for the cross arm to simulate a more severe scenario. The structural responses of the system when the cross arms were subjected to concentrated loads were carefully recorded. Experimental results showed that the concrete-filled GFRP tubes could offer a sufficient restraint to the deformation of the cross arm. No visible cracks were found on the GFRP tube at the corner of the cross arm where the stress and strain concentrated. Theoretical solutions based on available theories and equations were adopted to predict the displacement of the cross arms and a good agreement was achieved between the prediction results and experimental findings.

Experimental evaluation of built-in channel steel concrete-filled GFRP tubular stub columns under axial compression

This paper studies experimentally the structural behavior of channel steel reinforced concrete-filled glass fiber-reinforced polymer (GFRP) tubular stub columns. To understand their structural performance, we examined 27 specimens which subjected to axial compression. The variables of the specimen are concrete strength grade, diameter-to-thickness ratio of GFRP tube and steel ratio. The displacement-load curve, strain-load curve, ultimate load, axial compressive stiffness and failure characteristics of the specimens were analyzed. The results of the test show that the specimens’ ultimate bearing capacity increases as the concrete strength increases. And those specimens with higher concrete strength grade have greater initial stiffness and better deformation capacity than those with lower concrete strength grade. The varieties of the steel ratio have no significant effect on the specimens’ axial deformation property. The confinement coefficient is proposed to evaluate the constraint effect of the GFRP tube on both the inner channel steel and the core concrete. There was a negative correlation between the restraint effect and the diameter-thickness ratio of the GFRP tube. A simplified formula for calculating the axial bearing capacity of the composite columns is proposed.

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.

Behavior of reinforced concrete-filled GFRP tubes under eccentric compression loading

This paper presents the results of experimental and theoretical study on the behavior of reinforced concrete-filled glass fiber reinforced polymer (GFRP) tubes (RCFFTs) under eccentric compression loading. A total of six RCFFT specimens were tested, the effects of the following parameters were examined: GFRP tube thickness (4.5 and 6.0 mm), longitudinal reinforcement, inserted I-shaped steel, and eccentricity (20 and 40 mm). The results of this investigation indicate that the ultimate load capacity and ductility of the RCFFT specimens are improved in terms of increasing the thickness of the GFRP tube under eccentric load. However, increasing the eccentricity significantly decreases the load capacity of RCFFT specimens. The internal steel bar could enhance the rigidity and loading capacity of RCFFT specimens. Furthermore, ultimate load capacity and ductility of the specimen are increased significantly by inserting shaped steel into concrete filled GFRP tube, Also, the simplified design equations are proposed to predict the ultimate load capacities of RCFFT specimens.

Repair of corroded and buckled short steel columns using concrete-filled GFRP jackets

Many bridges and structures in the United States that are supported on steel columns or piles exhibit inadequate strength due to increasing load demand or aging due to corrosion, or both. The combination of increased load demand and reduction of capacity due to corrosion-induced section loss can lead to unexpected buckling of the piles. This paper investigates the effectiveness of a glass fiber reinforced polymer (GFRP)-based technique for rapid retrofit of buckled steel piles or columns. The system consists of a GFRP jacket, which is formed on-site and subsequently filled with an expansive concrete. Thirteen-buckled short steel columns with varying degrees of section loss were repaired and tested to failure under axial compression. The research results indicate that the repair system restored the capacity of the buckled columns to between 69% and 104% of the capacity of the undamaged control column. Further the repaired piles exhibited a hardening response in the non-linear range rather than the sudden loss of capacity and softening response that is characteristically associated with buckling of steel columns. The findings suggest that installation of concrete-filled GFRP jackets can be an effective technique to rapidly repair corroded and buckled short steel columns or piles.

Experimental study on flexural behavior of splicing concrete-filled GFRP tubular composite members connected with steel bars

Based on the experiment, this paper focuses on studying flexural behavior of splicing concrete-filled glass fiber reinforced polymer (GFRP) tubular composite members connected with steel bars. The test results indicated the confinement effects of GFRP tubes on the concrete core in compression zone began to produce, when the load reached about 50%<i>P_u</i> (<i>P_u</i>-ultimate load), but the confinement effects in tensile zone was unobvious. In addition, the failure modes of composite members were influenced by the steel ratio of the joint. For splicing unreinforced composite members, the steel ratio more than 1.96% could satisfy the splicing requirements and the steel ratio 2.94% was ideal comparatively. For splicing reinforced specimen, the bearing capacity of specimen with 3.92% steel ratio was higher 21.4% than specimen with 2.94% steel ratio and the latter was higher 21.2% than the contrast non-splicing specimen, which indicated that the steel ratio more than 2.94% could satisfy the splicing requirements and both splicing ways used in the experiment were feasible. So, the optimal steel ratio 2.94% was suggested economically. The experimental results also indicated that the carrying capacity and ductility of splicing concrete-filled GFRP tubular composite members could be improved by setting internal longitudinal rebars.

Composite Action of Concrete-Filled Rectangular GFRP Tubes

AbstractThis paper investigates the composite action and performance of rectangular concrete-filled glass fiber–reinforced polymer (GFRP) tubes in four-point bending. The study compares the performance of three different concrete-filled beam configurations with different levels of adhesive bonding of the concrete core to the GFRP tube. The three different configurations include (1) unbonded, (2) bonding of the flanges, and (3) bonding of the flanges and webs. The results show low composite action for the unbonded beam configuration up to full composite action for the completely bonded beam configuration. An analytical study is presented to provide insight into the failure mechanism for the fully bonded beam configuration and to predict ultimate capacity. For evaluation, the stiffness and strength of the fully bonded concrete-filled GFRP tube considered in this study is compared with a conventional steel reinforced concrete beam, concrete-filled steel tube, and concrete-filled GFRP tube with carbon FRP (CF...

Flexural Performance and Moment Connection of Concrete-Filled GFRP Tube–Encased Steel I-Sections

A hybrid system, concrete-filled fiber-reinforced polymer (FRP) tube (CFFT)-encased steel I-section, is introduced. The embedded steel section enhances flexural strength and stiffness, and provides a pseudoductile behavior. It also facilitates connection of the CFFT member to footings or other members. Phase I of the experimental program addresses the flexural behavior of the system through ten beam specimens, including steel and CFFT control specimens. The glass fiber-reinforced polymer (GFRP) tubes varied in thickness and laminate structure. The steel section enhanced performance considerably, especially pseudoductility, in tubes with cross-ply laminates, in which a significant sustained reserved strength remains stable over large deflections on fracture of the tube. CFFTs with angle-ply tubes showed a considerable inherent ductility on their own, in which case, adding the steel section enhanced strength and stiffness only. Phase II addresses a moment connection through five cantilever tests. The connections consist of steel base plates welded to the steel sections, which are embedded into the CFFT members at various length (Ls)-to-span-length (L) ratios ranging from 0.1 to 1.0. Three distinct failure modes are observed. At (Ls/L) ratios of up to 0.17, premature bond failure occurs. At ratios of 0.17 to 0.47, the CFFT member achieves flexural tension failure of the tube just beyond the free end of the steel section. Beyond a 0.47 ratio, the full plastic hinge capacity is developed at the fixed end. A simple design-oriented model that predicts strengths at the full range of (Ls/L) ratios is developed and validated.