Compressive behavior of hollow concrete columns reinforced with GFRP bars

Hollow concrete columns (HCCs) reinforced with steel bars have been employed extensively for bridge piers, ground piles, and utility poles because they offer higher structural efficiency compared to solid concrete columns with the same concrete area. Many experimental studies have been conducted to investigate the behavior of HCCs under different loading conditions and have found that the structural performance of HCCs is critically affected by the inner-to-outer diameter, reinforcement ratio, volumetric ratio, and concrete compressive strength. The improper design of the HCCs led to brittle failure behavior due to either buckling of the longitudinal bars or concrete wall crushing. Moreover, the corrosion of steel bars in HCCs is a critical issue due to their inner and outer exposed surfaces. Therefore, this research systematically investigated the fundamental behavior of HCCs reinforced with GFRP bars in compression to develop new, durable and structurally reliable construction systems. Firstly, HCCs with different inner-to-outer diameter (i/o) ratios was investigated by testing four concrete columns 250 mm in external diameter and reinforced longitudinally with six 15.9 mm diameter GFRP bars with different inner diameters (0, 40, 65, and 90 mm). One HCC reinforced with steel bars was also prepared and tested as a control sample. Based on the experimental results, increasing the i/o ratio up to 0.36 changed the failure behavior from brittle to ductile. GFRP-reinforced HCCs exhibited higher deformation capacity and confinement efficiency compared to the GFRP-reinforced SCC and steel-reinforced HCC. The optimal (i/o) ratio was found at 0.36 as it resulted in the highest confined strength and ductility for GFRP-reinforced HCC. Similarly, reinforcing with longitudinal GFRP bars enhanced the overall behavior of HCCs. The effect of varying the reinforcement ratio was investigated as the second study. To study this parameter, six HCCs reinforced longitudinally with GFRP bars with different reinforcement ratios (1.78%, 1.86%, 2.67%, 2.79%, 3.72%, and 4.00%) were prepared and tested. These reinforcement ratios were achieved by changing the bar diameter (12.7 mm, 15.9 mm, and 19.1 mm) and number of bars (4, 6, 8, and 9 bars). The test results show that the increase in the bar diameter and number enhanced the strength, ductility and confinement efficiency of HCCs. For columns with equal reinforcement ratios, using a higher number and smaller diameter of GFRP bars yielded 12% higher confinement efficiency than in the columns with a lesser number and larger diameter of GFRP bars. The capacity of the GFRP-reinforced HCC can be reliably predicted by considering the contribution of the concrete and up to 3000 ue in the longitudinal reinforcement. The crushing strain of the GFRP bars embedded in the HCCs was 52.1% of the ultimate tensile strain, and was affected by the confinement provided by the lateral reinforcements and the compressive strength of concrete. The effect of spiral spacing and concrete compressive strength was investigated as the third study. Seven large-scale HCCs with (i/o) ratio of 0.36, and reinforced with six longitudinal GFRP bars were prepared and tested. Out of these seven columns, three had spiral spacing of 50 mm, 100 mm, and 150 mm, and one had no spirals to investigate the effect of this design parameter. The fc of the other three columns were varied from 21 to 44 MPa to investigate the effect of the concrete compressive strength. Test results show that reducing the spiral spacing resulted in increasing the design load capacity, ductility, and confined strength of the HCCs due to the high lateral confinement. Increasing fc, on the other hand, increased the axial load capacity and reduced the ductility and confinement efficiency due to the brittle behavior of the high concrete compressive strength. The analytical model was then developed considering the contribution of the GFRP bars and the confined concrete core, which accurately predicted the post-loading behavior of the HCCs. The experimental results from the three experimental studies demonstrated that the (i/o) ratio, p, pv , and fc affect the overall behavior of GFRP-reinforced HCCs. Therefore, a new design-oriented model considering the effects of these design parameters was developed in the fourth study to accurately and reliably describe the behavior of the GFRP-reinforced HCCs. The new design-oriented model was based on the plasticity theory of concrete and considered the critical design parameters to precisely model the compressive load–strain behavior of GFRP-reinforced HCCs under monotonic and concentric loading. The results demonstrated that the proposed design-oriented model was accurate and yielding a very good representation of the axial compressive load behavior of GFRP-reinforced hollow concrete columns. From the results of this research, a detailed understanding on how the critical design parameters affect the structural performance of GFRP-reinforced HCCs was gained. Moreover, the results from this research will provide useful information in revealing the many benefits of this new structurally efficient and non-corrosive construction system, which support the work of the technical committees engaged in the development of design provisions for GFRP-reinforced concrete columns

Influence of Elevated Temperature on the Mechanical Properties of Hybrid Flax-Fiber-Epoxy Composites Incorporating Graphene

Natural fibers are now becoming widely adopted as reinforcements for polymer matrices to produce biodegradable and renewable composites. These natural composites have mechanical properties acceptable for use in many industrial and structural applications under ambient temperatures. However, there is still limited understanding regarding the mechanical performance of natural fiber composites when exposed to in-service elevated temperatures. Moreover, nanoparticle additives are widely utilized in reinforced composites as they can enhance mechanical, thermal, and physical performance. Therefore, this research extensively investigates the interlaminar shear strength (ILSS) and flexural properties of flax fiber composites with graphene at different weight percentages (0%, 0.5%, 1%, and 1.5%) and exposed to in-service elevated temperatures (20, 40, 60, 80, and 100 °C). Mechanical tests were conducted followed by microscopic observations to analyze the interphase between the flax fibers and epoxy resin. The results showed that a significant improvement in flexural strength, modulus, and interlaminar shear strength of the composites was achieved by adding 0.5% of graphene. Increasing the graphene to 1.0% and 1.5% gradually decreased the enhancement in the flexural and ILSS strength. SEM observations showed that voids caused by filler agglomeration were increasingly formed in the natural fiber reinforced composites with the increase in graphene addition

Long-Term Water Absorption of Hybrid Flax Fibre-Reinforced Epoxy Composites with Graphene and Its Influence on Mechanical Properties

Interest in the use of natural fibres as an alternative for artificial fibres in polymer composite manufacturing is increasing for various engineering applications. Their suitability for use in outdoor environments should be demonstrated due to their perceived hydrophilic behaviour. This study investigated the water absorption behaviour of hybrid flax fibre-reinforced epoxy composites with 0%, 0.5%, 1% and 1.5% graphene by weight that were immersed in water for 1000, 2000, and 3000 h. The flexural and interlaminar shear strength before and after immersion in water was then evaluated. The results showed that graphene nanoparticles improved the mechanical properties of the composites. The moisture absorption process of hybrid natural fibre composites followed the Fickian law, whereas the addition of graphene significantly reduced the moisture absorption and moisture diffusion, especially for hybrid composites with 1.5% graphene. However, the flexural and ILSS properties of the composites with and without graphene decreased with the increase in the exposure duration. The flexural strength of hybrid composites with 0%, 0.5%, 1% and 1.5% graphene decreased by 32%, 11%, 17.5% and 13.4%, respectively, after exposure for 3000 h. For inter-laminar shear strength at the same conditioning of 3000 h, hybrid composites with 0.5%, 1% and 1.5% graphene also decreased by 13.2%, 21% and 17.5%, respectively, compared to the dry composite’s strength. The specimens with 0.5% graphene showed the lowest reduction in strength for both the flexural and interlaminar tests, due to good filler dispersion in the matrix, but all of them were still higher than that of flax fibre composites. Scanning electron microscope observations showed a reduction in voids in the composite matrix after the introduction of graphene, resulting in reduced moisture absorption and moisture diffusion

Effect of spiral spacing and concrete strength on behavior of GFRP-reinforced hollow concrete columns

Hollow concrete columns (HCCs) are one of the preferred construction systems for bridge piers, piles, and poles because they require less material and have a high strength-to-weight ratio. While spiral spacing and concrete compressive strength are two critical design parameters that control HCC behavior, the deterioration of steel reinforcement is becoming an issue for HCCs. This study explored the use of glass fiber-reinforced polymer (GFRP) bars as longitudinal and lateral reinforcement for hollow concrete columns and investigated the effect of various spiral spacing and different concrete compressive strengths (f′c). Seven HCCs with inner and outer diameters of 90 and 250 mm, respectively, and reinforced with six longitudinal GFRP bars, were prepared and tested. The spiral spacing was no spirals, 50, 100, and 150 mm; the f′c varied from 21 to 44 MPa. Test results show that reducing the spiral spacing resulted in increased HCC uniaxial compression capacity, ductility, and confined strength due to the high lateral confining efficiency. Increasing f′c, on the other hand, increased the axial-load capacity but reduced the ductility and confinement efficiency due to the brittle behavior of high compressive-strength concrete. The analytical models considering the axial load contribution of the GFRP bars and the confined concrete core accurately predicted the behavior of the HCCs after the spalling of the concrete cover or at the post-loading behavior

Flexural behaviour of concrete slabs reinforced with GFRP bars and hollow composite reinforcing systems

Glass Fibre Reinforced Polymer (GFRP) bars are now attracting attention as an alternative reinforcement in concrete slabs because of their high resistance to corrosion that is a major problem for steel bars. Recentlyhollow concrete slab systems are being used to reduce the amount of concrete in the slab and to minimise the self-weight, but the internal holes makes them prone to shear failure and collapse. A hollow composite reinforcing system (CRS) with four flanges to improve the bond with concrete has recently been developed to stabilise the holes in concrete members. This study investigated the flexural behaviour of concrete slabs reinforced with GFRP bars and CRS. Four full-scale concrete slabs (solid slab reinforced with GFRP bars; hollow slab reinforced with GFRP bars; slab reinforced with GFRP bars and CRS; and slab reinforced with steel bars and CRS) were prepared and tested under four-point static bending to understand how this new construction system would perform. CRS is found to enhance the structural performance of hollow concrete slabs because it is more compatible with GFRP bars than steel bars due to their similar modulus of elasticity. A simplified Fibre Model Analysis (FMA) reliably predicted the capacity of hollow concrete slabs

Modelling flexural performance of hollow pultruded FRP profiles

Hollow Pultruded Fibre-Reinforced Polymer (PFRP) profiles, as novel construction material, require further development of design tool to broaden the applications. This paper proposes a combined experimental and numerical methodology as a design tool to investigate the failure modes of these profiles under four-point bending. Two different profiles, each with 10 samples, were tested until failure and were used to validate the numerical model. A finite element model was built based on a fast-convergence incremental approach that suits flexural loading and reduces the computational cost. The validated model was used to study the failure sequence thoroughly and perform an extensive parametric study on the design parameters. Each geometric parameter was studied individually first to determine the relevant levels for each parameter in the full factorial study. A full factorial design of experiment was used to capture the critical parametric interactions with over 81 numerical models. The design rules and recommendation were established for the optimal flexural behaviour of hollow box PFRP profiles to withstand local buckling of the top flange

Behavior of circular concrete columns reinforced with hollow composite sections and GFRP bars

Hollow concrete columns (HCCs) constitute a structurally efficient construction system for marine and offshore structures, including bridge piers and piles. Conventionally, HCCs reinforced with steel bars are vulnerable to corrosion and can lose functionality as a result, especially in harsh environments. Moreover, HCCs are subjected to brittle failure behavior by concrete crushing due to the absence of the concrete core. Therefore, this study investigated the use of glass fiber- reinforced polymer (GFRP) bars as a solution for corrosion and the use of hollow composite- reinforced sections (HCRSs) to confine the inner concrete wall in HCCs. Furthermore, this study conducted an in-depth assessment of the effect of the reinforcement configuration and reinforcement ratio on the axial performance of HCCs. Eight HCCs with the same lateral- reinforcement configuration were prepared and tested under monotonic loading until failure. The column design included a column without any longitudinal reinforcement, one reinforced longitudinally with an HCRS, one reinforced longitudinally with GFRP bars, three reinforced with HCRSs and different amounts of GFRP bars (4, 6, and 8 bars), and three reinforced with HCRSs and different diameters of GFRP bars (13, 16, 19 mm). The test results show that longitudinal reinforcement—whether GFRP bars or HCRSs—significantly enhanced the strength and displacement capacities of the HCCs. Increasing the amount of GFRP bars was more effective than increasing the bar diameter in increasing the confined strength and the displacement capacity. The axial-load capacity of the GFRP/HCRS-reinforced HCCs could be accurately estimated by calculating the load contribution of the longitudinal reinforcement, considering the axial strain at the concrete peak strength. A new confinement model considering the combined effect of the longitudinal and transverse reinforcement in the lateral confinement process was also developed

Providing person-centered palliative care in conflict-affected populations in the Middle East: What matters to patients with advanced cancer and families including refugees?

IntroductionUniversal health coverage highlights palliative care as an essential component of health services. However, it is unclear what constitutes person-centered care in populations affected by conflict, as they may have specific concerns in the dimensions of physical, emotional, social, and spiritual wellbeing. This study aimed to identify what matters to patients with advanced cancer and family caregivers in Jordan including refugees, to inform appropriate person-centered assessment and palliative care in conflict-affected populations.MethodsCross-sectional face-to-face, semi-structured interviews were conducted at two sites in Amman. Adult patients with advanced cancer and family caregivers were purposively sampled to maximize diversity and representation. Interviews were digitally audio recorded, anonymized, and transcribed verbatim for thematic analysis.FindingsFour themes were generated from 50 patients (22 refugees; 28 Jordanians) and 20 caregivers (7 refugees; 13 Jordanians) (1). Information, communication, and decision-making. Truth-telling and full disclosure from clinicians was valued, and participants expressed concerns that information was not shared in case patients would disengage with treatment. (2) Priorities and concerns for care and support. Participants’ top priority remained cure and recovery (which was viewed as possible). Other priorities included returning to their “normal” life and their “own” country, and to continue contributing to their family. (3) Role of spirituality and Islam. Most participants had strong faith in God and felt that having faith could comfort them. For refugees whose social network was fractured due to being away from home country, prayer and Quran reading became particularly important. (4) Unmet support needs of family caregivers. Family caregivers were affected physically and emotionally by worrying about and caring for the patients. They needed support and training, but often could not access this.DiscussionTruth-telling is highly valued and essential to achieving person-centered care and informed decision-making. This study also reveals specific concerns in conflict-affected populations, reflecting the experience of prior losses and fracturing of existing social networks and support. The role of religion is crucial in supporting refugee communities, and consideration should be paid to the needs of patients and caregivers when caring for a patient at home without access to their communities of origin and the support they accessed

Investigation of Circular Hollow Concrete Columns Reinforced with GFRP Bars and Spirals

Glass fiber-reinforced polymer (GFRP) reinforcements are useful alternatives to traditional steel bars in concrete structures, particularly in vertical structural elements such as columns, as they are less prone to corrosion, and impart increasing strength and endurance of buildings. There is limited research on the finite element analysis (FEA) of the structural behavior of hollow glass fiber-reinforced polymer reinforced concrete (GFRPRC) columns. The hollow portion can be used for the service duct and for reducing the self-weight of the members. Numerical analysis of the compressive response of circular hollow concrete columns reinforced with GFRP bars and spirals is performed in this study. This article aims to investigate the axial behavior of hollow GFRP concrete columns and compare it with that of solid steel reinforced concrete (RC) columns as well as hollow steel RC columns. The Abaqus software is used to construct finite element models. After calibration of modeling using an experimental test result as a control model, a parametric study is conducted. The columns with the same geometry, loading, and boundary conditions are analyzed in the parametric study. It is resulted that the hollow GFRP concrete columns provide a greater confinement effect than the solid steel RC columns. The average variation in the ultimate axial load-carrying capacities of the experimental results, from that of the FEA values, is noted to be only 3.87%, while the average difference in the corresponding deformations is 7.08%. Moreover, the hollow GFRP concrete columns possess greater axial load and deformation capacities compared with the solid steel RC columns