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

Axial performance of hollow concrete columns reinforced with GFRP composite bars with different reinforcement ratios

A hollow concrete column (HCC) is a structurally efficient construction system and uses less material. Conventionally, HCCs are reinforced with steel bars, which are prone to corrosion. This study explored the use of glass-fiber-reinforced-polymer (GFRP) composite bars as reinforcement for HCCs and evaluated the effect of the reinforcement ratio on HCC structural behavior. A total of 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 their behavior was investigated. The different 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 results show that increasing the diameter and number of bars enhanced the strength, ductility and confinement efficiency of HCC. For columns with equal reinforcement ratios, using more and smaller-diameter GFRP bars yielded 12% higher confinement efficiency than in the columns with fewer and larger-diameter bars. The crushing strain of the GFRP bars embedded the HCC was 52.1% of the ultimate tensile strain. Lastly, the axial-load capacity of the GFRP-reinforced HCC can be reliably predicted by considering the contribution of the concrete and up to 3000 με in the longitudinal reinforcement

Optimal design for epoxy polymer concrete based on mechanical properties and durability aspects

Polymer concrete has shown a number of promising applications in building and construction, but its mix design process remains arbitrary due to lack of understanding of how constituent materials influence performance. This paper investigated the effect of resin-to-filler ratio and matrix-to-aggregate ratio on mechanical and durability properties of epoxy-based polymer concrete in order to optimise its mix design. A novel combination of fire-retardant, hollow microsphere and fly ash fillers were used and specimens were prepared using resin-to-filler ratios by volume from 100:0 to 40:60 at 10% increment. Another group of specimens were prepared using matrix-to-aggregate ratios from 1:0 decreasing to 1:0.45, 1:0.90 and 1:1.35 by weight at constant resin-to-filler ratio. The specimens were inspected and tested under compressive, tensile and flexural loading conditions. The epoxy polymer matrix shows excellent durability in air, water, saline solution, and hygrothermal environments. Results show that the resin-to-filler ratio has significant influence on the spatial distribution of aggregates. Severe segregation occurred when the matrix contained less than 40% filler while a uniform aggregate distribution was obtained when the matrix had at least 40% filler. Moreover, the tensile strength, flexural strength and ductility decreased with decrease in matrix-to-aggregate ratio. Empirical models for polymer concrete were proposed based on the experimental results. The optimal resin-to-filler ratio was 70:30 and 60:40 for non-uniform and uniform distribution of aggregates, respectively, while a matrix-to-aggregate ratio of 1:1.35 was optimal in terms of achieving a good balance between performance and cost

Concentrically loaded recycled aggregate geopolymer concrete columns reinforced with GFRP bars and spirals

The increased quantity of construction and demolition waste and the high carbon footprint of cement production is creating significant environmental problems. This study explored the use of recycled coarse aggregates (RCA) in geopolymer concrete (GPC) and reinforced with glass fiber reinforced polymer (GFRP) bars and spirals to fabricate novel and structural GRAGC columns. A total of 9 GRAGC columns with 1150 mm in height and 250 mm in diameter were tested to failure under axial compression. The influence of a different number of longitudinal GFRP bars and spiral spacing on the cracking behaviour, ductility, and axial load-carrying capacity (LCC) were investigated. A nonlinear finite element model (FEM) was implemented to predict the axial compressive response of GRAGC columns. The experimental results depicted that an improvement in the ductility and lateral confinement was observed by decreasing the spacing of GFRP spirals. GRAGC columns with eight longitudinal GFRP bars portrayed the highest LCC. All tested GRAGC columns portrayed similar failure modes with the damage at the central region of the specimens. The theoretical model suggested over a database of 225 GFRP reinforced columns showed a high accuracy compared with the previous models. The present study suggests an efficient and environmental-friendly compression member

Bending and Shear Behaviour of Waste Rubber Concrete-Filled FRP Tubes with External Flanges

An innovative beam concept made from hollow FRP tube with external flanges and filled with crumbed rubber concrete was investigated with respect to bending and shear. The performance of the rubberised-concrete-filled specimens was then compared with hollow and normal-concrete-filled tubes. A comparison between flanged and non-flanged hollow and concrete-filled tubes was also implemented. Moreover, finite element simulation was conducted to predict the fundamental behaviour of the beams. The results showed that concrete filling slightly improves bending performance but significantly enhances the shear properties of the beam. Adding 25% of crumb rubber in concrete marginally affects the bending and shear performance of the beam when compared with normal-concrete-filled tubes. Moreover, the stiffness-to-FRP weight ratio of a hollow externally flanged round tube is equivalent to that of a concrete-filled non-flanged round tube. The consideration of the pair-based contact surface between an FRP tube and infill concrete in linear finite element modelling predicted the failure loads within a 15% margin of difference