Stress prediction model for FRP confined rectangular concrete columns with rounded corners

The paper uses the membrane hypothesis to formulate the confining behavior of fiber-reinforced polymer (FRP) confined rectangular columns. A model was developed to calculate the strength of FRP confined rectangular concrete columns. The model was verified using a database of 190 FRP confined rectangular concrete columns. The database covers unconfined concrete strength between 18.3 and 55.2 MPa, and specimens with dimensions ranging from 79-305 mm and 100-305 mm for short and long sides, respectively. The performance of the proposed model shows a very good correlation with the experimental results. In addition, the strain distribution of FRP around the circumference of the rectangular sections was examined to propose an equation for predicting the actual rupture strain of FRP. The minimum corner radius of the sections is also recommended to achieve sufficient confinement

Effect of helical pitch and tensile reinforcement ratio on the concrete cover spalling off load and ductility of HSC beams

[extract] In recent years a marked increase in the use of High Strength Concrete (HSC) has been evident in Australian building construction despite the fact that the current Australian design standard, AS3600 provides no design rules. HSC has been used extensively in civil construction projects world wide because it reduces the cross section and the weight for long construction members. High strength concrete and high strength steel are used together to increase the load capacity and reduce the beams\u27 cross section. Using these two materials to design over reinforced beams will lead to huge reduction of cost, which is a desirable issue. However, the problem is the lack of ductility, hence such use is not allowed by the current codes of practice

Axial load-axial deformation behaviour of circular concrete columns reinforced with GFRP bars and helices

Fibre Reinforced Polymer (FRP) bars has attracted a significant amount of research attention in the last three decades to overcome the problems associated with the corrosion of steel reinforcing bars in reinforced concrete members. A limited number of studies, however, have investigated the behaviour of concrete columns reinforced with FRP bars. Also, available design standards either ignore the contribution of or do not recommend the use of GFRP bars in compression members. This study reports the results of experimental investigations of concrete specimens reinforced with GFRP bars and GFRP helices as longitudinal and transverse reinforcement, respectively. A total of five circular concrete columns of 205 mm in diameter and 800 mm in height were cast and tested under axial compression. The experimental results showed that reducing the spacing of the GFRP helices or confining the specimens with CFRP sheet led to improvements in the strength and ductility of the specimens. Also, an analytical model has been developed for the axial load-axial deformation behaviour of the circular concrete columns reinforced with GFRP bars and helices. The model has been validated with the experimental results

Axial compressive behaviour of circular CFFT: Experimental database and design-oriented model

Concrete Filled Fibre Reinforced Polymer Tube (CFFT) for new columns construction has attracted significant research attention in recent years. The CFFT acts as a formwork for new columns and a barrier to corrosion accelerating agents. It significantly increases both the strength capacity (Strength enhancement ratio) and the ductility (Strain enhancement ratio) of reinforced concrete columns. In this study, based on predefined selection criteria, experimental investigation results of 134 circular CFFT columns under axial compression have been compiled and analysed from 599 CFFT specimens available in the literature. It has been observed that actual confinement ratio (expressed as a function of material properties of fibres, diameter of CFFT and compressive strength of concrete) has significant influence on the strength and ductility of circular CFFT columns. Design oriented models have been proposed to compute the strength and strain enhancement ratios of circular CFFT columns. The proposed strength and strain enhancement ratio models have significantly reduced Average Absolute Error (AAE), Mean Square Error (MSE), Relative Standard Error of Estimate (RSEE) and Standard Deviation (SD) as compared to other available strength and strain enhancement ratios of circular CFFT column models. The predictions of the proposed strength and strain enhancement ratio models match well with the experimental strength and strain enhancement ratios investigation results in the compiled database

Behavior of High-Strength Concrete Columns Reinforced with Galvanized Steel Equal-Angle Sections under Different Loading Conditions

Experimental results are presented for a new method of reinforcing concrete columns with galvanized steel equal-angle (GSEA) sections. For the same cross-sectional area, a GSEA section has a higher second moment of area than a conventional steel bar, which leads to a higher bending stiffness of the GSEA reinforced concrete member. In addition, the area of confined concrete is higher in GSEA reinforced concrete members than in steel bar reinforced members, which results in higher strength and ductility. The experimental program involved testing of 20 square, high-strength concrete (HSC) specimens under concentric axial load, eccentric axial load, and four-point loading. The specimens were reinforced longitudinally with either four N12 (12-mm-diameter deformed steel) bars or four GSEA sections and transversely with R10 (10-mm-diameter plain steel) bars. The specimens were 800 mm high with a 210 x 210 mm square cross section. Fifteen specimens were tested under either a concentric or eccentric axial load. The remaining five specimens were tested under four-point loading. Effects of the type of longitudinal reinforcement, spacing of transverse reinforcement, and loading conditions on the behavior of HSC specimens were investigated and discussed. Experimental results showed that, in general, specimens reinforced with GSEA sections had higher load-carrying capacities than the specimens reinforced with steel bars. In addition, the postpeak load-deformation behavior was observed to be more pronounced in specimens reinforced with GSEA sections than in specimens reinforced with steel bars

Investigation of engineering properties of normal and high strength fly ash based geopolymer and alkali-activated slag concrete compared to ordinary Portland cement concrete

Fly ash-based geopolymer (FAGP) and alkali-activated slag (AAS) concrete are produced by mixing alkaline solutions with aluminosilicate materials. As the FAGP and AAS concrete are free of Portland cement, they have a low carbon footprint and consume low energy during the production process. This paper compares the engineering properties of normal strength and high strength FAGP and AAS concrete with OPC concrete. The engineering properties considered in this study included workability, dry density, ultrasonic pulse velocity (UPV), compressive strength, indirect tensile strength, flexural strength, direct tensile strength, and stress-strain behaviour in compression and direct tension. Microstructural observations using scanning electronic microscopy (SEM) are also presented. It was found that the dry density and UPV of FAGP and AAS concrete were lower than those of OPC concrete of similar compressive strength. The tensile strength of FAGP and AAS concrete was comparable to the tensile strength of OPC concrete when the compressive strength of the concrete was about 35 MPa (normal strength concrete). However, the tensile strength of FAGP and AAS concrete was higher than the tensile strength of OPC concrete when the compressive strength of concrete was about 65 MPa (high strength concrete). The modulus of elasticity of FAGP and AAS concrete in compression and direct tension was lower than the modulus of elasticity of OPC concrete of similar compressive strength. The SEM results indicated that the microstructures of FAGP and AAS concrete were more compact and homogeneous than the microstructures of OPC concrete at 7 days, but less compact and homogeneous than the microstructures of OPC concrete at 28 days for the concrete of similar compressive strength

Axial Load and Bending Moment Behaviour of Square High Strength Concrete (HSC) Columns Reinforced with Steel Equal Angle (SEA) Sections

This paper presents the behaviour of square high-strength concrete (HSC) specimens reinforced longitudinally with steel equal angle (SEA) sections under different loading conditions. For the same cross-sectional area, a SEA section has a higher second moment of area than a steel bar, which results in a greater bending stiffness of the concrete member reinforced with SEA sections. Also, the area of confined concrete is greater in concrete members reinforced with SEA sections compared to members reinforced with steel bars, which results in higher strength and ductility. A total of 8 specimens of 210 mm square cross-section and 800 mm height were constructed and tested. The specimens were divided into two groups with four specimens in each group. Group R-S50 specimens serve as the reference group and were reinforced longitudinally with four N12 (12 mm diameter) deformed steel bars. Group A30-S50 specimens were reinforced longitudinally with four A30 (29.1 mm x 29.1 mm x 2.25 mm) SEA sections. All specimens were reinforced laterally with R10 (10 mm diameter) plain steel bars and spaced at 50 mm centres. The main variables considered in the study included the type of longitudinal reinforcement and the magnitude of load eccentricity. It was obtained from the experimental results that specimens reinforced longitudinally with SEA sections showed greater ductility compared to specimens reinforced longitudinally with steel bars under different loading conditions

Pengaruh Suhu dan Lama Penderaan secara Fisik pada Viabilitas Benih Buncis (Phaseolus Vulgaris L.)

Penelitian ini bertujuan untuk (1) mengetahui suhu yang efektif menurunkan viabilitas benih, (2) mengetahui lama penderaan yang efektif menurunkan viabilitas benih, (3) mengetahui pengaruh kombinasi suhu dan lama penderaan yang efektif menurunkan viabilitas benih. Penelitian ini dilaksanakan di desa Jatimulyo dan Laboratorium Benih Fakultas Pertanian Universitas Lampung pada bulan Juni 2012 sampai Agustus 2012. Rancangan yang digunakan adalah faktorial (2x6) dalam rancangan kelompok teracak sempurna (RKTS) dengan faktor utama adalah suhu 39°C dan 41°C dan faktor kedua adalah lama penderaan yang terdiri dari: 0 jam (kontrol), 24 jam, 48 jam, 72 jam, 96 jam dan 120 jam. Jika asumsi terpenuhi analisis data dilanjutkan dengan Uji Beda Nyata Terkecil (BNT) pada taraf 95%. Hasil penelitian menunjukkan pengaruh lama penderaan nyata menurunkan viabilitas benih buncis, sedangkan pengaruh suhu dan pengaruh interaksi suhu dan lama penderaan memberikan pengaruhtidak nyata. Viabilitas benih buncis sudah menurun secara nyata setelah didera selama 24 jam yang ditunjukkan oleh variabel kecepatan perkecambahan, sedangkan variabel kecambah normal total, kecambah normal kuat, dan benih mati mengalami penurunan viabilitas setelah didera selama 48 jam

Maximum axial load carrying capacity of Fibre Reinforced-Polymer (FRP) bar reinforced concrete columns under axial compression

In this study, a new equation is proposed to compute the maximum axial load carrying capacity of FRP bar reinforced concrete columns under axial compression. The equation proposed in this study was critically compared with the equations proposed in the previous research studies using a wide range of experimental data taken from the available literature. In general, it was found that computing the contribution of the FRP longitudinal bars in concrete columns based on the modulus of elasticity (stiffness) of the FRP bars provides more rational predictions than computing the contribution of the FRP longitudinal bars based on the ultimate tensile strength of the FRP bars. It was also found that using a concrete compressive strength-based empirical equation in estimating the axial strain in the FRP longitudinal bars in concrete columns provides more accurate predictions of the contribution of the longitudinal FRP bars in the axial load sustained by the FRP bar reinforced concrete columns

Experimental Investigation of Circular High-Strength Concrete Columns Reinforced with Glass Fiber-Reinforced Polymer Bars and Helices under Different Loading Conditions

Existing design codes and guidelines do not adequately address the design of concrete columns reinforced with fiber-reinforced polymer (FRP) bars. Accordingly, a number of research studies investigated the behavior of FRP bar-reinforced concrete columns. However, the previous studies were limited to FRP bar-reinforced normal-strength concrete (NSC) columns. In this study, the behavior of glass fiber-reinforced polymer (GFRP) bar-reinforced high-strength concrete (HSC) specimens under different loading conditions was investigated in terms of axial load-carrying capacity, confinement efficiency of the GFRP helices, as well as the ductility and post-peak axial load-axial deformation response. The effects of the key parameters such as the type of the reinforcement (steel and GFRP), the pitch of the transverse helices, and the loading condition (concentric, eccentric, and four-point loading) on the performance of the specimens were investigated. It was observed that the GFRP bar-reinforced HSC specimen sustained similar axial load under concentric axial compression compared to its steel counterpart, but the efficiency of GFRP bar-reinforced HSC specimens in sustaining axial loads decreased with an increase in the axial load eccentricity. Direct replacement of steel reinforcement by the same amount of GFRP reinforcement in HSC specimens resulted in about 30% less ductility under concentric axial load. However, it was found that the ductility and post-peak axial load-axial deformation behavior of the GFRP bar-reinforced HSC specimens can be significantly improved by providing closely spaced helices