Behavior Of Concrete Cylinders Research Articles

Mechanical properties of concrete subjected to cyclic thermal loading

This paper studies the effect of thermal cyclic loading on the mechanical properties of concrete such as cylinder and cube compressive strength, splitting and flexural tensile strengths, and weight loss. The specimens were exposed to 7–28 thermal cycles with peak temperatures of 100, 200 and 300 °C. A total of 120 specimens consisting of cubes, cylinders and prisms were tested in this study. The compressive strength of concrete enhances up to 7 or 14 thermal cycles and subsequently decreases but remains greater than the strength at ambient temperature at all temperature levels. The test results highlight the difference in compression behaviour of concrete cylinders and cubes. The effect of thermal cycles on splitting tensile strength of concrete is more pronounced than its effect on the modulus of rupture. Although the splitting tensile of concrete decreases with rise in the peak temperature and number of thermal cycles, the modulus of rupture increases up to seven cycles for exposure to the temperature cycles of 100 and 200 °C, which is even higher than the control. Models are developed to predict residual mechanical properties of concrete after exposure to the thermal cycles, which show close conformance with experiments.

Buckling of Radially Loaded Concrete Cylinders in Fire Condition

Concrete cylinders are commonly used in water treatment and sewerage plants, in the form of wells or basins. They are mainly subjected to axial compression resulting from soil lateral pressure and aqueous hydrostatic pressure, in case of the presence of a groundwater table; that is why they are mostly designed in the form of a circular hollow section. Concrete cylinders face a complicated case of loading in fire condition, as a result of material degradation in addition to thermally induced stresses. This paper studies buckling stability of that case where, a concrete cylinder is subjected to an internal fire load in addition to superimposed structural loads from the surrounding environment. The main objective of the research is to study buckling stability of concrete cylinders through identifying various structural and thermal parameters, controlling that behaviour. Finite element modelling using "Ansys 18.1" has been chosen as an approach to deal with the research problem. Twenty-five solid elements models have been prepared to study both thermal and structural behaviour of concrete cylinders in fire condition. Cylinder thickness, slenderness ratio, load ratio, and groundwater presence have been adopted as main research parameters to identify their effect on well's fire buckling endurance, in accordance with ISO 834 standard fire curve. A parametric study has been designed to study fire endurance vulnerability to cylinder thickness ranging from 50 mm up to 800 mm; diameter to thickness ratio [D/t] ranging from "10" up to "160"; full spectrum of structural load ratios; in addition to the presence of a surrounding groundwater. Outputs of the parametric study have been introduced in the form of figures, which could be used as preliminary design aids to identify buckling fire endurance as function of load ratio for various spectrums of thickness and slenderness ratios. Moreover, critical thicknesses and load ratios have been revealed.

Behavior of short concrete cylinders partially confined with GFRP composites

The confinement with Glass Fiber Reinforced Polymer (GFRP) composites of the concrete columns is effective in increasing their capacity as many authors have shown, but few studies dealt with partially wrapped columns. The main objective of this work is to study the influence of the partially confinement with Glass Fiber Reinforced Polymer (GFRP) composites on the behavior of the concrete cylinder under axial compressive load. Different heights of the confined area are considered in order to follow the evolution of the global mechanical response of the cylinder according to the parameter ‘x / h’ which represents the ratio of the height of the confined zone to the total height of the cylinder. The numerical results show that the partial confinement increases the ultimate stress of the confined short concrete cylinder and influences the mode of rupture. The confrontation of the numerical results with the experimental one shows a good concordance.

Durability of concrete with CFRP wrapping

Carbon fibre-reinforced polymer (CFRP) material has a high strength-to-weight ratio and good resistance to corrosion and environmental attacks. It has been widely used in rehabilitation of aged infrastructure. However, the durability of the strengthened system has not been yet assessed thoroughly since most of the previous study was conducted based on accelerated tests while the long-term investigation was less reported. This paper investigated the effect of CFRP wrapping on the axial behaviour of concrete cylinders subjected to different environments for more than 13 years. The specimens were exposed to five different conditions, including standard curing, immersion in distilled water, immersion in saturated Na2SO4 solution, outdoor sheltered from the rain, and outdoor without shelter from the rain. Axial compression tests were performed on the wrapped concrete cylinders. The load-bearing capacity and stress-strain responses were recorded. It was found that CFRP wrapping could effectively improve the ultimate strength and ductility of the columns. Though scatter existed, no significant effect of the environmental exposure on the load-bearing capacity of the cylinder specimens was observed which indicates a good durability of the strengthening system.

Numerical Analysis of Thermal Behavior of Concrete Cover Around FRP-Bars in Cold Region

The coefficient of thermal expansion of fiber reinforced polymer (FRP) in transverse direction is 3–8 times greater than that of hardened concrete. This thermal incompatibility between FRP bar and concrete in transverse direction may cause circumferential cracks within concrete at FRP bar/concrete interface under low temperatures and eventually the debonding of FRP bar from concrete. This paper presents numerical analysis using ADINA finite element software to investigate the thermal behavior of concrete cylinders reinforced with glass FRP bar (GFRP) in cold regions. The non-linear numerical results show that the first circumferential cracks occur within concrete at FRP bar/concrete interface at thermal loads ΔTcr varied between −35 and −25°C for GFRP bar-reinforced concrete cylinders having a ratio of concrete cover thickness to FRP bar diameter (c/db) varied from 0.8 to 3.6 and a concrete tensile strength of 4.1 MPa. The numerical radial tensile stresses in concrete at the interface compared with those predicted from the analytical model are similar until the appearance of the circumferential cracks in concrete whose analytical results are greater. The ratio c/db has no significant effect on the transverse thermal strains at FRP bar/concrete interface and also at external surface of concrete cover for a ratio of c/db ≥ 1.5. Also, the transverse thermal strains, at external surface of concrete cover, predicted from non-linear numerical model are in good agreement with those obtained from the linear analytical model and experimental tests.

Hysteretic Behavior of Concrete Cylinders Confined by Active Confining SMA Wire Jackets

Shape memory alloy (SMA) wire jackets are distinct from conventional jackets for concrete members since they can provide active confinement easily. The applications of SMAs in civil engineering are on the increase since SMAs show unique properties of shape memory effect and superelastic behavior. Especially, the seismic application of SMAs for confining concrete becomes a hot issues in recent. Thus, this study conducts cyclic compressive tests of concrete cylinders jacketed by shape memory alloy (SMA) wires which can provide active confinement due to shape memory effect. Monotonic compressive tests provide only the peak strength and the ultimate strain for confined concrete. However, confined concrete is exposed to the repeating of loading and unloading during an earthquake. Also, this study performs the same tests for concrete cylinders jacketed by steel jackets which provide only passive confinement and the results are compared to those of SMA wire jackets. This study provides the basic information of concrete behavior confined by active or passive external jackets.

Compressive behaviour of concrete cylinders reinforced by glass and polyester filaments

Concrete cylinders reinforced by various layers of glass or polyester filaments were fabricated. And the compressive strength of the cylinders with and without filament wrapping was tested. Comparisons of the compressive behaviour while using different fabrication parameters were made. It was revealed that the effect of the filament reinforcement was obvious. The modulus and the tensile strength of the filament played important role as far as the anti-compression behaviour of the reinforced cylinders is concerned. Increasing the filament layers enhanced the reinforcement effect.