Reinforced Concrete Cylinders Research Articles

A new model for predicting the axial compression capacity of reinforced concrete cylinders strengthened with CFRP

Numerous scholars have identified the shortcomings of imprecise terminology and substantial computational inaccuracies in the current models for predicting the axial compression capacity of CFRPstrengthened reinforced concrete (RC) cylinders. To improve the prediction accuracy of the axial compressive capacity model for CFRP-strengthened RC cylinders, the present axial compressive capacity model for CFRP-strengthened RC cylinders was scrutinized and evaluated. Drawing on Mander’s constraint theory and the concrete triaxial strength model, a novel axial compressive capacity model for CFRP-strengthened RC cylinders was proposed. This study collected 116 experimental data on the axial compression of CFRP-strengthened RC cylinders and analyzed the accuracy of various models using the data. The findings indicate that the model proposed in this study outperforms other models in predicting axial compression capacity and demonstrates high prediction accuracy. Furthermore, an analysis is conducted on the variation law of the model’s predicted value with respect to the design parameters. The proposed model in this study identifies concrete strength, stirrup spacing, and elastic modulus of CFRP as the primary factors that influence the axial compression capacity of CFRP-strengthened RC cylinders.

Failure mechanisms of corroded/non-corroded RC cylinder under axial compressive loading evaluated by AE technique

This study applied the acoustic emission (AE) technique to investigate mechanical behaviors and failure processes of corroded and non-corroded reinforced concrete (RC) cylinders, subjected to compressive loading. RC cylinders with 150 mm diameter and 300 mm height were tested. A set of twelve specimens was arranged into four groups of three specimens. These were the specimens corroded at the initiation stage, at the acceleration stage, at the deterioration stage of rebars, and another group was prepared as non-corroded specimens. The other set of twelve specimen was corroded as the same as the one, but axial rebars were coated with epoxy resin. After performing electrical corrosion, by applying 200 mA current under salt water immersion of 3% chloride concentration, axial compression tests were conducted on all specimens up to failure, using the AE technique. The corrosion of rebars inside the cylinders trends to decrease the compressive load-carrying performance of the RC cylinders, with the occurrence of early damages during the axial compression test. The analysis of the measured AE parameters enabled the classification of the generated damages into shear-type and tensile-type damages, which provided a characteristic signature of the failure mechanism of the tested cylinders. Next, it provided a 3D visualization of the damage events location and evolution inside the cylinders. Then, it gave the means to correlate the damage process of the RC cylinders, with their specific condition related to their corrosion level, prior to the compression test.

An Experimental Investigation and Computer Modeling of Direct Tension Pullout Test of Reinforced Concrete Cylinder

Executing the obligation of strengthened concrete is essential in investigating load exchanges from concrete to the inner reinforcing bar. The bond–displacement conduct and extreme pullout quality for pullout samples are essential information related to the durability of RC structures. The slip in the interface is basically due to a contrast in stresses between concrete and reinforcement. This distinction brings about the start of the split in encompassing concrete. This study examined the simple pullout solid 3D cylinder model strengthened by a reinforced steel bar, considered a line element for bond–slip conduct. The non-linear finite element model utilizing ANSYS software was established to concentrate on the concrete and steel reinforcement bond. Material nonlinearity because of cracking, crushing of concrete, and the steel reinforcing bar’s yielding were investigated. Test results showed that: a prediction model for early-age bond stress–slip relationship between steel bars and concrete was proposed based on modeling, which showed good agreement with test results. The precision of this model is explored by contrasting the finite element numerical analysis and that anticipated from test consequences of pullout examples. Immense homogeneity between the model and test results was found. This study could provide more accurate bond properties for structural analysis and design.

Investigation of the Compressive Strength of CFRP Wrapped Nylon Fiber Reinforced Concrete Cylinders

Nylon fibers are found to increase the mechanical properties of structural concrete like compressive and tensile strength when introduced into the concrete matrix by partially replacing fine aggregates. Since Nylon fibers are cheap waste materials, properly controlling their percentage into the matrix results in higher strength as well as cost control. This study discusses the compressive strength of nylon fiber induced concrete cylinders by wrapping them with 200gsm carbon fiber sheets as well as records the failure pattern, which is done by comparing the compressive strength of control specimens with sets of cylinders which are induced with nylon fiber and wrapped around with zero, one and three layers of CFRP laminates. Alongside the compressive test results, this study also reflects on several tensile tests carried out on CFRP strips which can be used as a measure to check hardener bond strengths in field. For that purpose, five coupons were prepared for flat tensile test and another five for overlap splice tensile test, stress-strain data were recorded; and the tests followed the guidelines stated in ACI code. The recorded tensile test data was found satisfactory with the recommended values for ACI 440.3R-04 and better compression capacity for cylinders were found with increasing CFRP layers. Journal of Engineering Science 13(1), 2022, 31-39

The Influence of the Curing Conditions on the Behavior of Jute Fibers Reinforced Concrete Cylinders

This paper presents an innovative method of reinforcement of concrete based on the use of the Jute fibers composites. These renewable raw bioresource fibers are available at a low cost. Moreover, they can be compared to Glass Fiber-Reinforced Polymer (GFRP) by enhancing the resistance of Jute Fiber-Reinforced Polymer (JFRP), while improving the compatibility between the fiber and the resin. For that purpose, this paper presents an experimental study that evaluates the influence of the curing conditions (time and temperature) on the behavior of JFRP laminates and concrete members strengthened by JFRP. The curing conditions at 30 °C for 2h 30min and at 50 °C for 1 h were the only two parameters studied and determined on the basis of Sikadur 330 properties and preliminary tests. Through the experimental tests, the maximum load capacity and observed failure modes are investigated. The results indicated that the curing at 30 °C for 2h 30min is the optimum curing condition. In addition, a low difference in the maximum load capacity was noted in the case of 50 °C. As to the failure modes, all the specimens cured with additional heat before being left under room conditions, have shown the ductile mode failure, especially in the case of specimens cured at 30 °C during 2h 30min. The analytical model conducted in this paper predicts the elastic modulus depending on temperature. The obtained results and proposed model can be used as input parameters in the analysis and design of externally strengthened members with Jute FRP composites.

Elastic wave based evaluation of CFRP protected RC structures subjected to corrosion

Determination of the state of hidden corrosion propagation inside concrete continues to be a major challenge for the evolving structural health monitoring industry. Numerous techniques such as Elastic wave-based methods, vibration-based methods, Electrochemical techniques, etc., have been deployed for corrosion detection. Once the corrosion progression is detected, a suitable retrofitting or corrosion impeding technique is of equal importance. In this paper, reinforced concrete (RC) cylinders subjected to corrosion-induced damage are protected passively and actively. Passive protection implied wrapping of reinforced concrete with carbon fiber reinforced polymer (CFRP) sheets whereas active protection implied providing cathodic protection in conjunction with application of wraps. RC cylinders corroded to 4 different levels of damage were protected after 4, 8, 12, and 20 days of exposure to accelerated corrosion. The corroding samples were monitored using an elastic wave-based non-destructive testing technique known as the Ultrasonic Guided wave technique. Two modes i.e. Surface seeking mode L (0, 1) at 0.1 MHz and L (0, 7) at 1 MHz were used. The variations in surface seeking mode and core seeking mode signal amplitudes indicated that corrosion impediment offered by active protection was superior. From the mass-loss measurements, the samples protected actively after 4, 8, 12, and 20 days underwent 2.11%, 2.3%, 4.25%, and 7.25% of mass-loss respectively, whereas the passively protected samples exhibited 3.1%, 3.4%, 5.1%, and 8.3% mass-loss for the same time intervals. Along with corrosion impediment, the actively protected samples exhibited higher pull- out strength (9.8 MPa, 9.6 MPa, 8.9 MPa, and 8.3 MPa) than passively protected samples (10.1 MPa, 9.2 MPa, 7.8 MPa, and 7.3 MPa) for protection initiation after 4, 8, 12 and 20 days of accelerated corrosion.

Size Effect on Strength of Reinforced Concrete Cylinders Confined by Carbon Fiber-Reinforced Polymer and Transverse Stirrup Reinforcement

Size Effect on Strength of Reinforced Concrete Cylinders Confined by Carbon Fiber-Reinforced Polymer and Transverse Stirrup Reinforcement

Residual load carrying capacity of reinforced concrete cylinders after heating at elevated temperature

The present research work is investigating the behavior of reinforced concrete (RC) cylinders after exposure to elevated temperatures. Reinforcement was done by using the longitudinal bars with closely spaced lateral ties (i.e. confinement). Experiments were carried out on the RC cylinders subjected to a single heating–cooling cycle of elevated temperature ranging from 200 to 800 °C with an interval of 200 °C for a holding time of 3 h. The crack patterns, color change, spalling and residual load carrying capacity of RC cylinders after exposure to elevated temperature have been observed. The residual load carrying capacity of RC cylinders has been compared with the load carrying capacity of control specimens at ambient temperature. The percent reduction in residual load carrying capacity after heating at 200 °C, 400 °C, 600 °C, and 800 °C temperature is 24.5%, 38.8%, 63.3%, and 83.7% respectively as compared with the load carrying capacity at ambient temperature. The finite element modeling (FEM) has been carried out to observe the thermal stresses and strains induced in the confined RC cylinders. Experimental observations of thermal strains and those obtained by the numerical model showed a good agreement. The scanning electron microscopy (SEM) has also been carried out to study the changes in the microstructure of confined high grade concrete and it was observed that the micro-cracks and pores increase and become more pervasive with increase in temperature.

Compression behavior of cylinder reinforced with aramid fiber reinforced polymer

Reinforced Concrete (RC) is a wonderful conglomerate material by the help of which, a structure or any structural element attains both compressive and tensile strength mesmerizingly. But due to different structural distresses and natural calamities, concrete structures loosen their strength on age which is a recent problem observed in old existing structures. Retrofitting of structures from these distresses and sensitive earthquakes became an essential constructional activity now a day for both concrete and steel structures as well. Results of the past experimental studies in this field showed a great positive impact in retrofitting of structures by using the Fiber Reinforced Polymers (FRPs). Owing to have a lot of drawbacks in the conventional methods of retrofication of structures, the technology offered by FRP techniques freshly became a new trend. This paper broaches an experimental study on RC cylindrical members confined with Aramid Fiber Reinforced Polymer (AFRP) and its effect on strengthening. In this experimental research, entirely twelve RC cylinders were prepared for testing to undergo the whole investigation including both un-strengthened and strengthened specimens. The conclusions articulated from the number of experiments acknowledged that, the load bearing capacity of the cylindrical specimens increased after the application of AFRP and also an exceptional interment of AFRP fabrics was observed. After the experimental inspections, the results obtained were correlated with the un-strengthened specimens and later the properties of the members were studied by plotting load–deflection curves, load-stiffness curves and axial stress–strain curves.

Cyclic stress-strain model incorporating buckling effect for steel reinforcing bars embedded in FRP-confined concrete

Buckling of steel reinforcement usually causes a sudden loss of the load-carrying capacity and the ultimate state of conventional reinforced concrete (RC) cylinders. However, reinforcing bars behave differently in fiber-reinforced polymer (FRP)-confined RC cylinders due to the lateral confinement effect of FRP. This paper presents a theoretical study into the buckling behavior of longitudinal steel reinforcing bars embedded in FRP-confined concrete subjected to cyclic axial compression. An empirical monotonic compressive stress-strain model considering the buckling effects proposed previously for laterally supported reinforcing bars is extended to a cyclic model by combining the monotonic envelope and the Menegotto-Pinto model accounting for the cyclic loops. The cyclic stress-strain models for both laterally supported reinforcing bars and FRP-confined plain concrete are then implemented into the OpenSees software platform and validated through comparisons with compressive test results on cyclically loaded FRP-confined plain and RC cylinders. The proposed cyclic stress-strain model for laterally supported reinforcing bars is expected to serve as a fundamental model for predicting the seismic behavior of FRP-strengthened RC cylinders with widely-spaced transverse ties under cyclic axial compression, in which case the local buckling of reinforcing bars usually occurs between two adjacent transverse ties.

Finite Element Modeling of Compressive and Splitting Tensile Behavior of Plain Concrete and Steel Fiber Reinforced Concrete Cylinder Specimens

Plain concrete and steel fiber reinforced concrete (SFRC) cylinder specimens are modeled in the finite element (FE) platform of ANSYS 10.0 and validated with the experimental results and failure patterns. Experimental investigations are conducted to study the increase in compressive and tensile capacity of cylindrical specimens made of stone and brick concrete and SFRC. Satisfactory compressive and tensile capacity improvement is observed by adding steel fibers of 1.5% volumetric ratio. A total of 8 numbers of cylinder specimens are cast and tested in 1000 kN capacity digital universal testing machine (UTM) and also modeled in ANSYS. The enhancement of compressive strength and splitting tensile strength of SFRC specimen is achieved up to 17% and 146%, respectively, compared to respective plain concrete specimen. Results gathered from finite element analyses are validated with the experimental test results by identifying as well as optimizing the controlling parameters to make FE models. Modulus of elasticity, Poisson’s ratio, stress-strain behavior, tensile strength, density, and shear transfer coefficients for open and closed cracks are found to be the main governing parameters for successful model of plain concrete and SFRC in FE platform. After proper evaluation and logical optimization of these parameters by extensive analyses, finite element (FE) models showed a good correlation with the experimental results.

Finite Element Modelling of Steel Corrosion in Reinforced Concrete Cylinders

Corrosion of reinforcement steel is a major factor affecting the deterioration of reinforced concrete structures. During corrosion, steel undergoes several phases of chemical reactions with consequent variation in steel section geometry and mechanical properties. At ultimate corrosion stage, the effective cross section area of steel is reduced with equivalent decrease in load carrying capacity leading to unsafe structures. During initial phase of corrosion, chemical reactions generate new products which irregularly increase steel bar diameters. The resulted products induce additional stresses on the structural member, causing cracking and spalling of the concrete cover, and subsequently faster deteriorate the member strength. This paper presents the effect of the induced stresses of corrosion products on concrete cracking experimentally and numerically. Experimentally several pull-out specimens were tested to identify the effect of corrosion at different stages, and, numerically, a two dimensional finite element model was developed to study the crack initiation and propagation in concrete using nonlinear analysis and specific properties for both steel and concrete elements.

Structural Behavior of RC Cylinders Confined with High Strength Transverse Reinforcement

The number of high-rise reinforced concrete (RC) buildings is steadily increasing since 1980’s. The use of high strength concrete is indispensible for high-rise RC construction to ensure sufficient strength of the structure. The effect of high strength concrete can be significantly improved by the use of high strength and large size reinforcing bars. The yield strength of transverse reinforcement is limited in the current design codes to prevent possible sudden concrete failure due to over reinforcement. This paper presents the effects of the yield strength of transverse reinforcement and compressive strength of concrete on the structural behavior of reinforced concrete cylinders. Two parameters were considered in this investigation: compressive strength of concrete and the yield strength of transverse reinforcement (472MPa, 880MPa, and 1,430 MPa). Analytical and experimental results indicated that the structural behavior of RC cylinders confined with high strength transverse reinforcement is strongly influenced by compressive strength of concrete.

FRP-confined Concrete Cylinders: Axial Compression Experiments and Strength Model

The present article deals with the analysis of experimental results, in terms of load-carrying capacity and strain, obtained from tests on plain- and reinforced-concrete (RC) cylinders strengthened with external carbon-fiber-reinforced polymer (CFRP). The parameters considered are the number of composite layers and the compressive strength of unconfined concrete. The effective circumferential FRP failure strain and the effect of the effective lateral confining pressure were investigated. In total, 30 cylinders were subjected to axial compression, which included control specimens. All the test specimens were loaded to failure in axial compression and the behavior of the specimens in the axial and transverse directions was investigated. Test results showed that the CFRP wrap increases the strength and ductility of plain- and RC cylinders significantly. A simple model is presented to predict the compressive strength and axial strain of FRP-confined columns.

Size Effect on Compressive Strength of Plain and Spirally Reinforced Concrete Cylinders

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Splitting Tensile Strength of Steel Fiber Reinforced Concrete Cylinders Consolidated by Rodding or Vibrating

The relative strength of rodded and externally vibrated steel fiber reinforced concrete cylinders are compared for both standard compression and split-cylinder tension tests. Fiber concentrations ranged from 0 to 8 percent by weight of concrete. Test results of this pilot program indicate that external vibration increased the split-cylinder tensile strength by as much as 20% over that of standard rodded cylinders. The tests also provided some data on the effect the addition of steel fibers has on the split-cylinder tensile and compressive strength of concrete.

Simplified Stress Analysis of Heated Reinforced Concrete Cylinders

Simplified Stress Analysis of Heated Reinforced Concrete Cylinders