• Steel and Composite Structures
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• v.22 no.3
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• pp.497-520
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• 2016

The confined concrete stress-strain curves utilised in computational models of concrete-filled steel tubular (CFST) columns can have a significant influence on the accuracy of the predicted behaviour. A generic model is proposed for predicting the stress-strain behaviour of confined concrete in short circular, elliptical and octagonal CFST columns subjected to axial compression. The finite element (FE) analysis is carried out to simulate the concrete confining pressure in short circular, elliptical and octagonal CFST columns. The concrete confining pressure relies on the geometric and material parameters of CFST columns. The post-peak behaviour of the concrete stress-strain curve is determined using independent existing experimental results. The strength reduction factor is derived for predicting the descending part of the confined concrete behaviour. The fibre element model is developed for the analysis of circular, elliptical and octagonal CFST short columns under axial loading. The FE model and fibre element model accounting for the proposed concrete confined model is verified by comparing the computed results with experimental results. The ultimate axial strengths and complete axial load-strain curves obtained from the FE model and fibre element model agree reasonably well with experimental results. Parametric studies have been carried out to examine the effects of important parameters on the compressive behaviour of short circular, elliptical and octagonal CFST columns. The design model proposed by Liang and Fragomeni (2009) for short circular, elliptical and octagonal CFST columns is validated by comparing the predicted results with experimental results.

• Advances in concrete construction
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• v.11 no.5
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• pp.357-365
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• 2021

High deformable concrete (HDC) elements have compressive strength rates equal to conventional concrete and have got a high compressive strain at about 20% to 50%. These types of concrete elements as prefabricated parts have an abundance of applications in the construction industry which is the most used in the construction of tunnels in squeezing grounds, tunnel passwords from fault zones or swelling soils as soft supports. HDC elements after reaching to compressive yield stress, in nonlinear behavior have hardening combined with increasing strain and compressive strength. The main aim of this laboratory and numerical research is to construct concrete elements with the above properties so the compressive stress-strain behavior of different concrete elements with four categories of mix designs have been discussed and finally one of them has been defined as HDC element mix design. Furthermore, two columns with and without implementing of HDC elements have been made and stress-strain curves of them have been investigated experimentally. An analysis model is presented for columns using finite element method adopted by ABAQUS. The results obtained from the ABAQUS finite element method are compared with experimental data. The main comparison is made for stress-strain curve. The stress-strain curves from the finite element method agree well with experimental results. The results show that the dimension of the HDC samples is significant in the stress-strain behavior. The use of the element greatly increases energy absorption and ductility.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.177-182
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• 2001

Based on the three reinforced concrete panel tests, a softened stress-strain curve of concrete subjected to reversed cyclic loading is proposed. The proposed model consists of seven stages in the compressive zones and six stages in the tensile zones. The proposed model is verified by comparing to the test results.

• Structural Engineering and Mechanics
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• v.69 no.2
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• pp.205-219
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• 2019

This paper analyzes nonlinear free vibration of the circular nano-tubes made of functionally graded materials in the framework of nonlocal strain gradient theory in conjunction with a refined higher order shear deformation beam model. The effective material properties of the tube related to the change of temperature are assumed to vary along the radius of tube based on the power law. The refined beam model is introduced which not only contains transverse shear deformation but also satisfies the stress boundary conditions where shear stress cancels each other out on the inner and outer surfaces. Moreover, it can degenerate the Euler beam model, the Timoshenko beam model and the Reddy beam model. By incorporating this model with Hamilton's principle, the nonlinear vibration equations are established. The equations, including a material length scale parameter as well as a nonlocal parameter, can describe the size-dependent in linear and nonlinear vibration of FGM nanotubes. Analytical solution is obtained by using a two-steps perturbation method. Several comparisons are performed to validate the present analysis. Eventually, the effects of various physical parameters on nonlinear and linear natural frequencies of FGM nanotubes are analyzed, such as inner radius, temperature, nonlocal parameter, strain gradient parameter, scale parameter ratio, slenderness ratio, volume indexes, different beam models.

• Ocean Systems Engineering
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• v.4 no.4
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• pp.309-325
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• 2014

Geotextile tubes are basically a huge sack filled with sand or dredged soil. Geotextile tubes are made of permeable woven or non-woven synthetic fibers (i.e., polyester or PET and polypropylene or PP). The geotextile tubes' performances in strength, dewatering, retaining solid particles and stacked stability have been studied extensively in the past. However, only little research has been done in the observation of the deformation behavior of geotextile tubes. In this paper, a large-scale apparatus for geotextile tube experiment is introduced. The apparatus is equipped with a slurry mixing station, pumping and delivery station, an observation station and a data station. For this study the large-scale apparatus was utilized in the studies regarding the stresses on the geotextile and the deformation behavior of the geotextile tube. Model tests were conducted using a custom-made woven geotextile tubes. Load cells placed at the inner belly of the geotextile tube to monitor the total soil pressure. Strain gauges were also placed on the outer skin of the tube to measure the geotextile strain. The pressure and strain sensors are attached to a data logger that sends the collected data to a desktop computer. The experiment results showed that the maximum geotextile strain occurs at the sides of the tube and the soil pressure distribution varies at each geotextile tube section.

• Journal of the Korean Society of Safety
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• v.26 no.6
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• pp.31-44
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• 2011

This paper has presented a finite element analysis of structural behaviour of box culvert during and after fires. The fire tests were carried out in a furnace on RC slabs using the ISO 834 standard fire curve. The load capacity after cooling of the RC slab that was not loaded during the fire tests was evaluated by means of additional 3 points bending tests. In the past, stress-strain models of concrete under fire loading have been proposed by several researchers. Comparisons are made with the load-displacement relations of RC slabs after fire loading using the existing stress-strain models with temperature, such as Schneider, EUROCODE 2, Lie, Shi and Nan model. By comparing the load-displacement relations, Lie model was found to result in a maximum load about 2.0% higher than that of test. Based on the fire test results of RC slabs, this paper presents an extensive analytical study on the fire response of box culvert during and after fires.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.89-100
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• 1999

The purpose of this study is to develop an analytic model of the concrete column strengthened with laminated CFS, and to provide a basic guideline for the strengthening design by CFS considering orthotropic properties of laminate. In this study, an analytical stress-strain model of laminated CFS is presented based on Tsai-Hill failure criterion. This model has been implemented in an algorithm which can evaluate the confinement effect of CFS. Through this algorithm, the stress-strain relationship of confined concrete is obtained and compared with experimental results of other studies. Using the constitutive relationships, section analyses of concrete column strengthened with CFS are done, and load-moment and load-curvature interaction curves are obtained. In addition, the strengthening effects of CFS according to various laminated angles are analyzed. Analytical results show that the strengthening effects of the strengthened concrete columns are significantly different in compression, flexure, and ductility according to the laminated ways. In compressive direction of principal stress shows the superiority, where an in flexural strengthening effects, [0/90]s does. In the aspect of ductility, [90]s shows the best effect.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.436-449
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• 2017

In this paper, the damage and failure behavior of triaxially braided textile composites was studied using progressive failure analysis. The analysis was performed at both micro and meso-scales through iterative cycles. Stress based failure criteria were used to define the failure states at both micro- and meso-scale models. The stress-strain curve under uniaxial tensile loading was drawn based on the load-displacement curve from the progressive failure analysis and compared to those by test and computational results from reference for verification. Then, the detailed failure initiation and propagation was studied using the verified model for both tensile and compression loading cases. The failure modes of each part of the model were assessed at different stages of failure. Effect of ply stacking and number of unit cells considered were then investigated using the resulting stress-strain curves and damage patterns. Finally, the effect of matrix plasticity was examined for the compressive failure behavior of the same model using elastic, elastic - perfectly plastic and multi-linear elastic-plastic matrix properties.

• Journal of The Korean Society of Agricultural Engineers
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• v.66 no.1
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• pp.15-24
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• 2024

Unlike artificially created homogeneous materials, the process of calculating the elastic modulus of natural soil involves the possibility of errors. Because the stress-strain behavior of soil is nonlinear, the secant modulus of elasticity is often used based on 1/2 of the stress at failure. Since soil has the property of changing its elastic modulus depending on the confining pressure, numerical analysis models that analyze its behavior inevitably include complex elements. The hyperbolic model, which relatively accurately simulates the behavior immediately after loading in soft ground, assumes that the stress-strain curve of the consolidated undrained triaxial test is hyperbolic and requires the slope of the tangent line at the starting point. However, the slope of the initial tangent in the stress-strain curve obtained from an actual triaxial test is difficult to have regularity according to changes in confining pressure. Additionally, due to the characteristics of a hyperbola, even small changes in related factors cause large changes in the hyperbola. Therefore, there is a lot of randomness in the process of calculating model parameters from the triaxial test results, which causes large differences in the results. Therefore, the method of calculating the initial elastic modulus by the consolidation test presented in this study is also used to verify the method by the triaxial test. It can be applied. However, since this study was applied to only one sample showing typical consolidation characteristics, it is necessary to check samples with various physical properties in the future.

• International Journal of Concrete Structures and Materials
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• v.6 no.2
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• pp.79-85
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• 2012

This paper presents the differences in growth of time-dependent strain values in reinforced cement concrete (RCC) and pre-stressed concrete (PSC) flexural members through experiment. It was observed that at any particular age, the time-dependent strain values were less in RCC beams than in PSC beams of identical size and grade of concrete. Variables considered in the study were percentage area of reinforcement, span of members for RCC beams and eccentricity of applied pre-stress force for PSC beams. In RCC beams the time-dependent strain values increases with reduction in percentage area of reinforcement and in PSC beams eccentricity directly influences the growth of time-dependent strain. With increase in age, a non-uniform strain develops across the depth of beams which influence the growth of concave curvature in RCC beams and convex curvature in PSC beams. The experimentally obtained strain values were compared with predicted strain values of similar size and grade of plane concrete (PC) beam using ACI 318 Model Code and found more than RCC beams but less than PSC beams.