• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.1
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• pp.42-50
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• 1987

The energy expressions are formulated for the axially stiffened shell treating the stiffeners as discrete elements. The principle of minimum potential energy is employed to formulate the buckling equations for a simply supported, axially stiffened shell under uniform axial compression. The displacement functions are expended into double trigonometric series. The mode assuming method employed in this paper makes it possible to reduce the matrix size of the eigenvalue problem considerably. Effects are made to investigate the transition from overall buckling to local buckling and to verify the existence of the minimum stiffness ratio of stiffener as in the case of stiffened plate. The results of the calculation show that the critical stiffener size increase linearly as the length of the shell increases. The results also show that the overall buckling load decreases and the local buckling load has a nearly constant value as the length of the shell increases. The results show very good agreements with other computational available.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.2059-2065
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• 2008

In this paper, quasi-static crushing tests of composite circular tubes under axial compression load are conducted to investigate the energy absorption characteristics. Circular tubes used for this experiment are glass/epoxy (GFRP) composite tubes, which is fabricated by the filament winding method. One edge of the composite tube is chamfered to reduce the initial peak load and to prevent catastrophic failure during crushing process. Two suggested trigger mechanisms for the composite tubes are investigated. Crushing modes are mainly affected by thickness/diameter ratio, and average crushing loads are mainly affected by their cross-sections. Energy absorption characteristics vary significantly as a function of the tube geometry, trigger mechanism, t/D ratio and the cross-sectional shape.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2000.11a
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• pp.157-160
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• 2000

In author's previous paper, a finite element algorithm was presented to calculate the buckling and crippling stresses of composite laminated stringers. In this study, for the validation of the finite element analysis, Z-section composite stringers of different lengths and flange-widths were tested in axial compression. The stacking sequence of graphite/epoxy is [$\pm$45/0/90]s. Strain gages were attached to each specimen to get the strain response. Deflection and end-shortening were obtained by a displacement transducer. The buckling and crippling loads are determined from the strain response, load vs. end-shortening curves, and load vs. out-of-plane deflection curves. Comparison between finite element and experimental results shows good agreement in the buckling, local buckling, and crippling stresses.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.27 no.2
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• pp.9-15
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• 2019

The initial buckling of thin walled structures does not result in immediate failure. This post buckling capability is used to achieve light weight design, and final failure of thin walled structure is called crippling. To predict the failure load, empirical methods are often used for thin walled structures in design stage. But empirical method accuracy depend on geometry. In this study, experimental, empirical and numerical study of the crippling behavior of I-section beam made of carbon-epoxy are performed. The progressive failure analysis model to simulate the crippling failure is evaluated using the test results. In this study, commercial software LS-DYNA is utilized to compute the collapse load of composite specimen. Six kinds of specimens were tested in axial compression where correlation between analytical and experimental results has performed. From the results, we have partially conclude that the flange width-to-thickness ratio is found to influence the accuracy of empirical and numerical method.

• Structural Engineering and Mechanics
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• v.76 no.4
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• pp.465-477
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• 2020

This paper presents an investigation on the dynamic behavior of SRC columns with built-in cross-shaped steels under impact load. Seven 1/2 scaled SRC specimens were subjected to low-speed impact by a gravity drop hammer test system. Three main parameters, including the lateral impact height, the axial compression ratios and the stirrup spacing, were considered in the response analysis of the specimens. The failure mode, deformation, the absorbed energy of columns, as well as impact loads are discussed. The results are mainly characterized by bending-shear failure, meanwhile specimens can maintain an acceptable integrity. More than 33% of the input impact energy is dissipated, which demonstrates its excellent impact resistance. As the impact height increases, the flexural cracks and shear cracks observed on the surface of specimens were denser and wider. The recorded time-history of impact force and mid-span displacement confirmed the three stages of relative movement between the hammer and the column. Additionally, the displacements had a notable delay compared to the rapid changes observed in the measured impact load. The deflection of the mid-span did not exceed 5.90mm while the impact load reached peak value. The impact resistance of the specimen can be improved by proper design for stirrup ratios and increasing the axial load. However, the cracking and spalling of the concrete cover at the impact point was obvious with the increasing in stiffness.

• Structural Engineering and Mechanics
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• v.70 no.1
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• pp.13-31
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• 2019

A nonlinear finite element model (FEM) using ATENA-3D software to simulate the axially compressive behavior of circular steel tube confined concrete (CSTCC) columns infilled with ultra high performance concrete (UHPC) was presented in this paper. Some modifications to the material type "CC3DNonlinCementitious2User" of UHPC without and with the incorporation of steel fibers (UHPFRC) in compression and tension were adopted in FEM. The predictions of utimate strength and axial load versus axial strain curves obtained from FEM were in a good agreement with the test results of eighteen tested columns. Based on the results of FEM, the load distribution on the steel tube and the concrete core was derived for each modeled column. Furthermore, the effect of bonding between the steel tube and the concrete core was clarified by the change of friction coefficient in the material type "CC3DInterface" in FEM. The numerical results revealed that the increase in the friction coefficient leads to a greater contribution from the steel tube, a decrease in the ultimate load and an increase in the magnitude of the loss of load capacity. By comparing the results of FEM with experimental results, the appropriate friction coefficient between the steel tube and the concrete core was defined as 0.3 to 0.6. In addition to the numerical evaluation, eighteen analytical models for confined concrete in the literature were used to predict the peak confined strength to assess their suitability. To cope with CSTCC stub and intermediate columns, the equations for estimating the lateral confining stress and the equations for considering the slenderness in the selected models were proposed. It was found that all selected models except for EC2 (2004) gave a very good prediction. Among them, the model of Bing et al. (2001) was the best predictor.

• Steel and Composite Structures
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• v.42 no.4
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• pp.513-538
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• 2022

This paper reports on experiments addressing the buckling and collapse behavior of an innovative built-up cold-formed steel (CFS) columns. The built-up column consists of four individual CFS lipped channels, two of them placed back-to-back at the web using two self-drilling screw fasteners at specified spacing along the column length, while the other two channels were connected flange-to-flange using one self-drilling screw fastener at specified spacing along the column length. In total, 12 experimental tests are reported, covering a wide range of column lengths from stub to slender columns. The initial geometric imperfections and material properties were determined for all test specimens. The effect of screw spacing, load-versus axial shortening behaviour and buckling modes for different lengths and screw spacing were investigated. Nonlinear finite element (FE) models were also developed, which included material nonlinearities and initial geometric imperfections. The FE models were validated against the experimental results, both in terms of axial capacity and failure modes of built-up CFS columns. Furthermore, using the validated FE models, a parametric study was conducted which comprises 324 models to investigate the effect of screw fastener spacing, thicknesses and wide range of lengths on axial capacity of back-to-back and flange-to-flange built-up CFS channel sections. Using both the experimental and FE results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australia/New Zealand (AS/NZS) standards is slightly conservative by 6% on average, while determining the axial capacity of back-to-back and flange-to-flange built-up CFS channel sections.

• Structural Engineering and Mechanics
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• v.86 no.3
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• pp.399-415
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• 2023

This paper presents the experimental and numerical evaluations on the circular SFRC columns reinforced GFRP rebars under the axial compressive loading. The test programs were designed to inquire and compare the effects of different parameters on the columns' structural behavior by performing experiments and finite element modeling. The research variables were conventional concrete (CC), fiber concrete (FC), types of longitudinal steel/GFRP rebars, and different configurations of lateral rebars. A total of 16 specimens were manufactured and categorized into four groups based on different rebar-concrete arrangements including GRCC, GRFC, SRCC, and SRFC. Adding steel fibers (SFs) into the concrete, it was essential to modify the concrete damage plastic (CDP) model for FC columns presented in the finite element method (FEM) using ABAQUS 6.14 software. Failure modes of the columns were similar and results of peak loads and corresponding deflections of compression columns showed a suitable agreement in tests and numerical analysis. The behavior of GFRP-RC and steel-RC columns was relatively linear in the pre-peak branch, up to 80-85% of their ultimate axial compressive loads. The axial compressive loads of GRCC and GRFC columns were averagely 80.5% and 83.6% of axial compressive loads of SRCC and SRFC columns. Also, DIs of GRCC and GRFC columns were 7.4% and 12.9% higher than those of SRCC and SRFC columns. Partially, using SFs compensated up to 3.1%, the reduction of the compressive strength of the GFRP-RC columns as compared with the steel-RC columns. The effective parameters on increasing the DIs of columns were higher volumetric ratios (up to 12%), using SFs into concrete (up to 6.6%), and spiral (up to 5.5%). The results depicted that GFRP-RC columns had higher DIs and lower peak loads compared with steel-RC columns.

• Geomechanics and Engineering
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• v.5 no.6
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• pp.499-517
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• 2013

In order to investigate shear behavior of granular materials due to excavation and associated unloading actions, load-controlled plane strain compression tests under decreasing confining pressure were performed under drained conditions and the results were compared with the conventional plane strain compression tests. Four types of granular material consisting of two quartz sands and two glass beads were used to investigate particle shape effects. It is clarified that macro stress-strain behavior is more easily influenced by stress level and stress path in sands than in glass beads. Development of localized deformation was analyzed using photogrammetry method. It was found that shear bands are generated before peak strength and shear band patterns vary during the whole shearing process. Under the same test condition, shear band thickness in the two sands was smaller than that in one type of glass beads even if the materials have almost the same mean particle size. Shear band thickness also decreased with increase of confining pressure regardless of particle shape or size. Local maximum shear strain inside shear band grew approximately linearly with global axial strain from onset of shear band to the end of softening. The growth rate is found related to shear band thickness. The wider shear band, the relatively lower the growth rate. Finally, observed shear band inclination angles were compared with classical Coulomb and Roscoe solutions and different results were found for sands and glass beads.

• KCI Concrete Journal
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• v.11 no.3
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• pp.5-17
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• 1999

In recent years. the concept of the modified compression field theory (MCFT) was develped and applied to the analysis of reinforced concrete beams subjected to shear, moment, and axial load. Although too complex for regular use in the shear design or beams. the procedure has value in its ability to provide a rational method of anlysis and design for reinforced concrete members. The objective of this paper is to review the MCFT and apply it for the prediction of the response and shear strength of reinforced concrete beams A Parametric analysis was Performed on a reinforced T-section concrete beam to evaluate and compare the effects of concrete strength. longitudinal reinforcement ratio shear reinforcement ratio, and shear span to depth ratio in two different approaches the MCFT and the ACI code. The analytical study showed that the concrete contribution to shear strength by the MCFT was higher than the one by the ACI code in beams without stirrups, while it was lower with stirrups. On the other hand. shear reinforcement contribution predicted by the MCFT was much higher than the one by the ACI code. This is because the inclination angle of shear crack is much smaller than 45$^{\circ}$assumed in the ACI code.