• Journal of the Korea Concrete Institute
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• 제28권2호
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• pp.129-139
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• 2016

Cast-in-place concrete-filled hollow PC (HPC) columns are used to reduce lifting load of heavy-weight PC columns and to improve the structural integrity of joints. In the present study, a new type of HPC column was proposed to improve the productivity and structural integrity of the concrete. To form the hollow PC columns, a permanent inner form was prefabricated using structural deck plates and penetrated lateral bars. Half-scale specimens of four HPC columns were tested under combined axial compression and lateral cyclic loading to evaluate the seismic resistance. In the design of test specimens, various parameters such as the spacing of lateral re-bars, the use of steel fiber, and the thickness of PC cover were considered. The test results showed that the proposed HPC columns generally exhibited satisfactory load-carrying capacity and deformation capacity without brittle failure of PC. If closely spaced hoops or fiber reinforcements are used for PC, the deformation capacity can be improved further by restraining PC spalling.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제7권2호
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• pp.29-36
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• 1987

In most of the structural members with initial cracks, the strength tends to decrease as the member size increases. This phenomenon is known as size effect. Among the structural materials of glass, metal or concrete, etc., concrete represents the size effect even without initial crack. According to the previous size effect law, the concrete member of very large size can resist little stress. Actually, however, even the large size member can resist some stress if there is no initial notch. This means that the fracture mechanism of very small or very large size member follows strength criterion, but the medium size member follows non-linear fracture mechanics (NLFM). In this study, the empirical models which are derived based on nonlinear fracture mechanics are proposed according to the regression analysis with the existing test data of large size specimens for uni-axial compression test, splitting tensile test and shear test of reinforced concrete beams.

• Journal of the Earthquake Engineering Society of Korea
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• 제19권4호
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• pp.195-205
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• 2015

Various non-seismic tie details are frequently used for one- and two-story small buildings because the seismic demand on their deformation capacities is not relatively significant. To evaluate the effects of the non-seismic tie details on the seismic performance of reinforced concrete columns, six square columns with a cross section of $400{\times}400mm$ and six rectangular columns with a cross section of $250{\times}640mm$ were tested. The anchorage details at both ends and spacing of tie hoops, along with the cross-sectional shape and the magnitude of axial load, were considered as the primary test parameters. Test results showed that square columns had higher stiffness and lower lateral deformation rather than rectangular columns. Both lap spliced tie and U-shaped tie provided comparable or improved seismic performance to $90^{\circ}$ hook tie in terms of maximum strength, ductility, and energy dissipation. The predicted curves with modeling parameters in ASCE41-13 were conservative for test results of lap spliced tie and U-shaped tie specimens since plastic behavior after flexural yielding could not be considered. For economical design, ASCE41-13 should be revised with various test results of tie details.

• Smart Structures and Systems
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• 제30권1호
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• pp.49-62
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• 2022

Experimental and discrete element methods were used to investigate the effects of triple joints lengths and triple joint angle on the failure behavior of rock mass under uniaxial compressive test. Concrete samples with dimension of 20 cm × 20 cm × 5 cm were prepared. Within the specimen, three imbedded joint were provided. The joint lengths were 2 cm, 4cm and 6 cm. In constant joint lengths, the angle between middle joint and other joints were 30°, 60°, 90°, 120° and 150°. Totally 15 different models were tested under compression test. The axial load rate on the model was 0.05 mm/min. Concurrent with experimental tests, the models containing triple joints, length and joint angle are similar to the experiments, were numerical by Particle flow code in two dimensions (PFC2D). Loading rate in numerical modelling was 0.05 mm/min. Tensile strength of material was 1 MPa. The results show that the failure behaviors of rock samples containing triple joints were governed by both of the angle and the length of the triple joints. The uniaxial compressive strengths (UCS) of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. Furthermore, it was shown that the compressive behavior of discontinuities is related to the number of the induced tensile cracks which are increased by decreasing the joint length. Along with the damage failure of the samples, the acoustic emission (AE) activities are excited. There were only a few AE hits in the initial stage of loading, then AE hits rapidly grow before the applied stress reached its peak. In addition, every stress drop was accompanied by a large number of AE hits. Finally, the failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

• Transactions of the Korean Society of Mechanical Engineers
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• 제11권3호
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• pp.454-464
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• 1987

The objective of this research is to analyze and evaluate the dynamic flow curve of metals under impact loading at both high strain rate (.epsilon.=1/h dh/dt > 10$\^$3/m/s/m) and large strain (.epsilon.=In h/h$\_$0/ > 1.0). A test method for dynamic compression of metal disc is described. The velocity of the striker face and the force on the anvil are measured during the impact period. From these primitive data the axial stress, strain, and strain rate of the disc are obtained. The Strain rate is determined by the striker velocity divided by the specimen height. This gives a slightly increasing strain rate over most of the deformation period. Strain rates of 100 to 10,000 per second are achieved. Attainable final strains are 150%. A discussion of several problem areas is presented. The friction on the specimen surfaces, the determination of the frictional coefficient, the influence of the specimen geometry (h$\_$0//d$\_$0/ ratio) on the friction effect, the lock-up condition for a given configuration, the friction correction factor, and the evaluation of several lubricants are given. The flow function(stress verus strain) is dependent on the material condition(e.g., prior cold work), specimen geometry, strain rate, and temperature.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제29권5A호
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• pp.519-529
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• 2009

Fiber reinforced composite materials have various advantages in mechanical and chemical aspects. Not only high fatigue and chemical resistance, but also high specific strength and stiffness are attained, and therefore, damping characteristics are beneficial to marine piles. Since piles used for marine structures are subjected to compression and bending as well, detailed research is necessary. Current study examine the mechanical behavior under flexural and/or compressive loads using concrete filled fiber reinforced plastic composite piles, which include large size diameter. 25 pile specimens which have various size of diameters and lengths were fabricated using hand lay-up or filament winding method to see the effect of fabrication method. The inner diameters of test specimens ranged from 165 mm to 600 mm, and the lengths of test specimens ranged from 1,350 mm to 8,000 mm. The strengths of the fill-in concrete were 27 and 40 MPa. Fiber volumes used in circumferential and axial directions are varied in order to see the difference. For some tubes, spiral inner grooves were fabricated to reduce shear deformation between concrete and tube. It was observed that the piles made using filament winding method showed higher flexural stiffness than those made using hand lay-up. The flexural stiffness of piles decreases from the early loading stage, and this phenomenon does not disappear even when the inner spiral grooves were introduced. It means that the relative shear deformation between the concrete and tube wasn't able to be removed.

• Journal of the Korean Geosynthetics Society
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• 제19권1호
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• pp.93-101
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• 2020

In order to predict the nonlinear behaviour of the soil, the elasto-plastic hyperbolic model was selected, which was considered to be relatively simple and highly predictable. The soil parameter determination and the behavior analysis program were developed by formalizing the functions related to the constitutive model. Each soil parameter was determined from the results of the drained triaxial compression tests of Baekma river sand with the change of relative density. The stress-strain behavior was predicted using the soil parameters determined under each condition. As a result, the deviator stress for the axial strain is verified to have a good match between the measured value and predicted value at each relative density. In the relationship between the volumetric stain and the axial strain, when the relative density is loose, the measured value and predicted value tend to match, and when relative density is dense, the predicted value of the volumetric strain appears somewhat smaller than the measured value due to the limitation of the constitutive model.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제28권6A호
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• pp.861-872
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• 2008

Concrete-filled glass fiber reinforced polymer tubes are often used for marine structures with the benefit of good durability and high resistance against corrosion under severe chemical environment. Current research presents results of a comprehensive experimental investigation on the behavior of axially loaded circular concrete-filled glass fiber reinforced polymer tubes. This paper is intended to examine several aspects related to the usage of glass fiber fabrics and filament wound layers used for outer shell of piles subjected to axial compression. The objectives of the study are as follows: (1) to evaluate the effectiveness of filament winding angle of glass fiber layers (2) to evaluate the effect of number of GFRP layers on the ultimate load and ductility of confined concrete (3) to evaluate the effect of loading condition of specimens on the effectiveness of confinement and failure characteristics as well, and (4) to propose a analytical model which describes the stress-strain behavior of the confined concrete. Three different types of glass fiber layers were chosen; fabric layer, ${\pm}45^{\circ}$ filament winding layer, and ${\pm}85^{\circ}$ filament winding layer. They were put together or used independently in the fabrication of tubes. Specimens that have various L:D ratios and different diameters have also been tested. Totally 27 GFRP tube specimens to investigate the tension capacity, and 66 concrete-filled GFRP tube specimens for compression test were prepared and tested. The behavior of the specimens in the axial and transverse directions, failure types were investigated. Analytical model and parameters were suggested to describe the stress-strain behavior of concrete under confinement.

• Journal of Mechanical Science and Technology
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• 제16권11호
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• pp.1412-1419
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• 2002

Dynamic shear tests for the tough-pitch copper at high strain and high strain rate was performed. The Split Hopkinson Pressure Bar (SHPB) compression test system was modified to yield a shear deformation in the specimen. Hat-shaped specimens for the tough-pitch copper were adopted to generate high strain of γ=3～4 and high strain-rate of γ= 10$^4$/s. The dynamic analysis by ABAQUS 5.5/EXPLICIT code verified that shear zone can be localized in hat-shaped specimens. A proper impact velocity and the axial length of the shear localization region wert determined through the elastic wave analysis. The displacement in a hat-shaped specimen is limited by a spacer ring which was installed between the specimen and the incident bar. The shear bands were obtained by measuring the direction of shear deformation and the width of deformed grain in the shear zone. The decrease of specimen length has been measured on the optical displacement transducer. Dynamic shear stress-strain relations in the tough-pitch copper were obtained at two strain-rates.

• Magazine of the Korea Concrete Institute
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• 제11권2호
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• pp.157-165
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• 1999

When the ultimate strength of a concrete flexural member is evaluated, the effect of member size is usually not considered. For various types of loading, however, the strength always decreases with the increment of member size. In this paper the size effect of a flexural compression member is investigated by experiments. For this purpose, a series of C-shaped specimens subjected to axial compressive load and bending moment was tested using three different sizes of specimens with a compressive strength of 528 kg/$cm^2$. According to test results the size effect on flexural compressive strength was apparent, and more distinct than that for uniaxial compressive strength of cylinders. Finally a model equation was derived using regression analyses with experimental data.