• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.25-35
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• 2012

For a member subjected to direct shear forces, forces are transferred across interface concrete area and resisted by shear transfer capacity. Shear-friction equations in recent concrete structural design provisions are derived from experimental test results where shear-friction capacity is defined as a function of steel reinforcement area contained in the interface. This empirical equation gave too conservative values for concrete members with large amounts of reinforcement. This paper presents a method to evaluate shear transfer strengths and to define ultimate conditions which result in crushing of concrete struts after yielding of longitudinal reinforcement perpendicular to the interface concrete. This method is based on the bi-axial stress field theory where different constitutive laws are applied in various means to gain accurate shear strengths by considering softening effects of concrete struts based on the modified compression-field theory and the softened truss model. The validity of the proposed method is examined by applying to some selected test specimens in literatures and results are compared with recent design code provisions. A general agreement is observed between predicted and measured values at ultimate loading stages in initially uncracked normal-strength concrete test.

• Journal of Biosystems Engineering
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• v.41 no.3
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• pp.153-160
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• 2016

Purpose: This study was conducted to experimentally investigate the structural safety of and identify critical locations in a front-end loader under impact loads. Methods: Impact and static tests were conducted on a commonly used front-end loader mounted on a tractor. In the impact test, the bucket of the front-end loader with maximum live load was raised to its maximum lift height and was allowed to free fall to a height of 500 mm above the ground where it was stopped abruptly. For the static test, the bucket with maximum live load was raised and held at the maximum lift height, median height, and a height of 500 mm from the ground. Strain gages were attached at twenty-three main locations on the front-end loader, and the maximum stresses and strains were measured during respective impact and static tests. Results: Stresses and strains at the same location on the loader were higher in the impact test than in the static test, for most of measurement locations. This indicated that the front-end loader was put under a severe environment during impact loading. The safety factors for stresses were higher than 1.0 at all locations during impact and static tests. Conclusions: Since the lowest safety factor was higher than 1.0, the front-end loader was considered as structurally safe under impact loads. However, caution must be exercised at the locations having relatively low safety factors because failure may occur at these locations under high impact loads. These important design locations were identified to be the bucket link elements and the connection elements between the tractor frame and front-end loader. A robust design is required for these elements because of their high failure probability caused by excessive impact stress.

• Journal of the Korean GEO-environmental Society
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• v.13 no.6
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• pp.5-17
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• 2012

The study of surface ground reinforcing method is supposed to be considered preferentially is not satisfied and also doesn't contemplate plastic flow because of repetitive drive of construction equipment. Also, Terzaghi's bearing-capacity equation and Yamanouchi's suggestion have been used to design the surface reinforcement, but most engineers depend on their experience and cases constructed before because of dispersed variables and inappropriate bearing-capacity factors. Hence, plate load test and repetitive plate load test were performed in the field which is reinforced with geotextile, Geogrid whose tensile strength are 200kN/m, 100kN/m and bamboo($0.4m{\times}0.4m$). The object of this study is to evaluate bearing capacity and behaviour of surface ground and to compare each reinforcement form test results. From the results bearing capacity ratio increased by a maximum of 1.5 times with bamboo reinforcement method comparing to others.

• Earthquakes and Structures
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• v.8 no.3
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• pp.619-637
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• 2015

A field based non-destructive hardness method is being developed to determine plastic strain in steel elements subjected to seismic loading. The focus of this study is on the active links of eccentrically braced frames (EBFs). The 2010/2011 Christchurch earthquake series, especially the very intense February 22 shaking, which was the first earthquake worldwide to push complete EBF systems into their inelastic state, generating a moderate to high level of plastic strain in EBF active links for a range of buildings from 3 to 23 storeys in height. Plastic deformation was confined to the active links. This raised two important questions: what was the extent of plastic deformation and what effect does that have on post-earthquake steel properties? A non-destructive hardness test method is being used to determine a relationship between hardness and plastic strain in active link beams. Active links from the earthquake affected, 23-storey Pacific Tower building in Christchurch are being analysed in the field and laboratory. Test results to date show clear evidence that this method is able to give a good relationship between plastic strain and demand. This paper presents significant findings from this project to investigate the relationship between hardness and plastic strain that warrant publication prior to the completion of the project. Principal of these is the discovery that hot rolled steel beams carry manufacturing induced plastic strains, in regions of the webs, of up to 5%.

• Journal of Biosystems Engineering
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• v.27 no.1
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• pp.11-18
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• 2002

One of the major obstructing factors against managing dairy farm in Korea has been a shortage of roughage supply, which resulted in excessive abuse of concentrate feed. In order to solve this problem, production of the wrap silage by the winter cereal forages raised in the fallow paddy field is strongly recommended in Korea. The main objective is to develop a tractor attached round bale wrapper which can process the silage by wrapping the round bales with thin plastic films. This is the first half of the study which is divided by two parts. In this first part, bale wrapping process was analyzed, and based on this results the followings were designed, developed and tested. 1. Bale wrapper which haying the maximum capacity of 1 ton bale with various functions such as loading, wrapping, discharging the round bales and supplying and cutting wrap films was designed. 2. An actuator and its hydraulic circuit of each process were developed and tested. 3. Also, the variations of hydraulic pressure and engine speed were investigated by operating bale wrapper developed. In this test, maximum pressure of the hydraulic circuit for the bale wrapping was 130 kg/㎠ when it raised the bale, which was quite below the relief pressure of 170 kg/㎠ of hydraulic circuit. In the engine speed test, speed drop was 20∼67 rpm, which meant that there was no over-load operation. Therefore, the experiment proved that developed hydraulic circuit and mechanism is stable in bale wrapping operation

• Geomechanics and Engineering
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• v.34 no.5
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• pp.577-595
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• 2023

A dynamic triaxial discrete element numerical model of lightweight soil was established using the discrete element method to study the microscopic mechanism of expanded polystyrene (EPS) particles in the soil under cyclic loading. The microscopic parameters of the discrete element model of the lightweight soil were calibrated depending on the dynamic triaxial test hysteresis curves. Based on the calibration results, the effects of the EPS particles volume ratio and amplitude on the contact force, displacement field, and velocity field of the lightweight soil under different accumulated strains were studied. The results showed that the hysteresis curves of lightweight soil exhibit nonlinearity, hysteresis, and strain accumulation. The strain accumulated in remolded soil is mainly tensile strain, and that in lightweight soil is mainly compressive strain. As the volume ratio of EPS particles increased, the contact force first increased and then decreased, and the displacement and velocity of the particles increased accordingly. With an increase in amplitude, the dynamic stress of the particle system increased, and the accumulation rate of the dynamic strain of the samples also increased. At 5% compressive strain, the contact force of the particles changed significantly and the number of particles deflected in the direction of velocity also increased considerably. These results indicated that the cemented structure of the lightweight soil began to fail at a compressive strain of 5%. Thus, a compressive strain of 5% is more reasonable than the dynamic strength failure standard of lightweight soil.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.3A
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• pp.429-437
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• 2006

Existing basic mechanical models which are methods characterizing viscoelastic materials were first reviewed to account for viscoelastic behavior of the asphalt pavement structure in this paper. A viscoelastic mechanical model considering a single load of vehicles subsequently was suggested and an equation that indicates the time-dependant behavior of asphalt pavements was derived from the proposed model. Non-destructive tests using falling weight deflectometer(FWD) were performed for a test section to estimate the application of the model. Both deflections and strains procured by the equation were compared to testing results according to loading history. By observing field measurements and theoretical evaluations, if two results are compared by the features of deflection according to time history, it could be concluded that the proposed model is expected to be suitable for prediction of the behavior of asphalt pavements because there is hardly difference between field data and calculated data.

• Journal of the Korea Concrete Institute
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• v.29 no.1
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• pp.23-32
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• 2017

The joints between precast PSC slabs of the intermediate road slab in double deck tunnel are inevitably generated in the road traffic vehicle traveling direction. Therefore, it is important to make the behavior of parts on the joint in one piece. The imtermediate road slab system of double deck tunnel in great depth proposed in this study will be constructed with precast PSC slab in order to minimize the construction period. And the joint connection between the precast slab has been developed in two methods: the 'Transverse tendon reinforcement method' and 'High strength bolts connection method'. Also, the experiments were performed for the full scale model in order to evaluate the performance of the intermediate road deck slab with two type joints systems, the structural stability was verified through the F.E.M analsysis. The results of static loading test and F.E.M analysis investigated a very stable behavior of intermediate road deck slab in double deck tunnel applying the joint methods developed in this study, in the cracks and deflections to satisfy the design standards of Highway Roads Bridges (2011), it was determined that there is no problem even servicebility.

• Journal of the Korean Geosynthetics Society
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• v.13 no.2
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• pp.31-39
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• 2014

The helical pile is a manufactured steel pile consisting of one or more helix-shaped bearing plates affixed to a central shaft. This pile is installed by rotating the shaft into the ground to support structural loads. The advantages of helical piles are no need for boring or grout process, and ability to install with relatively light devices. The bearing capacity of the helical pile is exerted by integrating the bearing capacity of each helix plate attached to the steel shaft. In this paper, to estimate the bearing capacity of moderate-size helical piles, 6 types of helical piles were constructed with different shaft diameter, plate configuration and the penetration depth. A series of field loading tests was performed to evaluate the effect of helical pile configuration on the bearing capacity of helical pile, constructed in two different shaft diameters (i.e. 73 mm and 114 mm). In the same way, the diameter of bearing plate was also changed from 400mm to 250mm with one or three plates. As well, the penetration depth was varied from 3m to 6m to analyze the relation between the penetration depth and the bearing capacity. As a result, not only the increase of the shaft diameter, but also the number or diameter of helix bearing plates enhances the bearing capacity. Especially the configuration of the helix plate is more critical than the shaft diameter.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.247-256
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• 2003

FEM analyses which are based on modified Cam-clay theory have been generally used in such cases as analyses of stability and displacement fur embankment construction on soft clays. However, the Modified Cam Clay Model can generate some problems in anisotropic stress conditions of field because the critical state theory has been developed through many laboratory tests in isotropic conditions. Thus, the applicability on the prediction of undrained shear strength and pore water pressure which was based on the critical state theory was evaluated by triaxial tests and numerical analyses in isotropic and anisotropic conditions. Used samples often come out in domestic area, together with general low plastic clays which are showing dilatant behavior in shearing process. They were evaluated by laboratory tests and FEM based on MCCM. From the results of test and numerical analysis, the predictions of undrained strength in low plastic clays well coincided with each other in both isotropic and anisotropic conditions. However, the generation of porewater pressure was often overestimated during undrained shearing in anisotropic conditions. The results can generate the errors in the prediction of stress path of field sites during loading such as construction of embankment on soft clays because the field is subjected to anisotropic conditions during loading.