• Geomechanics and Engineering
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• v.24 no.1
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• pp.29-42
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• 2021

The utilization of buildings can be improved by extending them vertically. However, the added load of the extension might require building foundations to be underpinned; otherwise, the loads on the foundations might exceed their bearing capacity. In this study, a preloading method was presented aiming at transferring partial loads from existing piles to underpinning piles. A pneumatic-type model preloading device was developed and used to carry out centrifuge experiments to evaluate the load-displacement behavior of piles, the pile-soil interaction during preloading, and the additional loading caused by vertical extension. The results showed that the preloading devices effectively transfer load from existing piles to underpinning piles. In the additional loading test of group piles, the load-sharing ratio of a pile increased with its stiffness. The load-sharing ratio of a preloaded micropile was less than that of a non-preloaded micropile as a result of the reduction in axial stiffness caused by preloading before additional loading. Therefore, a slight reduction of the load-sharing capacity of an underpinning pile should be considered if the preloading method is applied. Further, two full scale preloading devices was developed. The devices preload underpinning piles and thereby produce reaction forces on a reaction frame to jack existing piles upward, thus transferring load from the existing piles to the underpinning piles. Specifically, screw-type and hydraulic-jack type devices were developed for the practical application of foundation underpinning during vertical extension, and their operability and load transfer effect verified via full-scale structural experiments.

• Explosives and Blasting
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• v.30 no.1
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• pp.9-16
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• 2012

With the deterioration and functional loss of structures, there is an increasing demand for demolition and various demolition technologies have been developed. In case of a large-scale concrete foundation, application of some mechanical demolition techniques is limited because of the structural characteristics, and explosive demolition or explosive demolition combined with mechanical demolition is applied recently due to the effect to the surrounding environment by the ground vibration. In this study, we compared peak particle velocity of ground vibration depending on average fragment size in case of explosive demolition design for large-scale concrete foundation using the relation among specific charge, charge constant and transmitting medium constant as well as the relation between average concrete fragment size and specific charge.

• Journal of the Korea Institute of Building Construction
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• v.9 no.3
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• pp.95-101
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• 2009

Constructing large-scale mat foundation mass concrete is increasing for the stability of building structure, because a lot of high rise building are being built in order to make full use of limited space. However, It is of increasing concerns that because limited placing equipments, available job-site and systems for mass concete placement in construction field do not allow to place great quantity of concrete at the same time in large scale mat foundation, consistency between placement lift can not be secured. And also, it is likely to crack due to stress caused by the difference of hydration heat generation time. To find out the solution against above problems, this study is to reconfirm the performance of normal concrete designed by mix proportion and super retarding concrete. The Fundamental test shows what happens if low heat proportioning and control method of setting time are applied at the job-site of newly constructed high rise building. The test result show that slump flow of concrete has been somewhat increased as the target retarding time gets longer, while the air content has been slightly decreased but this is no great difference from normal concrete. The setting time shows to be retarded as target retarding time gets longer, the range of retarding time increases. It is necessary to increase the amount of mix of super retarding agent in the proportion ration by setting curing temperature high since outdoor curing is about 6 hours faster than standard curing, which means the temperature of the concrete will be higher than the temperature of the surrounding environment, due to its high hydration heat when applying in a construction site. The compressive strength of super retarding concrete appears to be lower than normal concrete due to the retarding action in the early stage. However, as the time goes by, the compressive strength gets higher, and by the 28th day the strength becomes the same or higher than normal concrete.

• Journal of Korean Society for Quality Management
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• v.36 no.2
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• pp.45-58
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• 2008

The importance of quality logistics service to the enterprises has kept growing considering the fierce competitions. It also asks for the sound definition and the scale explaining the construct of logistics service quality. The current study attempted to identify the construct of logistics service quality and develop the scale to measure it. Various qualitative and quantitative methodologies have been employed in order to provide the solid theoretical and psychometrical foundation of the proposed scale. In so doing, the conceptual definition of Logistics Service quality has been proposed and the 127-item scale measuring the construct of logistics service quality has been developed and found to be reliable and valid.

• Steel and Composite Structures
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• v.29 no.3
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• pp.349-362
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• 2018

Thermal buckling behavior of porous functionally graded nanobeam integrated with piezoelectric sensor and actuator based on the nonlocal higher-order shear deformation beam theory is investigated for the first time. Its material properties are assumed to be temperature-dependent and varying along the thickness direction according to the modified power-law rule. Note that the porosity with even type is considered herein. The equations of motion are obtained through Hamilton's principle. The influences of several parameters (such as type of temperature distribution, external electric voltage, material composition, porosity, small-scale effect, Ker foundation parameters, and beam thickness) on the thermal buckling of FG nanobeam are investigated in detail.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.646-657
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• 2010

Offshore wind power is one of the largest-scale solutions for a nuclear- and pollution-free electricity supply in the future. Recently, the research for offshore wind power has started in Korea. However, there has been little effort specifically made for the exploration and evaluation of mechanical characteristics for offshore underwater soil deposits. In offshore wind power system, this is important as consistent and safe maintenance of structural functionality of the system is key for the wind power system to be successfully implemented. In this study, case examples from foreign offshore wind power sites are selected and analyzed. And design methods and factors of offshore wind power system foundation are investigated.

• Journal of Ocean Engineering and Technology
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• v.26 no.1
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• pp.34-40
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• 2012

This paper presents an experimental modal analysis of a caisson-type breakwater to produce basic information for the structural health assessment of a caisson structure. To achieve the objective, the following approaches are implemented. First, modal analysis methods are selected to examine the modal characteristics of a caisson structure. Second, experimental modal analyses are performed using finite element analyses and lab-scale model tests. Third, damage scenarios that include several damage levels in a foundation-structure interface are designed. Finally, the effects of damage on the modal characteristics are analyzed for the purpose of utilizing them for damage identification.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.37.2-37.2
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• 2011

Nowadays, offshore wind energy experiences a rapid development because of its wind condition and no noise impact problem. Different from Europe, offshore wind is just started in Asia. More work and research are needed in Korea. In this work, a three-bladed upwind variable speed pitch controlled 5MW wind turbine on a jacket support structure is used. During the simulation, several design load cases are investigated in two different fully coupled aero-hydro-servo-elastic codes. Some critical loads on the foundation are compared and analyzed.

• Steel and Composite Structures
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• v.34 no.4
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• pp.615-623
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• 2020

In this paper, free vibration analysis of a functionally graded cylindrical nanoshell resting on Pasternak foundation is presented based on the nonlocal elasticity theory. A two-dimensional formulation along the axial and radial directions is presented based on the first-order shear deformation shell theory. Hamilton's principle is employed for derivation of the governing equations of motion. The solution to formulated boundary value problem is obtained based on a harmonic solution and trigonometric functions for various boundary conditions. The numerical results show influence of significant parameters such as small scale parameter, stiffness of Pasternak foundation, mode number, various boundary conditions, and selected dimensionless geometric parameters on natural frequencies of nanoshell.

• Magazine of the Korean Society of Agricultural Engineers
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• v.43 no.5
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• pp.106-115
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• 2001

This paper deals with the free vibrations of horizontally curved beams partially supported on elastic foundations. Taking account of the effects of rotatory inertia and shear deformation, differential equations governing the free vibrations of such beams are derived, in which the Pasternak foundation model is considered as the elastic foundation. Differential equations are numerically solved to calculate natural frequencies and mode shapes. The experiments were performed in which the free vibration frequencies of such curved beams in laboratorial scale were measured and these results agreed quite well with the present studies. In numerical examples, the circular, parabolic, sinusoidal and elliptic curved members are considered. The parametric studies are performed and the lowest four frequency parameters are reported in tables and figures as the non-dimensional forms. Also the typical mode shapes are presented.