• Structural Engineering and Mechanics
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• v.22 no.3
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• pp.371-399
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• 2006

The theoretical background and capabilities of the developed program, SAR-CWF, for stochastic analysis of 3D reinforced-concrete shear wall-frame structures subject to seismic excitations is presented. Incremental stiffness and strength properties of system members are modeled by extended Roufaiel-Meyer hysteretic relation for bending while shear deformations for walls by Origin-Oriented hysteretic model. For the critical height of shear-walls, division to sub-elements is performed. Different yield capacities with respect to positive and negative bending, finite extensions of plastic hinges and P-${\delta}$ effects are considered while strength deterioration is controlled by accumulated hysteretic energy. Simulated strong motions are obtained from a Gaussian white-noise filtered through Kanai-Tajimi filter. Dynamic equations of motion for the system are formed according to constitutive and compatibility relations and then inserted into equivalent It$\hat{o}$-Stratonovich stochastic differential equations. A system reduction scheme based on the series expansion of eigen-modes of the undamaged structure is implemented. Time histories of seismic response statistics are obtained by utilizing the computer programs developed for different types of structures.

• Journal of the Korean Ceramic Society
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• v.53 no.4
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• pp.435-443
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• 2016

Coal ash, a material generated from coal-fired power plants, can be classified as fly ash and bottom ash. The amount of domestic fly ash generation is almost 6.84 million tons per year, while the amount of bottom ash generation is 1.51 million tons. The fly ash is commonly used as a concrete admixture and a subsidiary raw material in cement fabrication process. And some amount of bottom ash is used as a material for embankment and block. However, the recyclable amount of the ash is limited since it could cause deterioration of physical properties. In Korea, the ashes are simply mixed and used as a replacement material for cement. In this study, an attempt was made to mechanically activate the ash by grinding process in order to increase recycling rates of the fly ash. Activated fly ash was prepared by controlling the mill types and the milling times and characteristics of the mortar containing the activated fly ash was analyzed. When the ash was ground by using a vibratory mill, physical properties of the mortar mixed with such fly ash were higher than the mortar mixed with fly ash ground by a planetary mill.

• Journal of the Korea Institute of Building Construction
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• v.7 no.1 s.23
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• pp.99-106
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• 2007

Water leakage could be caused deterioration of environmental conditions, user condition, reduction of life span and long term safety in underground concrete structure. Many materials and construction method to repair on these problems have been developed, however, it is not proper to successful repair or raise problem of increasing repair cost However, there are many limitations as practical appraisal methods due to different view of reliability for test methods. Because, it was not enough that the technical objectivity could be lack and also application of environmental condition is inadequate. In this paper, we suggest varied test methods divided to appraisal for property of matter, construction, manufacturing, specification and maintenance, friendly environmental condition. It could be more practical as a objective standard considering various angles. In summery, it should be subdivided and differentiated to accomplish proper application and to select proper materials and construction method for repair even if the synthetical condition is very complicated.

• Explosives and Blasting
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• v.34 no.1
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• pp.19-28
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• 2016

The number of industrial structures that must be demolished due to functional and structural deterioration has been increased. There is an increasing application of explosive demolition or explosive demolition combined with mechanical demolition to minimize temporal and spatial environmental hazardous factors created during the process of demolition. In this case study, to demolish the turbine foundation structure, which is a large-section reinforced concrete structure, the parital explosive demolition thchnique was conducted. As a result of the partial explosive demolition, the overall crushing of the blasting sections of beam-column joints structure with haunched beams and second-floor columns about the turbine foundation was satifactory, and the explosive demolition was completed without causing any damage to surrounding facilities.

• Steel and Composite Structures
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• v.15 no.6
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• pp.623-643
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• 2013

Concrete filled steel tubular members (CFST) become a popular choice for modern building construction due to their numerous structural benefits and at the same time aging of those structures and member deterioration are often reported. Therefore, actions like implement of new materials and strengthening techniques become essential to combat this problem. The application of carbon fibre reinforced polymer (CFRP) with concrete structures has been widely reported whereas researches related to strengthening of steel structures using fibre reinforced polymer (FRP) have been limited. The main objective of this study is to experimentally investigate the suitability of CFRP to strengthening of CFST members under flexure. There were three wrapping schemes such as Full wrapping at the bottom (fibre bonded throughout entire length of beam), U-wrapping (fibre bonded at the bottom throughout entire length and extended upto neutral axis) and Partial wrapping (fibre bonded in between loading points at the bottom) introduced. Beams strengthened by U-wrapping exhibited more enhancements in moment carrying capacity and stiffness compared to the beams strengthened by other wrapping schemes. The beams of partial wrapping exhibited delamination of fibre and were failed even before attaining the ultimate load of control beam. The test results showed that the presence of CFRP in the outer limits was significantly enhanced the moment carrying capacity and stiffness of the beam. Also, a non linear finite element model was developed using the software ANSYS 12.0 to validate the analytical results such as load-deformation and the corresponding failure modes.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.328-334
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• 2003

Evaluating stability of dam foundations is one of the prime areas of any rock engineering investigations. Despite best engineering efforts in the design and construction of dam foundations, the foundation regime of a constructed dam suffers deterioration due to continuous erosion from backwater current of dam discharge and dynamic effects of loading and unloading process. Even during construction, development of frequent cracks due to sudden thermal cooling of concrete blocks is not uncommon. This paper presents two case studies from India and Bhutan. In the first case, the back current of water discharge from the Srisailam dam in India had continuously eroded the apron and has eaten into the dam foundation. In the second case with dam construction at Tala Hydroelectric Project in Bhutan, sudden overflow of river during the construction stage of dam had led to development of three major cracks across the dam blocks. This was ascribed to adiabatic cooling effect of concrete blocks overlain by chilled water flow. Non-destructive evaluation of rock mass condition in the defect regime by the borehole GPR survey helped in arriving at the crux so as to formulate appropriate restoration plan.

• Smart Structures and Systems
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• v.3 no.4
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• pp.475-494
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• 2007

This paper deals with the development of an innovative distributed construction system based on smart prefabricated concrete elements for the real-time condition assessment of civil infrastructure. So far, two reduced-scale prototypes have been produced, each consisting of a $0.2{\times}0.3{\times}5.6$ m RC beam specifically designed for permanent instrumentation with 8 long-gauge Fiber Optic Sensors (FOS) at the lower edge. The sensing system is Fiber Bragg Grating (FBG)-based and can measure finite displacements both static and dynamic with a sample frequency of 625 Hz per channel. The performance of the system underwent validation in the laboratory. The scope of the experiment was to correlate changes in the dynamic response of the beams with different damage scenarios, using a direct modal strain approach. Each specimen was dynamically characterized in the undamaged state and in various damage conditions, simulating different cracking levels and recurrent deterioration scenarios, including cover spalling and corrosion of the reinforcement. The location and the extent of damage are evaluated by calculating damage indices which take account of changes in frequency and in strain-mode-shapes. The outcomes of the experiment demonstrate how the damage distribution detected by the system is fully compatible with the damage extent appraised by inspection.

• Structural Engineering and Mechanics
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• v.64 no.4
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2007.04a
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• pp.129-132
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• 2007

In this study, for the establishment of the performance evaluation methods of repair material and method for reinforced concrete structure and the quality control standards of durability recovery method, the quantitative exposure data by exposure experiment under the coastal and normal atmosphere environment is accumulated and analyzed. Investigating and evaluating the result of exposure experiment during 54 months of exposure age under the coastal and normal atmosphere environment, Micro crack, swelling and spatting of surface coating material, crack of repair boundary parts and the great potential difference between repair part and non-repair part were somewhat generated. And the result shown that exposure specimen of coastal environment had lower electrode potential than exposure specimen of normal atmosphere environment.

• Smart Structures and Systems
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• v.5 no.4
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• pp.443-455
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• 2009

The use of fiber reinforced polymer (FRP) reinforcement in concrete structures has been on the rise due to its advantages over conventional steel reinforcement such as corrosion. Reinforcing steel corrosion has been the primary cause of deterioration of reinforced concrete (RC) structures, resulting in tremendous annual repair costs. One application of FRP reinforcement to be further explored is its use in RC frames. Nonetheless, due to FRP's inherently elastic behavior, FRP-reinforced (FRP-RC) members exhibit low ductility and energy dissipation as well as different damage mechanisms. Furthermore, current design standards for FRP-RC structures do not address seismic design in which the beam-column joint is a key issue. During an earthquake, the safety of beam-column joints is essential to the whole structure integrity. Thus, research is needed to gain better understanding of the behavior of FRP-RC structures and their damage mechanisms under seismic loading. In this study, two full-scale beam-column joint specimens reinforced with steel and GFRP configurations were tested under quasi-static loading. The control steel-reinforced specimen was detailed according to current design code provisions. The GFRP-RC specimen was detailed in a similar scheme. The damage in the two specimens is characterized to compare their performance under simulated seismic loading.