The strategy for the management of earthquakes is shifting from post recovery to prevention; therefore, seismic performance management requires quantitative predictions of damage and the establishment of strategies for initial responses to earthquakes. Currently, seismic performance evaluation for seismic management in Korea consists of two stages: preliminary evaluation and detailed evaluation. Also, the priority of seismic performance management is determined in accordance with the preliminary evaluation. As a deterministic method, preliminary evaluation quantifies the physical condition and socio-economic importance of a facility by various predetermined indices, and the priority is decided by the relative value of the indices; however, with the deterministic method it is difficult to consider any uncertainty related to the return-year, epicenter, and propagation of seismic energy. Also this method cannot support tasks such as quantitative socio-economic damage and the provision of data for initial responses to earthquakes. Moreover, indirect damage is often greater than direct damage; therefore, a method to quantify damage is needed to enhance accuracy. In this paper, a Seismic Risk Assessment is used to quantify the cost of damage of road facilities in Pohang city and to support decision making.

It is inevitable to use the distinct element method in the analysis of structural dynamics for stacked stone pagoda system. However, the experimental verification of analytical results produced by the discrete element method is not sufficient yet, and the theory of distinct element method is not universal in Korea. This study introduces how to model the stacked stone pagoda system using the distinct element method, and draws some considerations in the seismic analysis procedures. First, the rocking mode and sliding mode are locally mixed in the seismic responses. Second, the vertical stiffness and the horizontal stiffness on the friction surface have the greatest influence on the seismic behavior. Third, the complete seismic analysis of stacked stone pagoda system requires a set of the horizontal, vertical, and rotational velocity time histories of the ground. However, earthquake data monitored in Korea are limited to acceleration and velocity signals in some areas.

This study proposes a numerical model to explain the closely placed double modes in the vibration of a layered stone pagoda system. The friction surface between the stones is modelled as the Timoshenko finite element while each stone layer is modelled as a rigid body. It is assumed that the irregular asperity on the friction surface enables the stone to be excited. This results in the closely placed modes that are composed of natural modes and self-excited modes. To examine the validity of the proposed model, a set of modal testing and analysis for a layered stone pagoda mock-up model has been conducted and a set of closely placed double modes are extracted. Applying the extended sensitivity-based system identification technique, the various system parameters are identified so that the modal parameters of the proposed numerical model are the same with those of the experimental mock-up. For a horizontal impulse excitation, the simulated acceleration responses are compared with measurements.

This work introduces a modal testing and analysis results of the mock-up for a layered stone pagoda. The pagoda has been horizontally excited by an impact hammer. As to the measured acceleration time responses, the first five lower mode shapes and natural frequency are extracted by the TDD technique. It is observed that the time delay of a shear wave occurs through friction surfaces. Such phenomena cannot be described by using the traditional analytical models such as a continuum cantilever beam model or a discrete shear building model. However, the time delay typically affects only the phases of the pagoda system. The frequencies of the pagoda system are not affected by such time delay. It is found in the first time that the layered stone pagoda system has a set of closely placed modes in near of natural frequency. It is believed that such modes are due to the friction characteristics in friction surfaces. Based on the stick-slip friction model, it seems that the one of the closely placed mode can be a self-excited one.

This paper investigates experimentally the confinement effect on concrete. For this purpose, outside lateral reinforcement members made of stainless steel and GFRP were employed. Then, uniaxial compressive tests on concrete cylinders incorporating the members were conducted. A total of 30 cylinder specimens, specifically, 6 unconfined specimens, 12 specimens confined by stainless steel and 12 specimens confined by GFRP, were fabricated. The failure patterns of both unconfined and confined specimens were assessed and discussed based on experimental results. The results proved that the maximum stress and corresponding strains of the cylinders confined using the proposed hoops are increased in comparison with those of the unconfined. This supports that the current work can be used for retrofitting concrete members and structures and thus may lead to increased stability of such structures.

This work examines the feasibility for estimating existing tensile stress on a stressed wire using the permeability of magnetic flux. A closed magnetic circuit has been constructed to induce magnetic flux inside a steel wire. With different tension stress levels on a wire, the permeability of magnetic flux on the wire has been measured. Two different experimental case studies have been conducted for the examination of sensitivity of permeability of magnetic flux on the stressed wire. One is a varying-length stress test, and the other is a fixed-length stress test. The results show that the permeability of magnetic flux in the varying-length stress test is inversely proportional to the applied stress, while the permeability in the fixed-length stress test is linearly proportional to the applied stress on the stressed wire. It is thus expected that the permeability of magnetic flux on a wire can be a promising indicator for the inspection of its tensile stress.

본 논문에서는 구조건전성모니터링(SHM)시스템이 설치된 케이블교량을 대상으로 장기적인 동적거동 특성을 분석하였다. 3차원 유한요소모델을 사용한 모드해석을 통해 모드변수를 추출하였다. 이를 교량에서 측정된 상시진동신호에 대해 주파수영역에서 분석한 고유진동수와 비교하여 정확한 기저모델이 구축되었음을 알 수 있었다. 지난 5년간의 고유진동수와 온도를 통계분석하여 고유진동수가 온도에 선형 반비례하고 있음을 확인하였고, 이러한 온도효과에 대한 평가를 수행하였다. 또한 상시진동신호를 시간영역에서 TDD기법을 적용하여 모드형상을 추출하였으며, 모드해석 결과와의 비교를 통해 케이블교량에 적용이 가능함을 검증하였다.

LED와 LD의 수명과 효율은 결정에 존재하는 결함의 밀도에 반비례하며, 이러한 결함의 밀도는 적당한 기판을 사용하거나, 기판의 표면을 적절하게 제어함으로써 줄일 수 있다. GaN성장시 원자 단위의 매끄러운 표면은 완충충 성장이나 질화처리를 함으로써 얻어질 수 있다. 이렇게 얻어진 원자 단위의 매끄러운 표면에 의해 기판과 박막상이의 계면 자유에너지가 감소하기 때문에 2D성장이 촉진된다. 사파이어(AI2O3(0001))기판을 사용한 GaN 왕충충성장과 진화처리에 대한 최적조건은 AFM(Atomic Force Microscope)측정 결과에 의해 결정되었다. AFM에 의해 얻어진 표면 평활도의 개념은 사파이어 기판을 사용한 GaN박막성장의 최적조건을 결정하는 데 있어서 높은 신뢰도를 가질 수 있다.

This paper presents the results of the tests on electrical impedance for the steel wire under the effect of ambient temperature and stress level shift. The experiments are carried out in variable temperature conditions ranging from 30 to 60 ℃ and different stress levels ranging from 10% to 70% of yield strength. The results show the relationship between electrical impedance and temperature is a linear correlation at all stress levels.

교량의 정밀안전진단시 고유진동수의 추출은 반드시 필요하다. 교량의 고유진동수 추출을 위해서 일반 진단 실무에서는 동재하실험을 실시된다. 그러나 교량의 가진신호 계측이 어려워, 응답만으로 고유진동수를 추출하여야 한다. 차량의 중량이 교량의 중량 대비 매우 작은 경우에 문제가 없으나, 차량의 중량이 무시 못할 정도로 큰 경우에는 차량 주행에 따른 가진 주파수가 응답스펙트럼에 나타나고, 진단 실무자는 종종 가진 모드를 교량의 1차 모드로 오인하는 경우가 적지 않다. 본 연 구는 교량의 고유진동수와 차량의 가진모드를 쉽게 구별할 수 있는 실무적인 방법을 제안한다.

This study introduces the experimental relation between impedance frequency and applied stress level on a wire. The impedance of a stressed wire in the range of frequency from DC to 5M Hz is examined for three different applied stress conditions. It is confirmed that the impedance of a wire is inversely proportional to applied stress rate for most frequency range. Also, some impedance peaks are observed at certain specific frequency regions.

Two sets of modal testing have been conducted for a layered stone pagoda with different boundary conditions. It is observed that the horizontal deflection mode of the pagoda system has a set of double modes which may be a rocking mode and a sliding mode. Due to the larger area of the base stone, the frequencies of the structural system are very sensitive with the ground surface conditions, while its mode shapes are not.

This feasibility study examines if the tensile stress on bonded PSC tendon could be estimated by means of measuring electrical impedance. The impedances of the five beam specimens with different tensile stress levels were measured. As tensile stress on the tendon increases, the impedance of the tendon considerably decreases. Thus, it seems that the estimation of the tensile stress on the tendon could be possible by measuring the electrical impedance.

To maintain the tension force of PS members is a very important issue for the safety of PSC structures. In practice many cases of corrosions and tensile force reduction in PC tendons, however, are reported from various causes. In the near future, thus the estimation of tensile forces in PC tendons would be major work of maintaining PSC structures. In this study, the approach using magnetic characteristics of PC tendons to estimate tensile force was investigated. Using simple but reasonable test procedures, the possibility of the approach like this was verified.