• 한국방재학회 논문집
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• 제5권2호
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• pp.29-35
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• 2005

우리나라에서는 홍수로 매년 90여개 이상의 교량이 붕괴되고 있으며, 이러한 교량의 붕괴는 대부분 기초의 세굴에 기인하고 있다. 그동안 교량의 설계 및 유지관리 분야에서 세굴에 대한 교량의 건전성을 정량적으로 평가하기 위한 평가기법 개발에 관한 연구는 체계적으로 수행되지 못한 실정이다. 본 연구에서는 홍수 발생 후 교각의 세굴 건전성을 평가하기 위한 긴급점검기법으로써 세굴로 인한 교각의 고유진동수 변화를 이용하기 위한 동적특성 평가실험을 수행하였다. 세굴을 모의한 확대기초 교각 모형의 동적특성 평가 실험결과 교각의 1차 모드 고유진동수를 이용하여 기초의 세굴을 평가할 수 있을 것으로 분석되었다.

• Structural Engineering and Mechanics
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• 제50권3호
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• pp.257-273
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• 2014

This paper introduces a novel optimization technique based on gravitational search algorithm (GSA) for numerical optimization and multi-objective optimization of foundation. In the proposed method, a chaotic time varying system is applied into the position updating equation to increase the global exploration ability and accurate local exploitation of the original algorithm. The new algorithm called global-local GSA (GLGSA) is applied for optimization of some well-known mathematical benchmark functions as well as two design examples of spread foundation. In the foundation optimization, two objective functions include total cost and $CO_2$ emissions of the foundation subjected to geotechnical and structural requirements are considered. From environmental point of view, minimization of embedded $CO_2$ emissions that quantifies the total amount of carbon dioxide emissions resulting from the use of materials seems necessary to include in the design criteria. The experimental results demonstrate that, the proposed GLGSA remarkably improves the accuracy, stability and efficiency of the original algorithm.

• 한국공간구조학회논문집
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• 제15권4호
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• pp.65-72
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• 2015

To overcome the weakness of spread foundation in large space structure, the research of precast pile for replace spread foundation have been conducted. The new type of joint between PHC pile and steel column is named HAT Joint(Hollow hAlf-sphere cast-sTeel Joint). It connected PHC Pile by bolt that verification of bolt connection should be accomplished. In this paper, pull-out test and flexural performance for HAT Joint to verifying the bolt connection is explained. As a result, the pull-out and flexural capacities of bolt were checked to use in real structure. Furthermore, the equation of pull-out strength was proposed.

• Earthquakes and Structures
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• 제16권6호
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• pp.691-704
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• 2019

This study simulates the responses of large-scale bridge piers under pseudo-dynamic tests to investigate the performance of four types of numerical models that consider the nonlinear behavior of the pier and the rocking behavior of the footing. In the models, beam-column elements with plastic hinges are used for the pier, two types of foundation models (rotational spring and distributed spring models) are adopted for the footing behavior, and two types of viscous damping models (Rayleigh and dashpot models) are applied for energy dissipation. Results show that the nonlinear pier model combined with the distributed spring-dashpot foundation model can reasonably capture the behavior of the piers in the tests. Although the commonly used rotational spring foundation model adopts a nonlinear moment-rotation property that reflects the effect of footing uplift, it cannot suitably simulate the hysteretic moment-rotation response of the footing in the dynamic analysis once the footing uplifts. In addition, the piers are susceptible to cracking damage under strong seismic loading and the induced plastic response can provide contribution to earthquake energy dissipation.

• Earthquakes and Structures
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• 제7권6호
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• pp.1001-1024
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• 2014

The size of spread footings was found to be unnecessarily large from some actual engineering practices constructed in Taiwan, due to the strict design provisions related to footing uplift. According to the earlier design code in Taiwan, the footing uplift involving separation of footing from subsoil was permitted to be only up to one-half of the foundation base area, as the applied moment reaches the value of plastic moment capacity of the column. The reason for this provision was that rocking of spread footings was not a favorable mechanism. However, recent research has indicated that rocking itself may not be detrimental to seismic performance and, in fact, may act as a form of seismic isolation mechanism. In order to clarify the effects of the relative strength between column and foundation on the rocking behavior of a column, six circular reinforced concrete (RC) columns were designed and constructed and a series of rocking experiments were performed. During the tests, columns rested on a rubber pad to allow rocking to take place. Experimental variables included the dimensions of the footings, the strength and ductility capacity of the columns and the intensity of the applied earthquake. Experimental data for the six circular RC columns subjected to quasi-static and pseudo-dynamic loading are presented. Results of each cyclic loading test are compared against the benchmark test with fixed-base conditions. By comparing the experimental responses of the specimens with different design details, a key parameter of rocking behavior related to footing size and column strength is identified. For a properly designed column with the parameter higher than 1, the beneficial effects of rocking in reducing ductility and the strength demand of columns is verified.

• 한국지반환경공학회 논문집
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• 제8권3호
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• pp.41-49
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• 2007

강관말뚝과 확대기초를 연결하는 대표적인 두부보강공법은 +자 보강 덮개판을 이용한 볼트식 말뚝두부 보강방법이다. 본 논문에서는 실물 크기의 +자 보강 덮개판을 이용한 말뚝머리 보강방법과 훅타입의 새로운 말뚝 두부보강공법을 적용한 실물크기의 확대기초를 제작하여 연직재하시험과 수평재하시험을 수행하여 말뚝두부 결합부의 안정성을 평가하였다. 실물모형 기초의 연직재하 시험결과 볼트타입 및 훅타입으로 보강된 말뚝기초는 강관말뚝 재료의 항복내력을 8.5~21% 초과하는 것으로 나타나 압축력에 대해 충분한 안전성을 확보하고 있는 것으로 확인되었다. 수평재하 시험결과 훅타입 두부보강장치의 최대 파괴하중은 41.1tonf으로 볼트타입 두부보강 시험체에 비해 약 33%정도 크게 나타났다.

• 전산구조공학
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• 제9권1호
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• pp.23-32
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• 1996

본 논문에서는 건물 기초 설계의 자동화를 위한 규칙 기반 시스템을 개발하였다. 상부구조의 설계 결과와 지반 조사 보고서로부터의 지반에 관한 자료를 읽어 들여 허용지내력을 추정하고 주어진 상황에 적절한 기초형식을 추론하는 방법을 제안하였다. 허용지내력은 표준관입시험치로부터 추정하였고, 이를 바탕으로 각 기중과 벽체의 기초형식은 우선 독립기초와 벽체기초라고 가정하여 그 크기를 계산하고 각 기초의 중첩여부를 조사하여 중첩되는 기초들은 본 논문에서 개발한 기초 합병의 방법을 이용하여 새로운 기초형식으로 변경되도록 하였다. 개발된 시스템은 주어진 상부구조 설계결과와 지반조건에 대하여 적절한 기초형식을 선정하여 그에 따른 배근 설계를 쉽게 할 수 있도록 해준다.

• ETRI Journal
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• 제37권1호
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• pp.1-10
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• 2015

A blind hopping phase estimator is proposed for the demodulation of received signals in frequency-hopping spread spectrum systems. The received signals are assumed to be bandwidth limited with a shaping filter, modulated as frequency modulation (FM) or binary frequency shift keying (BFSK), and hopped by predetermined random frequency sequences. In the demodulation procedure in this paper, the hopping frequency tracking is accomplished by choosing a frequency component with maximum amplitude after taking a discrete Fourier transform, and the hopping phase estimator performs the conjugated product of two consecutive signals and moving-average filtering. The probability density function and Cramer-Rao low bound (CRLB) of the proposed estimator are evaluated. The proposed scheme not only is very simple to implement but also performs close to the CRLB in demodulating hopped FM/BFSK signals.

• 한국공간구조학회논문집
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• 제15권1호
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• pp.103-110
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• 2015

To overcome disadvantages of usual spread foundation in large space structure, some prototypes of a joint of the PHC pile to steel pipe column that directly connects a column to a PHC pile are analytically studied. With the consideration of strength requirement and stress concentration of joint of the PHC pile to column, we suggest the most appropriate one.

• Journal of Chest Surgery
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• 제56권3호
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• pp.220-223
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• 2023

Well-differentiated papillary mesothelial tumor (WDPMT) is an uncommon tumor, formerly named well-differentiated papillary mesothelioma in the 2015 World Health Organization classification. It has a characteristic papillary architecture, bland cytologic features, a tendency toward superficial spread without invasion, and a good prognosis due to its clinically indolent behavior with prolonged survival. Rare cases with superficial invasion are termed WDPMT with invasive foci. WDPMT occurs primarily in the peritoneum of reproductive-age women, but also rarely in the pleura. We report a case of a 60-year-old woman who developed WDPMT with minimal invasion in the pleura with atypical radiological features and a family history of mesothelioma and indirect asbestos exposure.