Numerical and Experimental Investigation on the Scaling Law of Strip Model Foundation on Cohesionless Soils

김동휘,남부현,윤희정 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.3

In this study, a revised scaling law for laboratory test models of strip foundations on cohesionless soils is proposed. The centrifuge model tests were conducted on a strip model foundation at four different gravity levels (1 g, 5 g, 7.5 g, and 10 g), and the test results were used to calibrate numerical simulations. A set of numerical models were created to simulate full-scale tests and laboratory-scale tests. From the numerical simulations, the behavior of a foundation in the centrifuge model test is similar to that of the full-scale test but is different from the behavior in the laboratory-scale test under the 1 g condition. A parametric study was performed by varying the key variables that are internal friction angle, foundation width, and gravitational acceleration. The stress scale ratio is approximate to the geometric scale ratio in the 1 g model test. However, the settlement conversion requires both the geometric scale ratio and the settlement scale ratio newly proposed. The settlement scale ratio increases with increasing the internal friction angle and geometric scale ratio; accordingly, an equation for calculating the settlement scale ratio is proposed.

삼병렬 터널의 안정성 검토를 위한 모형실험 연구

김종우(Jong-Woo Kim),배우석(Woo-Seok Bae) 한국암반공학회 2008 터널과지하공간 Vol.18 No.4

삼병렬 터널은3개의 터널이 서로 나란히 배열되는 형태의 터널이다.본 연구에서는 터널간 이격거리, 터널단면 형상,지보조건,지반조건 등이 서로 다른 7가지 삼병렬 터널 모형들에 대한 축소모형실험을 통하여 모형별 균열개시압력과 터널 주변지반의 변형거동을 조사하였다. 터널간 이격거리가 작은 모형일수록 낮은 압력 수준에서 필러의 파괴가 일어나고 터널의 내공변형량도 증가하여 터널의 안정성은 감소하였다. 터널단면의 형상이 아치형,편평아치형,사각형인 모형들 중에서 사각형 단면을 가진 터널의 안정성이 가장 작았으며, 천반곡률 반경이 작은 아치형 터널이 편평아치형 터널보다 안정성이 우수하였다. 터널의 천장부에 모형 록볼트를 설치한 모형은 무지보 터널 모형에 비하여 균열개시압력이 클 뿐만 아니라 천단침하량도 적게 나타나 지보의 효과를 확인할 수 있었다. 이방성 암반내 터널 모형은 등방성 모형과 매우 다른 변형거동을 나타내었으며, FLAC을 사용한 수치해석 결과는 모형실험의 결과와 정성적으로 부합하였다. In this study, scaled model tests were performed to investigate the stability of three parallel tunnels. Seven types of test models which had respectively different pillar widths, tunnel sectional shapes, support conditions and ground conditions were experimented, where crack initiating pressures and deformation behaviors around tunnels were investigated. In order to evaluate the effect of pillar widths on stability, various models were experimented. As results, the models with shallower pillar widths proved to be unstable because of lower crack initiating pressures and more tunnel convergences than the models with thicker pillar widths. In order to find the effect of tunnel sectional shape on stability, the models with arched, semi-arched and rectangular tunnels were experimented. Among them rectangular tunnel model was the most unstable, where the arched tunnel model with small radius of roof curvature was more stable than semi-arched one. The model with rockbolt showed higher crack initiating pressure and less roof lowering than the unsupported model. The deformation behaviors of tunnels in the anisotropic ground model were quite different from those in the isotropic ground model. Futhermore, the results of FLAC analysis were qualitatively coincident with the experimental results.

Investigation of the effects of particle size and model scale on the UCS and shear strength of concrete using PFC2D

Hadi Haeri,Vahab Sarfarazi,Zheming Zhu,Hossein Ali Lazemi 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.67 No.5

In this paper, the effects of particle size and model scale of concrete has been investigated on the failure mechanism of PFC2D numerical models under uniaxial compressive test. For this purpose, rectangular models with same particle sizes and different model dimensions, i.e., 3 mm×6 mm, 6 mm×12 mm, 12 mm×24 mm, 25 mm×50 mm and 54 mm×108 mm, were prepared. Also rectangular models with dimension of 54 mm×108 mm and different particle sizes, i.e., 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, 1.87 mm and 2.27 mm were simulated using PFC2D and tested under uniaxial compressive test. Concurrent with uniaxial test, direct shear test was performed on the numerical models. Dimension of the models were 75×100 mm. Two narrow bands of particles with dimension of 37.5 mm × 20 mm were removed from upper and lower of the model to supply the shear test condition. The particle sizes in the models were 0.47 mm, 0.57 mm, 0.67 mm and 0.77 mm. The result shows that failure pattern was affected by model scale and particle size. The uniaxial compressive strength and shear strength were increased by increasing the model scale and particle size.

Investigation of the effects of particle size and model scale on the UCS and shear strength of concrete using PFC2D

Haeri, Hadi,Sarfarazi, Vahab,Zhu, Zheming,Lazemi, Hossein Ali Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.67 No.5

In this paper, the effects of particle size and model scale of concrete has been investigated on the failure mechanism of PFC2D numerical models under uniaxial compressive test. For this purpose, rectangular models with same particle sizes and different model dimensions, i.e., $3mm{\times}6mm$, $6mm{\times}12mm$, $12mm{\times}24mm$, $25mm{\times}50mm$ and $54mm{\times}108mm$, were prepared. Also rectangular models with dimension of $54mm{\times}108mm$ and different particle sizes, i.e., 0.27 mm, 0.47 mm, 0.67 mm, 0.87 mm, 1.07 mm, 1.87 mm and 2.27 mm were simulated using PFC2D and tested under uniaxial compressive test. Concurrent with uniaxial test, direct shear test was performed on the numerical models. Dimension of the models were $75{\times}100mm$. Two narrow bands of particles with dimension of $37.5mm{\times}20mm$ were removed from upper and lower of the model to supply the shear test condition. The particle sizes in the models were 0.47 mm, 0.57 mm, 0.67 mm and 0.77 mm. The result shows that failure pattern was affected by model scale and particle size. The uniaxial compressive strength and shear strength were increased by increasing the model scale and particle size.

쌍계사 오층석탑 실물 크기 모델의 동적 거동 시험

김재관,류혁 한국지진공학회 2001 한국지진공학회논문집 Vol.5 No.4

1936년 7월 4일 경상남도 하동군 화개면을 진앙지로 하는 규모 5의 지진이 발생하였다. 이 지진으로 인하여 쌍계사 경내 건물과 문화재가 손상을 입었으며 금당 앞에 위치한 오층석탑의 탑두(종형석)가 추락하였다. 쌍계사 지진의 세기를 정량적으로 평가하기 위하여 철저한 고층을 거쳐서 실물크기의 석탑 모델을 제작하였다. 제작된 석탑모델을 진동대에 탑재하여 낮은 진폭에서 석탑모델의 동특성을 확인하는 예비시험과 지진파의 지진가속도를 증가시켜 가면서 석탑모델의 거동 특성을 규명하는 본 시험을 실시하였다. 석탑모델의 제작과정과 시험 절차에 관하여 상세히 기술하였고 진동대 시험 결과를 제시하고 그 결과에 관하여 논하였다. There occurred a moderate size earthquake of Magnitude 5 in Whagae-Myun, Hadong-GUn, Kyongsangnam-Do on July 4, 1936. It caused severe damage to the buildings and other structures in Sang-Gye-Sa, a Buddhist Temple. The top component of a five-story stone pagoda was tipped over and fell down to the ground during the earthquake. In order to have accurate and quantitative estimate of the peak acceleration level of that earthquake, a full-scale model was constructed through rigorous verification process. The complete model was mounted on a shaking table and subjected to the dynamic tests. Two kinds of tests were performed: exploratory test and fragility test. The exploratory test was done with low acceleration level. In the fragility test, the behavior of the model was carefully monitored while increasing the acceleration level. The construction details of the model are provided and test procedures are reported. Finally important test results are presented and their implications are discussed.

축소모형실험 및 PFC2D해석에 따른 발파해체 거동분석

채희문(Hee Moon Chae),전석원(Seokwon Jeon) 한국암반공학회 2004 터널과지하공간 Vol.14 No.1

본 연구에서는 경제성장기에 고층 구조물 시공에서 널리 사용된 철근콘크리트(RC, Reinforced Concrete) 구조물을 대상으로 발파해체 축소모형실험을 수행하고 전산실험결과와 이를 비교하였다. 발파해체 공법으로는 파괴거동을 비교적 쉽게 확인할 수 있는 점진붕괴공법을 적용하였으며, 축소모형실험은 Hobbs(1969)에 의한 축소율의 개념에 따라 차원해석을 실시하여 축소된 강도특성을 계산하였다. 시용재료로는 석고, 모래, 물의 혼합액을 콘크리트 대용으로 사용하였다. 모래와 석고의 중량 비를 다양하게 변화시키면서 이에 따른 강도의 변화를 측정하고 최적의 강도 값을 갖는 배합 비를 결정하였다. 또한 연성을 가지고 있으며 축소강도로 비교할 때 철근과 유사한 특성을 지니는 땜용 납선을 철근대용 재료로 사용하였다. 수치해석 프로그램으로는 요소의 파괴거동을 육안으로 확인할 수 있는 개별요소법(DEM, Distinct Element Method)에 의해 수행되는 상용코드인 PFC2D(Particle Flow Code 2-Dimension)을 사용하였다. 모형의 제작은 실내에서 미리 양생된 부재들을 현장으로 옮겨 연결부만을 타설하여 일체화 시키는 방법으로 이루어졌다. 먼저 3차원 무근 콘크리트 라멘 구조의 모형을 설계하고 그 축소 모형을 발파해체하여 그 거동을 촬영하였다. 이를 수치적인 해석과 비교하는 과정을 통해 2차원 해석이라는 한계성은 존재하지만 대체로 유사한 형태의 거동을 보임을 알 수 있었다. 사전해석의 경험과 RC 보의 실내 굴곡 실험결괴를 근거로 하여 RC 구조모형의 발파해체 사전해석을 실시하였다. 시치는 200 ㎳로 하여 점진적으로 붕괴되도록 설계하였다. 모형실험과는 달리 2차원 해석이라는 한계에도 불구하고 900 ㎳ 까지 매우 유사한 거동을 보이며 붕괴되었다. In this study, scaled model tests were performed on blasting demolition of reinforced concrete structures and the experimental results were analyzed in comparison with the results of numerical analysis. The tests were designed to induce a progressive collapse, and physical properties of the scaled model were determined using scale factors obtained from dimension analysis. The scaled model structure was made of a mixture of plaster, sand and water at the ratio determined to yield the best scaled-down strength. Lead wire was used as a substitute for reinforcing bars. The scaled length was at the ratio of 1/10. Selecting the material and scaled factors was aimed at obtaining appropriately scaled-down strength. PFC2D (Particle Flow Code 2-Dimension) employing DEM (Distinct Element Method) was used for the numerical analysis. Blasting demolition of scaled 3-D plain concrete lahmen structure was filmed and compared to results of numerical simulation. Despite the limits of 2-D simulation, the resulting demolition behaviors were similar to each other. Based on the above experimental results in combination with bending test results of RC beam, numerical analysis was carried out to determine the blasting sequence and delay times. Scaled model test of RC structure resulted in remarkably similar collapse with the numerical results up to 900 ㎳ (mili-second).

학년 간 내용 연계성을 고려한 검사구성이 수직척도에 미치는 영향

박소연,지은림 한국교육평가학회 2014 교육평가연구 Vol.27 No.2

본 연구는 학년 간 내용 연계성을 고려한 검사구성이 수직척도화에 미치는 영향을 살펴보고자 하였다. 이를 위해 초6-중2의 수학성취도 검사를 연계형과 비연계형으로 제작하고 각 학년별로 250명 이상의 학생을 대상으로 검사를 실시하였다. 또한 공통문항 설계방법으로 자료를 수집하고, 0.3 logits 차이 검증법을 활용하여 공통문항의 안정성을 검토하였으며, 분리추정방법을 사용하여 문항모수를 추정하였다. 선형변환 계수는 평균/표준편차 방법을 사용하였으며, 수직척도화를 실시한 후에 검사특성곡선, 수직척도점수의 성장패턴, 효과크기를 살펴보았다. 검사특성곡선을 통해 살펴본 검사의 난이도와 수직척도점수의 성장패턴, 효과크기가 연계형 검사에서는 학년이 올라감에 따라 지속적으로 상승하는 형태를 보였으나, 비연계형 검사에서는 학년 상승과 관계없이 상승 또는 하락하는 형태를 보였다. 이는 검사의 연계성이 수직척도 구축에 영향을 미친다는 것을 의미한다. 본 연구는 검사의 연계성에 따른 수적척도화 결과 차이를 실증적인 자료를 통해 비교함으로써, 학생 성장을 파악하기 위해 수직척도화가 검사 내용의 연계성을 고려해야 한다는 것을 보여주었다. 이는 향후 성취도 검사의 종단 자료 구축을 위한 검사 설계에서 검사 내용 구성에 대한 방향을 제안해 줄 수 있다. The study aimed to investigate the effects of test alignment on vertical scaling in terms of test difficulty, growth pattern, and effect size. Two different sets of tests (Connected Form tests and Non-connected Form tests) were administered to grade 6, 7, and 8 students for the subject of mathematics and vertical scales were constructed using the Rasch model. For vertical scaling, data were collected with the design of comon item equating and parameters were estimated by the separate caibration method. The outcomes of vertical scaling were compared with Connected Form tests and Non-connected Form tests for test characteristic curve, growth pattern, and effect size. The results showed that all of test difficulty, growth pattern, and effect size increased as grades went higher with the Connected Form tests, while they failed to consistently increased as grades went higher with the Non-connected Form tests. This implies that the tests should be designed under the consideration of test connectivity to produce vertical scaling for exploring students' growth.

진동대를 이용한 역사적 지진 작용 전통목구조(봉정사 대웅전)의 동적 특성

황재승(Hwang, Jae-Seung),황종국(Hwang, Jong-Kook) 대한건축학회 2015 大韓建築學會論文集 : 構造系 Vol.31 No.11

The objective of this paper is to investigate the response characteristics of Korean traditional wooden structure subject to dynamic earthquake load. To accomplish this research purpose, as a typical example of Korean traditional wooden structures, Bongjeong-sa(temple) constructed in the fifteenth century and classified as a treasure is selected. One-third scale model of Bongjeong-sa is designed and set up on a sliding table of 5.5m by 4.5m to perform shaking table test in the laboratory. To find similarity condition on the natural frequency between real structure and scaled test model, free vibration test was performed for real structure and test model. The natural frequencies of real structure were calculated from acceleration responses measured from ambient vibration test. The test model on shaking table was moved instantaneously toward x-direction of test model structure from 1mm to 10mm for the free vibration test while varying the roof mass in order to adjust similarity condition on the natural frequency. The earthquake signal of Elcentro, Kobe and Hachinohe were used to perform seismic test. The magnitude of earthquake acceleration was controlled as 4 types of 0.07g, 0.11g, 0.167g and 0.22g. The characteristic of instantaneous natural frequency and damping ratio with respect to the magnitude of displacement, velocity and acceleration responses of roof were analyzed.

축소형 틸트로터 무인기의 전자동 비행시험을 위한 문제해결과정

강영신,박범진,유창선,구삼옥,이장호 한국항공우주연구원 2009 항공우주기술 Vol.8 No.1

The ground integration test of Smart UAV has been performed according to the flight test plan. The flight test of full scaled model will be performed followed by 4 DOF ground rig test and a tethered hover test. Smart UAV is the first indigenous tiltrotor aircraft which can fly with fast cruise speed and take off or land vertically. In order to prove the flight control law of Smart UAV, the 40% scaled airplane was developed and have been tested. During flight test of small scaled model, many unique and unexpected problems occurred. After clearing these problems, fully automatic flight test was performed successfully. The experiences about many trouble shooting and resolving the problems would be basic material to avoid the unexpected but similar flight test problems hidden behind of the full scaled Smart UAV. This paper presents the detailed procedures of trouble shootings to solve the unique problems which occurred during the flight test of small scaled tiltrotor UAV. 스마트무인기는 수직이착륙과 고속비행이 동시에 가능하도록 헬리콥터와 고정익 항공기의 장점을 결합한 틸트로터 항공기이다. 현재 지상통합시험을 수행중이며, 4자유도 지상치구시험과 안전줄 호버시험을 거쳐 비행시험을 수행할 예정이다. 스마트무인기에 적용된 제어법칙을 검증하기 위해서 40%축소기를 개발하여 비행시험을 수행하였다. 비행시험결과 예측하기 어려웠던 틸트로터 항공기의 고유한 기술적인 문제점들이 발생하였으며, 이러한 문제점을 해결하여 전자동 비행시험을 완료하였다. 본 논문에서는 국내 최초로 수행된 축소형 틸트로터 항공기의 비행시험 과정 중에 발생한 주요한 문제점을 서술하고, 그 해결과정을 상세하게 기술하였다. 축소형 틸트로터 항공기의 전자동 비행시험 수행을 통해 경험한 시행착오와 개선사항은 향후 계획된 스마트 무인기의 실물기 비행시험을 성공할 수 있는 훌륭한 초석이 될 것이다.

부유식 해상풍력발전기용 반잠수식 계류 풀리의 강도 성능평가를 위한 구조해석과 축소 모형시험

송창용 해양환경안전학회 2023 해양환경안전학회지 Vol.29 No.5

Recently, the destructive power of typhoons is continuously increasing owing to global warming. In a situation where the installation of floating wind turbines is increasing worldwide, concerns about the huge loss and collapse of floating offshore wind turbines owing to strong typhoons are deepening. A new type of disconnectable mooring system must be developed for the safe operation of floating offshore wind turbines. A new submersible mooring pulley considered in this study is devised to more easily attach or detach the floating offshore wind turbine with mooring lines compared with other disconnectable mooring apparatuses. To investigate the structural safety of the initial design of submersible mooring pulley that can be applied to an 8MW-class floating type offshore wind turbine, scale-down structural models were developed using a 3-D printer and structural tests were performed on the models. For the structural tests of the scale-down models, tensile specimens of acrylonitrile butadiene styrene material that was used in the 3-D printing were prepared, and the material properties were evaluated by conducting the tensile tests. The finite element analysis (FEA) of submersible mooring pulley was performed by applying the material properties obtained from the tensile tests and the same load and boundary conditions as in the scale-down model structural tests. Through the FEA, the structural weak parts on the submersible mooring pulley were reviewed. The structural model tests were conducted considering the main load conditions of submersible mooring pulley, and the FEA and test results were compared for the locations that exceeded the maximum tensile stress of the material. The results of the FEA and structural model tests indicated that the connection structure of the body and the wheel was weak in operating conditions and that of the body and the chain stopper was weak in mooring conditions. The results of this study enabled to experimentally verify the structural safety of the initial design of submersible mooring pulley. The study results can be usefully used to improve the structural strength of submersible mooring pulley in a detailed design stage. 최근 지구 온난화의 영향으로 태풍의 파괴력이 증가함에 따라 부유식 해상풍력발전기의 막대한 유실과 붕괴에 대한 우려가 깊어지고 있다. 부유식 해상풍력발전기의 안전한 운영을 위해 새로운 형태의 탈착형 계류 시스템 개발이 요구되고 있다. 본 연구에서 고려한 새로운 반잠수식 계류 풀리는 기존의 탈착형 계류 장치에 비해 계류 라인으로 부유식 해상풍력 터빈을 보다 쉽게 탈부착할 수 있도록 고안되었다. 8MW급 부유식 해상풍력발전기에 적용 가능한 반잠수식 계류 풀리의 초기 설계에 대한 구조적 안전성을 검토하기 위해 3D 프린터를 이용하여 축소구조모형을 제작하고, 이 모형에 대한 구조시험을 수행하였다. 축소 모형의 구조시험을 위해 3D 프린팅에 사용된 ABS 소재의 인장 시편을 제작하고 인장시험을 수행하여 소재의 물성을 평가하였다. 인장시험에서 얻은 재료 특성과 축소모형 구조시험과 동일한 하중 및 경계 조건을 적용하여 반잠수식 계류 풀리의 유한요소해석을 수행하였다. 유한요소해석을 통해 반잠수식 계류 풀리의 구조적 취약 부분을 검토하였다. 반잠수식 계류 풀리의 주요 하중조건을 고려하여 구조모형시험을 수행하였으며, 재료의 최대인장응력 이상이 발생하는 위치에 대해 유한요소해석과 시험 결과를 비교하였다. 유한요소해석과 모형시험의 결과로부터 작동조건에서는 Body와 Wheel의 연결부 구조가 취약한 것으로 파악되었고, 계류조건에서는 Body와 Chain stopper의 연결부 구조가 취약한 것으로 검토되었다. 축소모형 구조시험에서 나타난 SMP의 구조 취약부는 구조해석의 결과와 일치하는 것으로 나타났다. 연구 결과를 통해 반잠수식 계류 풀리의 초기 설계에 대한 구조적 안전성을 실험적으로 검증할 수 있었다. 또한, 본 연구 결과는 상세설계 단계에서 반잠수식 계류 풀리의 구조 강도를 향상시키는데 유용하게 활용될 수 있을 것으로 판단된다.