단일 현장타설말뚝의 변단면 분석을 통한 최적 기둥-말뚝 직경비 제안

김재영,정상섬,안상용,Kim, Jaeyoung,Jeong, Sangseom,Ahn, Sangyong 대한토목학회 2013 대한토목학회논문집 Vol.33 No.5

In this study, the behavior characteristics of bent pile structures with varying cross-section was examined through the measured results of field load test. A framework for determining the bending stress is calculated based on the stresses in the circumference of the pile using 3D finite element analysis. It is found that the bending stress near the pile-column joint changes rapidly and fracture zones occurs easily at variable cross-sections in bent pile structures. Also, the optimized column-pile diameter ratio was analyzed through the relationship between the column-pile diameter ratio and lateral crack load ratio. Based on this study, the optimized column-pile diameter ratio can be obtained near the inflection point of the curve between the column-pile diameter ratio and lateral crack load ratio. Therefore, a present study by considering the optimized variable cross-section condition would be improved bent pile structures design. 본 연구에서는 변단면 단일 현장타설말뚝의 거동 특성을 평가하고자 현장재하시험 사례를 분석하였으며, 또한 3차원 유한요소해석을 이용하여 말뚝 내부에서 발생하는 응력을 통해 심도별 휨응력을 산정하였다. 분석 결과, 단일 현장타설말뚝의 변단면 부근에서 휨응력이 집중되어 재료파괴가 발생하기 가장 쉬운 것을 알 수 있었다. 이를 토대로, 단일 현장타설말뚝의 기둥-말뚝 직경비와 수평 균열하중비 관계를 통해 최적의 기둥-말뚝 직경비를 제안하였다. 연구 결과, 최적의 기둥-말뚝 직경비는 기둥-말뚝 직경비와 수평 균열하중비 관계 곡선의 변곡점 부근에서 산정되었으며, 단일 현장타설말뚝 설계에 최적 변단면 특성을 고려한다면 개선된 설계가 이루어질 수 있을 것으로 판단되었다.

저축력과 반복수평력을 받는 콘크리트충전 강관기둥의 이력특성

최성모,강석빈,김대중,Choi, Sung Mo,Kang, Suk Bin,Kim, Dae Joong 한국강구조학회 2003 韓國鋼構造學會 論文集 Vol.15 No.2

콘크리트충전 강관구조는 합성효과에 의해 강관과 콘크리트의 단점을 상호보완하여 역학적으로 우수한 성능을 발휘할 수 있다. 그래서, 최근에는 고층건물에 구조시스템의 대안으로서 주목을 받고 있다. 본 연구의 목적은 일정축력과 반복 수평력을 받는 콘크리트충전 강관기둥의 내력 및 변형성능을 평가하는 것이다. 이 실험의 변수로는 강관의 폭두께비, 축력비 및 강관의 형상으로 정하여 총 18개의 실험체를 제작하여 실험하였다. 실험결과로부터 실험체의 최대내력 및 변형성능에 대해 검토하였다. The Concrete Filled Steel Tube (M) Column has excellent structural capacities that are in accordance with the interaction effect between the steel tube and concrete. CFT structure has been focussed on a struc tural system for high-rise buildings. The purpose of this study is to evaluate the strength and deformation capacities of CFT columns that are subject to constant axial and cyclic lateral load. The test parameters are diameters to the thickness ratio of the steel tube, axial load ratios, and the shapes of the tube. Total eighteen specimens were fabricated to clarify the energy absorption capacity of the CFT columns. Experimental results were summarized for their ultimate strengths and deformation capacities.

중심과 편심축력을 받는 중공 프리캐스트 콘크리트 합성기둥의 압축강도

이승준(Lee, Seung-Jun),서수연(Seo, Soo-Yeon),김강수(Kim, Kang-Su) 대한건축학회 2015 大韓建築學會論文集 : 構造系 Vol.31 No.2

In this paper, in order to evaluate the applicability of KBC formula in calculating the strength of hollow-precast concrete (HPC) column for design purpose, a compressive capacity was evaluated through the concentric and eccentric test for the columns with various material strength and hollow size, respectively. Based on the test result, the suitability of code formulae was checked and the lateral confining effect of HPC composite column was also evaluated by using Mander’s stress-strain relationship. Also, nonlinear sectional analysis process was performed. As a result, it was found that the strength of the HPC composite column could be suitably predicted by using KBC code formulae for design purpose. In the calculation of the compressive strength of the column by using Mander model considering the lateral confining effect of hoop, the confining effect of it in HPC was less than that in reinforced concrete column and changed corresponding to the concrete strength ratio between PC and CIP (Cast-In-Place). The effect decreases when the concrete strength of CIP is not less than that of PC. The flexural-compression capacity of HPC composite column can be suitably evaluated by using the effective strength of concrete.

대구경 콘크리트 충전형 합성기둥의 전단 설계식 분석

정은비,염희진,유정한,Jung, Eun Bi,Yeom, Hee Jin,Yoo, Jung Han 한국강구조학회 2015 韓國鋼構造學會 論文集 Vol.27 No.4

콘크리트 충전형 합성기둥(Concrete filled steel tube, CFT)은 철근콘크리트, 강구조보다 뛰어난 변형 능력과 강도 갖고 있다. CFT 현장타설말뚝은 지진하중, 토양액상화 등에 의해 큰 국부전단력을 경험하게 되며 이를 방지하기 위해 큰 직경으로 설계되어 진다. 그러나 현행 기준의 전단 설계식은 CFT의 구속효과를 고려하지 못하고 있으며, 상당히 보수적인 설계식을 제시하고 있다. 전단 설계식의 개선을 위한 선행 전단 실험연구가 거의 없으며 그조차 소구경의 실험연구로만 존재한다. 이 연구는 대구경 콘크리트 충전형 합성기둥의 개선된 전단 설계식을 제안하기 위한 기초연구로써, 원형 CFT 기둥 전단의 선행 실험연구와 현행 설계기준 비교분석을 실행하였다. Concrete filled steel tube(CFT) has outstanding deformation capacity and strength in comparison with reinforced concrete or steel tube. CFT drilled shaft, which is developed large shear force due to seismic load and soil liquefaction, is designed as large diameter. However, shear design equations of the current standards do not consider bond stress of CFT and it results in extremely conservative design. Currently, previous studies for improving shear equations scarcely exist and are impossible applied to large CFT drilled shafts since these studies focus on only small scale experimental research. In this study, eventually to propose improving shear equation of large diameter CFT, it is preliminary research to compare and investigate the previous studies and current standards.

소성변형과의 상관성 및 추정모델을 통한 변형강도 시험장치 변수 분석

김광우,이문섭,김성태,이순제,Kim, Kwang-Woo,Lee, Moon-Sup,Kim, Sung-Tae,Lee, Soon-Jae 한국도로학회 2002 한국도로포장공학회 논문집 Vol.4 No.4

This study dealt with analysis of size effect of testing apparatus for Kim test which measures rut resistance characteristics of asphalt mixture under static loading. Two columns in different diameter with each column having different radios of round cut (Curvature) at the bottom were used for testing asphalt mixture. Deformation load ($P_{max}$) and deformation strength ($K_D$) were found to have relatively high correlation with rut depth and dynamic stability of asphalt concrete. Diameter of specimen was not a significant factor in this test. From the statistical correlation analysis with rutting properties, the radius of curvature and diameter of loading column were found to be important factor affecting the results of the test. Among the radios (r) of curvatures, r=0.5cm and 1.0cm showed much higher correlation than the column without curvature, and r=1.0cm being better between the two. The column with diameter of 4cm showed better correlation than diameter of 3cm. Therefore, the column of 4cm diameter with r=1.0cm was found to be the best among various apparatus sizes. Prediction models for rut depth and dynamic stability were developed for each aggregate mixture based on Kim test variables using SAS STEPWISE procedure. Therefore, if this test method is validated through further study, Kim test can be used for selecting asphalt mixture with the highest resistance against permanent deformation. 본 연구는 아스팔트 콘크리트 포장의 소성변형 추정을 보다 쉽게 하기 위하여 새로운 시험기법인 김테스트의 변형강도 및 시험 장비를 개발함에 있어 적정규격을 선정하기 위한 것이나. 김테스트에서 하중봉의 직경(D) 및 하중봉 하단의 원형처리 반경(r)이 시험결과에 미치는 영향을 파악하기 위하여 다양한 혼합물에 대하여 D와 r을 변화시켜가며 실험을 수행하였다. r에 따른 변형강도 및 변형하중과의 상관관계 분석결과 r=0.5와 1.0cm로 원형 처리한 측정값에서 소성변형과 높은 상관성을 보여주었다. 공시체의 직경(S)은 중요 변인이 아니었으며, 하중봉은 직경 4cm에 반드시 하단을 원형처리를 해야하고 이때의 절삭 반경 r은 1.0cm가 가장 좋은 것으로 나타났다. 통계프로그램 SAS의 STEPWISE 를 이용하여 골재별로 변형강도로부터 소성변형 깊이 및 동적 안정도를 추정하기 위해 모델을 개발하였으며 $R^2$은 0.95이상이 얻어졌다. 향후 보다 많은 실험을 통해 이 시험법의 표준화 연구가 지속적으로 이루어져야 할 것이며, 새로운 배합설계 방법을 개발한다면 본 실험법의 적용을 검토해 볼 필요가 있을 것이다.

중심과 편심축력을 받는 중공 프리캐스트 콘크리트 합성기둥의 압축강도

이승준,서수연,김강수,Lee, Seung-Jun,Seo, Soo-Yeon,Kim, Kang-Su 大韓建築學會 2015 大韓建築學會論文集 : 構造系 Vol.31 No.2

In this paper, in order to evaluate the applicability of KBC formula in calculating the strength of hollow-precast concrete (HPC) column for design purpose, a compressive capacity was evaluated through the concentric and eccentric test for the columns with various material strength and hollow size, respectively. Based on the test result, the suitability of code formulae was checked and the lateral confining effect of HPC composite column was also evaluated by using Mander's stress-strain relationship. Also, nonlinear sectional analysis process was performed. As a result, it was found that the strength of the HPC composite column could be suitably predicted by using KBC code formulae for design purpose. In the calculation of the compressive strength of the column by using Mander model considering the lateral confining effect of hoop, the confining effect of it in HPC was less than that in reinforced concrete column and changed corresponding to the concrete strength ratio between PC and CIP (Cast-In-Place). The effect decreases when the concrete strength of CIP is not less than that of PC. The flexural-compression capacity of HPC composite column can be suitably evaluated by using the effective strength of concrete.