• 콘크리트학회논문집
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• 제14권4호
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• pp.578-588
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• 2002

철근콘크리트 구조물은 일반적으로 지진에 연성적으로 거동하도록 설계되며, 이러한 연성적인 거동을 위하여 구조부재는 주의 깊게 상세 설계되어진다. 모멘트 연성골조 구조물의 경우 기둥의 소성힌지 구역에서 횡보강근의 상세는 중요한 고려사항이다. 수 년 동안 강도와 연성을 항상시키기 위한 횡보강근의 상세에 대한 인구가 많은 연구자들에 의해 진행되어 왔고, 그 결과 횡보강근에 의한 코아 콘크리트의 적절한 구속과 주근의 횡방향 지지는 기둥의 연성을 가장 효과적으로 증진시키는 것으로 증명되었다. 횡보강근에 의해 구속된 콘크리트의 강도와 연성증진을 고려한 응력-변형률 특성에 대한 연구는 지난 30년 동안 급속하게 이루어졌다. 그러나 현재까지도 구속된 고강도 콘크리트의 특성을 정확하게 예측할 수 있는 모델은 거의 없으며, 이에 대한 자료도 부족한 것으로 보고되고 있다. 따라서 본 연구에서는 콘크리트 강도, 횡보강근의 체적비, 횡보강근의 배근형태 및 간격, 주근의 배열을 주요변수로 하여 고 강도 콘크리트를 사용한 Large-Scale의 기둥을 대상으로 구조실험을 수행하였다. 연구결과 기존 모델의 일부는 최대 응력을 과대평가, 최대 응력에서의 변형률을 과소평가하는 것으로 나타났으며, 대부분의 모델이 응력-변형률 곡선의 하강부분을 합리적으로 예측하지 못하는 것으로 나타났다. 따라서 구속된 고 강도 콘크리트의 거동을 정확히 예측하여 설계에 반영될 수 있는 합리적이면서 실용적인 모델의 개발이 요구된다 하겠다.

• 한국강구조학회 논문집
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• 제17권3호통권76호
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• pp.357-363
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• 2005

건축물이 고층이 될 수록 고강도 강재의 사용요구가 증대된다. 그러나 고강도 강재는 일반 강재와는 전혀 다른 기계적 특성을 갖고 있다. 고강도 강재를 건축구조물에 적용하기 위해서는 비탄성 영역에서의 거동이 일반 강재와 동등한가를 확인해야 한다. 본 연구에서는 SM570TMC 강재로 제작된 박스형 및 H형 단면을 갖는 기둥의 국부좌굴강도를 평가하기 위해서 중심압축실험을 세장비를 변수로 수행하였다. 단주압축 실험결과 판폭두께비의 제한치를 만족하는 기둥부재의 최대내력은 국부좌굴에 의해 결정되며, 판폭두께비를 만족시키지 못하는 경우에는 최대내력에 도달하기 전에 국부좌굴이 발생되었으나 급격한 내력저하는 발생되지 않았다. 장주압축 실험결과 SM570TMC 강재는 허용응력도 설계법과 한계상태 설계법에서 정하고 있는 설계기준을 만족하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제15권1호
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• pp.103-111
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• 2011

이 연구에서는 나선철근으로 횡구속된 순환골재 콘크리트의 구조적 거동을 평가하였다. 주요 실험변수는 골재의 종류와 나선철근의 철근비로 계획하였다. 총 18체의 실험체를 제작하였으며, 실험체의 직경과 높이는 각각 150mm와 300mm이었다. 실험체는 사용된 굵은 골재의 종류에 따라 2가지로 구분할 수 있으며, 나선철근의 철근비는 0%에서 1.75%까지 변화하도록 계획하였다. 실험체의 축방향 및 횡방향 변형을 측정하기 위하여, 6개의 LVDT를 실험체에 부착하였다. 또한 나선철근의 변형률을 측정하기 위하여 스트레인 게이지를 120도 간격으로 나선철근에 부착하였다. 실험결과로부터, 나선철근으로 횡구속된 순환 골재 콘크리트의 구조 성능은 나선철근의 철근비와 관계없이 천연골재 콘크리트와 서로 유사함을 확인하였다.

• 한국강구조학회 논문집
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• 제19권5호
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• pp.483-492
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• 2007

최근 대형 장스팬 규모에 많이 적용되는 PEB 시스템은 휨모멘트의 크기에 따라 부재형상을 최적화 한 변단면부재를 사용함으로써 경제적인 경쟁력을 갖는 구조시스템이다. 그러나 PEB 시스템의 관련기술은 대부분 외국에서 수입된 것으로 구조거동에 관한 연구 및 국내 설계규준이 미비하다. 특히 PEB 시스템에서의 변단면부재(래프터)들은 비조밀단면(noncompact section) 또는 세장단면(slender section)을 갖는 경우가 많으므로 좌굴에 대한 영향을 많이 받게 된다. 따라서 본 연구에서는 웨브의 판폭두께비, 스티프너 유무, 횡비지지길이 등을 변수로 하여 총 4개의 실대형 실험체를 제작 휨성능 실험을 수행하였다. 이에 대하여 세장한 웨브 변단면 부재의 구조 안정성을 실험적으로 평가하고 PEB 시스템의 설계를 위한 기초자료를 제공하고자 한다.

• Steel and Composite Structures
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• 제47권6호
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• pp.709-728
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• 2023

Experimental and analytical studies were conducted to clarify the influencing mechanisms of the longitudinal reinforcement on performance of axially loaded Reinforced Concrete-Filled Steel Tube (R-CFST) short columns. The longitudinal reinforcement ratio was set as parameter, and 10 R-CFST specimens with five different ratios and three Concrete-Filled Steel Tube (CFST) specimens for comparison were prepared and tested. Based on the test results, the failure modes, load transfer responses, peak load, stiffness, yield to strength ratio, ductility, fracture toughness, composite efficiency and stress state of steel tube were theoretically analyzed. To further examine, analytical investigations were then performed, material model for concrete core was proposed and verified against the test, and thereafter 36 model specimens with four different wall-thickness of steel tube, coupling with nine reinforcement ratios, were simulated. Finally, considering the experimental and analytical results, the prediction equations for ultimate load bearing capacity of R-CFSTs were modified from the equations of CFSTs given in codes, and a new equation which embeds the effect of reinforcement was proposed, and equations were validated against experimental data. The results indicate that longitudinal reinforcement significantly impacts the behavior of R-CFST as steel tube does; the proposed analytical model is effective and reasonable; proper ratios of longitudinal reinforcement enable the R-CFSTs obtain better balance between the performance and the construction cost, and the range for the proper ratios is recommended between 1.0% and 3.0%, regardless of wall-thickness of steel tube; the proposed equation is recommended for more accurate and stable prediction of the strength of R-CFSTs.

• Steel and Composite Structures
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• 제50권1호
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• pp.1-13
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• 2024

The objective of this research is to study experimentally and numerically the behavior of steel beam columns with openings. Although the presence of openings in the beam columns is inevitable, finding ways to maintain strength is crucial. The studied parameters are opening shape, the ratio between opening height to specimen height, the percentage of opening location from support to beam column length, and web slenderness. Experimental tests are conducted including twelve specimens to study the effect of these parameters and record failure load, load deflection curve, and stress strain curve. Two failure modes are observed: local and flexural buckling. Interaction curves plotted from finite element model analysis are also used to expand the parametric study. Changing the location of the opening can decrease failure load by up to 7% and 60% in both normal and moment ratios respectively. Increasing the opening dimension can lead to a drop in the axial ratio by up to 29% and in the moment ratio by up to 74%. The weakest beam column behavior is noticed in specimens with rectangular openings which results from uneven and concentrated stresses around the opening. The main results of this research illustrate that the best location for opening is at 40% - 50% from beam column support. Also, it is advisable to use circular openings instead of rectangular openings in specimens having slender webs because moment ratios are raised by 85% accompanied by a rise in normal ratios by 9%.

• Structural Engineering and Mechanics
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• 제73권6호
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• pp.685-698
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• 2020

The dynamic stability of a functionally graded polymer microbeam reinforced by graphene oxides subjected to a periodic axial force is investigated. The microbeam is assumed to rest on an elastic substrate and is subjected to various immovable boundary restraints. The weight fraction of graphene oxides nanofillers is graded across the beam thickness. The effective Young's modulus of the functionally graded graphene oxides reinforced composite (FG-GORC) was determined using modified Halpin-Tsai model, with the mixture rule used to evaluate the effective Poisson's ratio and the mass density. An improved third order shear deformation theory (TSDT) is used in conjunction with the Chebyshev polynomial-based Ritz method to derive the Mathieu-Hill equations for dynamic stability of the FG-GORC microbeam, in which the scale effect is taken into account based on modified couple stress theory. Then, the Mathieu-Hill equation was solved using Bolotin's method to predict the principle unstable regions of the FG-GORC microbeams. The numerical results show the effects of the small scale, the graphene oxides nanofillers as well as the elastic substrate on the dynamic stability behaviors of the FG-GORC microbeams.

• 콘크리트학회논문집
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• 제16권4호
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• pp.565-572
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• 2004

The mechanical behavior of concrete-filled glass fiber reinforced polymer columns is affected by various factors including concrete strength, stiffness of tube, end confinement effect, and slenderness ratio of members. In this research the behavior of slender columns was examined both experimentally and analytically. Experimental works include 1) compression test with 30cm long glass fiber composite columns under different end confinement conditions, 2) uni-axial compression test for 7 slender columns, which have various slenderness ratios. Short-length stocky columns gave high strength and ductility revealing high confinement action of FRP tubes. The strength increment and strain change were examined under different end confinement conditions. With slender columns, failure strengths, confinement effects, and stress-strains relations were examined. Through analytical work, effective length was computed and it was compared with the amount of reduction in column strength, which is required to predict design strength with slender specimens. This study shows the feasibility of slender concrete-filled glass fiber reinforced polymer composite columns.

• Geomechanics and Engineering
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• 제8권6호
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• pp.769-781
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• 2015

The skin friction of a pile foundation is important and essential for its design and analysis. More attention has been given to the softening behaviour of skin friction of a pile. In this study, to investigate the load-transfer mechanism in such a case, an analytical solution using a nonlinear softening model was derived. Subsequently, a load test on the pile was performed to verify the newly developed analytical solution. The comparison between the analytical solution and test results showed a good agreement in terms of the axial force of the pile and the stress-strain relationship of the pile-soil interface. The softening behaviour of the skin friction can be simulated well when the pile is subjected to large loads; however, such behaviour is generally ignored by most existing analytical solutions. Finally, the effects of the initial shear modulus and the ratio of the residual skin friction to peak skin friction on the load-settlement curve of a pile were investigated by a parametric analysis.

• Geomechanics and Engineering
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• 제7권3호
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• pp.279-295
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• 2014

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.