• Earthquakes and Structures
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• 제22권1호
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• pp.39-51
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• 2022

The axial compression behavior of nine self-compacting concrete columns confined with CFRP-PVC spirals was studied. Three parameters of spiral reinforcement spacing, spiral reinforcement diameter and height diameter ratio were studied. The test results show that the CFRP strip and PVC tube are destroyed first, and the spiral reinforcement and longitudinal reinforcement yield. The results show that with the increase of spiral reinforcement spacing, the peak bearing capacity decreases, but the ductility increases; with the increase of spiral reinforcement diameter, the peak bearing capacity increases, but has little effect on ductility, and the specimen with the ratio of height to diameter of 7.5 has the best mechanical properties. According to the reasonable constitutive relation of material, the finite element model of axial compression is established. Based on the verified finite element model, the stress mechanism is revealed. Finally, the composite constraint model and bearing capacity calculation method are proposed.

• Computers and Concrete
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• 제29권 5호
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• pp.285-301
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• 2022

This study aims at developing a torsional strength model based on a nonlinear analysis method presented in the previous studies. To this end, flexural neutral axis depth of a reinforced concrete section and effective thickness of an idealized thin-walled tube were formulated based on reasonable approximations. In addition, various sectional force components, such as shear, flexure, axial compression, and torsional moment, were considered in estimating torsional strength by addressing a simple and linear strain profile. Existing test results were collected from literature for verifications by comparing with those estimated from the proposed model. On this basis, it can be confirmed that the proposed model can evaluate the torsional strength of RC members subjected to combined loads with a good level of accuracy, and it also well captured inter-related mechanisms between shear, bending moment, axial compression, and torsion.

• 한국강구조학회 논문집
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• 제24권4호
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• pp.361-369
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• 2012

본 연구에서는 고강도 앵글을 사용한 선조립 합성기둥(PSRC 합성기둥)을 연구하였다. 2/3 축소모델의 PSRC 실험체 및 단면 중앙부에 H형강을 매입한 일반 SRC 실험체를 제작하여 중심압축실험을 수행하였다. 강재비와 횡철근 간격을 실험 변수로 고려하였다. 실험결과 단면 코너부 앵글에 의한 콘크리트 구속효과로 인하여 PSRC 합성기둥 실험체는 일반 SRC 합성기둥과 비교하여 하중 재하능력 및 변형능력이 우수한 것으로 나타났다. 또한 KBC 2009 설계기준에 의한 공칭압축강도보다 높은 하중저항능력을 나타냈다. 기존의 횡보강 콘크리트 재료모델을 적용하여 단면해석을 수행한 결과, 초기강성, 최대강도, 최대강도 이후의 강도 및 강성 저하 등에서 실험 및 해석결과가 비교적 잘 일치하는 것으로 나타났다.

• Steel and Composite Structures
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• 제27권4호
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• pp.495-508
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• 2018

In this paper, cyclic loading tests on composite frame inner joints of steel-reinforced recycled concrete (SRRC) column-steel beam were conducted. The main objective of the test was to obtain the shear behavior and analyze the shear strength of the joints. The main design parameters in the test were recycled coarse aggregate (RCA) replacement percentage and axial compression ratio. The failure process, failure modes, hysteresis curves and strain characteristics of the joints were obtained, and the influences of design parameters on the shear strength of the joints have been also analysed in detail. Results show that the failure modes of the joints area are typical shear failure. The shear bearing capacity of the joints maximally decreased by 10.07% with the increase in the RCA replacement percentage, whereas the shear bearing capacity of the joints maximally increased by 16.6% with the increase in the axial compression ratio. A specific strain analysis suggests that the shear bearing capacity of the joints was mainly provided by the three shear elements of the recycled aggregate concrete (RAC) diagonal compression strut, steel webs and stirrups of the joint area. According to the shear mechanism and test results, the calculation formulas of the shear bearing capacity of the three main shear elements were deduced separately. Thus, the calculation model of the shear bearing capacity of the composite joints considering the adverse effects of the RCA replacement percentage was established through a superposition method. The calculated values of shear strength based on the calculation model were in good agreement with the test values. It indicates that the calculation method in this study can reasonably predict the shear bearing capacity of the composite frame inner joints of SRRC column-steel beam.

• 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.

• 국제강구조저널
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• 제18권5호
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• pp.1525-1540
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• 2018

A test rig with multi-functional purposes was specifically designed and manufactured to study the behavior of multi-planar welded tubular joints subjected to multi-planar concurrent axial loading. An experimental investigation was conducted on full-scale welded tubular joints with each consisting of one chord and eight braces under monotonic loading conditions. Two pairs or four representative specimens (two specimens for each joint type) were tested, in which each pair was reinforced with two kinds of different internal stiffeners at the intersections between the chords using welded rectangular hollow steel sections (RHSSs) and the braces using rolled circular hollow steel sections (CHSSs) and welded RHSSs. The effects of different internal stiffeners at the chord-brace intersection on the load capacity of joints under concurrent multi-planar axial compression/tension are discussed. The test results of joint strengths, failure modes, and load-stress curves are presented. Finite element analyses were performed to verify the experimental results. The study results show that the two different joint types with the internal stiffeners at the chord-brace intersection under axial compression/tension significantly increase the corresponding ultimate strength to far exceed the usual design strength. The load carrying capacity of welded tubular joints decreases with a higher degree of the manufacturing imperfection in individual braces at the tubular joints. Furthermore, the interaction effect of the concurrent axial loading applied at the welded tubular joint on member stress is apparent.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.108-113
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• 2004

The compressive axial collapse tests were performed to investigate energy absorption characteristics of Al/CFRP compound tubes which are aluminum tubes wrapped with CFRP (Carbon Fiber Reinforced Plastics) outside the aluminum circular and square tubes. Based on collapse characteristics of aluminum tubes and CFRP tubes respectively, the axial collapse tests were performed for Al/CFRP compound tubes which have different fiber orientation angles. Test results showed that Al/CFRP compound tubes supplemented the unstable brittle failure of CFRP tubes due to ductile nature of inner aluminum tubes. In the light-weight aspect, specific energy absorption were the highest for Al/CFRP, CFRP in the middle, and aluminum the lowest. Also, specific energy absorption of circular tubes was higher than square tubes'. It turned out that fiber orientation angle of Al/CFRP compound tubes influence specific energy absorption together with the collapse modes of the tubes.

• 한국터널지하공간학회 논문집
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• 제10권3호
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• pp.303-312
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• 2008

암석의 물성평가 및 파괴모델 실험을 위하여 다축압축 실험이 자주 사용된다. 다축압축 실험을 통한 암반의 거동 평가시 정확한 결과의 산출을 위하여 실험체와 가압판 경계면에서의 경계조건에 대한주의를 기울일 필요가 있다. 일반적으로 철제로 된 일체형 가압판의 사용시 실험체의 경계면과 하중재하판사이에서 발생하는 마찰저항으로 인하여 실험체 경계부에서부터 응력회전 현상이 발생하여 경계면에서부터 작용하는 외력의 방향은 회전하게 된다. 이와 같은 실험체/하중재하판 경계면 사이에서 발생하는 마찰저항을 감소시키기 위하여 다양한 방법이 제시되었다. 그 중 대표적인 예가 빗살구조의 하중재하판이다. 본 논문에서는 빗살구조의 하중재하판의 단점을 극복하고 하중재하판의 공간이 상대적으로 덜 차지하는 롤러로 지지된 피스톤 형태의 하중재하판을 소개하고 있다. 롤러로 지지된 피스톤 형태의 하중재하판은 지지강성이 충분한 짧은 피스톤 후면에 샤프트 형태의 롤러를 설치하여 실험체의 변형과 동시에 각 피스톤이 동반하여 거동하도록 구성되었다. 본 논문에서는 롤러 지지된 피스톤의 구조 상세 및 요구되는 기능에 대한 검증을 위하여 측면부 마찰저항 실험과 이축압축 실험이 수행되었으며 실험결과와 수치해석 결과의 비교를 통하여 장비의 적용성에 대한 검증이 이루어 졌다.

• Advances in concrete construction
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• 제11권3호
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• pp.193-206
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• 2021

Extensive research has been conducted on the basic mechanical property and structural applications of engineered cementitious composites (ECC). Despite the high tensile ductility and high toughness of ECC, transverse steel reinforcement is still necessary to confine ECC for high performance. However, limited research has examined performance of ECC confined with practical amount of transverse reinforcement. This paper presents the results of axial compression tests on 14 square ECC columns and 4 conventional concrete columns (used as control specimens) with transverse reinforcement. The test variables were spacing, configuration (square ties or square and diamond shape ties), and yield strength of stirrups. The test showed that ECC columns confined with steel stirrup had good compressive ductility, and the stirrup spacing had the greatest effect on the compressive performance. The self-confinement effect of ECC results in a more uniform but slower expansion of the whole column compared with CC ones. The test results are then compared against the predictions from a number of existing models for conventional confined concrete. It is indicated that these models fail to predict the axial strains at peak axial stress and the trend of the stress-strain curve of steel stirrups-confined ECC with sufficient accuracy. Several new equations are then proposed for the compressive properties of steel-confined ECC based on test results and potential approaches for future studies are proposed.

• Steel and Composite Structures
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• 제16권4호
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• pp.437-454
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• 2014

The influence of spacers on the behaviour and ultimate capacity of intermediate length CFS open section columns under axial compression is investigated in this paper. The focus of the research lies in the cross- section predominantly, failed by distortional buckling. This paper made an attempt to either delay or eliminate the distortional buckling mode by the introduction of transverse elements referred herein as spacers. The cross-sections investigated have been selected by performing the elastic buckling analysis using CUFSM software. The test program considered three different columns having slenderness ratios of 35, 50 & 60. The test program consisted of 14 pure axial compression tests under hinged-hinged end condition. Models have been analysed using finite element simulations and the obtained results are compared with the experimental tests. The finite element package ABAQUS has been used to carry out non-linear analyses of the columns. The finite element model incorporates material, geometric non-linearities and initial geometric imperfection of the specimens. The work involves a wide parametric study in the column with spacers of varying depth and number of spacers. The results obtained from the study shows that the depth and number of spacers have significant influence on the behaviour and strength of the columns. Based on the nonlinear regression analysis the design equation is proposed for the selected section.