• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.4 s.74
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• pp.375-387
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• 2006

Different from the previous studies which investigated seismic P-$\Delta$ effect in slender columns though comparison of response spectra according to stability coefficients obtained from the analyses based on the assumed moment-curvature relationship, the axial force and P-$\Delta$ effect in RC columns are investigated on the basis of the layered section method which can effectively consider the changes of stiffness and yield strength due to the application of axial force in RC members. Practical ranges of slenderness and stability coefficient are assumed, and sixty sets of horizontal/vertical earthquake inputs are used in the analysis. From the parametric study, it is noted that the maximum deformation of the slender RC column is hardly affected by P-$\Delta$ effect or vortical earthquake but dominantly affected by the applied axial force. Therefore, it can be concluded that no additional consideration for the P-$\Delta$ effect and vortical earthquake is required in the seismic design of a slender RC column if the axial force effect is taken into account in the analysis and design procedures.

• 기술발표회
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• s.2006
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• pp.193-198
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• 2006

서울지하철 0호선 000 공구 000 정거장 구간은 버팀보 7단, 어스앵커 2단, 그리고 록볼트 3단의 개착식 가시설로 설계되어 있다. 버팀보 및 앵커 축력 계측을 위해 변형률계 및 하중계를 설치하고 연속계측 중, 4~6단 버팀보 수 개소에서 5월부터 하중이 급격히 증가하엿다. 따라서 굴착작업을 즉시 중단하고 관리기준치를 초과하는 하중이 계측된 STA.9k+750~800 구간의 5, 6단 버팀보 위치에 격간으로 총 20본(10본${\times}$2단), 그리고 STA.9k+900~920 구간의 7단 버팀보 위치에 격간으로 총 9본(9본${\times}$1단)의 버팀보를 추가적으로 설치 완료하였다. 이 때, 추가 버팀보는 선행하중잭을 이용하여 10ton의 선행하중을 재하하였으며, 향후 추가 보강 필요시 재하하중 증가가 가능하도록 조치하였다. 또한, 추가 설치된 버팀보, 그리고 이상하중이 발생된 버팀보에 계측기를 추가 설치하여 지속적으로 계측중이며, 띠장의 변위발생 구간은 스티프너 및 앵글 등을 응급조치하였다. 본 사례 연구에서는 보강 전.후의 계측결과 및 수치해석적 분석을 이용하여 가시설 굴착시 버팀보의 하중증가 원인 및 보강 효과를 규명하고, 향후 추가 굴착시의 안정성 여부를 검토해 보고자 하였다. 계측값 분석 결과, 추가버팀보 보강 후의 기존버팀보 축력 계측 결과 보강 직후 기존버팀보의 축력이 어느정도 감소하였으며, 이후 시간이 지남에 따라 축력이 더 이상 증가하지 않고 일정한 값에 수렴하는 경향을 보였다. 또한 수치해석 결과 온도 증가가 버팀보 축력증가에 미치는 영향은 버팀보 위치의 지반강성이 클수록 크며, 축력증가는 온도증가에 대체적으로 비례하였고, 추가버팀보의 보강 효과는 선행하중의 크기에 비례하는 것으로 나타났으며, 잔여굴착은 전반적으로 기존 버팀보의 축력 증가에 영향을 미치는 것으로 나타났다. 따라서 추가굴착시 지속적인 계측을 수행하며, 급격한 축력증가가 관찰될 경우 현재 보강된 버팀보의 선행하중 추가 재하, 굴착에 가장 큰 영향을 받는 최하단 버팀보의 추가보강 등의 대책방안을 제시하였다.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.85-92
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• 2015

It is well known that axial tension decreases the shear strength of RC & PSC beams without transverse reinforcement, and axial compression increases the shear resistance. What is perhaps not very well understood is how much the shear resistance capacity is influenced by axial load. RC beams without shear reinforcement subjected to large axial compression and shear may fail in a very brittle manner at the instance of first diagonal cracking. As a result, a conservative approach should be used for such members. According to the ACI Code, the shear strength in web is calculated by effect of axial force and the vertical force in the stirrups calculated by $45^{\circ}$ truss model. This study was performed to examine the effect of axial force in reinforced concrete beams by nonlinear FEM program (ATENA-2D).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.11
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• pp.4418-4426
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• 2010

Muscle fatigue often induces deterioration of postural balance and muscle contraction, such as strength or maximal voluntary contraction(MVC). This study was to investigate the effects of transcutaneous electrical stimulation(TENS) applied to the fatigued muscles on postural imbalance and decline in muscle strength following fatigue of triceps surae. For the 4 months from March, 2010, twenty healthy subjects without vestibular disease and visual disturbance were recruited and induced muscle fatigue of triceps surea performed by repeated voluntary contraction. TENS was applied to gastocnemius immediately after development of muscle fatigue. Postural sway length, velocity and MVC were recorded under these conditions: pre-fatigue, post-fatigue, and TENS application to fatigued muscle during post-fatigue. Muscle fatigue increased postural imbalance as expressed by sway length and velocity and decreased muscle contraction(p<.05), while TENS improved the postural imbalance and MVC following muscle fatigue during stance(p<.05). The results suggested that fatigue on plantar flexor is associated with postural balance and muscle contraction, and TENS application to fatigued muscle was effective in improving postural imbalance and decline in muscle strength following muscle fatigue. TENS will be an effective method in exercise, working environment and daily life.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.173-180
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• 2014

In the design of tunnel segment structure, axial and moment forces are considered as significant forces. Since axial force is much greater than moment force, the whole section of segment remains in compression. Therefore crack width can be reduced. But the axial force is not considered in criteria for serviceability check. This fact leads service condition more severe compared to ultimate condition and makes the required steel reinforcement increase to meet the serviceability criteria. In this study, the effect of axial force on serviceability of tunnel segment is evaluated, experimentally and analytically. Mock-up tests on segments with actual size were performed and investigated in terms of initial crack resistance. The evaluation proves that more comprehensive design could be achieved when the axial force is considered in the procedure for the serviceability check in design of tunnel segment.

• Fire Science and Engineering
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• v.24 no.6
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• pp.104-111
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• 2010

The strength of steel in a concrete filled steel tube (CFT) is reduced in a fire, but the concrete filled structurally ensures the fire resistance due to its high thermal capacity. This research analyzed the fire resistance performance due to the variances of concrete strength filled inside of steel tube and the load ratios, which can influence on the fire resistance of CFT. As $280{\times}280{\times}6$ CFT columns with the concrete strengths of 24 MPa and 40 MPa and the axial load ratios of 0.9, 0.6, and 0.2 in accordance with KS F 2257-1 and 7 were heated with loading to examine the fire resistance performance, the fire resistance used to 24 MPa concrete showed 27, 113, and 180 minutes according to the axial load ratios, 0.9, 0.6, and 0.2 respectively. In case of 40 MPa concrete, the fire resistance were turned out to be 19 and 28 minutes for the axial load ratios, 0.9 and 0.6 respectively. The results of fire resistance with 40 MPa concrete showed the much lower fire resistance performance than those of 24 MPa concrete. In case of 40 MPa, the fire resistance performance was not increased significantly according to the axial load ratio than that of 24 MPa. The main reason why the higher concrete strength showed lower fire resistance than that of lower guessed the internal stress had the concrete strength weak.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.297-300
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• 2010

본 논문에서는 일반적인 해석, 시공단계를 고려한 해석, 시공단계와 장기거동을 고려한 해석의 3가지 해석방법을 사용하여 수평부재의 설계에 적합한 해석방법을 제안하였다. 80층의 2D 구조모델에 3가지 해석방법을 적용하여 각 해석방법에 따라 부등축소량, 수직부재에 작용하는 축력, 수평부재의 단부에 작용하는 내력의 해석결과를 얻어 비교하였다. 또한 부재의 내부에서 철근과 콘크리트의 하중분담율의 시간에 따른 변화양상을 알아보았다. 해석결과 시공단계에 의한 영향은 수평부재에 작용하는 축력과 부등축소량 예측, 부재 내력 해석에 있어서 반드시 고려되어야 함을 알 수 있었다. 장기거동의 효과는 기둥축소에는 크게 영향을 미치지만 수직부재의 축력, 수평부재의 내력에는 변형만큼의 영향은 보이지 않는다. 시공시의 보정량을 결정하기 위해서는 장기거동이 반드시 고려되어야 하지만 부재의 단면설계의 목적으로는 제외되어도 무방할 것으로 판단된다.

• Journal of Korean Society of Steel Construction
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• v.12 no.2 s.45
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• pp.209-219
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• 2000

Concrete Filled steel Tube(CFT) Column has an excellent structural capacities in accordance with an interaction effect between the steel tube and concrete. Recently, CFT structure has been focussed on a structural system for a high-rise buildings. The purpose of this study is to evaluate a strength and deformation capacity of CFT square columns subjected to constant axial and cyclic lateral load. The test parameters are diameters to thickness ratio of steel tube, axial load ratios, concrete strengths, load applying types and whether or not filled concrete. Total sixteen specimens are fabricated to clarify the energy absorbtion capacity of CFT columns. Experimental results are summarized for maximum strength, initial stiffness and deformation capacity.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.161-168
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• 2006

An experimental investigation was conducted to examine the hysteretic behaviors of ultra-high strength concrete tied columns. The purpose of this study is to investigate the safety of ultra-high strength concrete columns with 100 MPa compressive strength for the requirement of ACI provisions. Eight 1/3 scaled columns were fabricated to simulate an 1/2 story of actual structural members with the cross section $300{\times}300mm$ and the aspect ratio 4. The main variables are axial load ratio, configurations and volumetric ratios of transverse reinforcement. The results show that the deformability of columns are affected by the configurations and volumetric ratios of transverse reinforcement. Especially, it has been found that the behavior of columns are affected by axial load ratio rather than the amounts and the configurations of transverse reinforcement. Consequently, to secure the ductile behavior of 100 MPa ultra-high strength concrete columns, ACI provisions for the requirement of transverse steel may considered axial load level and the details of transverse reinforcement.

• Journal of Korean Society of Steel Construction
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• v.15 no.1
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• pp.87-96
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• 2003

The Ssteel-Cconcrete (SC) Ccomposite Ccolumn is a new Ccomposite Ccolunin system, where hoops are welded between flanges of H-shapesd steel and concrete is filled in spaces between flanges are filled with con crete. Tests of SC composite columns were performed previously to determine their compression, bending and shear strength, and it showed good structural behavior. But sSince a column is usually subjected to an axial compression force, and bending it ihas needed to be bent forevaluate its structural behavior to be evaluated when its axial load and bending isaresimultaneously applied to the SC composite column. In this paper, tests were conducted to investigate the bending strength of SC composite columns subjected to axial compression force and bending moment. The parameters of the tests were concrete, a stud bolt, a hoop and a magnitude of axial compression. The test results showed that the maximum bending strength and ductility of an SC composite column were increased by 33-42% and 33-63%, respectively, comparinged to those of a bare steel column. Also, the results obtained bywith the Korean Limit State Design Code (LSD) presents a considerably safe side value compared to those of the Eurocode-4 and the Japan Code. However, wWhen the axial compression force is was increased, however, there awere considerable differences between the maximum strength obtained by the test and the LSD analysis. For this reason, it is recommended tothe use of the Eurocode-4 is recommended when calculates the strength of an SC composite column is being calculated, since the Eurocode-4 gives us a better estimation.