• Steel and Composite Structures
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• 제34권3호
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• pp.377-391
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• 2020

A concrete filled steel tube (CFT) column with stiffeners has preferable behavior subjected to axial loading condition due to delay local buckling of the steel wall than traditional CFT columns without stiffeners. Welding lines in welded built-up steel box columns is expected to behave as longitudinal stiffeners. This study has presented a numerical investigation into the behavior of built-up concrete filled steel tube columns under axial pressure. At first stage, a finite element model (FE) has been built to simulate the behavior of built-up CFT columns. Comparing the results of FE and test has shown that numerical model passes the desired conditions and could accurately predict the axial performance of CFT column. Also, by the raise of steel tube thickness, the load bearing capacity of columns has been increased due to higher confinement effect. Also, the raise of concrete strength with greater cross section is led to a higher load bearing capacity compared to the steel tube thickness increment. In CFT columns with greater cross section, concrete strength has a higher influence on load bearing capacity which is noticeable in columns with more welding lines.

• 콘크리트학회논문집
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• 제11권5호
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• pp.3-10
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• 1999

Earthquake resistant R/C frame structures are generally designed to prevent the columns from plastic hinging. R/C columns under higher axial load or strong earthquake showed a brittle behavior due to the deterioration of strength and stiffness degradation. An experimental study was conducted to examine the behavior and to find the relationship between amounts of lateral reinforcements and compressive strength of ten R/C column specimens subjected to reversed cyclic lateral load and higher axial load. Test results are follows : An increase in the amount of lateral reinforcement results in a significant improvement in both ductility and energy dissipation capacities of columns. R/C columns with sub-tie provide the improved ductility capacity than those with closely spaced lateral reinforcement only. While the load resisting capacity of the high strength R/C columns is higher than the normal strength concrete columns under both an identical ratio of lateral reinforcement, however the ductility capacity of high strength R/C columns is decreased considerably. Therefore, the amounts of lateral reinforcement must be designed carefully to secure the sufficient ductility and economic design of HSC columns under higher axial load.

• Architectural research
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• 제7권1호
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• pp.39-48
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• 2005

Main objective of this research is to evaluate performance of high-strength concrete (HSC) columns for ductility and strength. Eight one-third scale columns with compressive strength of 69 MPa were subjected to a constant axial load corresponding to 30 % of the column axial load capacity and a cyclic horizontal load-inducing reversed bending moment. The variables studied in this research are the volumetric ratio of transverse reinforcement (${\rho}_s=1.58$, 2.25 %), tie configuration (Type H, Type C and Type D) and tie yield strength ($f_{yh}=549$ and 779 MPa). Test results show that the flexural strength of every column exceeds the calculated flexural capacity based on the equivalent concrete stress block used in the current design code. Columns with 42 % higher amounts of transverse reinforcement than that required by seismic provisions of ACI 318-02 showed ductile behaviour, showing a displacement ductility factor (${\mu}_{{\Delta}u}$) of 3.69 to 4.85, and a curvature ductility factor (${\mu}_{{\varphi}u}$) of over 10.0. With an axial load of 30 % of the axial load capacity, it is recommended that the yield strength of transverse reinforcement be held equal to or below 549 MPa.

• 콘크리트학회지
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• 제9권4호
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• pp.207-214
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• 1997

본 연구는변형구속에 의해 생기는 축력이 철근콘크리트 휨부재의 역학적 거동과 평균 균열간격에 미치는 영향을 검토하기 위해 수행되었다. 이를 위하여 변형구속 및 무구속 조건하에서의 휨강도와 휨강성을 실험으로 구하였으며, 또한 축방향 구속을 받는 휨부재의 평균 균열간격을 예측하는 식을 제안하였다.

• 대한토목학회논문집
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• 제33권5호
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• pp.1765-1775
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• 2013

콘크리트 공시체의 압축강도와 연성성능을 향상시키기 위하여 FRP 와이어의 적용을 실험적으로 연구하였다. 와이어 보강겹수와 콘크리트 압축강도의 변화가 고려된 와이어 보강 공시체의 압축실험을 실시하였다. FRP 와이어 보강 공시체 압축실험에서 측정된 축방향변형률, 원주방향변형률, 체적변형률에 의한 와이어 내부 콘크리트의 손상상태를 분석하여 와이어 보강효과를 평가하였다. FRP 와이어 보강 공시체의 응력-변형률 선도는 두 개의 직선구간과 변환구간으로 구성된 것으로 측정되었으며, 균열이후구간에서 응력상승거동하였다. 와이어 보강 공시체의 균열강도와 최대강도는 와이어 보강겹수에 비례하여 증가하는 것으로 평가되었다. 와이어가 3겹 보강된 35 MPa 공시체의 최대강도는 무보강 공시체의 압축강도보다 286% 높게 측정되었다. FRP 와이어 보강 공시체의 내부 콘크리트 파괴형태는 i) 수직균열 또는 경사균열파괴; ii) 수평균열파괴로 구분되었다. 특히, 수평균열파괴는 와이어에 의한 구속약화로 인하여 갑자기 내부 콘크리트가 팽창하는 부분과 와이어가 아직 내부 콘크리트를 효과적으로 구속하는 부분의 전단효과로 발생하였으며, 수평균열은 공시체의 중앙부를 기준으로 여러 면으로 발생하였으며, 와이어에 의한 구속효과가 우수한 공시체에 발생하였다. FRP 와이어 보강 공시체 압축실험에서 와이어 최대파단변형률에 대한 인장파단변형률의 비가 55-90%로 측정되었으며, 평균 69.5%로 나타났다. 이는 일반 FRP 시트 보강 공시체 실험에서 측정된 시트 파단변형률보다 다소 높은 값으로 FRP 와이어 보강 공법의 우수성을 입증한다.

• Geomechanics and Engineering
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• 제12권4호
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.761-764
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• 2008

본 연구는 40, 60, 80MPa급 고강도콘크리트의 변형특성에 있어서 $20{\sim}700^{\circ}C$ 범위로 상승되는 온도의 영향을 연구하는데 그 목적이 있다. 본 연구에서 시험의 종류는 설계하중 사전재하 및 잔존 강도 시험방법으로서 시험체를 가열하기 전에 극한강도의 25%하중을 사전재하한 후 가열을 실시하고, 가열하는 동안 하중을 유지하며, 목표온도에 도달한 후 고온상태 및 상온에서 24시간 냉각상태에서 시험체가 파괴될 때까지 재하를 실시했다. 시험은 W/B 46%, 32% 및 25%로 이루어진 콘크리트 시험체에 대하여 $20{\sim}700^{\circ}C$의 다양한 온도하에서 실시하였다. 시험결과 콘크리트 강도가 증가할수록 고온에서의 상대적인 탄성계수는 감소하였으며, 최대하중에서의 축방향 변형은 설계하중 사전 재하와 상관성이 높은 것으로 나타났다. 또한 온도상승에 따른 콘크리트의 열팽창변형은 압축강도뿐만 아니라 초기사전재하의 영향을 받는 것으로 나타났다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.941-946
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• 2001

The objectives of this study are to investigate effective stiffness of Rectangular reinforced concrete bridge columns. It is reasonable to use yielding effective stiffness of columns in seismic bridge design, especially in case that plastic hinges form at the bridge columns. In this study, the material nonlinear analysis was conducted for 3, 240 column sections of which variables were the concrete compressive stress, the steel yielding stress, the longitudinal steel location parameter, the longitudinal steel ratio, the axial load level, and the diameter of section. Based on the analytical results, an effective stiffness including two variables(longitudinal steel ratio and axial load ratio) was proposed by regression analyses, and it is compared with test results and the proposed equation for yielding effective stiffness of circular bridge columns.

• Steel and Composite Structures
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• 제21권3호
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• pp.461-477
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• 2016

Steel-concrete-steel (SCS) sandwich composite wall has been proposed for building and offshore constructions. An ultra-lightweight cement composite with density1380 kg/m3 and compressive strength up to 60 MPa is used as core material and inter-locking J-hook connectors are welded on the steel face plates to achieve the composite action. This paper presents the numerical models using nonlinear finite element analysis to investigate the load displacement behavior of SCS sandwich walls subjected to axial compression. The results obtained from finite element analysis are verified against the test results to establish its accuracy in predicting load-displacement curves, maximum resistance and failure modes of the sandwich walls. The studies show that the inter-locking J-hook connectors are subjected to tension force due to the lateral expansion of cement composite core under compression. This signifies the important role of the interlocking effect of J-hook connectors in preventing tensile separation of the steel face plates so that the local buckling of steel face plates is prevented.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.468-474
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• 1997

High strength concrete is a more effective material for columns subject to axial force and moment than for other structural elements. The purpose of this study is to review strength calculation methods for high strength concrete columus by comparison of analytical values and experimental results. The variables of column test under eccentric loading were concrete compressive strength, longitudinal steel ratio, and eccentricity of load. The tied column sections of 120×120mm and 210×210mm were tested and the eccentricity of load varied in the range from 0.16 times to 0.54 times the column depth. The analytical results using the stress-strain relationship to 0.54 times the column depth. The analytical results using the stress-strain relationship as well as the ACI's rectangular block, Zia's modified block, and the trapezoidal block are compared with experimentally obtained data, and discussed in this paper.