• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
• /
• pp.487-492
• /
• 2003

High-strength concrete(HSC) is a new construction material with enormous potential. Structures using high-strength concrete are to be coming more and more popular. But high-strength reinforced concrete columns show brittle behavior. It, therefore, is necessary to improve the ductility of HSC members. The purpose of this study is to investigate the ductility and strength of high-strength columns with variable lateral confinement under concentric axial load. Five HSC columns with compressive strength 68㎫ are designed with variable lateral confinements such as carbon fiber sheet(CFS), glass fiber sheet(GFS), and metal lath. Test results indicate that specimen confined by CFS show 11% higher maximum strength, 2.74 times ductility than A specimen using hoop. On comparing with the specimen A and B confined metal lath instead of hoop, strength decrease of 3%, and ductility increase of 1.21 times were observed.

• Computers and Concrete
• /
• 제25권5호
• /
• pp.383-400
• /
• 2020

Due to higher stiffness to weight, higher corrosion resistance, higher strength to weight ratios and good durability, concrete composite structures provide many advantages as compared with conventional materials. Thus, they have wide applications in the field of concrete construction. This research focuses on the structural behavior of steel-tube CFRP confined concrete (STCCC) columns under axial concentric loading. A nonlinear finite element analysis (NLFEA) model of STCCC columns was simulated using ABAQUS which was then, calibrated for different material and geometric models of concrete, steel tube and CFRP material using the experimental results from the literature. The comparative study of the NLFEA predictions and the experimental results indicated that the proposed constitutive NLFEA model can accurately predict the structural performance of STCCC columns. After the calibration of NLFEA model, an extensive parametric study was performed to examine the effects of different critical parameters of composite columns such as; (i) unconfined concrete strength, (ii) number of CFRP layers, (iii) thickness of steel tube and (iv) concrete core diameter, on the axial load capacity. Furthermore, a large database of axial strength of 700 confined concrete compression members was developed from the previous researches to give an analytical model that predicts the ultimate axial strength of composite columns accurately. The comparison of the predictions of the proposed analytical model was done with the predictions of 216 NLFEA models from the parametric study. A close agreement was represented by the predictions of the proposed constitutive NLFEA model and the analytical model.

• 한국강구조학회 논문집
• /
• 제8권4호통권29호
• /
• pp.59-76
• /
• 1996

Concrete filled steel tube column has a large load carrying capacity through its steel and concrete interaction which makes it useful in construction. However, it has not been used often in a practical construction field. This is partly due to the non-destructive inspection method for concrete filling which has yet to be established. Furthermore, there are the lack of test data and a practical method in evaluating the ultimate load carrying capacity of concrete filled steel tube column. This paper will attempt to predict the ultimate strength of short concrete filled square tubular steel columns through conducting several tests. To accumulate the new test data on concrete filled steel tube columns, a total of 42 specimens of steel tubular columns were monotonically tested under concentric axial force, having the slenderness ratio(${\lambda}=10,\;15,\;20$), width-thickness ratio(d/t=25.0, 33.3) and concrete strengths($F_{c}=210,\;240,\;270kg/cm^{2}$). The hollow sections and concrete filled steel columns were compared to check the lateral confinded effects by steel tube. Through these test results, we propose a coefficient k=3.64 for the strength evaluation formula(10) of concrte filled tubular steel short columns.

• 콘크리트학회논문집
• /
• 제20권2호
• /
• pp.221-229
• /
• 2008

와이어로프와 T형 강판을 이용한 개선된 비부착형 기둥보강 공법이 개발되었다. 제시된 절차에 따라 보강된 기둥 8개와 동일한 조건의 무보강 기둥 1개가 중심 축하중 하에서 실험되었다. 주요 변수는 와이어로프 체적비와 T 강판의 플랜지 폭 및 배치 형상이다. 실험된 기둥의 축하중 내력과 연성비는 각각 ACI 318-05의 예측값과 Chung et al.에 의해 수행된 일반 띠기둥의 실험 결과와 비교되었다. 게다가 와이어로프와 T 강판으로 구속된 콘크리트의 응력-변형률 관계를 평가하기 위한 모델이 제시되었다. 실험 결과로부터 기둥의 축하중 내력과 연성은 와이어로프의 체적비와 T 강판의 플랜지 폭의 증가와 함께 증가하였다. 특히 동일 횡보강근 지수에서 와이어로프 체적비가 0.0039 이상일 때 보강된 기둥의 연성비는 띠철근 기둥에 비해 현저히 높았다. 개발된 보강기술에 의해 구속된 콘크리트의 응력-변형률 관계 모델이 제시되었다. 예측된 응력-변형률 관계는 실험 결과와 잘 일치하였다.

• Coupled systems mechanics
• /
• 제13권3호
• /
• pp.201-217
• /
• 2024

This study aims to develop a new model to obtain the minimum area in circular isolated footings with eccentric column taking into account that the surface in contact with the ground works partially in compression, i.e., a part of the contact area of the footing is subject to compression and the other there is no pressure (pressure zero). The new model is formulated from a mathematical approach based on a minimum area, and it is developed by integration to obtain the axial load "P", moment around the X axis "M_x" and moment around the Y axis "M_y" in function of σ_max (available allowable soil pressure) R (radius of the circular footing), α (angle of inclination where the resultant moment appears), y₀ (distance from the center of the footing to the neutral axis measured on the axis where the resultant moment appears). The normal practice in structural engineering is to use the trial and error procedure to obtain the radius and area of the circular footing, and other engineers determine the radius and area of circular footing under biaxial bending supported on elastic soils, but considering a concentric column and the contact area with the ground works completely in compression. Three numerical problems are given to determine the lowest area for circular footings under biaxial bending. Example 1: Column concentric. Example 2: Column eccentric in the direction of the X axis to 1.50 m. Example 3: Column eccentric in the direction of the X axis to 1.50 m and in the direction of the Y axis to 1.50 m. The new model shows a great saving compared to the current model of 44.27% in Example 1, 50.90% in Example 2, 65.04% in Example 3. In this way, the new minimum area model for circular footings will be of great help to engineers when the column is located on the center or edge of the footing.

• Steel and Composite Structures
• /
• 제2권5호
• /
• pp.379-396
• /
• 2002

The paper describes the mechanical behavior of short concrete-filled steel tube (CFT) columns with circular section. The efficiency of the steel tube in confining the concrete core depending on concrete strength and the steel tube thickness was examined. Fifteen columns were tested to failure under concentric axial loading. Furthermore, a mechanical model based on the interaction between the concrete core and the steel tube was developed. The model employs a volumetric strain history for the concrete, characterized by the level of applied confining stress. The situation of passive confinement is accounted for by an incremental procedure, which continuously updates the confining stress. The post-yield behavior of the columns is greatly influenced by the confinement level and is related to the efficiency of the steel tube in confining the concrete core. It is possible to classify the post-yield behavior into three categories: strain softening, perfectly plastic and strain hardening behavior. The softening behavior, which is due to a shear plane failure in the concrete core, was found for some of the CFT columns with high-strength concrete. Nevertheless, with a CFT column, it is possible to use high-strength concrete to obtain higher load resistance and still achieve a good ductile behavior.

• Computers and Concrete
• /
• 제10권4호
• /
• pp.331-347
• /
• 2012

This paper describes the varying material model, the analysis method and the software development for reinforced concrete circular columns confined by spiral or hoop transverse steel reinforcement and subjected to eccentric loading. The widely used Mander model of concentric loading is adapted here to eccentric loading by developing an auto-adjustable stress-strain curve based on the eccentricity of the axial load or the size of the compression zone to generate more accurate interaction diagrams. The prediction of the ultimate unconfined capacity is straight forward. On the other hand, the prediction of the actual ultimate capacity of confined concrete columns requires specialized nonlinear analysis. This nonlinear procedure is programmed using C-Sharp to build efficient software that can be used for design, analysis, extreme event evaluation and forensic engineering. The software is equipped with an elegant graphics interface that assimilates input data, detail drawings, capacity diagrams and demand point mapping in a single sheet. Options for preliminary design, section and reinforcement selection are seamlessly integrated as well. Improvements to KDOT Bridge Design Manual using this software with reference to AASHTO LRFD are made.

• 한국강구조학회 논문집
• /
• 제14권4호
• /
• pp.471-479
• /
• 2002

본 논문에서는 고강도콘크리트충전 각형강관장주에 대한 실험결과와 탄소성해석결과를 비교분석했다. 실험체는 모두 고강도콘크리트 충전 각형강관장주로 18개를 제작하였으며, 편심비에 따라 중심 및 편심가력하였다. 본 연구의 주요 파라메타는 단면폭에 대한 유효좌굴 길이의 비($L_K$/D)= 4, 8, 12, 24, 30와 가력편심비(e)=0, k, 3k이다. 본 논문에서 고강도콘크리트 충전 각형강관장주의 내력에 관한 해석 및 실험을 통하여 다음과 같은 결과를 얻었다. $L_K$/D=12 이하의 고강도콘크리트충전 각형강관단주는 콘크리트 감소계수 $c{\gamma}u=0.85$를 고려한 전소성내역에 도달했으나, $L_K$/D=18 이상의 장주실험체는 콘크리트 감소계수를 고려한 전소성내력에 도달하지 않았다. 실험에 의한 고강도콘크리트충전 각형강관장주의 탄소성거동은 제안된 해석치의 종국내력$N_{ASSUMED}$과 비교적 양호한 접근을 보여주었다. 콘크리트 압축강도의 감소계수 $c{\gamma}u=0.85$를 고려하지 않은 CFT설계기준과 고강도 콘크리트를 충전한 각형강관기둥의 실험결과치는 비교적 잘 일치함을 알 수 있었다.

• 한국정밀공학회지
• /
• 제29권3호
• /
• pp.324-333
• /
• 2012

The conventional medium and large caliber gun, in general, utilize the hydro-pneumatic recoil mechanism to control the firing impulse and to return to the battery position. However, this kind of mechanism may cause the problems like the leakages and the property changes in oil and gas due to the temperature variations between low and high temperatures. Accordingly, the friction spring mechanism has recently been researched as an alternative system. The friction spring mechanism consists of a set of closed inner and outer rings with the concentric tapered contact surfaces assembled in the columnar form, and can only be used under the compression load. When the spring column is axially loaded, the tapered surfaces become overlapped, causing the outer rings to expand while the inner rings are being contracted in diameter allowing an axial displacement. Because of friction between tapered contact surfaces, much higher spring stiffness is obtained on the stroke at the increase in load than the stroke at the decrease. In this paper, the dynamic equations regarding the friction spring system and the design approach have been investigated. It is also tried for a dynamic model representing the recoil motion and the friction spring forces. And the model has been proved from firing test using a gun system with friction springs. All the results show that the recoil mechanism using friction springs can substitute for the classic hydro-pneumatic recoil system.

• Advances in Computational Design
• /
• 제3권3호
• /
• pp.233-267
• /
• 2018

Conventional seismic design of concentrically braced frame (CBF) structures suggests that the gusset plate connecting a steel brace to beams and/or columns should be designed as non-dissipative in earthquakes, while the steel brace members should be designed as dissipative elements. These design intentions lead to thicker and larger gusset plates in design on one hand and a potentially under-rated contribution of gusset plates in design, on the other hand. In contrast, research has shown that compact and thinner gusset plates designed in accordance with the elliptical clearance method rather than the conventional standard linear clearance method can enhance system ductility and energy dissipation capacity in concentrically braced steel frames. In order to assess the two design methods, six cyclic push-over tests on full scale models of concentric braced steel frame structures were conducted. Furthermore, a 3D finite element (FE) shell model, incorporating state-of-the-art tools and techniques in numerical simulation, was developed that successfully replicates the response of gusset plate and bracing members under fully reversed cyclic axial loading. Direct measurements from strain gauges applied to the physical models were used primarily to validate FE models, while comparisons of hysteresis load-displacement loops from physical and numerical models were used to highlight the overall performance of the FE models. The study shows the two design methods attain structural response as per the design intentions; however, the elliptical clearance method has a superiority over the standard linear method as a fact of improving detailing of the gusset plates, enhancing resisting capacity and improving deformability of a CBF structure. Considerations were proposed for improvement of guidelines for detailing gusset plates and bracing members in CBF structures.