• 한국지진공학회논문집
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• 제15권4호
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• pp.45-54
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• 2011

경계요소를 가지는 철근콘크리트 전단벽의 비선형 해석을 위한 간편 모델을 제안하였다. 이 간편 모델은 전단벽의 휨 및 전단 거동을 스프링요소로 나타낸 거시적 모델이다. 휨거동은 벽체의 단면해석을 기초로 한 모멘트강도와 회전능력을 벽체 양단의 수직 스프링요소로 나타내었다. 경계요소를 가지는 전단벽은 휨거동에 의해 지배되므로 전단거동은 휨거동에 바탕하여 변수를 계산하였고 중앙부 수평 스프링요소로 나타내었다. 제안된 모델은 전단벽 정적이력시험 결과와 비교한 후 비선형동적해석을 수행하여 사용된 이력법칙 및 변수들의 타당성을 조사하였다. 비선형동적해석을 이용한 변수연구를 통하여 내진성능평가의 주요변수인 요구값과 성능값에 미치는 영향을 검토하였다. 그 결과 전단력-전단변형 관계에서 약간의 차이가 있지만 전단벽의 전체거동은 잘 일치하였으며, 주요 변수의 변화에 대해 요구값과 성능값도 일정하게 변화하므로 제안된 해석모델은 경계요소를 가진 철근콘크리트 전단벽에 알맞은 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제70권6호
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• pp.703-710
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• 2019

While fiber-reinforced plastic (FRP) materials have been largely used in the retrofitting of concrete buildings, its application has been limited because of some problems such as de-bonding of FRP layers from the concrete surface. This paper is the part of a wide experimental and analytical investigation about flexural retrofitting of reinforced concrete (RC) columns using FRP and mechanical fasteners (MF). A new generation of MF is proposed, which is applicable for retrofitting of RC columns. Furthermore, generally, to evaluate a retrofitted structure the nonlinear static and dynamic analyses are the most accurate methods to estimate the performance of a structure. In the nonlinear analysis of a structure, accurate modeling of structural elements is necessary for estimation the reasonable results. So for nonlinear analysis of a structure, modeling parameters for beams, columns, and beam-column joints are essential. According to the concentrated hinge method, which is one of the most popular nonlinear modeling methods, structural members shall be modeled using concentrated or distributed plastic hinge models using modeling parameters. The nonlinear models of members should be capable of representing the inelastic response of the component. On the other hand, in performance based design to make a decision about a structure or design a new one, numerical acceptance should be determined. Modeling parameters and numerical acceptance criteria are different for buildings of different types and for different performance levels. In this paper, a new method was proposed for FRP retrofitted columns to avoid FRP debonding. For this purpose, mechanical fasteners were used to achieve the composite behavior of FRP and concrete columns. The experimental results showed that the use of the new method proposed in this paper increased the flexural strength and lateral load capacity of the columns significantly, and a good composition of FRP and RC column was achieved. Moreover, the modeling parameters and acceptance criteria were presented, which were derived from the experimental study in order to use in nonlinear analysis and performance-based design approach.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.12-16
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• 2002

Dynamic characteristics of smart laminated composite plates with passive constrained layer damping have been investigated to design structure with maximum possible damping capacity. The equations of motion are derived for flexural vibrations of symmetrical, multi-layer laminated plates. The damping ratio and modal damping of the first bending and torsional modes are calculated by means of iterative complex eigensolution method. The structural damping index(SDI) is introduced to determine the optimum placement of viscoelastic patch. This paper addresses a design strategy of laminated composite plate under vibrations.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 가을 학술발표회 논문집
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• pp.453-456
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• 2003

This research is to evaluate the seismic performance of reinforced concrete bridge piers with lap-spliced longitudinal reinforcement steels in the plastic hinge region, and to develop the enhancement scheme of their seismic capacity. Six circular columns of 0.6m diameter and 1.5m height were made with two confinement steel ratios. They were damaged under series of artificial earthquakes that could be compatible in Korean peninsula. Directly after the pseudo-dynamic test, damaged columns were retested under inelastic reversal cyclic loading simultaneously under an axial load, P=$0.1f_{ck}A_{g}$, and residual seismic performance of damaged columns was evaluated. Test results show that RC bridge piers with lap-spliced longitudinal steels behaved with minor damage even under artificial earthquakes with 0.22g PGA, but failed at low ductility subjected to the subsequent quasi-static load test. This failure was due to the debonding of the lap splice. The specimens externally wrapped with composite FRP straps in the potential plastic hinge region showed significant improvement both in flexural strength and displacement ductility.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 추계 학술발표회 제16권2호
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• pp.61-64
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• 2004

This study presents results from an experimental work for two normal prestressed concrete beams and three dual prestressed concrete beams. The dual prestressed concrete beams made with normal concrete in compression zone and high performance steel fiber reinforced concrete in partial depth of tension zone. Through cyclic loading test under low frequency, structural behavior and resistance to dynamic loading for dual prestressed concrete beams are investigated. Considerable increase of crack and yield load capacity of Dual prestressed concrete beam is shown compared with normal prestressed concrete beam. In addition, re-loading and un-loading rigidity of dual prestressed concrete beam under cyclic loading are increased comparing with normal prestressed concrete beam.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 추계학술대회 논문집
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• pp.32-36
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• 2002

High-speed movement and high-precision machining are the two most important requirements of present machine tool structures to reduce machining time and to increase the precision of products in various industrial fields such as semiconductor, automobile, and mold fabrication. The high speed operation of machine tools tue usually restricted not only by the low stiffness but also by the low damping of machine tool structures, which induces vibration during high speed machining. If the damping of machine tool structures is low, self induced or regenerative vibrations are bound to occur at high speed operation because the natural frequencies of machine tool structures can not be increased indefinitely. Therefore, the high damping capacity of a machine tool structure is an important factor for high speed machine tool structures. Polymer concrete has high potential for machine tool bed due to its good damping characteristics. In this study, a polymer concrete bed combined with welded steel structure i.e., a hybrid structure was desisted and manufactured for a high-speed gantry-type milling machine through static and dynamic analyses using finite element method. Then the dynamic characteristics were tested experimentally.

• Steel and Composite Structures
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• 제30권4호
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• pp.365-382
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• 2019

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.

• 한국도로학회논문집
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• 제19권6호
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• pp.129-137
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• 2017

PURPOSES : The purpose of this study is to develop bridge deck concrete materials based on ordinary Portland cement concrete, and to evaluate the applicability of the developed materials through material properties tests. METHODS : For field implementation, raw material (cement, fine aggregate, and coarse aggregate) properties, fresh concrete properties (slump and air content), strength (compressive, flexural and bond strength) gain, and durability (freeze-thaw resistance, scaling resistance, and rapid chloride penetrating resistance) performance were evaluated in the laboratory. RESULTS : For the selected binder content of $410kg/m^3$, W/B = 0.42, and S/a = 0.48, the following material performance results were obtained. Considering the capacity of the deck finisher, a minimum slump of 150 mm was required. At least 6 % of air content was obtained to resist freeze-thaw damage. In terms of strength, 51.28 MPa of compressive strength, 7.41 MPa of flexural strength, and 2.56 MPa of bond strength at 28 days after construction were obtained. A total of 94.9 % of the relative dynamic modulus of elasticity after 300 cycles of freeze-thaw resistance testing and $0.0056kg/m^2$ of weight loss in a scaling resistance test were measured. However, in a chloride ion penetration resistance test, the result of 3,356 Coulomb, which exceeds the threshold value of the standard specification (1000 Coulomb at 56 days) was observed. CONCLUSIONS : Instead of using high-performance modified bridge deck materials such as latex or silica fume, we developed an optimum mix design based on ordinary Portland cement concrete. A test construction was carried out at ramp bridge B (bridge length = 111 m) in Gim Jai City. Immediately after the concrete was poured, the curing compound was applied, and then wet mat curing was applied for 28 days. Considering the fact that cracks did not occur during the monitoring period, the applicability of the developed material is considered to be high.

• 한국지반공학회논문집
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• 제25권11호
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• pp.27-38
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• 2009

본 연구에서는 조밀한 포화 사질토 지반과 느슨한 포화 사질토 지반에 근입된 모형말뚝을 대상으로 다양한 말뚝휨 강성과 입력 가속도 진폭, 그리고 입력 가속도 진동수 조건에서 1g 진동대 실험을 수행하였다. 그 결과로, 조밀한 포화 사질토 지반조건에 대해, 각 실험 p-y 곡선 상 최대 지반 반력이 나타나는 꼭지점들을 연결하여 등가정적해석에 적용할 수 있는 동적 p-y 중추곡선을 쌍곡선 함수로 나타내었으며, 중추곡선을 쌍곡선 함수로 나타내는데 필요한 초기 기울기($k_{ini}$)와 극한 저항력($p_u$)을 결정하기 위한 경험식을 마찰각과 구속압의 함수로 제안하였다. 제안한 동적 p-y 중추곡선의 적용성을 기존 문헌에 발표된 원심모형실험 결과와 비교하여 검증하였으며, 실제 설계에 적용되고 있는 기존의 p-y 곡선들과도 비교, 분석하였다. 또한 느슨한 포화 사질토 지반조건에서, 진동 중 발생하는 과잉간극수압에 따라 지반 저항이 감소하는 정도를 나타내는 동적 지반 저항 감소 계수($S_F$)를 제안하였다.

• 대한기계학회논문집A
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• 제25권2호
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• pp.250-263
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• 2001

The up and down speed of heddle frames that produce woven cloth by insertion of weft yarns between warp yarns has been increased recently much for productivity improvement, which induces higher inertial stresses and vibrations in the heddle frame. the heddle frame is required to reduce its mass because the heddle frame contributes the major portion of the stresses in the heddle frames during accelerating and decelerating. Conventional aluminum heddle frames have fatigue life of around 5 months at 550rpm due to their low fatigue flexural strength as well as low bending stiffness. In this work, since carbon/epoxy composite materials have high specific fatigue strength(S/p), high specific modulus(E/p), high damping capacity and sandwich construction results in lower deflections and higher buckling resistance, the sandwich structure composed of carbon/epoxy composite skins and polyurethane foam were employed for the high-speed heddle frame. The design map for the sandwich beams was accomplished to determine the optimum thickness and the stacking sequences for the heddle frames. Also the effects of the number of ribs on the stress of the heddle frame were investigated by FEM analyses. Finally, the high-speed heddle frames were manufactured with sandwich structures and the static and dynamic properties of the aluminum and the composite heddle frames were tested and compared with each other.