• Steel and Composite Structures
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• 제37권1호
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• pp.15-26
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• 2020

The top-and-seat angles with double web angles are commonly used in the design of beam-to-column joints in Asian and North American countries. The seismic behavior analysis of these joints with large cross-section size of beam and column (often connected by four or more bolts) is a challenge due to the effects from the relatively larger size of stiffened angles and the composite action from the adjacent concrete slab. This paper presents an experimental investigation on the seismic performance of exterior composite beam-to-column joints with stiffened angles under cyclic loading. Four full-scale composite joints with different configuration (only one specimen contain top angle in concrete slab) were designed and tested. The joint specimens were designed by considering the effects of top angles, longitudinal reinforcement bars and arrangement of bolts. The behavior of the joints was carefully investigated, in terms of the failure modes, slippage, backbone curves, strength degradation, and energy dissipation abilities. It was found that the slippage between top-and-seat angles and beam flange, web angle and beam web led to a notable pinching effect, in addition, the ability of the energy dissipation was significantly reduced. The effect of anchored beams on the behavior of the joints was limited due to premature failure in concrete, the concrete slab that closes to the column flange and upper flange of beam plays an significant role when the joint subjected to the sagging moment. It is demonstrated that the ductility of the joints was significantly improved by the staggered bolts and welded longitudinal reinforcement bars.

• Structural Engineering and Mechanics
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• 제65권3호
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• pp.303-314
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• 2018

Shear walls are a typical member under a complex stress state and have complicated mechanical properties and failure modes. The separated-elements model Genetic Evolutionary Structural Optimization (GESO), which is a combination of an elastic-plastic stress method and an optimization method, has been introduced in the literature for designing such members. Although the separated-elements model GESO method is well recognized due to its stability, feasibility, and economy, its adequacy has not been experimentally verified. This paper seeks to validate the adequacy of the separated-elements model GESO method against experimental data and demonstrate its feasibility and advantages over the traditional elastic stress method. Two types of reinforced concrete shear wall specimens, which had the location of an opening in the middle bottom and the center region, respectively, were utilized for this study. For each type, two specimens were designed using the separated-elements model GESO method and elastic stress method, respectively. All specimens were subjected to a constant vertical load and an incremental lateral load until failure. Test results indicated that the ultimate bearing capacity, failure modes, and main crack types of the shear walls designed using the two methods were similar, but the ductility indexes including the stiffness degradation, deformability, reinforcement yielding, and crack development of the specimens designed using the separated-elements model GESO method were superior to those using the elastic stress method. Additionally, the shear walls designed using the separated-elements model GESO method, had a reinforcement layout which could closely resist the actual critical stress, and thus a reduced amount of steel bars were required for such shear walls.

• 한국압력기기공학회 논문집
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• 제4권2호
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• pp.13-19
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• 2008

In order to predict a remaining life of a plant, it is necessary to select the components that are critical to the plant life. The remaining life of those components shall be evaluated by considering the aging effect of materials used as well as numerous factors. However, when evaluating reliability of nuclear structural components, some problems are quite formidable because of lack of information such as operating history, material property change and uncertainty in damage models. Accordingly, if structural integrity and safety are evaluated by the deterministic fracture mechanics approach, it is expected that the results obtained are too conservative to perform a rational evaluation of plant life. The probabilistic fracture mechanics approaches are regarded as appropriate methods to rationally evaluate the plant life since they can consider various uncertainties such as sizes and shapes of cracks and degradation of material strength due to the aging effects. The objective of this study is to evaluate the structural integrity for a reactor pressure vessel under the small break loss of coolant accident by applying the deterministic and probabilistic fracture mechanics. The deterministic fracture mechanics analysis was performed using the three dimensional finite element model. The probabilistic integrity analysis was based on the Monte Carlo simulation. The selected random variables are the neutron fluence on the vessel inside surface, the content of copper, nickel, and phosphorus in the reactor pressure vessel material, and initial RTNDT.

• 한국강구조학회 논문집
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• 제18권2호
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• pp.147-160
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• 2006

본 논문에서는 개선소성힌지해석과 유전자 알고리듬을 이용한 평면 강골조 구조물의 퍼지최적설계 방법을 제시하였다. 개선소성힌지해석에서는 강골조 구조물의 기하학적 비선형성을 고려하기 위해 보-기둥 요소의 안정함수를 사용하였으며, 재료적 비선형을 고려하기 위해 잔류응력, 소성힌지, 그리고 기하학적 불완전성 등에 의한 점진적인 강성감소모델을 사용하였다. 유전자 알고리듬에서는 토너먼트 선택방법과 마이크로 유전자 알고리즘을 사용하였다. 목적함수로는 구조물의 총중량을 사용하였으며, 제약조건으로는 하중-저항능력, 사용성, 연성도, 그리고 시공성에 관한 기준을 고려하였다. 퍼지최적설계에서는 명확한 목적함수와 퍼지제약을 가지는 경우에 한하여 허용 오차는 제한값의 5%로 선택하고 비소속함수와 레벨컷 방법을 이용하여 0에서 1까지 0.2간격으로 나누어 최적화하였다. 여러 평면 강골조 구조물의 최적설계를 수행하여 일반GA최적설계와 퍼지GA최적설계의 최적값을 비교하였다.

• Advances in concrete construction
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• 제8권3호
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• pp.173-185
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• 2019

This article presents a comparative study of the effect of steel layouts on the seismic behavior of transition steel-concrete composite connections, both experimental and analytical investigations of concrete filled steel tube-reinforced concrete (CFST-RC) and steel reinforecd concrete-reinforced concrete (SRC-RC) structures were conducted. The steel-concrete composite connections were subjected to combined constant axial load and lateral cyclic displacements. Tests were carried out on four full-scale connections extracted from a real project engineering with different levels of axial force. The effect of steel layouts on the mechanical behavior of the transition connections was evaluated by failure modes, hysteretic behavior, backbone curves, displacement ductility, energy dissipation capacity and stiffness degradation. Test results showed that different steel layouts led to significantly different failure modes. For CFST-RC transition specimens, the circular cracks of the concrete at the RC column base was followed by steel yielding at the bottom of the CFST column. While uncoordinated deformation could be observed between SRC and RC columns in SRC-RC transition specimens, the crushing and peeling damage of unconfined concrete at the SRC column base was more serious. The existences of I-shape steel and steel tube avoided the pinching phenomenon on the hysteresis curve, which was different from the hysteresis curve of the general reinforced concrete column. The hysteresis loops were spindle-shaped, indicating excellent seismic performance for these transition composite connections. The average values of equivalent viscous damping coefficients of the four specimens are 0.123, 0.186 and 0.304 corresponding to the yielding point, peak point and ultimate point, respectively. Those values demonstrate that the transition steel-concrete composite connections have great energy dissipating capacity. Based on the experimental research, a high-fidelity ABAQUS model was established to further study the influence of concrete strength, steel grade and longitudinal reinforcement ratio on the mechanical behavior of transition composite connections.

• Computers and Concrete
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• 제26권6호
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• pp.547-563
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• 2020

In this paper, the influence of axial compression ratio on the mechanical properties of new type joints of side span of rectangular concrete-filled steel tubular column-H-type steel beam is studied. Two new types of side-span joints of rectangular concrete-filled steel tubular column-H-type steel beam are designed and quasi-static tests of five new type joints with 1:2 scale reduction ratios are performed. The axial compression ratio of joint JD1 is 0.3, 0.4 and 0.5, and the axial compression ratio of joint JD2 is 0.3 and 0.5. In the joint test, different axial forces were applied to the top of the column according to different axial compression ratios, and low-cyclic reciprocating load was applied on the beam. The stress and strain distribution, beam and column deformation, limit state, failure process, failure mechanism, stiffness degradation, ductile deformation and energy dissipation capacity of the joint were measured and analyzed. The results show that: with the increase of axial compression ratio, the ultimate bearing capacity of the joint decreases slightly, the plastic deformation decreases, and the stiffness and ductility decrease. According to the energy dissipation curve of the specimen, the equivalent damping coefficient also increases with the increase of axial compression ratio in a certain range, indicating that the increase of axial compression ratio can improve the seismic performance of the joint to a certain extent. The finite element method is used to simulate the joint test, and the test results are in good agreement with the simulation results.

• Steel and Composite Structures
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• 제45권6호
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• pp.797-818
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• 2022

Steel-precast ultra-high-performance concrete (UHPC) composite beams with demountable high-strength friction-grip bolt (HSFGB) shear connectors can be used for accelerated bridge construction (ABC) and achieve excellent structural performance, which is expected to be dismantled and recycled at the end of the service life. However, no investigation focuses on the demountability and reusability of such composite beams, as well as the installation difficulties during construction. To address this issue, this study conducted twelve push-out tests to investigate the effects of assembly condition, bolt grade, bolt-hole clearance, infilling grout and pretension on the crack pattern, failure mode, load-slip/uplift relationship, and the structural performance in terms of ultimate shear strength, friction resistance, shear stiffness and slip capacity. The experimental results demonstrated that the presented composite beams exhibited favorable demountability and reusability, in which no significant reduction in strength (less than 3%) and stiffness (less than 5%), but a slight improvement in ductility was observed for the reassembled specimens. Employing oversized preformed holes could ease the fabrication and installation process, yet led to a considerable degradation in both strength and stiffness. With filling the oversized holes with grout, an effective enhancement of the strength and stiffness can be achieved, while causing a difficulty in the demounting of shear connectors. On the basis of the experimental results, more accurate formulations, which considered the effect of bolt-hole clearance, were proposed to predict the shear strength as well as the load-slip relationship of HSFGBs in steel-precast UHPC composite beams.

• 콘크리트학회논문집
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• 제14권5호
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• pp.734-741
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• 2002

중앙부 철골조와 단부 RC조로 이루어진 혼합구조보인 RS 보와 RC 기둥으로 이루어진 접합부의 비탄성 거동 및 내진성능을 구명하기 위하여 반복가력에 의한 접합부 실험을 진행하였다. 본 연구는 RC-RS 접합부의 모멘트비를 변수로 하여 두 개의 내부접합부와 한 개의 외부접합부 등 총 3개의 시험체를 제작하여 실험을 진행하였다. 실험결과, 강도와 연성능력은 충분히 발휘하였으나, 접합부의 강성은 부족한 결과를 나타내었다. 이는 RS 보를 구성하는 철골보와 RC 보를 연결하는 강재매입구간에서의 철골 보의 미끄러짐에 의한 변위의 증가로 인하여 강성의 저하가 발생한 것으로 판단된다. 또한 Hawkins의 제안안에 의한RC-RS 접합부의 내진성능을 평가해 본 결과, 접합부의 초기강성의 부족으로 부재각 0.5 %에서의 공칭강도의 발현은 만족하지 못하였으나, 그외의 내진성능 평가지표인 강도유지능력, 상대 에너지소산비 및 종국후 초기강성비나 초기강도비 등의 측면에서는 우수한 능력을 발휘하였다. 따라서 구조물에서 RC-RS 접합부를 적용할 경우, RC 코어 월과 같은 초기 횡 강성을 보완할 수 있는 적절한 구조시스템과 병행하여 적용하면 강진지역의 구조물에도 충분히 적용이 가능하다고 판단된다.

• 콘크리트학회논문집
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• 제17권1호
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• pp.85-94
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• 2005

PPS(post-tensioned precast concrete system)공법은 U자형 PC로 제작한 넓은 보와 PC 또는 현장 타설 콘크리트로 제작한 기둥으로 구성되며 PC 보와 기둥의 일체성 확보를 위하여 프리스트레스를 도입하였다. 본 연구는 PPS 공법 개발의 일부로 넓은 보의 기둥 폭 내부에 정착되어진 휨철근의 양에 따른 거동특성을 분석하고자 실험적 연구를 수행하였다. 실험체는 기둥 폭내, 외부에 위치한 휭 철근의 양을 달리한 정착비와 동일한 정착비내에서 철근과 긴장재의 양을 주요변수로 하여 대상건물의 내부접합부를 대상으로 1/2크기로 제작하였다. 그 결과 NEHRP 권고사항에서 규정한 한계변위각 0.035까지 내력저하 없이 충분한 내력을 보유하였으며, 보의 휨 파괴가 주요 파괴모드로 접합부에서 전단파괴는 일어나지 않았다. 그리고 넓은 보에 포스트텐션을 도입한 PPS 공법은 기둥 폭 내부의 정착비가 $35\%$인 경우 다소 높은 비틀림 응력을 나타내었으나, 기둥 폭 외부에 위치한 인장철근의 항복 이후 긴장재가 응력을 충분히 발휘함으로서 일체식 구조의 넓은 보-기둥 접합부와 달리 비탄성 이력거동을 통하여 에너지를 효과적으로 소산하였다. 또한 ACI의 proposed provisional standard의 PC 접합부 구조성능 평가지침에 의해 분석한 결과, 모든 실험체에서 허용기준을 모두 만족하고 있으며, 강도의 큰 저하 없이 연성적인 거동을 하고 있음을 알 수 있었다.

• 콘크리트학회논문집
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• 제24권1호
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• pp.3-14
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• 2012

이 논문에서는 비내진상세 골조의 손상완화능력 향상을 위한 연구의 일환으로 변형경화형 시멘트 복합체 끼움벽의 내진성능을 실험적으로 평가하였다. SHCC의 인장변형능력 및 균열거동 특성이 끼움벽의 전단 거동에 미치는 영향을 구명하기위해 총 3개의 끼움벽 실험체를 제작하여 반복하중 하에서 실험을 실시하였다. 이 연구에서 사용된 시멘트 복합체의 종류는 콘크리트와 SHCC로 하였다. SHCC는 인장 특성에 따른 영향을 검토하기위해 PVA1.3%+PE0.2% 및 PVA0.75%+PE0.75%로 두 종류의 배합조건을 갖도록 계획하였다. 끼움벽의 균열손상 발생 부위를 중앙부로 유도하기위해 모든 끼움벽 실험체의 좌 우측면에 100 mm 깊이의 노치를 설치하였다. 실험 결과, SHCC 끼움벽의 경우 철근 콘크리트 끼움벽에 비해 우수한 균열제어성능을 나타냈으며, 최대하중 도달 시점에서의 층간변위 또한 높게 나타났다. 특히, 초기 경사균열 발생 이후에도 SHCC 내의 보강 섬유간 섬유가교작용에 기인하여 완만한 강성 저하 양상을 나타냈다. 게다가 끼움벽의 균열폭을 기준으로 손상 식별 단계를 분석한 결과, PIW-SHD 실험체가 PIW-SLD 실험체에 비해 약 3배에 해당하는 우수한 내진성능을 나타냈다. 또한 대각 보강근의 변형률 진전 양상을 비교한 결과, 우수한 균열분산 특성에 기인하여 철근에 집중되는 인장응력을 SHCC 매트릭스가 일정 부분 부담하는 것으로 나타났다.