• Structural Engineering and Mechanics
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• 제77권2호
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• pp.179-196
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• 2021

Experimental investigations on the seismic behaviors of the PVC-FRP Confined Reinforced Concrete (PFCRC) columns under low cyclic loading are carried out and two variable parameters including CFRP strips spacing and axial compression ratio are considered. The PFCRC column finally fails by bending and is characterized by the crushing of concrete and yielding of the longitudinal reinforcement, and the column with a high axial compression ratio is also accompanied by the cracking of the PVC tube and the fracture of CFRP strips. The hysteretic curves and skeleton curves of the columns are obtained from the experimental data. With the increase of axial compression ratio, the stiffness degradation rate accelerates and the ductility decreases. With the decrease of CFRP strips spacing, the unloading sections of the skeleton curves become steep and the ductility reduces significantly. On the basis of fiber model method, a numerical analysis approach for predicting the skeleton curves of the PFCRC columns is developed. Additionally, a simplified skeleton curve including the elastic stage, strengthening stage and unloading stage is suggested depending on the geometric drawing method. Moreover, the loading and unloading rules of the PFCRC columns are revealed by analyzing the features of the skeleton curves. The quantitative expressions that are used to predict the unloading stiffness of the specimens in each stage are proposed. Eventually, an analytical model for the PFCRC columns under low cyclic loading is established and it agrees well with test data.

• 실천공학교육논문지
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• 제16권2호
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• pp.185-193
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• 2024

스마트폰의 발달로 인해 사람들은 언제 어디서나 인터넷을 통해 다양한 정보를 접할 수 있게 되었다. 차량 내에서도 인터넷을 이용할 수 있는 시대가 도래했고, 사용자는 웹과 앱을 통해 매일 정보를 얻고 있다. 하지만 데이터 처리량이 증가함에 따라 프로그램의 응답 속도가 느려지는 경우가 발생하고, 사용자는 기다리라는 메시지를 받게 된다. 사용자의 대기는 불편한 경험이지만, 데이터 처리에 필요한 시간이 있기 때문에 사용자 대기를 최소화하는 것이 최선의 방법이다. 그러나 서비스 처리 시간이 예상치를 넘어가면 사용자는 더욱 심한 지루함과 고통을 겪게 된다. 그래서 사용자의 대기 지루함을 완화하기 위한 다양한 방법과 연구가 진행되고 있다. 사용자의 대기 지루함을 완화하기 위해 가장 흔히 사용되는 방법은 로딩이다. 이 연구에서는 최신의 로딩 기법인 Skeleton 로딩이 사용자 대기 경험에 어떤 효과를 가져오는지, 다른 로딩 기법과 비교하여 UI 측면에서 얼마나 매력적인 디자인 기법인지를 조사하였다. 실험 결과, Skeleton 로딩은 사용자 대기 경험을 개선하고, UI 디자인 측면에서도 매력적인 결과를 보여주었다.

• 국제강구조저널
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• 제18권5호
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• pp.1761-1771
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• 2018

In this paper, a hysteretic model of rectangular hollow section (RHS) columns that includes the deteriorating range caused by local buckling is proposed. The proposed model consists of the skeleton curve, the Bauschinger part that appears before reaching the maximum strength, the strength increasing part of the deteriorating range, and the unloading part. Of these, the skeleton curve, including the deterioration range caused by local buckling, which is considered to be equivalent to the load-deformation relationship under monotonic loading, is obtained through an analytical method. Bi-linear hysteretic models based on experimental results are applied to the Bauschinger part and the strength increasing part. The elastic stiffness is applied to the unloading part. The proposed model is verified by comparing with experimental results of RHS columns under monotonic and cyclic loading.

• Steel and Composite Structures
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• 제49권6호
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• pp.615-631
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• 2023

To investigate the seismic behavior of steel slag self-stressing concrete-filled circular steel tubular (SSSCFCST) columns, 14 specimens were designed, namely, 10 SSSCFCST columns and four ordinary steel slag (SS) concrete (SSC)-filled circular steel tubular (SSCFCST) columns. Comparative tests were conducted under low reversed cyclic loading considering various parameters, such as the axial compression ratio, diameter-thickness ratio, shear-span ratio, and expansion ratio of SSC. The failure process of the specimens was observed, and hysteretic and skeleton curves were obtained. Next, the influence of these parameters on the hysteretic behavior of the SSSCFCST columns was analyzed. The self stress of SS considerably increased the bearing capacity and ductility of the specimens. Results indicated that specimens with a shear-span ratio of 1.83 exhibited compression bending failure, whereas those with shear-span ratios of 0.91 or 1.37 exhibited drum-shaped cracking failure. However, shear-bond failure occurred in the nonloading direction. The stiffness of the falling section of the specimens decreased with increasing shear-span ratio. The hysteretic curves exhibited a weak pinch phenomenon, and their shapes evolved from a full shuttle shape to a bow shape during loading. The skeleton curves of the specimens were nearly complete, progressing through elastic, elastoplastic, and plastic stages. Based on the experimental study and considering the effects of the SSC expansion rate, shear-span ratio, diameter-thickness ratio, and axial compression ratio on the seismic behavior, a peak displacement coefficient of 0.91 was introduced through regression analysis. A simplified method for calculating load-displacement skeleton curves was proposed and loading and unloading rules for SSSCFCST columns were provided. The load-displacement restorative force model of the specimens was established. These findings can serve as a guide for further research and practical application of SSSCFCST columns.

• 전산구조공학
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• 제2권4호
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• pp.79-88
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• 1989

철골 건축 구조물이 횡하중을 받을 때 합성보의 거동에 대한 연구가 수행되었다. 실험으로부터 얻어진 결과와 수치해석에 의한 결과를 이용하여 합성보의 강성과 연결부에서의 강도를 위한 수학적 모델이 연결부의 상세를 고려하여 개발되었다. 또한 캔티레버 합성보의 skeleton 곡선과 hysteresis 곡선을 위한 해석모델이 제시되었다. 탄성보와 부재내의 비탄성 변형이 응집된 양 단부스프링으로 구성된 단일요소모델에 의한 합성보 요소가 컴퓨터 프로그램, DRAIN-2D에 포함되었으며, 해석결과는 실험결과의 비교를 통해 검정되었다.

• Steel and Composite Structures
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• 제22권6호
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• pp.1217-1238
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• 2016

Mega composite structure systems have been widely used in high rise buildings in China. Compared to other structures, this type of composite structure systems has a larger cross-section with less weight. Concrete filled steel tubular (CFST) laced column to box-beam connections are gaining popularity, in particular for the mega composite structure system in high rise buildings. To enable a better understanding of the destruction characteristics and aseismic performance of these connections, three different connection types of specimens including single-limb bracing, cross bracing and diaphragms for core area of connections were tested under low cyclic and reciprocating loading. Hysteresis curves and skeleton curves were obtained from cyclic loading tests under axial loading. Based on these tested curves, a new trilinear hysteretic restoring force model considering rigidity degradation is proposed for CFST laced column to box-beam connections in a mega composite structure system, including a trilinear skeleton model based on calculation, law of stiffness degradation and hysteresis rules. The trilinear hysteretic restoring force model is compared with the experimental results. The experimental data shows that the new hysteretic restoring force model tallies with the test curves well and can be referenced for elastic-plastic seismic analysis of CFST laced column to composite box-beam connection in a mega composite structure system.

• 한국산학기술학회논문지
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• 제16권8호
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• pp.5654-5663
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• 2015

부(-)의 간극수압으로서 불포화토 내에 작용하는 석션은 입자간 응력을 증가시키며, 이에 따라 토립자 골격의 항복응력 및 소성전단강성을 증대시키는 등, 불포화토의 역학적 특성에 지대한 영향을 미친다. 따라서, 본 연구에서는 이러한 석션의 효과를 지진 등의 동적 하중조건에서 고려하기 위하여 불포화토에 대해 확장된 반복탄소성구성식에 근거한 응력-변형율 관계를 제 1 항복함수 및 제 2 항복함수를 고려하여 유도하였다. 본 관계를 2차원 및 3차원 수치해석에서 액상화 이후의 압밀거동 예측 등에 적용하는 경우에는 평균골격응력(Mean skeleton stress)의 변화를 반영하는 제 2 항복함수의 도입이 필요하나, 요소시뮬레이션에서는 제 1 항복함수만으로도 수치해석을 위한 각 물성치 및 석션 파라미터 결정이 가능할 것으로 사료된다. 본 관계와 응력반전을 반영한 반복재하 루틴을 함께 코딩(Coding)할 경우 불포화조건 하에서의 반복삼축압축시험에 대한 수치해석적 모사가 가능할 것으로 보이며, 본 연구결과는 동적 하중이 작용하는 불포화토 거동 예측의 정확도 제고에 기여할 것으로 전망된다.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.501-519
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• 2023

This paper introduces a new hybrid structural connection joint that combines shear walls with section steel beams, fundamentally resolving the construction complexity issue of requiring pre-embedded connectors in the connection between shear walls and steel beams. Initially, a quasi-static loading scheme with load-deformation dual control was employed to conduct low-cycle repeated loading experiments on five new connection joints. Data was acquired using displacement and strain gauges to compare the energy dissipation coefficients of each specimen. The destruction process of the new connection joints was meticulously observed and recorded, delineating it into three stages. Hysteresis curves and skeleton curves of the joint specimens were plotted based on experimental results, summarizing the energy dissipation performance of the joints. It's noteworthy that the addition of shear walls led to an approximate 17% increase in the energy dissipation coefficient. The energy dissipation coefficients of dog-bone-shaped connection joints with shear walls and cover plates reached 2.043 and 2.059, respectively, exhibiting the most comprehensive hysteresis curves. Additionally, the impact of laminated steel plates covering composite concrete floors on the stiffness of semi-rigid joint ends under excessive stretching should not be disregarded. A comparison with finite element analysis results yielded an error of merely 2.2%, offering substantial evidence for the wide-ranging application prospects of this innovative joint in seismic performance.

• Steel and Composite Structures
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• 제13권5호
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• pp.451-471
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• 2012

Concrete filled steel tube (CFST) structures have been used widely in high-rise buildings and bridges due to the efficiency of structurally favourable interaction between the steel tube and the concrete core. In the current design codes only one loading condition in the column members is considered, i.e., the load is applied on the steel tube and concrete core at the same time. However, in engineering practice the tube structures may be subjected to various loading conditions such as loading on the concrete core only, preloading on the steel tube skeleton before filling of concrete core, and so on. In this research, a series of comparative experiments were carried out to study the structural performance of concrete filled circular steel tube columns subject to four concentric loading schemes. Then, a generalized prediction method is developed to evaluate the ultimate load capacity of CFST columns subject to various loading conditions. It is shown that the predictions by the proposed method agree well with test results.

• Earthquakes and Structures
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• 제11권2호
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• pp.315-326
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• 2016

This paper presents the results of cyclic loading tests on concrete beams reinforced with various reinforcement, including ordinary steel bars, CFRP bars and CFRP prestressed concrete prisms(PCP). The main variable in the test program was the level of prestress and the cross section of PCP. The seismic performance indexes including hysteretic loops, skeleton curve, ductility, energy dissipation capacity and stiffness degradation were analyzed. The results show that the CFRP prestressed concrete prisms as flexural reinforcement of concrete beams has good seismic performance. And the ductility and the energy dissipation capacity were good, the hysteresis loops were full and had large area.