• Steel and Composite Structures
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• 제42권6호
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• pp.791-804
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• 2022

As a type of semi-rigid connection, the top and seat angle connections are popular in current structures owing to their good cyclic performance and simple erection. However, their stiffness and load bearing capacity are relatively insufficient. This study proposes two strengthening methods to further increase the stiffness and strength of bolted-angle joints while maintaining satisfactory energy dissipation capacity (EDC) and ductility. Cyclic loading tests were conducted on six joint specimens with different strengthened angle components. Based on the test results, the influence of the following important factors on the cyclic behavior of steel joint specimens was investigated: the position of the rib stiffeners (edge rib stiffeners and middle rib stiffener), steel strength grade of rib stiffeners (Q345 and Q690), and additional stiffeners or not. In addition, the finite element models of these specimens were built and validated through a comparison of experimental and numerical results. The stiffness and bearing capacity of the bolted-angle joints could be improved significantly by utilizing the novel strengthened joints proposed in this study. Moreover, this can be achieved with almost no increase in the amount of steel required, and the EDC of this joint could also satisfy the requirements of seismic codes from various countries.

• 한국지반신소재학회논문집
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• 제13권3호
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• pp.39-47
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• 2014

호남고속철도에 부설된 동일한 궤도노반시스템을 실제 열차하중이 가능한 실대형 가진시험을 통해 성능을 평가하였다. 실험결 과 Odemark 등가깊이 이론에 의한 노반압력과 매우 유사한 것을 확인하였다. 콘크리트궤도에서 정적하중 330 kN을 재하시 노반 상부의 토압은 50 kPa 이내로 발생하였고, 정적하중시험과 반복하중시험 결과는 비교적 큰 차이가 없었다. HSB의 탄성변위는 증속시험 시 관리기준값 1 mm에 비해 약 1/100 수준이며, 노반의 탄성변위량과 비교해볼 때 1/175 정도로 매우 작은 변위가 발생하였다. 가진주파수의 크기에 따라 궤도노반의 동적거동은 가진주파수가 35 Hz이하에서는 모든 측정값이 거의 선형적으로 증가하였으나, 35 Hz이상에서는 윤중, 변위, 지반가속도 등이 감소하였다.

• 한국강구조학회 논문집
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• 제25권6호
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• pp.635-647
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• 2013

PSRC 기둥은 앵글을 콘크리트에 매입시킨 기둥으로, 단면의 외곽 코너에 배치되는 앵글이 기둥의 휨-압축에 저항한다. 본 연구에서는 KBC 2009에 따라 압축력을 가한 기둥에 대하여 횡방향 반복가력 실험을 통하여 내진성능을 검증하였다. 기둥 종류, 연속후프근 적용, 앵글에 스터드 적용을 실험 변수로 고려하였으며, 2/3 스케일을 갖는 한 개의 SRC 합성기둥과 세 개의 PSRC 합성기둥을 실험하였다. 실험결과, KBC 2009로 예측한 PSRC 합성기둥의 하중재하능력은 실험결과와 잘 일치하였으며, 변형능력과 에너지 소산에 있어서 우수한 성능을 보여주었다. PSRC 합성기둥은 반복하중으로 인한 콘크리트 피복 탈락 이후, 앵글 및 주철근의 좌굴에 의해 실험체의 하중재하능력이 감소하였다. 특히, 연속후프근을 적용한 PSRC 합성기둥은 앵글의 조기 국부좌굴이 억제되어 기존 PSRC 합성기둥에 비해 연성능력이 향상되었다.

• Steel and Composite Structures
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• 제26권6호
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• pp.719-731
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• 2018

Concrete filled steel tubular (CFST) laced columns have been widely used in high rise buildings in China. Compared to solid-web columns, this type of columns has a larger cross-section with less weight. In this paper, four concrete filled steel tubular laced columns consisting of 4 main steel-concrete tubes were tested under cyclic loading. Hysteresis and failure mechanisms were studied based on the results from the lateral cyclic loading tests. The influence of each design parameter on restoring forces was investigated, including axial compression ratio, slenderness ratio, and the size of lacing tubes. The test results show that all specimens fail in compression-bending-shear and/or compression-bending mode. Overall, the hysteresis curves appear in a full bow shape, indicating that the laced columns have a good seismic performance. The bearing capacity of the columns decreases with the increasing slenderness ratio, while increases with an increasing axial compression ratio. For the columns with a smaller axial compression ratio (< 0.3), their ductility is increased. Furthermore, with the increasing slenderness ratio, the yield displacement increases, the bending failure characteristic is more obvious, and the hysteretic loops become stouter. The results obtained from the numerical analyses were compared with the experimental results. It was found that the numerical analysis results agree well with the experimental results.

• Steel and Composite Structures
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• 제27권4호
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• pp.495-508
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• 2018

In this paper, cyclic loading tests on composite frame inner joints of steel-reinforced recycled concrete (SRRC) column-steel beam were conducted. The main objective of the test was to obtain the shear behavior and analyze the shear strength of the joints. The main design parameters in the test were recycled coarse aggregate (RCA) replacement percentage and axial compression ratio. The failure process, failure modes, hysteresis curves and strain characteristics of the joints were obtained, and the influences of design parameters on the shear strength of the joints have been also analysed in detail. Results show that the failure modes of the joints area are typical shear failure. The shear bearing capacity of the joints maximally decreased by 10.07% with the increase in the RCA replacement percentage, whereas the shear bearing capacity of the joints maximally increased by 16.6% with the increase in the axial compression ratio. A specific strain analysis suggests that the shear bearing capacity of the joints was mainly provided by the three shear elements of the recycled aggregate concrete (RAC) diagonal compression strut, steel webs and stirrups of the joint area. According to the shear mechanism and test results, the calculation formulas of the shear bearing capacity of the three main shear elements were deduced separately. Thus, the calculation model of the shear bearing capacity of the composite joints considering the adverse effects of the RCA replacement percentage was established through a superposition method. The calculated values of shear strength based on the calculation model were in good agreement with the test values. It indicates that the calculation method in this study can reasonably predict the shear bearing capacity of the composite frame inner joints of SRRC column-steel beam.

• 한국해양공학회지
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• 제26권5호
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• pp.73-80
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• 2012

It is well known that a considerable amount of scatter is shown in experimental results relating to fatigue crack growth even under identical and constant amplitude cyclic loading conditions. Moreover, flux cored arc welding (FCAW) is a common method used to join thick plates such as the structural members of large scale offshore structures and very large container ships. The objective of this study was to investigate the macro- and microscopic observations of the fatigue crack growth (FCG) behavior of the FCAWed API 2W Gr. 50 steel joints typically applied for offshore structures. In order to clearly understand the randomness of the fatigue crack growth behavior in the materials of three different zones, the weld metal (WM), heat affected zone (HAZ), and base metal (BM), experimental fatigue crack growth tests for each of five specimens were performed on ASTM standard compact tension (CT) specimens under constant amplitude cyclic loading. Special focus was placed on the fatigued fracture surfaces. As a result, a different behavior was observed at the macro-level, depending on the type of material property: BM, HAZ, or WM. The variability in the fatigue crack growth rate for WM was higher than that of BM and HAZ.

• Geomechanics and Engineering
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• 제37권2호
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• pp.123-133
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• 2024

This study investigates the effects of loading frequency (f) and specimen size on the liquefaction resistance of clean sand. A series of cyclic direct simple shear tests were conducted on Jumunjin sand with varying consolidated relative densities (40% and 80%), f values (0.05, 0.10, and 0.20 Hz), and diameter to height (D/H) ratios (3.63, 3.18, 2.82, and 2.54). The results demonstrated the significant influence of f and D/H ratio on the number of cycles to liquefaction (N_cyc-liq) and the cyclic resistance ratio (CRR₁₅). It was observed that increasing f linearly increased N_cyc-liq. Increasing the specimen height also led to higher N_cyc-liq values irrespective of the f or relative density. Moreover, a positive correlation between CRR₁₅ and f indicated that higher f yielded higher CRR₁₅. This relationship was more pronounced in dense sand than in loose sand. Specimen height also significantly affected CRR₁₅, with increasing the specimen height resulting in higher CRR₁₅ values. Furthermore, the effect of f on CRR₁₅ was less significant compared to the influence of specimen height. The effect of f on the normalized cyclic resistance ratio (NCRR) was relatively negligible for loose sand but more substantial for dense sand depending on the D/H ratio. Data analysis revealed that the NCRR generally decreases as the D/H ratio increases. An interpolation formula was provided to calculate the NCRR based on the D/H ratio regardless of the f and relative density.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.77-80
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• 2008

Low-cycle fatigue (LCF) tests were carried out to investigate the effect of loading direction on the cyclic deformation behavior and fatigue resistance of rolled AZ31 magnesium alloy. The as-received alloy showed a strong basal texture indicating that the most of basal planes of hexagonal close-packed structure were located parallel to the rolling direction. Two types of specimens whose loading directions were oriented parallel (RD) and vertical (ND) to the rolling direction. respectively, were used for the comparison. It was found that RD specimens yielded at much lower stresses during compression, while vice versa for the ND specimens, which was mainly attributed to the formation of primary twins. This anisotropic deformation behavior resulted in the different mean stresses during the cycling of RD and ND specimens, affecting the fatigue resistance of two specimens. The ND specimen showed a superior fatigue resistance as compared to the RD specimen under strain-controlled condition.

• Steel and Composite Structures
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• 제18권4호
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• pp.925-946
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• 2015

This paper presents a new cost-effective hybrid GFRP-Concrete deck system that the GFRP panel serves as both tensile reinforcement and stay-in-place form. In order to understand the fatigue behavior of such hybrid deck, fatigue test on a full-scale specimen under sagging moment was conducted, and a series of static tests were also carried out after certain repeated loading cycles. The fatigue test results indicated that such hybrid deck has a good fatigue performance even after 3.1 million repeated loading cycles. A three-dimensional finite element model of the hybrid deck was established based on experimental work. The results from finite element analyses are in good agreement with those from the tests. In addition, flexural fatigue analysis considering the reduction in flexural stiffness and modulus under cyclic loading was carried out. The predicted flexural strength agreed well with the analytical strength from finite element simulation, and the calculated fatigue failure cycle was consistent with the result based on related S-N curve and finite element analyses. However, the flexural fatigue analytical results tended to be conservative compared to the tested results in safety side. The presented overall investigation may provide reference for the design and construction of such hybrid deck system.

• Steel and Composite Structures
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• 제19권6호
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• pp.1581-1598
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• 2015

A concentric braced steel frame is a very efficient structural system because it requires relatively smaller amount of materials to resist lateral forces. However, primarily developed as a structural system to resist wind loads based on an assumption that the structure behaves elastically, a concentric braced frame possibly experiences the deterioration in energy dissipation after brace buckling and the brittle failure of braces and connections when earthquake loads cause inelastic behavior. Consequently, plastic deformation is concentrated in the floor where brace buckling occurs first, which can lead to the rupture of the structure. This study suggests reinforcing H-shaped braces with non-welded cold-formed stiffeners to restrain flexure and buckling and resist tensile force and compressive force equally. Weak-axis reinforcing members (2 pieces) developed from those suggested in previous studies (4 pieces) were used to reinforce the H-shaped braces in an inverted V-type braced frame. Monotonic loading tests, finite element analysis and cyclic loading tests were carried out to evaluate the structural performance of the reinforced braces and frames. The reinforced braces satisfied the AISC requirement. The reinforcement suggested in this study is expected to prevent the rupture of beams caused by the unbalanced resistance of the braces.