• 국제강구조저널
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• 제18권5호
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• pp.1525-1540
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• 2018

A test rig with multi-functional purposes was specifically designed and manufactured to study the behavior of multi-planar welded tubular joints subjected to multi-planar concurrent axial loading. An experimental investigation was conducted on full-scale welded tubular joints with each consisting of one chord and eight braces under monotonic loading conditions. Two pairs or four representative specimens (two specimens for each joint type) were tested, in which each pair was reinforced with two kinds of different internal stiffeners at the intersections between the chords using welded rectangular hollow steel sections (RHSSs) and the braces using rolled circular hollow steel sections (CHSSs) and welded RHSSs. The effects of different internal stiffeners at the chord-brace intersection on the load capacity of joints under concurrent multi-planar axial compression/tension are discussed. The test results of joint strengths, failure modes, and load-stress curves are presented. Finite element analyses were performed to verify the experimental results. The study results show that the two different joint types with the internal stiffeners at the chord-brace intersection under axial compression/tension significantly increase the corresponding ultimate strength to far exceed the usual design strength. The load carrying capacity of welded tubular joints decreases with a higher degree of the manufacturing imperfection in individual braces at the tubular joints. Furthermore, the interaction effect of the concurrent axial loading applied at the welded tubular joint on member stress is apparent.

• Structural Engineering and Mechanics
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• 제82권2호
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• pp.173-189
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• 2022

This study presents an experimental and numerically study about the effects of fiber reinforcement ratio on the behavior of concrete-filled steel tubes (CFST) under dynamic impact loading. In literature have examined the behavior of GFRP and FRP wrapped strengthened CFST elements impact loads. However, since the direction of potential impact force isn't too exact, there is always the probability of not being matched the impact force of the area where the reinforced. Therefore, instead of the fiber textile wrapping method which strengthens only a particular area of CFST element, we used fiber-added concrete-filled elements which allow strengthening the whole element. Thus, the effect of fiber-addition in concrete on the behavior of CFST elements under impact loads was examined. To do so, six simply supported CFST beams were constructed with none fiber, 2% fiber and 10% fiber reinforcement ratio on the concrete part of the CFST beam. CFST beams were examined under two different impact loads (75 kg and 225 kg). The impactors hit the beam from a 2000 mm free fall during the experimental study. Numerical models of the specimens were created using ABAQUS finite element software and validated with experimental data. The obtained results such as; mid-span displacement, acceleration, failure modes and energies from experimental and numerical studies were compared and discussed. Furthermore, the Von Misses stress distribution of the CFST beams with different ratio of fiber reinforcements were investigated numerically. To sum up, there is an optimum amount limit of the fiber reinforcement on CFST beams. Up to this limit, the fiber reinforcement increases the structural performances of the beam, beyond that limit the fiber reinforcement decreases the performances of the CFST beam under transverse impact loadings.

• Steel and Composite Structures
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• 제44권3호
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• pp.295-307
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• 2022

The objective of this research is to study experimentally the behavior of stiffened steel tubes (CFSTs). Considered parameters are stiffening methods by through-bolts or shear connectors with different configurations. In addition, the effect of global (ratio between length to diameter) and local (proportion between diameter to thickness) slenderness ratios are investigated. Load application either applied on steel only or both steel and concrete is studied as well. Case of loading on steel only happens when concrete inside the column shrinks. The purpose of the research is to improve the behavior of CFSTs by load transfer between them and different stiffening methods. A parametric experimental study that incorporates thirty-three specimens is carried out to highlight the impact of those parameters. Different outputs are recorded for every specimen such as load capacities, vertical deflections, longitudinal strains, and hoop strains. Two modes of failure occur, yielding and global buckling. Shear connectors and through-bolts improve the ultimate load by up to 5% for sections loaded at steel with different studied global slenderness and local slenderness equal 63.5. Meanwhile, shear connectors or through bolts increase the ultimate load by up to 6% for global slenderness up to 15.75 for sections loaded on composite with local slenderness equals 63.50. Recommendations for future design code development are outlined.

• Structural Engineering and Mechanics
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• 제81권6호
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• pp.715-728
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• 2022

A new type of buckling-restrained braces (BRBs) with a longitudinally profiled steel plate working as the core (LPBRB) is proposed and experimentally investigated. Different from conventional BRBs with a constant thickness core, both stiffness and strength of the longitudinally profiled steel core along its longitudinal direction can change through itself variable thickness, thus the construction of LPBRB saves material and reduces the processing cost. Four full-scale component tests were conducted under quasi-static cyclic loading to evaluate the seismic performance of LPBRB. Three stiffening methods were used to improve the fatigue performance of LPBRBs, which were bolt-assembled T-shaped stiffening ribs, partly-welded stiffening ribs and stiffening segment without rib. The experimental results showed LPBRB specimens displayed stable hysteretic behavior and satisfactory seismic property. There was no instability or rupture until the axial ductility ratio achieved 11.0. Failure modes included the out-of-plane buckling of the stiffening part outside the restraining member and core plate fatigue fracture around the longitudinally profiled segment. The effect of the stiffening methods on the fatigue performance is discussed. The critical buckling load of longitudinally profiled segment is derived using Euler theory. The local bulging behavior of the outer steel tube is analyzed with an equivalent beam model. The design recommendations for LPBRB are presented finally.

• Steel and Composite Structures
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• 제41권5호
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• pp.663-679
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• 2021

To elucidate the differences in the collapse behavior between a single-story beam-column assembly and multi-story frame, two 1/3-scale two-bay composite frames, including a single-story composite beam-column assembly and a three-story composite sub-frame, were designed and quasi-statically tested. The load-displacement responses, failure modes, and internal force development of the two frames were analyzed and compared in detail. Furthermore, the resistance mechanisms of the two specimens were explored, and the respective contributions of different load-resisting mechanisms to the total resistances were quantitatively separated to gain deeper insights. The experimental tests indicated that Vierendeel action was present in the two-dimensional multi-story frames, which led to an uneven internal force distribution among the three stories. The collapse resistance of TSDWA-3S in the flexural stage was not significantly increased by the structural redundancy provided by the additional story, as compared to that of TSDWA-1S. Although the development of the load response was similar in the two specimens at flexural stage, the collapse mechanisms of the multi-story composite frame were much more complicated than those of the single-story beam-column assembly, and the combined action between stories was critical in determining the internal force redistribution and rebalancing of the remaining structure.

• 한국전산구조공학회논문집
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• 제35권6호
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• pp.357-365
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• 2022

냉매 오충전은 에어컨에서 빈번하게 발생하는 고장 모드 중 하나로, 적정 충전량 대비 부족 및 과충전 모두 냉방 성능의 저하를 유발하므로 충전된 냉매량을 정확하게 판단하는 것이 중요하다. 본 연구에서는 퍼지 군집화 기법을 통한 정상상태 식별을 통해 냉매 오충전량을 다중 분류하는 모델을 개발하였다. 정상상태 식별을 위해 에어컨 운전 데이터에 대해 이동 평균 간의 차이를 활용한 퍼지 군집화 알고리즘을 적용하였으며, IFDR를 통해 기존 연구된 정상상태 판단 기법들과 식별 결과를 비교하였다. 이후, 시스템 내 상관성을 고려한 mRMR을 이용해 특징을 선택하였으며, 도출된 특징을 이용해 SVM 기반의 다중 분류 모델이 생성되었다. 제안된 방법은 시험 데이터를 통해 만족할 만한 분류 정확도와 강건성을 도출하였다.

• Structural Engineering and Mechanics
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• 제86권3호
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• pp.399-415
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• 2023

This paper presents the experimental and numerical evaluations on the circular SFRC columns reinforced GFRP rebars under the axial compressive loading. The test programs were designed to inquire and compare the effects of different parameters on the columns' structural behavior by performing experiments and finite element modeling. The research variables were conventional concrete (CC), fiber concrete (FC), types of longitudinal steel/GFRP rebars, and different configurations of lateral rebars. A total of 16 specimens were manufactured and categorized into four groups based on different rebar-concrete arrangements including GRCC, GRFC, SRCC, and SRFC. Adding steel fibers (SFs) into the concrete, it was essential to modify the concrete damage plastic (CDP) model for FC columns presented in the finite element method (FEM) using ABAQUS 6.14 software. Failure modes of the columns were similar and results of peak loads and corresponding deflections of compression columns showed a suitable agreement in tests and numerical analysis. The behavior of GFRP-RC and steel-RC columns was relatively linear in the pre-peak branch, up to 80-85% of their ultimate axial compressive loads. The axial compressive loads of GRCC and GRFC columns were averagely 80.5% and 83.6% of axial compressive loads of SRCC and SRFC columns. Also, DIs of GRCC and GRFC columns were 7.4% and 12.9% higher than those of SRCC and SRFC columns. Partially, using SFs compensated up to 3.1%, the reduction of the compressive strength of the GFRP-RC columns as compared with the steel-RC columns. The effective parameters on increasing the DIs of columns were higher volumetric ratios (up to 12%), using SFs into concrete (up to 6.6%), and spiral (up to 5.5%). The results depicted that GFRP-RC columns had higher DIs and lower peak loads compared with steel-RC columns.

• Restorative Dentistry and Endodontics
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• 제48권1호
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• pp.4.1-4.10
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• 2023

Objectives: This study aimed to compare the torsional and cyclic fatigue resistance of ProGlider (PG), WaveOne Gold Glider (WGG), and TruNatomy Glider (TNG). Materials and Methods: A total of 15 instruments of each glide path system (n = 15) were used for each test. A custom-made device simulating an angle of 90° and a radius of 5 millimeters was used to assess cyclic fatigue resistance, with calculation of number of cycles to failure. Torsional fatigue resistance was assessed by maximum torque and angle of rotation. Fractured instruments were examined by scanning electron microscopy (SEM). Data were analyzed with Shapiro-Wilk and Kruskal-Wallis tests, and the significance level was set at 5%. Results: The WGG group showed greater cyclic fatigue resistance than the PG and TNG groups (p < 0.05). In the torsional fatigue test, the TNG group showed a higher angle of rotation, followed by the PG and WGG groups (p < 0.05). The TNG group was superior to the PG group in torsional resistance (p < 0.05). SEM analysis revealed ductile morphology, typical of the 2 fracture modes: cyclic fatigue and torsional fatigue. Conclusions: Reciprocating WGG instruments showed greater cyclic fatigue resistance, while TNG instruments were better in torsional fatigue resistance. The significance of these findings lies in the identification of the instruments' clinical applicability to guide the choice of the most appropriate instrument and enable the clinician to provide a more predictable glide path preparation.

• Composites Research
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• 제22권6호
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• pp.23-31
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• 2009

압축하중 및 굽힘하중을 받는 유리섬유플라스틱(GFRP) 표피/ 알루미늄 하니컴 코어(GF-AH) 하이브리드 복합재료의 음향방출(AE) 특성을 다양한 파괴과정과 연결시켜 연구하였다. 표피층 파괴, 표피/코어간의 계면박리, 하니컴 알루미늄 벽의 국부적인 소성항복 좌굴 및 셀벽간의 접착수지 박리와 같은 다양한 파괴모드가 하니컴 코어/GFRP표피 복합재를 이용한 AE주파수 분포 해석과 진폭분포 해석결과를 통해 분류되었다. 높은 진폭을 가진 AE 사상율의 분포는 셀벽 접착수지의 파괴, 표피층과 심층 사이의 박리및 미세파괴, 섬유파단에 대응하였으며 다른 피크 주파수의 분포는 알루미늄 셀벽의 소성변형, 셀벽간의 마찰로부터 발생한 것이다. 결론적으로 GF-AH 하이브리드 복합재료의 파괴거동 특성은 AE기법을 활용한 비파괴 평가를 통해 분석 가능하였다.

• Computers and Concrete
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• 제31권6호
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• pp.513-525
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• 2023

This research presents the experimental and theoretical evaluations on circular steel-fiber-reinforced-concrete (SFRC) columns reinforced by glass-fiber-reinforced-polymer (GFRP) rebar under the axial compressive loading. Test programs were designed to investigate and compare the effect of different parameters on the structural behavior of columns by performing tests. Theses variables included conventional concrete (CC), fiber concrete (FC), steel/GFRP longitudinal rebars, and transversal rebars configurations. A total of 16 specimens were constructed and categorized into four groups in terms of different rebar-concrete configurations, including GFRP-rebar-reinforced-CC columns (GRCC), GFRP-rebar-reinforced-FC columns (GRFC), steel-rebar-reinforced-CC columns (SRCC) and steel-rebar- reinforced-FC columns (SRFC). Experimental observations displayed that failure modes and cracking patterns of four groups of columns were similar, especially in pre-peak branches of load-deflection curves. Although the average ultimate axial load of columns with longitudinal GFRP rebars was obtained by 17.9% less than the average ultimate axial load of columns with longitudinal steel rebars, the average axial ductility index (DI) of them was gained by 10.2% higher than their counterpart columns. Adding steel fibers (SFs) into concrete led to the increases of 7.7% and 6.7% of the axial peak load and the DI of columns than their counterpart columns with CC. The volumetric ratio had greater efficiency on peak loads and DIs of columns than the type of transversal reinforcement. A simple analytical equation was proposed to predict the axial compressive capacity of columns by considering the axial involvement of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop rebar. There was a good correlation between test results and predictions of the proposed equation.