• Earthquakes and Structures
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• 제9권3호
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• pp.541-562
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• 2015

This paper aims at developing the knowledge on the seismic behavior of dowel beam-to-column connections, typically employed in precast buildings in Europe. Despite the large diffusion of the industrial buildings, a high seismic vulnerability was exhibited by these structures, mostly due to the connection systems deficiencies, during some recent earthquakes (Emilia 2012, Turkey 2011). An experimental campaign was conducted on a typical dowel connection between an external column and a roof beam. In this paper, the performed cyclic shear test is described. According to the experimental results, the seismic response of the system is evaluated in terms of strength, stiffness and failure mechanism. Moreover, the complete damage pattern of the test is described by means of the instrumentations records. The connection failure occurred due to the concrete cover failure in the column (splitting failure). Such a mechanism corresponds to a negligible energy dissipation capacity of the connection, compared to the overall seismic response of the structure. The experimental results are also compared with the results of a similar monotonic shear test, as well as with some literature relationships for predicting the strength of dowel connections under horizontal (seismic) loads.

• 대한기계학회논문집A
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• 제34권3호
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• pp.315-321
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• 2010

반복 인장하중이 가해지는 외면겹치기 동시경화조인트는 피접합물의 경계면 가장자리에서 균열이 발생하여 전체 파손에 이르게 되는데, 그 과정 중 피접합물의 경계면에서 발생하는 부식 현상이 중요한 영향을 미치게 된다. 그러므로 본 논문에서는 외면겹치기 동시경화조인트의 피로 파괴에 미치는 부식 현상의 영향을 규명하기 위하여 접합부 계면의 표면조도와 피접합물의 하나인 복합재료의 적층 각도의 변화에 따른 피로실험을 수행하였으며 유한요소해석을 통하여 얻은 경계면 응력 분포와 비교, 분석하였다.

• 한국공간구조학회논문집
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• 제13권3호
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• pp.45-55
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• 2013

The core aim of this paper is to empirically scrutinize a strength characteristic and ductility of the beam-column frame of reinforced with steel subjected to the cyclic lateral load. First and foremost, I the author embarks upon making four prototypes vis-$\grave{a}$-vis this research. Through this endeavour, the author has analysed cyclic behavior, fracture shape, ductility and energy dissipation of the normal beam-column frame and a beam-column frame of reinforced with steel. In addition, the survey has revealed the exact stress transfer path and the destructive mechanism in order to how much a beam-column frame of reinforced with steel has resistance to earthquake regarding all types of building, as well as school construction. To get the correct data, the author has compared the normal beam-column frame and three types of the beam-column frame of reinforced with steel following these works, the characteristic of cyclic behavior, destructive mechanism, ductility, and Energy dissipation of normal beam-column frame and a beam-column frame of reinforced with steel have been examined clearly.

• Earthquakes and Structures
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• 제17권4호
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• pp.399-409
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• 2019

This paper presents the experimental investigations on the seismic performance of a peculiar steel-concrete vertical hybrid structural system referred to as steel truss-RC tubular column hybrid structure. It is typically applied as the supporting structural system to house air-cooled condensers in thermal power plants (TPPs). Firstly, pseudo-dynamic tests (PDTs) are performed on a scaled substructure to investigate the seismic performance of this hybrid structure under different hazard levels. The deformation performance, deterioration behavior and energy dissipation characteristics are analyzed. Then, a cyclic loading test is conducted after the final loading case of PDTs to verify the ultimate seismic resistant capacity of this hybrid structure. Finally, the failure mechanism is discussed through mechanical analysis based on the test results. The research results indicate that the steel truss-RC tubular column hybrid structure is an anti-seismic structural system with single-fortification line. RC tubular columns are the main energy dissipated components. The truss-to-column connections are the structural weak parts. In general, it has good ductile performance to satisfy the seismic design requirements in high-intensity earthquake regions.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.693-707
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• 2023

In order to deeply reveal the working mechanism of ultra-high performance concrete (UHPC) filled steel tubular columns (UHPCFSTs) under cyclic loading, a three-dimension (3D) macro-mesoscale finite element (FE) model was established considering the randomness of steel fibers and the damage of UHPC. Model correctness and reliability were verified based on the experimental results. Next, the whole failure process of UHPC reinforced with steel fibers, passive confinement effect and internal force distribution laws were comprehensively analyzed and discussed. Finally, a simplified and practical method was proposed for predicting the ultimate bending strengths of UHPCFSTs. It was found that the non-uniform confinement effect of steel tube occurred when the drift ratio exceeded 0.5%, while the confining stress increased then decreased afterwards. There was preferable synergy between the steel tube and UHPC until failure. Compared with experimental results, the ultimate bending strengths of UHPCFSTs were undervalued by the current code provisions such as AISC360-10, EC4 and GB50936 with computed mean values (MVs) of 0.855, 0.880 and 0.836, respectively. The proposed practical method was highly accurate, as evidenced by a mean value of 1.058.

• Bulletin of the Korean Chemical Society
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• 제31권4호
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• pp.989-998
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• 2010

The titled dye of DBPI gives amplified spontaneous emission (ASE) with maximum at 580 nm upon pumping by nitrogen laser (${\lambda}_{ex}\;=\;337.1\;nm$). The ground state absorption cross section (${\sigma}_A$) and emission cross section (${\sigma}_E$) as well as effective emission cross section(${\sigma}^*_E$) have been determined. The electronic absorption spectra of DBPI were measured in ethanol and tetrahydrofuran at room and low temperature. DBPI displays molecular aggregation in water. The photochemical reactivity of DBPI was also studied in carbon tetrachloride upon irradiation with 525 nm light. The electrochemical investigation of DBPI dye has been carried out using cyclic voltammetry and convolution deconvolution voltammetry combined with digital simulation technique at a platinum electrode in 0.1 mol/L tetrabutyl ammonium perchlorate (TBAP) in two different solvents acetonitrile ($CH_3CN$) and dimethylformamide (DMF). The species were reduced via consumption of two sequential electrons to form radical anion and dianion (EE mechanism). In switching the potential to positive direction, the compound was oxidized by loss of two sequential electrons, which were followed by a fast dimerization and/or aggregation process i.e $EC_{dim1}EC_{dim2}$ mechanism. The electrode reaction pathway and the chemical and electrochemical parameters of the investigated compound were determined using cyclic and convolutive voltammetry. The extracted electrochemical parameters were verified and confirmed via digital simulation method.

• Steel and Composite Structures
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• 제27권2호
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• pp.229-242
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• 2018

High strength steel is widely used in industrial applications to improve the load-bearing capacity and reduce the overall weight and cost. To take advantage of the benefits of this type of steel in construction, an innovative hybrid fabricated member consisting of high strength steel tubes welded to mild steel plates has recently been developed. Component-scale uniaxial and multiaxial cyclic experiments have been conducted with simultaneous constant or varying axial compression loads using a multi-axial substructure testing facility. The structural interaction of high strength steel tubes with mild steel plates is investigated in terms of member capacity, strength and stiffness deterioration and the development of plastic hinges. The deterioration parameters of hybrid specimens are calibrated and compared against those of conventional steel specimens. Effect of varying axial force and loading direction on the hysteretic deterioration model, failure modes and axial shortening is also studied. Plate and tube elements in hybrid members interact such that the high strength steel is kept within its ultimate strain range to prevent sudden fracture due to its low ultimate to yield strain ratio while the ductile performance of plate governs the global failure mechanism. High strength material also significantly reduces the axial shortening in columns which prevents undesirable frame deformations.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3795-3799
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• 2013

The second-order rate constants ($k_N$) have been measured spectrophotometrically for nucleophilic substitution reactions of Y-substituted-phenyl 2-methylbenzoates (6a-e) with a series of cyclic secondary amines in MeCN at $25.0{\pm}0.1^{\circ}C$. Comparison of the $k_N$ values for the reactions of 4-nitrophenyl 2-methylbenzoate (6d) with those reported previously for the corresponding reactions of 4-nitrophenyl 2-methoxybenzoate (5) reveals that 6d is significantly less reactive than 5, indicating that modification of 2-MeO in the benzoyl moiety of 5 by 2-Me (i.e., $5{\rightarrow}6d$) causes a significant decrease in reactivity. This supports our previous report that aminolysis of 5 proceeds through a six-membered cyclic intermediate, which is highly stabilized through intramolecular H-bonding interactions. The Br${\o}$nsted-type plot for the reactions of 6d with a series of cyclic secondary amines is linear with ${\beta}_{nuc}=0.71$, which appears to be a lower limit of ${\beta}_{nuc}$ for a stepwise mechanism with breakdown of an intermediate ($T^{\pm}$) being rate-determining step (RDS). The Br${\o}$nsted-type plot for the reactions of 6a-e with piperidine is curved, i.e., the slope of Br${\o}$nsted-type plot (${\beta}_{lg}$) decreases from -1.05 to -0.41 as the leaving-group basicity decreases. The nonlinear Br${\o}$nsted-type plot has been taken as evidence for a stepwise mechanism with a change in RDS (e.g., from the $k_2$ step to the $k_1$ process as the leaving-group basicity decreases). Dissection of $k_N$ into the microscopic rate constants associated with the reactions of 6a-e with piperidine (e.g., $k_1$ and $k_2/k_{-1}$ ratio) also supports the proposed mechanism.

• 동력기계공학회지
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• 제14권4호
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• pp.37-42
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• 2010

This paper deals with the sealing mechanism of the gasket component and the effects of design parameters for the exhaust manifold. The finite element model includes hot-end exhaust system and a simplified gasket model supplied by ABAQUS software. The mechanical behaviors of bead and body of a gasket are measured after several times of cyclic loads by gasket supplier. From the finite element analysis due to the cyclic thermal loads, the flange of exhaust manifold shows thermal expansion and contraction in longitudinal direction as well as convex and concave deformations with respect to the engine cylinder head. And, the contact pressures of the gasket beads suddenly changes by normal deformation of inlet flanges. Therefore, the magnitudes of contact pressures could be used to determine the sealing characteristics of the exhaust gas in the exhaust system. The distributions of contact pressures in gasket bead lines shows a good agreement with the engine test results.

• 약학회지
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• 제25권4호
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• pp.167-173
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• 1981

Spectroscopic investigation has been carried out to know the binding mechanism of riboflavin with barbiturates, such as phenobarbital and amobarbital in chloroform solution by using infrared and nuclear magnetic resonance spectra. Phenobarbital and isoalloxazine form a 1:1 cyclic hydrogen bonded dimer through the 3-N imino and the 2-C carbonyl groups of the isoalloxazine ring of the latter, and the 1-N (or 3-N) imino and the 2-C carbonyl groups of the pyrimidine ring of the former. Amobarbital and riboflavin form a 1:1 cyclic hydrogen bonded dimer by the same mode of phenobarbital.