Strong Axis Research Articles

Orientation-dependent magnetic behavior in aligned nanoparticle arrays constructed bycoaxial electrospinning

A modified electrospinning process has been utilized to align magnetite (Fe3O4) nanoparticles inside highly oriented poly(ethylene oxide) nanofibers. The structuralcharacterization of the fiber encapsulated nanoparticle arrays via electron microscopy hasbeen detailed, and the magnetic behavior has been studied using vibrating samplemagnetometry. The fiber encapsulated nanoparticle arrays exhibit orientation-dependentmagnetic behavior with respect to the applied magnetic field. A strong anisotropy alongorthogonal axes is obtained for aligned arrays and is manifested as a notable increase in thecoercivity and remanence magnetization in the parallel field configuration. The magneticbehavior of isotropic fibers is also examined as a reference and no orientation dependence isobserved. The results were found to corroborate theoretical predictions from thechain-of-spheres model. Such hybrid nanoparticle arrays may find relevance in applicationsrequiring an orientation-dependent physical response and in the directional transfer ofsignals.

Radio and optical orientations of galaxies

We investigate the correlations between optical and radio isophotal position angles for 14302 SDSS galaxies with $r$ magnitudes brighter than 18 and which have been associated with extended FIRST radio sources. We identify two separate populations of galaxies using the colour, concentration and their principal components. Surprisingly strong statistical alignments are found: late-type galaxies are overwhelmingly biased towards a position angle differences of $0^{\circ}$ and early-type galaxies to $90^{\circ}$. The late-type alignment can be easily understood in terms of the standard picture in which the radio emission is intimately related to areas of recent star-formation. In early-type galaxies the radio emission is expected to be driven by accretion on to a nuclear black hole. We argue that the observed correlation of the radio axis with the minor axis of the large-scale stellar distribution gives a fundamental insight into the structure of elliptical galaxies, for example, whether or not the nuclear kinematics are decoupled form the rest of the galaxy. Our results imply that the galaxies are oblate spheroids with their radio emission aligned with the minor axis. Remarkably the strength of the correlation of the radio major axis with the optical minor axis depends on radio loudness. Those objects with a low ratio of FIRST radio flux density to total stellar light show a strong minor axis correlation while the stronger radio sources do not. This may reflect different formation histories for the different objects and we suggest we may be seeing the different behaviour of rationally supported and non-rotationally supported ellipticals.

Triangular and Kagome Antiferromagnets with a Strong Easy-Axis Anisotropy

We consider S>3/2 kagome and triangular lattice magnets with strong easy-axis single-ion anisotropy D and antiferromagnetic exchange J. When D>>J, the low energy states selected by the anisotropy map onto configurations of the corresponding classical Ising antiferromagnet. Subleading O(J;{3}S/D;{2}) multispin interaction arising from the transverse quantum dynamics makes the low-temperature behavior very different from the well-known classical case: The kagome magnet goes into a semiclassical spin-liquid state with distinctive and unusual short-range correlations below a crossover temperature T;{*} approximately 0.08J;{3}S/D;{2}, while the triangular magnet undergoes a first-order transition at T_{c} approximately 0.1J;{3}S/D;{2} to an orientationally ordered collinear state that gives rise to a novel zero-magnetization plateau for small magnetic fields along the easy axis. Possible experimental implications are also discussed.

SRC기둥-RC보 약축방향 접합부 상세의 구조성능에 대한 실험적 연구

본 연구는 SRC기둥-RC보 약축방향 접합부에 대한 구조성능 평가 실험 연구이다. 현재 국내현장에서 많이 사용하고 있는 약축방향 접합방식은 구조성능이 명확하게 규명되지 않은 방식이 많으며, 이에 대한 안전성 확보 여부의 검증 및 문제점에 대한 개선도 시급하다. 따라서 본 연구에서는 표준갈고리형 실험체 3개와 접합부 형상 개선 실험체 3개 등 총 6개의 실험체를 제작하였다. 표준갈고리형 실험체들은 기준실험체, 정착길이 보정 실험체, 쉬어코넥터 및 전단보강근에 의한 보강 실험체 등으로 구성되어 있다. 접합부 형상 개선 실험체들은 주철근배치 방식과 용접 그리고 정착길이 확보 실험체 등이다. 반복가력에 의한 실험을 통하여 하중-변위 곡선, 최대강도, 강도저감 등을 평가하였다. 실험결과, 표준갈고리형 실험체들은 RC보의 주철근이 기둥면 내 콘크리트를 물고 떨어지는 쪼개짐 파괴현상을 나타내었으며, 구조성능도 불량하였다. 그러나 새로운 접합부 형상 개선 실험체들은 표준갈고리형 실험체들과 같이 기둥면 내 콘크리트를 물고 떨어지는 쪼개짐 파괴현상도 나타나지 않았으며, 구조성능도 양호하였다.

Analysis and design of rehabilitated built-up hybrid steel compression members

Compression members in steel bridges designed before 1960 may be deficient according to current design code requirements and so require strengthening. This paper explores the response of steel wide-flange columns reinforced with new steel flange cover plates, accounting for: residual and locked-in dead-load stresses; different yield strengths of the original W shape and the new cover plates; initial out-of-straightness; and load eccentricity at the member ends. A refined numerical analysis model is formulated and validated that computes the compressive resistance from principles of equilibrium, compatibility, and force–deformation relationships. Parametric studies conducted indicate that the capacity of the reinforced column is relatively insensitive to the magnitude of the locked-in dead-load stress in the original member, and that the strong axis capacity is insensitive to the magnitude of the residual stresses in the original member. A preliminary approach for designing strengthening for these members is presented and illustrated with an example calculation.

Seismic behavior of wide-flange steel column with confined potential plastic hinge

This experimental project investigates and validates an innovative method to confine the potential plastic hinge zone of hot-rolled H-shape (or wide-flange) steel column for improved seismic behavior. Based on fundamental mechanics, the concept aims at controlling the local buckling of the flange and web elements of the H-shape steel in the potential plastic hinge region of a column. In the experimental program, six model columns were tested under constant axial load and cyclic lateral forces acting in either the weak or the strong axes. Compared with the conventional H-shape steel model columns, the model columns with their potential plastic hinge zone confined by either steel strips or reinforced concrete cover, exhibited excellent seismic performance with large ductility. Analytical efforts to compare with the test results were also made using simple moment-curvature analysis.

Proportioning of steel beam–column members based on RSD optimization methodology

Due to the cost and energy embodied in steel production, a reduction in the cross-sectional area of a steel structural member could imply a significant saving of money and reduction in greenhouse gas emissions. Hernandez-Montes et al. [Hernández-Montes E, Aschheim M, Gil-Martin LM. The impact of optimal longitudinal reinforcement on the curvature ductility capacity of reinforced concrete column sections. Mag Concrete Res 2004;56(9):499–512; Hernández-Montes E, Gil-Martín LM, Aschheim M. The design of concrete members subjected to uniaxial bending and compression using reinforcement sizing diagrams. ACI Struct J 2005;102(1):150–8] proposed an analytical approach for reducing the amount of longitudinal reinforcement in reinforced concrete members subjected to the action of axial force and bending moment acting about a principal axis of the cross-section. The approach, which makes use of Reinforcement Sizing Diagrams (RSD), makes use of a graphical representation of all possible reinforcement solutions for a particular concrete cross-section subjected to a combined loading consisting of bending moment and axial load ( M , N ) . The common symmetric solution is recognized as just one of the infinite number of possible solutions. The RSD methodology used in that approach is extended in the present paper to steel sections having at least one axis of symmetry, subjected to axial force, bending moment about the strong axis, and shear acting in the plane of the bending moment. Special considerations are introduced to address the instabilities associated with slender steel elements. The methodology is developed following the Eurocode 3 provisions for compact steel members.

Analytical formulation for the deformations of I-shapes and RHS at the plastic strain ultimate limit state

The development of “full plastic hinges” in the most stressed cross-sections is a common hypothesis considered in the elastic–plastic design of steel structures. The equations for the internal forces at the plastic limit state are then based on equilibrium conditions only, and they do not allow the global deformations corresponding to each combination of internal forces at this ultimate limit state to be estimated. This paper presents a simplified analytical model for the elastic–plastic analysis of rectangular hollow sections and bisymmetrical I-sections bent about their strong axis. This model states the relations between the global deformations (axial deformation and bending curvature) and the corresponding internal forces (axial force and bending moment) at the cross-section plastic strain ultimate limit state. It allows a realistic evaluation of the cross-section ductility, based on a relevant strain limitation at the most strained cross-section fibres.

Higher-frequency wavenumber shift and frequency shift in a cracked, vibrating beam

Explicit wavenumber shift and frequency shift expressions are derived for the resonances of a cracked, transversely vibrating beam. These explicit expressions apply to beams with both shallow and deeper cracks. The explicit expressions are approximate, however, and are therefore generally inaccurate for the fundamental beam mode, and for a crack located in a boundary near field. The explicit expressions indicate that wavenumber shift and frequency shift are approximately proportional to the potential energy in the uncracked beam at the (future) crack location. Experimental results are presented for a freely vibrating, free–free beam with a midspan, single-edge slot. Data was collected for bending about both the strong axis and the weak axis. The experimental wavenumber shift curves generally agree well with the theoretical wavenumber shift curves.

Proposals for limit states torsional strength design of wide-flange steel members

This paper addresses the design of wide-flange steel members subjected to torsional forces as well as axial forces and moments about their strong and weak axes. The current Canadian steel design standard (CSA S16–01) gives no specific guidance on methodology with respect to torsional design. Codes of other countries (American, British, Australian) provide useful insight but are different in format from the Canadian standard and cannot be used directly in conjunction with it. Specialized second-order finite element programs have the capacity for torsional analysis, but are too complicated and costly to use in design practice. There is, therefore, a need for a practical design method that would allow engineers to account for the effects of torsion simply and accurately. This paper, written by a practicing design engineer, suggests a number of approaches that, subject to discussion and approval by experts in the field, could constitute the basis for design of steel members in torsion.

LOCAL BUCKLING RESTRAINT CONDITIONS FOR CORE PLATE IN BUCKLING RESTRAINED BRACES

Buckling Restrained Braces (BRBs) are commonly used as ductile bracing elements in seismic lateral resistance systems. A key limit state governing BRB behavior is overall flexural buckling. However, when the wall thickness of the restrainer is relatively small compared to the core plates section, the restraint conditions against local buckling of the core plate about its strong axis can be critical for the stability and strength of the BRB. In this study, cyclically-loaded experiments and numerical analyses were carried out using various tube restrainer configurations, and the local buckling restraint conditions are discussed and proposed using these results.

INELASATIC BEHAVIOR OF H-SHAPED STEEL BEAM-COLUMNS SUBJECTED TO TWO-DIMENSIONAL HORIZONTAL MONOTONIC LOAD

In this study, an inelastic biaxial bending experiment in which a horizontal force is loaded in a direction at a certain angle to the principal axis of the section was carried out for H-shaped steel beam-columns each with a relatively small slenderness ratio having an inelastic energy absorption capacity. As the result of studies on the elasto-plastic behavior as well as on the analysis results, it was made clear that the maximum strength ratio (the ratio of the maximum moment to the full plastic moment), the ductility factor and the energy absorption capacity decrease with the change in the loading angle from 0°(strong axis bending load) to 90°(weak axis bending load).

Cambering structural steel I-girders using cold bending

Cambering is often required in structural steel beams to compensate for dead load deflections. In this process, permanent deformations are induced in the girder after it is fabricated in order to match a required vertical profile under service loads. Traditionally, cambering is achieved by application of heat (heat cambering) or force (cold cambering). As in heat curving, heat cambering is time-consuming and costly. Cold cambering is faster and is most commonly used by fabricators. However, in the absence of data relating loads to deformations, the process is based on trial and error and relies on the fabricator’s skills and expertise. Recently, closed form equations and fabrication aids were derived for cold curving based on an available proprietary cold bending system. This paper extends this analysis to cambering where a girder is bent about its strong axis compared to weak axis bending in curving. New equations are derived and guidelines proposed that set limits on the maximum load and permanent residual strains to ensure they are within acceptable norms and prevent local failure. A comprehensive numerical example is included to illustrate this procedure.

A new structural system: friction-resistant dry-masonry

A new structural type is proposed and tested: steel-reinforced brick based on distributed unbond prestress theory (SRB-DUP). This is a dry-masonry structure with a friction-resistant stress-transfer mechanism. The elements comprising the entire assembly are not bonded to each other, allowing deconstruction for their easy reuse or recycling. Laboratory tests are reported on the structural performance of walls, beams and columns. Horizontal loading tests of walls and bending tests of beams along their strong axes reveal that the energy-absorbing capacities of both are high. Bending tests on walls and columns along their weak axis showed that both have high elastic deformation capacity. The SRB-DUP structure is a newly proposed type of earthquake resilient construction, different from other structural systems such as earthquake resistant construction, vibration control construction, and construction of vibration isolation. After meeting strict Japanese structural standards, the construction of two experimental houses using SRB-DUP structures was authorized. A new type of brick, with a uniform height achieved by covering it with fly-ash slurry mortar, has also been developed. Cet article présente un nouveau type de structure ainsi que les essais auxquels il a été soumis: il s'agit d'une brique renforcée à l'acier conçue selon la théorie du précontraint non collé distribué (SRB-DUP). C'est une structure en maçonnerie sèche avec un mécanisme de transfert des contraintes résistant au frottement. Les éléments qui composent l'ensemble ne sont pas collés les uns aux autres, ce qui permet et facilite leur déconstruction et leur réutilisation ou leur recyclage. L'article rend compte de tests menés en laboratoire sur les performances structurales de murs, de poutres et de colonnes. Des tests de charge horizontale menés sur des murs et des tests de flexion menés sur des poutres le long de leur axe fort révèlent que les capacités d'absorption d'énergie sont élevées dans les deux cas. Les tests de flexion sur des murs et des colonnes le long de leur axe faible montrent que dans les deux cas, la capacité de déformation élastique est élevée. La structure SRB-DUP est un nouveau type proposé de construction dont la résilience permet de résister aux séismes et qui est différent des autres systèmes structuraux comme les constructions antisismiques, les constructions antivibratoires et la construction d'amortisseurs de vibrations. Conforme à des normes structurales strictes japonaises, la construction de deux maisons expérimentales utilisant des structures SRB-DUP a été autorisée. Un nouveau type de brique, avec une hauteur uniforme obtenue par recouvrement d'un mortier-coulis à base de cendres volantes, a également été développé. Mots clés: technologie alternative, brique, déconstruction, maçonnerie sèche, conception antisismique, innovation, construction en maçonnerie, réutilisation

Amphibian species richness across environmental gradients

Large‐scale field patterns are a fundamental source of inferences on processes responsible for variation in species richness among habitats. We examined species richness of larval amphibian communities in 37 ponds over seven years on the Univ. of Michigan's E. S. George Reserve. Ordination of the community incidence matrix indicated a strong major axis of variation in species associations that was correlated with pond hydroperiod, surface area and forest canopy cover. Communities were significantly nested with those species found in ponds with high canopy cover, small area and short hydroperiod being nested subsets of those found in ponds with contrasting characteristics. Presence of fish had strong negative effects on species richness; relaxation of this effect also was apparent when fish were extirpated from ponds by drought. We employed a model selection analysis to identify the most appropriate statistical model for predicting the long‐term average species richness of these ponds from local abiotic and biotic (predator and competitor density) factors. A model including only the abiotic factors was overwhelmingly superior for the anurans; hierarchical partitioning indicated that area and canopy cover alone accounted for over 70% of the independent effects of predictor variables. The global model including both abiotic and biotic factors was the best supported model for the caudates, and correspondingly hierarchical partitioning suggested that area, hydroperiod, invertebrate predators and caudate biomass all accounted for 9–16% of the independent effects. Overall, biotic factors accounted for much less of the variation in species richness than abiotic factors. The patterns in larger, open‐canopy ponds provided little evidence of competitive effects on species richness, though there were patterns consistent with competitive effects in small, closed‐canopy ponds. The unusual temporal and spatial extent of these data enabled us to critically evaluate ideas regarding patterns in larval amphibian communities, and the effects of area, disturbance (hydroperiod) and productivity (canopy cover) on species richness of these communities. These results have important implications to the conservation of amphibian species richness in freshwater wetlands, which are among the most threatened ecosystems worldwide.

Personal Accounts: The System Stole My Identity

Personal Accounts: The System Stole My Identity

SRC기둥-RC보 강축 접합부 상세의 구조성능 평가

SRC기둥-RC보 강축 접합부 상세의 구조성능 평가

TEM & EBSD Study on Deformation Behavior of High Nitrogen Austenitic Fe-18Cr-18Mn-2Mo-0.9N Stainless Steel

Deformation behavior of high nitrogen austenitic Fe-18Cr-18Mn-2Mo-0.9N stainless steel was investigated utilizing electron back-scattered diffraction (EBSD) and transmission electron microscopy (TEM). During deformation, the <110> grains rotated and the trace of these grains moved towards into the dodecahedral plane (the line connecting (001) and (111) planes). Misorientation mapping in EBSD showed that the special boundaries (almost Σ3) gradually diminished whereas the low-angle boundaries were developed. TEM observation showed that (i) the low-angle boundaries developed corresponded to the deformation twinning with {111}<112> component, (ii) the deformation twinning showed the strong orientation dependence relative to tensile axis, and (iii) the deformed microstructure was characterized by extended stacking faults, planar dislocation array in low strain regime, and by well-developed deformation twinning in high strain region, respectively.

Nitride film growth morphology using remote plasma enhanced chemical vapor deposition

Gallium nitride and indium nitride films have been grown by remote plasma enhanced chemical vapor deposition (RPECVD) at temperatures between 570 and 650 °C for GaN and between 350 and 570 °C for InN on different substrates. For GaN vast improvements in film morphology and quality have resulted from reductions in background impurities when compared to previous reports. Epitaxial material can now be grown at 650 °C under optimized growth conditions. Columnar growth still occurs for growth on some substrates, however film coalescence is observed when using appropriate buffer layers and epitaxial growth can also be observed. High resolution SEM images show examples of this. The root-mean-square surface roughness of epitaxial samples, as measured using atomic force microscopy, shows values of as little as 10 Angstroms. While X-ray diffraction shows that these surfaces are not amorphous but have a strong (0001) preferred axis with FWHM limited by instrumental effects to (2θ) 0.085 degrees. The improvement in film quality has allowed heavily doped n-type films to be grown with an electron mobility of 160 cm2/V·s for a carrier concentration of ∼ 1x1019 cm–3 at 650 °C. Moss-Burstein shifted absorption data confirms the high doping level. For InN film growth by RPECVD, columnar growth is commonly observed in the temperature region of interest for films grown directly on sapphire, however film coalescence and epitaxial films are also observed for this material. X-ray diffraction indicates very sharp (0002) peaks with FWHM of (2θ) 0.07 degrees. High resolution SEM images show examples of film morphology at different growth temperatures. Electron backscattered diffraction images indicate a wurtzite structure even for InN films with strong deviations from the accepted lattice parameters. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Strength of Class 3 steel W sections in weak axis bending

This technical note considers weak axis moment capacity of wide-flange steel members of different section classes. In CSA S16-01 Limit states design of steel structures, there is a disconnect in moment capacity of laterally supported members between Classes 2 and 3: when the section crosses the Class 2 boundary, its calculated capacity drops in the ratio of the elastic to plastic section modulus. This effect is relatively minor for strong axis bending but is rather significant for weak axis bending. A rational theory is presented that explains the phenomena on the transition of the two Classes and proves that the noted gap in the design capacity does not exist. An improved design formula is proposed to mitigate this problem.Key words: bending, class, flange, local buckling, steel beams, strong axis, weak axis.