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This paper discusses the shear and torsion induced in low-rise and medium-rise buildings, according to wind load specifications provided in NBCC 2015. Results from experimental studies, carried out in wind tunnels were compared with corresponding NBCC 2015 provisions under different upstream roughness conditions. These comparisons demonstrated notable discrepancies for the case of torsion in low-rise buildings. Further, comparisons between the wind load specifications given in NBCC 2015 and ASCE/SEI7-10 standard were carried out. Following both sets of provisions, wind-induced shear and torsion were computed and compared for five low-rise and medium-rise buildings with the same horizontal dimensions but different heights. Emphasis was directed towards the cases that create maximum shear forces and (or) maximum torsions to reflect critical design conditions. For low-rise buildings, the ASCE/SEI-7-10 and NBCC-2015 yield similar shear coefficients but quite different torsional coefficients; while for medium-rise buildings, clear agreement was found, for both shear and torsion. The diversity of the results is discussed and some suggestions for improvement of code provisions are made. A definition for medium-rise buildings was provided. Key words: wind loads, code provisions, shear, torsion, low-rise and medium-rise buildings. Dans le cadre de cet article, on aborde la torsion et le cisaillement induits dans les immeubles bas et de hauteur moyenne, selon les specifications de charge due au vent fournies dans le Code national du batiment du Canada (CNB) de 2015. Les resultats provenant d'etudes experimentales et effectuees dans des tunnels aerodynamiques ont ete compares aux dispositions correspondantes du CNB de 2015 sous differentes conditions de rugosite en amont. Ces comparaisons ont demontre des ecarts notables pour le cas de torsion induite dans les immeubles bas. De plus, on a effectue des comparaisons entre les specifications de charge due au vent fournies par le CNB de 2015 et celles de la norme 7-10 du << Structural Engineering Institute >> (SEI) de l'<< American Society of Civil Engineers>>(ASCE). Conformement aux deux ensembles de dispositions, la torsion et le cisaillement induits par le vent ont ete calcules et compares pour cinq immeubles bas et de hauteur moyenne de memes dimensions horizontales, mais de hauteurs differentes. On a mis l'accent sur les cas qui creent les cisaillements maximaux et (ou) les torsions maximales afin de refleter les conditions de conception critiques. Pour les immeubles bas, la norme 7-10 SEI de l'ASCE et les dispositions du CBN 2015 donnent des coefficients de cisaillement semblables, mais des coefficients de torsion tout a fait differents; tandis que pour les immeubles de hauteur moyenne, il y avait une concordance claire, tant pour le cisaillement que la torsion. On traite de la diversite des resultats et on fait quelques suggestions pour Amelioration des dispositions du code. On a fourni une definition pour les immeubles de hauteur moyenne. [Traduit par la Redaction] Mots-cles: charge due au vent, dispositions du code, cisaillement, torsion, immeubles bas et de hauteur moyenne., Introduction Wind loading, especially its torsional effect, plays a critical role on building design. Torsion always occurs even in a perfectly symmetrical building, given that the wind direction towards the [...]

Drilled shaft foundations supporting mast arm assemblies are subjected to significant torsion and lateral load during severe wind loading (e.g., hurricane). Past centrifuge studies in granular soils suggest that the design of such foundations should be performed for a coupled load case, since the lateral resistance is considerably reduced by the concurrent application of torsion. However, current design practice still considers lateral load and torsion independently due to the lack of field verification of centrifuge results. This paper reports on a full-scale test program to investigate the coupled load behavior of drilled shafts. A novel load test setup (with a heavy-duty mast arm assembly) and instrumentation were used for the combined torsion and lateral loading (e.g., wind loading). The study revealed a significant reduction in lateral resistance due to the influence of torque as observed from previous centrifuge studies. Torsional resistance was reduced (approximately 20%) by the impact of lateral load when compared with the anticipated torsional resistance based on unit skin friction values, derived from the axial load test results (i.e., no influence of lateral load). A comparison of measured torsional resistance during the combined loading with the predicted values using different approaches was also made. O'Neill and Hassan's beta (β) method (sand) and alpha method (clay) are found to predict the torsional resistance reasonably well (± 10%), while all other methods based on the standard penetration test and cone penetration test considered in the study overpredicted or underpredicted the resistance. Key words: drilled shaft, lateral load, torsion, full-scale load test, coupled loading. Les fondations en puits fores qui soutiennent des ensembles de bras de mat sont soumises a une torsion significative et a une charge laterale lors d'une charge de vent severe (par ex., des ouragans). Les anciennes etudes a centrifuge dans les sols granulaires suggerent que la conception de ces fondations doit etre effectuee pour un cas de charge couplee puisque la resistance laterale est considerablement reduite par l'application simultanee de torsion. Cependant, la pratique de la conception actuelle considere toujours la charge laterale et la torsion independamment du fait de l'absence de la verification sur le terrain des resultats a centrifuge. Cet article presente un programme de test a grande echelle pour etudier le comportement de charge couplee de puits fores. Une configuration novatrice de test de charge (avec un ensemble de bras de mat lourds) et l'instrumentation ont ete utilisees pour le chargement combine de torsion et laterales (par ex., charge de vent). L'etude a revele une reduction significative de la resistance laterale due a l'influence d'un couple telle qu'observee dans les etudes a centrifuge precedentes. La resistance a la torsion a ete reduite (environ 20 %) par l'impact de la charge laterale par rapport a la resistance a la torsion prevue en fonction des valeurs de friction de la peau de l'unite, provenant des resultats d'essai a charge axiale (a savoir, sans influence de la charge laterale). Une comparaison de la resistance a la torsion mesuree pendant le chargement combine avec les valeurs predites en utilisant differentes approches a egalement ete realisee. La methode (sable) beta (β) et la methode alpha (argile) de O'Neill et Hassan peuvent predire la resistance a la torsion raisonnablement bien (± 10 %), tandis que toutes les autres methodes basees sur l'essai de penetration standard et l'essai de penetration d'un cone pris en compte dans l'etude ont sous- evaluee ou sur evaluee la resistance. [Traduit par la Redaction] Mots-cles: puits fore, charge laterale, torsion, test de charge a pleine echelle, charge couple., Introduction In Florida, miscellaneous structures (e.g., mast arms for traffic signs, signals, and luminaries) are supported by drilled shaft foundations. In general, a pole-mast arm assembly needs to be designed [...]

Building structures of low or medium height are usually designed with a pseudostatic approach using a base shear much lower than that predicted from an elastic spectrum. Given this shear force, the objective of this paper is to evaluate the effect of the element strength assignment (as determined by several building codes) on the torsional response of inelastic single-storey eccentric structures and to provide guidelines for minimizing this structural behaviour. It is demonstrated that the expected torque about the centre of mass (CM) may be, with equal probability, positive (counterclockwise) or negative (clockwise). This result means that the torsional strength should also be provided in equal terms in both rotational directions, and therefore the base shear and torque (BST) surface of a given system must be symmetrical (or approximately symmetrical). In stiffness-eccentric systems, appropriate BST surfaces may be obtained when a structural design is based on a pair of design eccentricities in a symmetrical order about CM, and this is shown in representative single-storey building models under characteristic ground motions. Key words: earthquake engineering, design eccentricities, modal analysis, inelastic structures. Les batiments de faible ou de moyenne hauteur sont normalement con^us en utilisant une approche pseudo-statique avec un cisaillement a la base bien inferieur a celui predit a partir d'un spectre elastique. Etant donne cette force de cisaillement, l'objectif de l'article est d'evaluer l'effet de l'assignation de la resistance d'un element (telle que determinee dans plusieurs codes du batiment) sur la reponse en torsion de structures excentriques inelastiques d'un seul etage et de fournir les lignes directrices visant a minimiser ce comportement structural. Il est demontre que le moment attendu autour centre de masse peut etre, en probabilite egale, positif (antihoraire) ou negatif (horaire). Cela signifie que la resistance en torsion devrait egalement etre fournie en termes egaux dans les deux directions de rotation; ainsi, la surface de moment-cisaillement a la base (BST) d'un systeme donne doit etre de forme symetrique (ou presque symetrique). Dans les systemes de rigidite excentrique, les surfaces BST appropriees peuvent etre obtenues lorsque la conception structurale est basee sur une paire d'excentricites de conception dans un ordre symetrique autour du centre de masse; cela est demontre dans les modeles representatifs de batiments a un seul etage soumis a des mouvements de sols caracteristiques. [Traduit par la Redaction] Mots-cles: ingenierie parasismique, excentricites de conception, analyse modale, structures inelastiques., Introduction For low- and medium-height regular buildings, seismic codes require that the design base shear be determined from the acceleration design spectrum in relation to the fundamental period, T, of [...]

First-principles calculations were carried out to investigate the torsional potential energy surface (PES) of the secbutyl radical. All the wave function methods employed predict a cis-like stable conformation with a dihedral angle of about 47° in addition to the trans-like global minimum conformation and a gauche conformation. However, most of the popular density functional approaches predict only the latter two local minima and lack the cis conformation that was experimentally observed. On the other hand, some density functional methods that incorporate the exact exchange and asymptotically corrected correlation functionals can locate the cis conformation successfully. The basis-set effect was also measured using popular B3LYP and MP2 Hamiltonians: only moderate shape changes were found for PES profiles upon basis-set variations. The stationary structures and their Hessians were obtained at both MP2 and B3LYP levels, with or without incorporating the zero-point energies. Opposite to the relative stability within the Born-Oppenheimer approximation, the cis conformation is more stable than the gauche conformation upon the zero-point correction, consistent with the experiment observations. Key words: sec-butyl, torsional potential energy surface, density functional theory, wave function theory. On a effectue des calculs theoriques a partir des principes premiers pour etudier la surface d'energie potentielle (SEP) de torsion du radical sec-butyle. Toutes les methodes de fonction d'onde utilisees predisent qu'il existe sous une conformation de type cis stable avec un angle diedre de 47° a cote d'une conformation de type trans avec minimum global et d' une conformation gauche. Toutefois, la plupart des approches populaires par la fonctionnelle de la densite ne predisent l' existence que des deux derniers minima locaux sans predire celle de la conformation cis observee experimentalement. Par ailleurs, certaines methodes de la fonctionnelle de la densite qui incorporent l' echange exact et des fonctionnelles de correlation corrigees d'une facon asymptotique permettent de localiser avec succes la conformation cis. On a aussi mesure l'effet de l'ensemble de base en faisant appel aux hamiltoniens populaires B3LYP et MP2 : toutefois, avec ces changements d'ensembles de base, on n'a pu observer que des changements moderes de la forme des profils de la surface d'energie potentielle (SEP). On a obtenu les structures stationnaires et leurs matrices hessiennes aux niveaux MP2 ainsi que B3LYP, avec et sans incorporation des energies du point zero. Contrairement a la stabilite relative observee dans l'approximation de Born-Oppenheimer, la conformation cis est plus stable que la conformation gauche lorsqu'on introduit une correction pour l' energie au point zero et ceci est en accord avec les observations experimentales. Mots-cles: sec-butyle, surface d'energie potentielle de torsion, theorie de la fonctionnelle de la densite, theorie de la fonction d'onde. [Traduit par la Redaction], Introduction Torsional potential energy surfaces (PESs) of many chemical species have been studied numerous times because they provide the key information for molecular thermodynamic state functions. At the same time, [...]

Supersolidity, the appearance of zero-viscosity flow in solids, was first indicated in helium-4 torsional oscillator (TO) experiments, in this apparatus, the irrotationality of the superfluid component causes it to decouple from the underlying normal solid, leading to a reduction in the resonant period of the TO. However, the resonant period may be altered for reasons other than supersolidity, such as the temperature dependence of the elastic modulus of solid helium. Superimposing rotation onto oscillatory measurements may distinguish between supersolidity and classical effects. We performed such simultaneous measurements of the TO and the shear modulus, and observed substantial change in the resonant period with rotational speed where the modulus remained unchanged. This contrasting behavior suggests that the decrease in the TO period is a result of supersolidity. 10.1126/science.1196409

Early diastolic left ventricular (LV) untwisting has been evaluated as a manifestation of LV recoil, reflecting the release of elastic energy stored during systole. The primary goal of this study was to characterize the relationship between systolic strain (e.g., circumferential strain and the shear strains that comprise twist) with the resulting early diastolic shear strain rates, including the rate of untwisting. A further goal was to characterize these relationships regionally from apical to basal locations. Cardiac magnetic resonance imaging tissue tagging was used to measure circumferential strain, global and regional (apex, mid, basal) twist ([theta]), and circumferential-longitudinal ([[member].sub.CL]) and circumferential-radial ([[member of].sub.CR]) shear strains along with the corresponding untwisting rates (d[theta]/dt and diastolic shear strain rates (d[member of]/dt in 32 healthy males (33 [+ or -] 7 yr). LV untwisting rates and shear strain rates measured during early diastole varied significantly with the measurement location from apex to base (P < 0.001) but demonstrated significant linear correlation with their corresponding preceding systolic strains (P < 0.001). Untwisting rates and diastolic shear strain rates were not significantly correlated with circumferential systolic strain or endsystolic volume (P > 0.05). Normalization of the untwisting rates to the peak twist (d[theta]/[dt.sub.Norm] = -13.6 [+ or -] 2.1 [s.sup.-1]) or shear strain rates to peak systolic shear strain (d[[member of].sub.CL]/[dt.sub.Norm] = -15.0 [+ or -] 5.4 [s.sup.-1], and d[[member of].sub.CR]/[dt.sub.Norm] = -14.2 [+ or -] 7.7 [s.sup.-1]) yielded a uniform measure of early diastolic function that was similar for all shear strain and twist components and for all locations from apex to base. These findings support a linear model of torsional recoil in the healthy heart, where diastolic shear strain rates (e.g., untwisting rates) are linearly related to the corresponding preceding systolic shear stain component. Furthermore, these findings suggest that torsional recoil is uncoupled from end-systolic volumes or the associated strains, such as circumferential strain. relaxation; torsion; untwisting doi: 10.1152/ajpheart.00353.2010.

This paper provides a critical summary of the European standards and design methods available for calculating the strength of cold-formed stainless steel compression members. The standards considered (so far mainly applied to columns failing by flexural buckling) are applied to the case of lipped channel section columns failing by combined distortional and overall flexural-torsional buckling. As observed during the tests presented in a companion paper, distortional buckling is found to have a considerable effect on the cross section resistance and is prone to interact with the global flexural-torsional mode. It is investigated how the different formulations account for the two buckling modes and their interaction and how accurate strength predictions they provide. A new direct strength method taking into account these failure modes is then presented and compared to the test results. DOI: 10.1061/(ASCE)ST.1943-541X.0000147 CE Database subject headings: Stainless steel; Steel structures; Buckling; Design; Cold-formed steel; Failure modes. Author keywords: Stainless steel structures; Distortional buckling; Member buckling; Interaction buckling; Design; Direct strength method.

This paper presents a series of 48 full-scale tests on press-braked stainless steel lipped channel section columns subjected to concentric compression. The tests were carried out between fixed ends in the Structures Laboratory of the University of Liege and the test specimens were designed such that distortional buckling developed in the section prior to overall flexural-torsional buckling. The stainless steel alloy was 1.4003 chromium weldable steel, popularly known as 3Cr12. Three different geometries were tested using the same experimental setup. A critical summary of the standards and methods for calculating the carrying capacity of cold-formed stainless steel compression members is presented in a companion paper by the same writers. DOI: 10.1061/(ASCE)ST.1943-541X.0000130 CE Database subject headings: Stainless steel; Steel structures; Buckling; Full-scale tests; Experimentation; Columns. Author keywords: Stainless steel structures; Distortional buckling; Member buckling; Interaction buckling; Full-scale tests.

We present an analytical model, derived using the principle of virtual work, for closed and open thin-walled beams subjected to torsion. Nonclassical effects like primary and secondary torsional warping are taken into account. A closed-form expression for mode II stress-intensity factor for thin-walled beams with a longitudinal crack is derived. We start by finding analytical solutions based on Vlasov's torsional beam theory for thin-walled beams with any cross sections. We then use the calculated stress of a rectangular thin-walled beam to determine an analytical expression for mode II stress-intensity factor. Finally, we add a correction factor to account for complex behavior of long cracks. Examples are presented to illustrate the effectiveness of the current model, and it is validated by comparison with detailed finite element results obtained using ABAQUS. DOI: 10.2514/1.45393

In this paper the elastic nonuniform torsion analysis of composite cylindrical bars of arbitrary cross section consisting of materials in contact, each of which can surround a finite number of inclusions, taking into account the effect of geometric nonlinearity is presented employing the boundary element method (BEM). All of the cross section's materials are perfectly bonded together, that is separation is not allowed. The torque-rotation relationship is computed based on the finite displacement (finite rotation) theory, that is the transverse displacement components are expressed so as to be valid for large rotations and the longitudinal normal strain includes the second-order geometric nonlinear term often described as the 'Wagner strain.' The proposed formulation does not stand on the assumption of a thin-walled structure and therefore the cross section's torsional rigidity is evaluated exactly without using the so-called Saint-Venant's torsional constant. The torsional rigidity of the cross section is evaluated directly employing the primary warping function of the cross section depending on its shape. Three boundary value problems with respect to the variable along the beam axis angle of twist, to the primary and to the secondary warping functions are formulated. The first one, employing the Analog Equation Method (a BEM based method), yields a system of nonlinear equations from which the angle of twist is computed by an iterative process. The rest two problems are solved employing a pure BE method. Numerical results are presented to illustrate the method and demonstrate its efficiency and accuracy. The developed procedure retains most of the advantages of a BEM solution over a pure domain discretization method, although it requires domain discretization. DOI: 10.1061/(ASCE)EM.1943-7889.0000056 CE Database subject headings: Bars; Torsion; Geometry; Shear stress; Warpage; Boundaries; Cross sections.

Orthogonal dipolar interactions between amide C=O bond dipoles are commonly found in crystal structures of small molecules, proteins, and protein--ligand complexes. We herein present the experimental quantification of such interactions by employing a model system based on a molecular torsion balance. Application of a thermodynamic double-mutant cycle allows for the determination of the incremental energetic contributions attributed to the dipolar contact between 2 amide C=O groups. The stabilizing free interaction enthalpies in various apolar and polar solvents amount to -2.73 kJ [mol.sup.-1] and lie in the same range as aromatic-aromatic C-H ... [pi] and [pi]-[pi] interactions. High-level intermolecular perturbation theory (IMPT) calculations on an orthogonal acetamide/N-acetylpyrrole complex in the gas phase at optimized contact distance predict a favorable interaction energy of -9.71 kJ [mol.sup.-1]. The attractive dipolar contacts reported herein provide a promising tool for small-molecule crystal design and the enhancement of ligand--protein interactions during lead optimization in medicinal chemistry. mutant cycle | protein folding | torsion balance | medicinal chemistry

Abstract: The equations of nonlinear flexural-flexural-torsional vibrations of rotating beams with asymmetric cross-sections are derived. As the cross-section is asymmetric the centre of gravity and shear centre of a beam [...]

Although steel single angle sections are commonly used as beams to support distributed loads which cause biaxial bending and torsion, their behavior may be extremely complicated, and the accurate prediction of their strengths very difficult. Further, many design codes do not have design rules for torsion, while some recommendations are unnecessarily conservative, or are of limited application, or fail to consider some effects which are thought to be important. This paper is one of a series on the behavior and design of single angle section steel beams. Two previous papers have studied the biaxial bending and torsion of restrained beams, a third has studied the lateral buckling of unrestrained beams, a fourth the biaxial bending of unrestrained beams, and a fifth and sixth the buckling and torsion of unrestrained beams. In each paper, simple design methods have been developed. In this present paper, an approximate method of predicting the second-order deflections and twist rotations of steel equal angle section beams under biaxial bending and torsion is developed. This method is then used to determine the approximate maximum biaxial bending moments in such beams, which are then used with the section moment capacity proposals of the first paper and the lateral buckling proposals of the third paper to approximate the member capacities. DOI: 10.1061/(ASCE)0733-9445(2007)133:1(78) CE Database subject headings: Steel beams; Buckling; Bending; Elasticity.

An experiment was conducted to produce impurity free [Cu.sub.60][Zr.sub.20][Ti.sub.20] metallic glass using the high-pressure torsion (HPT) technique. Disk-shape specimen of composition [Cu.sub.60][Zr.sub.20][Ti.sub.20] with a diameter of 10mm and thickness of about 200 [mu]m was produced by HPT, which observed that the deformation during the HPT process created a detectable amount of amorphous phase in the top layer of the disk.

The small wind research turbine (SWRT) testing project was initiated with the goal of better characterizing both small wind turbine loads and dynamic behavior. The main purpose of the testing was to produce high quality, data sets for model development and validation and to help the wind industry further their understanding of small wind turbine behavior, including furling. Previous papers have discussed modeling results for the SWRT using the FAST aeroelastic simulator. This paper summarizes modeling results from both the FAST and ADAMS aeroelastic simulators. The ADAMS model allows for blade torsional stiffness to be modeled, which is shown to significantly improve the agreement between model and test results for rotor speed and explain variances in previous comparisons between the SWRT FAST modeling results and the SWRT test data. The ADAMS model results also show that the aerodynamic pitching moment impacts the blade torsion more than the inertial forces. [DOI: 10.1115/1.2349551]

A theoretical formulation of the linear elastic in-plane and torsional behavior of corrugated web I-girders under in-plane loads is presented. A typical corrugated web steel I-girder consists of two steel flanges welded to a corrugated steel web. Under a set of simplifying assumptions, the equilibrium of an infinitesimal length of a corrugated web I-girder is studied, and the cross-sectional stresses and stress resultants due to primary bending moment and shear are deduced. The analysis shows that a corrugated web I-girder will twist out-of-plane simultaneously as it deflects in-plane under the action of in-plane loads. In the paper, the in-plane bending behavior is analyzed using conventional beam theory, whereas the out-of-plane torsional behavior is analyzed as a flange transverse bending problem. The results for a simply supported span subjected to a uniformly distributed load are presented. Finally, finite element analysis results are presented and compared to the theoretical results for validation. CE Database subject headings: Corrugating; Flanges; Flexure: Shear: Steel: Torsion; Webs; Girders.

As a result of recent changes in the requirements involving hurricane extreme events (e.g., wind velocities), the Florida Department of Transportation has moved away from cable-stayed signs, signals, and lights systems to mast arm/pole structures. Unfortunately, the newer systems develop significant lateral and torque loading on their foundations (e.g., drilled shafts). Current design practice for a mast arm/pole foundation is to treat lateral loading and torsion separately (i.e., uncoupled); however, recent field-testing suggests otherwise. This paper reports on the results of 91 centrifuge tests. 54 of the tests were conducted in dry sand and 37, in saturated sands. The tests varied the lateral load to torque ratios, shaft embedment depths, and soil strengths. The experiments revealed that even though the torsional resistances of the shafts were not influenced by lateral load, the shafts' lateral resistance was significantly impacted by torsion. Reductions in lateral resistance of 50% were recorded for shafts under high torque to lateral load ratios. Using the free earth support assumption and the ultimate soil pressure the soil pressure distribution along the shaft was developed. Using force and moment equilibrium, as well as the applied torque, maximum shear, and moments were computed. The predicted values were found to be within 25% (10% on average, except for the tests in saturated dense sand with polymer slurry) of the experimental results. CE Database subject headings: Drilled shafts; Lateral loads; Torsion; Slurries; Sand.

Abstract: In the main drive system of a rolling mill, shaft torsional vibration is often generated when a motor and a roll are connected with a flexible shaft. State feedback [...]

A theoretical study of torsional vibrations in isotropic elastic plates is presented. Comparisons between the theoretical predictions and experimental measurements show close agreements in the resonance frequencies of trapped torsional modes.

The measurement and analysis of five new (D2O)5 bands through vibration-rotation-tunneling (VRT) spectroscopy as well as a preliminary description of a second (H2O)5 band are presented. The results concluded that at least three torsional-puckering manifolds are probed and that the lowest-energy manifold is highly compacted.

This paper is concerned with large twist rotations of elastic thin-walled open section beams that induce additional longitudinal stresses, which exert nonlinear 'Wagner' stiffening torques. The nonlinear behavior of a narrow rectangular beam is first analyzed and then extended to elastic beams of general cross section. Expressions are derived for the nonlinear Wagner section constants for narrow rectangular sections, doubly symmetric I sections, and monosymmetric equal angle sections. A general finite element method of analyzing nonlinear torsion is described, and used to develop a computer program FENLT. This program can analyze a beam of general cross section under any combination of concentrated and distributed torques and concentrated bimoments, and which may be prevented from twisting or warping at points along its length. The program is validated by comparison with closed form or numerical solutions for a number of simple examples. DOI: 10.1061/(ASCE)0733-9445(2005) 131:7(1135) CE Database subject headings: Elasticity: Torsion; Thin wall structures: Finite element method: Beams.

A study was carried out to establish the mechanism for intramolecular triplet energy transfer and to enquire if the rate may be modulated by changes in torsion angle. It was found that the involvement of an intermediate charge-transfer (CT) state does not decay directly to the ground state but is favored by a polar solvent and ambient temperature.

Torsional oscillations greatly affect performance and determine the bandwidth (BW) and damping of speed loops. Backlash due to gear reducers can also contribute to the triggering of oscillations, especially when the drive runs at very low load torque. This paper presents a detailed evaluation of these effects in typical electromechanical drive trains applied to paper machine sections. The cases evaluated consider torsional oscillations in two-mass and three-mass systems, and the effect of shaft diameter and length on the resonant frequencies of three typical paper machine sections. Time-domain response plots are evaluated to show the effect of speed response overshoot, reducer backlash, and step or ramp speed commands. Based on these results, mechanical design guidelines are given for the most significant drive train components in order to minimize torsional oscillations of the speed-controlled drive system. Index Terms--Backlash, frequency-response analysis, jackshaft and reducer torsional stiffness, two- and three-mass modeling, resonance, torsional oscillations.

A mixed beam approach that combines both the stiffness and the flexibility formulation in a unified manner has been performed to model and analyze coupled composite blades with closed, multiple-celled cross sections. The analysis model includes the effects of elastic couplings, shell wall thickness, transverse shear deformation, torsion warping, and constrained warping. Reissner's semicomplementary energy functional is used to derive the beam force-displacement relations. The influence of the shell bending strain measures as well as the membrane strain measures are incorporated in the formulation. For completeness required in a rigorous beam theory, four separate continuity conditions are imposed on each cell of the closed, multicelled sections. The theory is validated against experimental test data, detailed finite element analysis results, and other analytical results found in the literature for coupled composite beams and blades with various cross sections. These include two-cell box beams with bending-torsion and/or extension-torsion couplings and bending-torsion coupled composite blades with two-cell airfoils. The correlation between the present theory and other methods is found to be good, dependent on the geometries and material distributions adopted in the blades. Numerical results showing the effects of including the shell bending strain measures are examined. The effects of inappropriate treatment of the direction of integration for two-celled composite beams are also investigated in the current framework of the analysis.

A method is presented for calculating the stress relaxation due to scission in elastomeric components that operate at a fixed deformation while at an elevated temperature. A relationship is established between stresses at different temperatures that is called the correspondence principle for scission/healing materials. Two examples involving cylinders illustrate its use. The first example involves combined tension-torsion, for which an axial force-twisting moment relation is derived, that might be useful in experimental studies to assess the applicability of the correspondence principle. The second example provides a criterion for estimating the lifetime of an annular seal. [DOI: 10.1115/1.1794701]

We report on the observation of nonclassical rotational inertia in solid helium-4 confined to an annular channel in a sample cell under torsional motion, demonstrating superfluid behavior. The effect shows up as a drop in the resonant oscillation period as the sample cell is cooled below 230 milliketvin. Measurement of 17 solid samples allows us to map out the boundary of this superfluid-like solid or supersolid phase from the melting line up to 66 bars. This experiment indicates that superfluid behavior is found in all three phases of matter., At temperatures below 2.176 K, liquid [sup.4]He enters into a superfluid state and flows without any friction (1, 2). The onset of superfluidity is associated with Bose-Einstein condensation (3, 4), [...]

New torsional parameters for the OPLS-AA force field, is reported which achieved substantially better accuracy with respect to high level gas-phase quantum chemical calculations. It is demonstrated that these new parameters also lead to qualitatively improved side chain prediction accuracy.

A coupled rotor-fuselage flight dynamic model that includes a maneuvering free wake model and a coupled flap-lag-torsion flexible blade model, as well as the results of an investigation on some effects of inflow and blade modeling on the free-flight response of a hingeless rotor helicopter to pilot inputs, are described. The wake model is a relaxation type free wake, capable of modeling the wake geometry changes due to maneuvers; no assumptions are made on the wake geometry, which is free to evolve based on the maneuver. Theoretical predictions are compared with flight-test data. The results show that the free-flight, on-axis response to pilot pitch and roll inputs can be predicted with good accuracy with a relatively unsophisticated model. It is possible to predict the off-axis response from first principles, that is, without empirically derived correction factors and without assumptions on the wake geometry. To do so, however, requires sophisticated modeling. Both a free wake model that includes the wake distortions caused by the maneuver and a refined flexible blade model must be used. Most features of the off-axis response can be captured using a dynamic inflow theory extended to account for maneuver-induced wake distortions, for a fraction of the cost of using a free wake model. The most cost-effective strategy, for typical flight dynamic analyses and if vibratory loads are not required, is probably to calibrate such a theory using the more accurate free wake based model, and then use it in all calculations.

Byline: Teik-Cheng Lim (1) Keywords: bond torsion; conversion matrices; force field Abstract: A set of mathematical relationship between torsion potential functions such as trigonometric and Fourier series is presented herein. A harmonic approximation form is also introduced, and its stiffness constant is related to the parameters of trigonometric and Fourier series. Mathematical relationships between various force field parameters are presented in the form of conversion matrices. Author Affiliation: (1) Dean's Office, Faculty of Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore, 117576, Republic of Singapore Article History: Registration Date: 12/10/2004

A simple composite beam theory that contains only the four classical beam variables is constructed from a general variational-asymptotic framework. The results of the theory are contained in closed-form expressions for the stiffness matrices of single- and double-celled composite thin-walled beams. The accuracy of the approach is demonstrated by several examples. The most important feature of these solutions, which distinguishes them from those previously published in the literature, is that shell bending strain measures are consistently taken into consideration. This is shown to be important for correct treatment of certain closed-cell configurations, the torsional stiffness of which can be off by a factor of two when bending strain measures or hoop moments are neglected. Correlation of the present formulas with finite element analysis is demonstrated to be excellent.

A new antigalloping device for overhead lines with bundle conductors was introduced ten years ago, after laboratory tests and observations on actual 400-kV lines. A systematic full-scale test was performed in Kazakhstan in order to better evaluate torsional damper and detuner (TDD) efficiency. This report details the test station and the results obtained over a several month period of testing and measurement. The tests were carried out thanks to the mutual efforts of the ESSP and the Kazakh Power Research Institute (KazNIIE) at the field tests stand located in Chokpar. Index Terms--Measurement, power transmission lines, test facilities, vibration control.

The effect of thrust on the flutter of a high-aspect-ratio wing is investigated. The wing is represented by a beam using a nonlinear mixed finite element method. Aerodynamic forces are calculated using a finite state, two-dimensional unsteady aerodynamic model. The effect of thrust is modeled as a follower force of prescribed magnitude. Without the thrust force, the wing is shown to become unstable for freestream airspeeds greater than the flutter speed. On the other hand, in the absence of aerodynamic forces, the wing becomes unstable for values of the thrust in excess of a critical magnitude of the force. When both effects are present, the airspeed at which the instability occurs depends on the thrust magnitude. For validation, an analytical solution for the in vacuo case (accounting only for the effect of thrust) was developed and shown to match closely results from the numerical method. Parametric studies show that the predicted stability boundaries are very sensitive to the ratio of bending stiffness to torsional stiffness. Indeed, the effect of thrust can be either stabilizing or destabilizing, depending on the value of this parameter. An assessment whether or not the magnitude of thrust needed to influence the flutter speed is practical is made for one configuration.

Open cross-section, thin-walled, cold-formed steel columns have at least three competing buckling modes: local, distortional, and Euler (i.e., flexural or flexural-torsional) buckling. Closed-form prediction of the buckling stress in the local mode, including interaction of the connected elements, and the distortional mode, including consideration of the elastic and geometric stiffness at the web/flange juncture, are provided and shown to agree well with numerical methods. Numerical analyses and experiments indicate postbuckling capacity in the distortional mode is lower than in the local mode. Current North American design specifications for cold-formed steel columns ignore local buckling interaction and do not provide an explicit check for distortional buckling. Existing experiments on cold-formed channel, zed, and rack columns indicate inconsistency and systematic error in current design methods and provide validation for alternative methods. A new method is proposed for design that explicitly incorporates local, distortional and Euler buckling, does not require calculations of effective width and/or effective properties, gives reliable predictions devoid of systematic error, and provides a means to introduce rational analysis for elastic buckling prediction into the design of thin-walled columns. DOI: 10.1061/(ASCE)0733-9445(2002)128:3(289) CE Database keywords: Thin-wall structures; Columns; Buckling; Cold-formed steel.

The description of a beam element by only the displacement of its centerline leads to some difficulties in the representation of the torsion and shear effects. For instance such a representation does not capture the rotation of the beam as a rigid body about its own axis. This problem was circumvented in the literature by using a local coordinate system in the incremental finite element method or by using the multibody floating frame of reference formulation. The use of such a local element coordinate system leads to a highly nonlinear expression for the inertia forces as the result of the large element rotation. In this investigation, an absolute nodal coordinate formulation is presented for the large rotation and deformation analysis of three dimensional beam elements. This formulation leads to a constant mass matrix, and as a result, the vectors of the centrifugal and Coriolis forces are identically equal to zero. The formulation presented in this paper takes into account the effect of rotary inertia, torsion and shear, and ensures continuity of the slopes as well as the rotation of the beam cross section at the nodal points. Using the proposed formulation curved beams can be systematically modeled.

This part of these two companion papers demonstrates the computer implementation of the absolute nodal coordinate formulation for three-dimensional beam elements. Two beam elements that relax the assumptions of Euler-Bernoulli and Timoshenko beam theories are developed. These two elements take into account the effect of rotary inertia, shear deformation and torsion, and yet they lead to a constant mass matrix. As a consequence, the Coriolis and centrifugal forces are identically equal to zero. Both beam elements use the same interpolating polynomials and have the same number of nodal coordinates. However, one of the elements has two nodes, while the other has four nodes. The results obtained using the two elements are compared with the results obtained using existing incremental methods. Unlike existing large rotation vector formulations, the results of this paper show that no special numerical integration methods need to be used in order to satisfy the principle of work and energy when the absolute nodal coordinate formulation is used. These results show that this formulation can be used in manufacturing applications such as high speed forming and extrusion problems in which the element cross section dimensions significantly change.

End effects or displacements and stresses of a self-equilibrated state in an inhomogeneous, anisotropic cylinder are represented by eigendata extracted from an algebraic eigensystem. Such states are typical of traction and/or displacement boundary conditions that do not abide by the distributions according to Saint-Venant's solutions, whose construction were discussed in the first paper of this series of three. This type of analysis of end effects quantitifies Saint-Venant's principle, and the algebraic eigensystem providing the eigendata is based on homogeneous displacement equations of equilibrium with an exponential decaying displacement form. The real parts of the eigenvalues convey information on the inverse decay lengths and their corresponding eigenvectors are displacement distributions of self-equilibrated states. Stress eigenvetors can be formed by appropriate differentiation of the displacement eigenvectors. The eigensystem and its adjoint system provide complete sets of right and left-handed eigenvectors that are interrelated by two bi-orthogonality relations. Displacement and stress end effects can be represented by means of an expansion theorem based on these bi-orthogonality relations or by a least-squares solution. Two examples, a beam with a homogeneous, isotropic cross section and the other of a two layer beam with a [+ or -] 30 deg angle-ply composite cross section, are given to illustrate the representation of various end effects. [DOI: 10.1115/1.1363597]

First, an attempt is made to experimentally test the validity of the linear deformation derivative results earlier developed for the multilayered wire-rope strands under tension and torsion. The theoretical results are next utilized to obtain analytical expressions for the maximum contact stresses induced in the multilayered strands with metallic wire core. These closed-form solutions provide some useful design insights into the influence of several important cable parameters and material properties on the resulting contact stresses. The strong influence of the material modulus of elasticity on the critical stresses is highlighted. Significantly, the analysis brings out how the contact stresses can rise to an order of magnitude higher levels than that of the nominal stresses. [DOI: 10.1115/1.1355777]

Cross-sectional properties of a prismatic inhomogeneous, anisotropic cylinder are determined from Saint-Venant solutions for extension-bending-torsion and flexure, whose method of construction was presented in a previous paper. The coupling of extensional, bending, and twisting deformations due to anisotropy and inhomogeneity leads to some very interesting features. Herein, it is shown that for an inhomogeneous, anisotropic cylinder whose cross-sectional plane is not a material symmetry plane, distinct modulus-weighted and compliance-weighted centroids and distinct principal bending axes are possible. A line of extension-bending centers is given on which an axial force causes extension and bending only but no twist. Two shear centers are given, one using the Griffith-Taylor definition that ignores cross-sectional warpages and the other by stipulating a zero mean rotation over the cross section. The center of twist is discussed, and this property depends on root end fixity conditions that are prescribed in terms of their mean values based on integrals over the cross section rather than by a pointwise specification. While these shear center and center of twist definitions have some rational bases, it is recognized that other definitions are possible, for example those based on modulus or compliance-weighted integrals. Two examples, an angle and a channel, both composed of a two-layer [+ or -] 30 deg angle-ply composite material illustrate the procedures for determining these cross-sectional properties. [DOI: 10.1115/1.1365152]

In this paper, the first in a series of three, a procedure based on semi-analytical finite elements is presented for constructing Saint-Venant solutions for extension, bending, torsion, and flexure of a prismatic cylinder with inhomogeneous, anisotropic cross-sectional properties. Extension-bending-torsion involve stress fields independent of the axial coordinate and their displacements may be decomposed into two distinct parts which are called the primal field and the cross-sectional warpages herein. The primal field embodies the essence of the kinematic hypotheses of elementary bar and beam theories and that for unrestrained torsion. The cross-sectional warpages are independent of the axial coordinate and they are determined by testing the variationally derived finite element displacement equations of equilibrium with the primal field. For flexure, a restricted three-dimensional stress field is in effect where the stress can vary at most linearly along the axis. Integrating the displacement field based for extension-bending-torsion gives that for the flexure problem. The cross-sectional warpages for flexure are determined by testing the displacement equations of equilibrium with this displacement field. In the next paper, the cross-sectional properties such as the weighted-average centroid, center of twist and shear center are defined based on the Saint-Venant solutions established in the present paper and numerical examples are given. In the third paper, end effects or the quantification of Saint-Venant's principle for the inhomogeneous, anisotropic cylinder is considered. [DOI: 10.1115/1.1363598]

Research is presented concerning the use of multimode scanning acoustic force microscopy and lateral force microscopy to investigate the influence of vertical and in-plane surface oscillation components on cantilevers.

Byline: A. R. Snitser (1) Abstract: Torsion waves on a cylindrical cavity in a semiinfinite elastic medium are investigated. The waves are generated by steady-state torsional vibrations of a flat, circular punch coupled with the half-space. A technique of contour transformation of the integrals involved in problems of this kind is described. An algorithm and numerical results are given for calculating the modulus of the complex amplitude of the displacement vector on the cylindrical surface as a function of the vertical coordinate in both the near and far fields. Author Affiliation: (1) Simferopol State University, Ukraine Article History: Registration Date: 17/10/2004

Byline: A. R. Snitser (1), N. N. Markovskaya (1) Abstract: A previously published algorithm [9] is implemented in application to the Reissner--Sagoci problem for a layer bonded to a half-space containing a cylindrical cavity. The influence of the mechanical and geometrical parameters of the layer and the half-space on the amplitude-frequency response curves of the punch oscillations is analyzed. Practical applications of the results are proposed for ensuring the seismic isolation of buildings on the investigated foundation in the presence of dynamic torsional excitations. Author Affiliation: (1) Simferopol University, Ukraine Article History: Registration Date: 06/10/2004

Research was conducted to examine the stable conformations and vibrational spectra of 2-methody-3-methyl-1,4-benzoquinone via density functional methods. The calculations reveal how sensitive the energetics of the methoxy group orientation as well as relative energies of stable conformations can depend on protein-chromophore interactions. Findings confirm previously reported speculations that the different properties of Q(sub A) and Q(sub B) in the photosynthetic reaction center of Rhodobacter sphaeroides could be caused by different methoxy group orientations due to differences in protein-chromophore interactions.

Many column bracing details employed in steel construction do not prevent twist, and subsequently, torsional buckling may control the column capacity. This mode of buckling is not adequately considered in design codes and is often overlooked. This paper documents a finite-element investigation of the torsional buckling behavior of columns with lateral bracing located at different points on the cross section. The location of the lateral bracing on the cross section has a significant effect on torsional buckling. Equations are developed for the stiffness and strength requirements of bracing to control torsional buckling. Details for torsional bracing are discussed and presented. A connection detail must be provided between the column and the brace that controls cross-sectional distortion. A design example illustrates the use of the bracing recommendations.