Dynamic interaction analysis of a LIM train and elevated bridge system

H. Xia,W. W. Guo,C. Y. Xia,Y.-L. Pi,M. A. Bradford 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.12

A three-dimensional dynamic interaction model is developed for a LIM (linear induction motor) train and elevated bridge system, which is composed of a LIM-driven vehicle submodel and a finite element bridge submodel. Each LIM vehicle is modeled by a 27 degrees-of-freedom dynamic system. The expressions for the electromagnetic force between the linear motor and the reaction plate are derived, and the force model is established. By applying a modal superposition technique to the bridge submodel and using the measured track irregularities as the self-excitations of the train-bridge system, the equations of motion are established for analyzing the dynamic responses of the LIM vehicle and the elevated bridge. The proposed framework is applied to a 3-span elevated bridge with 29.9 m simply-supported girders. The full histories of the LIM train traversing the bridge are simulated, from which the dynamic responses of the LIM vehicle and elevated bridge system are obtained. The proposed method may help to find a way to assess the dynamic properties of elevated bridges and the running safety of a LIM train with reasonable computational effort.

Buckling of post-tensioned composite beams

Bradford, M.A. Techno-Press 1994 Structural Engineering and Mechanics, An Int'l Jou Vol.2 No.1

A method for computing the elastic buckling prestressing force of a post-tensioned composite steel-concrete tee-beam is presented. The method is based on a virtual work formulation, and incorporates the restraint provided by the concrete slab to the buckling displacements of the steel beam. The distortional buckling solutions are shown to be given by a quadratic equation. The application of the analysis to calculation buckling strengths is given, based on codified rules for beam-columns. Conclusions are then drawn on the importance of distortional buckling when a post-tensioned composite beam is stressed during jacking.

Elastic local buckling of thin-walled elliptical tubes containing elastic infill material

Bradford, M.A.,Roufegarinejad, A. Techno-Press 2008 Interaction and multiscale mechanics Vol.1 No.1

Elliptical tubes may buckle in an elastic local buckling failure mode under uniform compression. Previous analyses of the local buckling of these members have assumed that the cross-section is hollow, but it is well-known that the local buckling capacity of thin-walled closed sections may be increased by filling them with a rigid medium such as concrete. In many applications, the medium many not necessarily be rigid, and the infill can be considered to be an elastic material which interacts with the buckling of the elliptical tube that surrounds it. This paper uses an energy-based technique to model the buckling of a thin-walled elliptical tube containing an elastic infill, which elucidates the physics of the buckling phenomenon from an engineering mechanics basis, in deference to a less generic finite element approach to the buckling problem. It makes use of the observation that the local buckling in an elliptical tube is localised with respect to the contour of the ellipse in its cross-section, with the localisation being at the region of lowest curvature. The formulation in the paper is algebraic and it leads to solutions that can be determined by implementing simple numerical solution techniques. A further extension of this formulation to a stiffness approach with multiple degrees of buckling freedom is described, and it is shown that using the simple one degree of freedom representation is sufficiently accurate for determining the elastic local buckling coefficient.

Time-dependent analysis of reinforced concrete structures using the layered finite element method

Bradford, M.A.,Gilbert, R.I.,Sun, S.C.H. Techno-Press 1999 Structural Engineering and Mechanics, An Int'l Jou Vol.8 No.6

The response of a reinforced concrete structure to loading is both immediate and time-dependent. Under a sustained load, the deflections caused by creep and shrinkage may be several times their instantaneous values. The paper describes a general finite element procedure, based on the so-called layered model, to analyse reinforced concrete members, and shows in particular how the simple Step by Step Method may be incorporated into this procedure. By invoking the Modified Newton Raphson Method as a solution procedure, the accuracy of the finite element method is verified against independent test results, and then applied to a variety of problems in order to demonstrate its efficacy. The method forms a general method for analysing highly indeterminate concrete structures in the time domain.

Contributions of Nanoscale Roughness to Anomalous Colloid Retention and Stability Behavior

Bradford, Scott A.,Kim, Hyunjung,Shen, Chongyang,Sasidharan, Salini,Shang, Jianying American Chemical Society 2017 Langmuir Vol.33 No.38

<P>All natural surfaces exhibit nanoscale roughness (NR) and chemical heterogeneity (CH) to some extent. Expressions were developed to determine the mean interaction energy between a colloid and a solid-water interface, as well as for colloid-colloid interactions, when both surfaces contain binary NR and CH. The influence of heterogeneity type, roughness parameters, solution ionic strength (IS), mean zeta potential, and colloid size on predicted interaction energy profiles was then investigated. The role of CH was enhanced on smooth surfaces with larger amounts of CH, especially for smaller colloids and higher IS. However, predicted interaction energy profiles were mainly dominated by NR, which tended to lower the energy barrier height and the magnitudes of both the secondary and primary minima, especially when the roughness fraction was small. This dramatically increased the relative importance of primary to secondary minima interactions on net electrostatically unfavorable surfaces, especially when roughness occurred on both surfaces and for conditions that produced small energy barriers (e.g., higher IS, lower pH, lower magnitudes in the zeta potential, and for smaller colloid sizes) on smooth surfaces. The combined influence of roughness and Born repulsion frequently produced a shallow primary minimum that was susceptible to diffusive removal by random variations in kinetic energy, even under electrostatically favorable conditions. Calculations using measured zeta potentials and hypothetical roughness properties demonstrated that roughness provided a viable alternative explanation for many experimental deviations that have previously been attributed to electrosteric repulsion (e.g., a decrease in colloid retention with an increase in solution IS; reversible colloid retention under favorable conditions; and diminished colloid retention and enhanced colloid stability due to adsorbed surfactants, polymers, and/or humic materials).</P> [FIG OMISSION]</BR>

A general method of analysis of composite beams with partial interaction

G. Ranzi,M. A. Bradford,B. Uy 국제구조공학회 2003 Steel and Composite Structures, An International J Vol.3 No.3

This paper presents a generic modelling of composite steel-concrete beams with elastic shear connection. It builds on the well-known seminal technique of Newmark, Siess and Viest, in order to formulate the partial interaction formulation for solution under a variety of end conditions, and lends itself well for modification to enable direct quantification of effects such as shrinkage, creep, and limited shear connection slip capacity. This application is possible because the governing differential equations are set up and solved in a fashion whereby inclusion of the kinematic and static end conditions merely requires a statement of the appropriate constants of integration that are generated in the solution of the linear differential equations. The method is applied in the paper for the solution of the well-studied behaviour of simply supported beams with partial interaction, as well as to provide solutions for a beam encastré at its ends, and for a propped cantilever.

Elastic distortional buckling of tapered composite beams

Bradford, M.A.,Ronagh, H.R. Techno-Press 1997 Structural Engineering and Mechanics, An Int'l Jou Vol.5 No.3

The overall buckling mode in a composite steel-concrete beam over an internal support is necessarily lateral-distortional, in which the bottom compressive range displaces laterally and twists, since the top flange is restrained by the nearly rigid concrete slab. An efficient finite element method is used to study elastic lateral-distortional buckling in composite beams whose steel portion is tapered. The simplified model for a continuous beam that is presented herein is a fixed ended cantilever whose steel portion is tapered, and is subjected to moment gradient. This is intended to give an insight into distortion in a continuous beam that occurs in the negative bending region, and the differences between the cantilever representation and the continuous beam are highlighted. An eigenproblem is established, and the buckling modes and loads are determined in the elastic range of structural response. It is found from the finite element study that the buckling moment may be enhanced significantly by using a vertical stiffener in the region where the lateral movement of the bottom range is greatest. This enhancement is quantified in the paper.

Growth and Characterization of ZnMgS and ZnMgS/ZnSe Quantum Wells grown on GaAs (100) by Using MBE

C. Bradford,R. T. Moug,A. Curran,D. Thuau,R. J. Warburton,K. A. Prior 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

Structures containing Zn1-xMgxS have been grown lattice matched to GaAs by using molecular beam epitaxy (MBE) with ZnS as the source of S. The composition of the alloy produced has been determined using double-crystal X-ray spectroscopy and X-ray interference measurements. Both techniques indicate that 0.88 ≤ x ≤ 0.93. This result is conrmed by both secondary ion mass spectroscopy and an Auger analysis carried out on the material. These results show that the crystalline quality of the material produced is excellent and that it has been grown coherently to the GaAs substrate. Photoluminescence spectroscopy shows a high intensity emission with a narrow full width half maximum, confirming the suitability of this alloy as a high-bandgap barrier material. Structures containing Zn1-xMgxS have been grown lattice matched to GaAs by using molecular beam epitaxy (MBE) with ZnS as the source of S. The composition of the alloy produced has been determined using double-crystal X-ray spectroscopy and X-ray interference measurements. Both techniques indicate that 0.88 ≤ x ≤ 0.93. This result is conrmed by both secondary ion mass spectroscopy and an Auger analysis carried out on the material. These results show that the crystalline quality of the material produced is excellent and that it has been grown coherently to the GaAs substrate. Photoluminescence spectroscopy shows a high intensity emission with a narrow full width half maximum, confirming the suitability of this alloy as a high-bandgap barrier material.

Inelastic lateral-distortional buckling of continuously restrained rolled I-beams

Mark A. Bradford,Dong-Sik Lee 국제구조공학회 2002 Steel and Composite Structures, An International J Vol.2 No.4

An energy method of analysis is presented which can be used to study the inelastic lateral-distortional buckling of hot-rolled I-sections continuously restrained at the level of the tension flange. The numerical modelling leads to the incremental and iterative solution of a fourth-order eigenproblem, with vey rapid solutions being obtainable, so as to enable a study of the factors that influence the strength of continuously restained I-beams to be made. Although hot-rolled I-scetions generally have stocky webs and are not susceptible to reductions in their overall buckling loads as a result of cross-sectional distortion, the effect of elastic restraints, particulartly against twist rotation, can lead to buckling modes in which the effect of distortion is quite severe. While the phenomenon has been studied previously for elastic lateral-distortional buckling, it is extended in this paper to include the constitutive relationship characteristics of mild steel, and incorporates both the so-called 'polynomial' and 'simplified' models of residual stresses. The method is validated against inelastic lateral-torsional buckling solutions reported in previous studies, and is applied to illustrate some inelastic buckling problems. It is noted that over a certain range of memeber slenderness the provisions of the Australian AS4100 steel standard are unconservative.

Surface Reconstructions of Zincblende MgS (100) Observed by Using RHEED

Richard T. Moug,Christine Bradford,Kevin A. Prior 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

RHEED patterns from zincblende MgS (100) surfaces have been observed during growth, during annealing, and both before and after irradiation of the surface with an Mg flux. The c(2×2) pattern is observed during growth and is stable during annealing, but a Mg flux removes it permanently. Exposing the surface to Mg at temperatures above 310 ℃ creates a rough 1×1 surface. Below that temperature, the surface is flatter, and a 4×1 reconstruction is observed with Mg irradiation, becoming a 2×1 reconstruction after annealing in vacuo. These results are compatable with a c(2×2) surface being formed from a ZnMgS alloy, which converts to a pure MgS 4×1 surface on Zn irradiation. The conversion from a 4×1 to a 2×1 surface results from the evaporation of excess Mg.