The Experts below are selected from a list of 33 Experts worldwide ranked by ideXlab platform
Osama Bedair - One of the best experts on this subject based on the ideXlab platform.
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economical design procedures for built up box sections subject to compression and bi axial bending
Structures, 2015Co-Authors: Osama BedairAbstract:Abstract The paper offers to practitioners economical procedures that can be utilized to optimize the design of built up box sections subject to compression and biaxial bending. Little emphasis appeared in the published literature that addressed this general loading condition. The analysis methodology and Structural Idealization are first overviewed. Diagrams are presented showing buckling behavior of the section by accounting rotational and lateral restraints. The post-buckling response is also illustrated for various applied stress ratios. A design space concept is then introduced showing interaction of serviceability and strength limit states. These procedures are cost effective and appropriate for industrial implementation to optimize the Structural design.
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analysis and limit state design of stiffened plates and shells a world view
Applied Mechanics Reviews, 2009Co-Authors: Osama BedairAbstract:Stiffened plates and shells are encountered in many engineering applications. Several analytical and numerical procedures were developed over the past decades for analysis of these structures. Empirical and simplified analytical models were also developed to estimate their ultimate strength for various limit states. The paper reviews and pieces together engineering work developed for all the applications. The first part reviews the analytical, numerical, and orthotropic plate procedures that were developed for analysis of stiffened plates and shells. The Structural Idealization, the theoretical basis, and the merits of each method are also discussed. The second part of the paper reviews the design philosophies that were developed to predict the ultimate strength of these structures. The influence of various parameters affecting the Structural performance, such as geometric and material imperfections, stiffener profile, etc., is discussed. The optimization procedures to minimize the weight of the structure are also reviewed. The paper offers a comprehensive and unique “reference-manual” for all types of stiffened plate applications.
T H G Megson - One of the best experts on this subject based on the ideXlab platform.
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chapter 20 Structural Idealization
Aircraft Structures for Engineering Students (Sixth Edition), 2017Co-Authors: T H G MegsonAbstract:The principle of Structural Idealization is discussed and the method of idealizing a simple panel is established. The effect of Structural Idealization on the analysis of open and closed section thin-walled beams is investigated and illustrated by examples. Expressions for the shear forces and moments corresponding to a constant shear flow in a curved panel are derived and an alternative method for the calculation of shear flow distribution in the walls of thin-walled beam sections is described. Finally, the calculation of displacements due to shear and bending in thin-walled beams is demonstrated.
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chapter 20 Structural Idealization
Aircraft Structures for Engineering Students (Fifth Edition), 2013Co-Authors: T H G MegsonAbstract:Publisher Summary Relatively uncomplicated Structural sections are formed from thin plate or by the extrusion process. While these sections exist as Structural members in their own right, they are frequently used to stiffen more complex Structural shapes such as fuselages, wings, and tail surfaces. Thus, a two spar wing section could take the form, in which Z-section stringers are used to stiffen the thin skin, while angle sections form the spar flanges. Clearly, the analysis of a section of this type is complicated and tedious unless some simplifying assumptions are made. Generally, the number and nature of these simplifying assumptions determine the accuracy and the degree of complexity of the analysis; the more complex the analysis, the greater the accuracy obtained. The degree of simplification introduced is governed by the particular situation surrounding the problem. For a preliminary investigation, speed and simplicity are often of greater importance than extreme accuracy; on the other hand, a final solution must be as exact as circumstances allow. Complex Structural sections may be idealized into simpler mechanical model forms, which behave, under given loading conditions, in the same, or very nearly the same, way as the actual structure. This chapter shows that different models of the same structure are required to simulate actual behavior under different systems of loading. The chapter starts with a discussion of the principle of Structural Idealization and then discusses Idealization of a panel and effect of Idealization on the analysis of open and closed section beams.
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chapter 19 Structural Idealization
Introduction to Aircraft Structural Analysis, 2010Co-Authors: T H G MegsonAbstract:The principle of Structural Idealization is discussed and the method of idealizing a simple panel is established. The effect of Structural Idealization on the analysis of open and closed section thin-walled beams is investigated and illustrated by examples. Expressions for the shear forces and moments corresponding to a constant shear flow in a curved panel are derived and an alternative method for the calculation of shear flow distribution in the walls of thin-walled beam sections is described. Finally, the calculation of displacements due to shear and bending in thin-walled beams is demonstrated.
Khan J.z. - One of the best experts on this subject based on the ideXlab platform.
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Static, dynamic and aeroelastic behaviour of thin-walled composite structures with application to aircraft wings
1Co-Authors: Khan J.z.Abstract:Theoretical and experimental investigations of the static and dynamic behaviour of thin-walled structures are carried out with the ultimate aim of improving prediction procedures for various aeroelastic phenomena. The dynamic stiffness matrix approach is used for Structural Idealization, while strip theory and Theodorsen's function C(k) are used for the aerodynamic Idealization. The dynamic composite beam with with an axial load centroid, has been carried out using Special cases, that been identified and stiffness matrix for a thin-walled geometric and material coupling together (compressive or tensile) applied at the developed. An exact analysis was then the derived dynamic stiffness matrix. are derivatives of the general case have discussed. A three stage program was developed to compute various static and dynamic properties of thin-walled closed or open section composite beams. In the first stage, equivalent elastic constants (overall laminate moduli) were evaluated for a given stacking sequence and material properties. In the second stage, various sectional properties were computed. When the outputs from these two stages were combined, valuable data on sectional rigidities, mass per unit length, polar mass moment of inertia, and shear centre location from the centroid were obtained. In the third stage of the program, all these properties were used to compute the natural frequencies and normal mode shapes of thin-walled composite structures. These programs can be used individually as well as in a combined manner. An experimental investigation of composite thin plates with varying degrees of bending-torsion coupling was conducted. Flexural and torsional rigidities, natural frequencies, normal mode shapes and flutter speed and frequency were experimentally determined. The results obtained were in close agreement with the theoretical predictions. Various open composite sections were experimentally studied for their static and dynamic properties. The results demanded a more refined investigation of the theory. In addition to the experimental study of composite open sections, a parametric study of uncoupled and coupled frequencies of such sections with common boundary conditions was also conducted. Thin-walled closed aerofoil shaped cantilevered structures were tested to establish flexural and torsional rigidities, shear centre, and the polar-mass-moment of inertia. Natural frequencies and normal mode shapes were also determined. The aeroelastic behaviour of these sections was investigated to establish divergence and flutter characteristics. Comparisons of the experimental results with theoretical predictions of flutter speed and frequency were in general satisfactory and the results provided an insight into the aeroelastic behaviour of thin-walled composite beams. The results are discussed and commented on
Hansgunther Reimerdes - One of the best experts on this subject based on the ideXlab platform.
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Structural Idealization of flexible generic wings in computational aeroelasticity
2010Co-Authors: J Kengmogne A Tchakam, Hansgunther ReimerdesAbstract:In the present contribution concepts of reduced Structural models for Computational Aero-Elastic simulation (CAE) on aircraft wings are presented. Here the Idealization approach relies on analytical methods with the aim to shorten in comparison to a typical finite element method computational cost and time, by preserving nearly the same accuracy. Prior to more detailed investigations using higher order models, these simplified models allow an earlier access of insight regarding the aeroelastic and Structural behavior of the wing at the very beginning of the design process. At first a one-dimensional Idealization that extends the Timoshenko beam by taking into account additional effects due to warpings is developed. To better describe the influence of swept, a three dimensional Idealization is derived. Both Idealizations yield good agreements in results concerning the global static deformation and the modal behavior of the wing.
Anil K Chopra - One of the best experts on this subject based on the ideXlab platform.
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dynamics of structures theory and applications to earthquake engineering
2006Co-Authors: Anil K ChopraAbstract:I. SINGLE-DEGREE-OF-FREEDOM SYSTEMS. 1. Equations of Motion, Problem Statement, and Solution Methods. Simple Structures. Single-Degree-of-Freedom System. Force-Displacement Relation. Damping Force. Equation of Motion: External Force. Mass-Spring-Damper System. Equation of Motion: Earthquake Excitation. Problem Statement and Element Forces. Combining Static and Dynamic Responses. Methods of Solution of the Differential Equation. Study of SDF Systems: Organization. Appendix 1: Stiffness Coefficients for a Flexural Element. 2. Free Vibration. Undamped Free Vibration. Viscously Damped Free Vibration. Energy in Free Vibration. Coulomb-Damped Free Vibration. 3. Response to Harmonic and Periodic Excitations. Viscously Damped Systems: Basic Results. Harmonic Vibration of Undamped Systems. Harmonic Vibration with Viscous Damping. Viscously Damped Systems: Applications. Response to Vibration Generator. Natural Frequency and Damping from Harmonic Tests. Force Transmission and Vibration Isolation. Response to Ground Motion and Vibration Isolation. Vibration-Measuring Instruments. Energy Dissipated in Viscous Damping. Equivalent Viscous Damping. Systems with Nonviscous Damping. Harmonic Vibration with Rate-Independent Damping. Harmonic Vibration with Coulomb Friction. Response to Periodic Excitation. Fourier Series Representation. Response to Periodic Force. Appendix 3: Four-Way Logarithmic Graph Paper. 4. Response to Arbitrary, Step, and Pulse Excitations.Response to Arbitrarily Time-Varying Forces. Response to Unit Impulse. Response to Arbitrary Force. Response to Step and Ramp Forces. Step Force. Ramp or Linearly Increasing Force. Step Force with Finite Rise Time. Response to Pulse Excitations. Solution Methods. Rectangular Pulse Force. Half-Cycle Sine Pulse Force. Symmetrical Triangular Pulse Force. Effects of Pulse Shape and Approximate Analysis for Short Pulses. Effects of Viscous Damping. Response to Ground Motion. 5. Numerical Evaluation of Dynamic Response. Time-Stepping Methods. Methods Based on Interpolation of Excitation. Central Difference Method. Newmark's Method. Stability and Computational Error. Analysis of Nonlinear Response: Central Difference Method. Analysis of Nonlinear Response: Newmark's Method. 6. Earthquake Response of Linear Systems. Earthquake Excitation. Equation of Motion. Response Quantities. Response History. Response Spectrum Concept. Deformation, Pseudo-Velocity, and Pseudo-Acceleration Response Spectra. Peak Structural Response from the Response Spectrum. Response Spectrum Characteristics. Elastic Design Spectrum. Comparison of Design ad Response Spectra. Distinction between Design and Response Spectra. Velocity and Acceleration Response Spectra. Appendix 6: El Centro, 1940 Ground Motion. 7. Earthquake Response of Inelastic Systems. Force-Deformation Relations. Normalized Yield Strength, Yield Strength Reduction Factor, and Ductility Factor. Equation of Motion and Controlling Parameters. Effects of Yielding. Response Spectrum for Yield Deformation and Yield Strength. Yield Strength and Deformation from the Response Spectrum. Yield Strength-Ductility Relation. Relative Effects of Yielding and Damping. Dissipated Energy. Energy Dissipation Devices. Inelastic Design Spectrum. Applications of the Design Spectrum. Comparison of Design and Response Spectra. 8. Generalized Single-Degree-of-Freedom Systems. Generalized SDF Systems. Rigid-Body Assemblages. Systems with Distributed Mass and Elasticity. Lumped-Mass System: Shear Building. Natural Vibration Frequency by Rayleigh's Method. Selection of Shape Function. Appendix 8: Inertia Forces for Rigid Bodies. II. MULTI-DEGREE-OF-FREEDOM SYSTEMS. 9. Equations of Motion, Problem Statement, and Solution Methods. Simple System: Two-Story Shear Building. General Approach for Linear Systems. Static Condensation. Planar or Symmetric-Plan Systems: Ground Motion. Unsymmetric-Plan Building: Ground Motion. Symmetric-Plan Buildings: Torsional Excitation. Multiple Support Excitation. Inelastic Systems. Problem Statement. Element Forces. Methods for Solving the Equations of Motion: Overview. 10. Free Vibration. Natural Vibration Frequencies and Modes. Systems without Damping. Natural Vibration Frequencies and Modes. Modal and Spectral Matrices. Orthogonality of Modes. Interpretation of Modal Orthogonality. Normalization of Modes. Modal Expansion of Displacements. Free Vibration Response. Solution of Free Vibration Equations: Undamped Systems. Free Vibration of Systems with Damping. Solution of Free Vibration Equations: Classically Damped Systems. Computation of Vibration Properties. Solution Methods for the Eigenvalue Problem. Rayleigh's Quotient. Inverse Vector Iteration Method. Vector Iteration with Shifts: Preferred Procedure. Transformation of kA A = ...w2mA A to the Standard Form. 11. Damping in Structures.Experimental Data and Recommended Modal Damping Ratios. Vibration Properties of Millikan Library Building. Estimating Modal Damping Ratios. Construction of Damping Matrix. Damping Matrix. Classical Damping Matrix. Nonclassical Damping Matrix. 12. Dynamic Analysis and Response of Linear Systems.Two-Degree-of-Freedom Systems. Analysis of Two-DOF Systems without Damping. Vibration Absorber or Tuned Mass Damper. Modal Analysis. Modal Equations for Undamped Systems. Modal Equations for Damped Systems. Displacement Response. Element Forces. Modal Analysis: Summary. Modal Response Contributions. Modal Expansion of Excitation Vector p (t) = s p(T). Modal Analysis for p (t) = s p(T). Modal Contribution Factors. Modal Responses and Required Number of Modes. Special Analysis Procedures. Static Correction Method. Mode Acceleration Superposition Method. Analysis of Nonclassically Damped Systems. 13. Earthquake Analysis of Linear Systems.Response History Analysis. Modal Analysis. Multistory Buildings with Symmetric Plan. Multistory Buildings with Unsymmetric Plan. Torsional Response of Symmetric-Plan Buildings. Response Analysis for Multiple Support Excitation. Structural Idealization and Earthquake Response. Response Spectrum Analysis. Peak Response from Earthquake Response Spectrum. Multistory Buildings with Symmetric Plan. Multistory Buildings with Unsymmetric Plan. 14. Reduction of Degrees of Freedom. Kinematic Constraints. Mass Lumping in Selected DOFs. Rayleigh-Ritz Method. Selection of Ritz Vectors. Dynamic Analysis Using Ritz Vectors. 15. Numerical Evaluation of Dynamic Response. Time-Stepping Methods. Analysis of Linear Systems with Nonclassical Damping. Analysis of Nonlinear Systems. 16. Systems with Distributed Mass and Elasticity. Equation of Undamped Motion: Applied Forces. Equation of Undamped Motion: Support Excitation. Natural Vibration Frequencies and Modes. Modal Orthogonality. Modal Analysis of Forced Dynamic Response. Earthquake Response History Analysis. Earthquake Response Spectrum Analysis. Difficulty in Analyzing Practical Systems. 17. Introduction to the Finite Element Method.Rayleigh-Ritz Method. Formulation Using Conservation of Energy. Formulation Using Virtual Work. Disadvantages of Rayleigh-Ritz Method. Finite Element Method. Finite Element Approximation. Analysis Procedure. Element Degrees of Freedom and Interpolation Function. Element Stiffness Matrix. Element Mass Matrix. Element (Applied) Force Vector. Comparison of Finite Element and Exact Solutions. Dynamic Analysis of Structural Continua. III. EARTHQUAKE RESPONSE AND DESIGN OF MULTISTORY BUILDINGS. 18. Earthquake Response of Linearly Elastic Buildings. Systems Analyzed, Design Spectrum, and Response Quantities. Influence of T 1 and r on Response. Modal Contribution Factors. Influence of T 1 on Higher-Mode Response. Influence of r on Higher-Mode Response. Heightwise Variation of Higher-Mode Response. How Many Modes to Include. 19. Earthquake Response of Inelastic Buildings. Allowable Ductility and Ductility Demand. Buildings with "Weak" or "Soft" First Story. Buildings Designed for Code Force Distribution. Limited Scope. Appendix 19: Properties of Multistory Buildings. 20. Earthquake Dynamics of Base-Isolated Buildings. Isolation Systems. Base-Isolated One-Story Buildings. Effectiveness of Base Isolation. Base-Isolated Multistory Buildings. Applications of Base Isolation. 21. Structural Dynamics in Building Codes. Building Codes and Structural Dynamics. International Building Code (United States), 2000. National Building Code of Canada, 1995. Mexico Federal District Code, 1993. Eurocode 8. Structural Dynamics in Building Codes. Evaluation of Building Codes. Base Shear. Story Shears and Equivalent Static Forces. Overturning Moments. Concluding Remarks. Appendix A: Frequency Domain Method of Response Analysis.Appendix B: Notation.Appendix C: Answers to Selected Problems.Index.
