DOCSLIB.ORG

Basic Energy Principles in Stiffness Analysis

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Basic Energy Principles in Stiffness Analysis Basic Energy Principles E = Elastic (or Young’s) modulus G = Shear modulus in Stiffness Analysis = Poisson ratio Stress-Strain Relations Normally, the shear modulus is The application of any theory expressed in terms of the elastic requires knowledge of the physical modulus and Poisson ratio as properties of the material(s) E G comprising the structure. We are 2(1 ) limiting our attention to linear The most widely used civil elastic structural response. engineering structural materials, Further assuming that the material steel and concrete, have uniaxial is homogenous and isotropic, we stress-strain diagrams of the types only need to know two of the shown in Fig. 1. Mild steels yield following three material constants: 1 2 offset criterion. Yield strengths for steel vary from less than 250 MPa to more than 700 MPa. For practical purposes, steel behaves as an ideal material in both tension and compression below the yield Fig. 1: Typical Stress () – Strain (e) or buckling stress. The elastic Curves for (a) Steel and (b) Concrete modulus and Poisson ratio for with a pronounced permanent steel are always close to 200,000 MPa and 0.3, respectively. elongation at a stress ym (Fig.1a). High strength steels yield gra- Concrete is less predictable, but dually, which requires an arbitrary under short-duration compressive stress not greater than u/3 – u/2, definition of its yield strength yh, its behavior is reasonably linear such as the commonly used 0.2%3 4 1 Work and Energy (Fig. 1b in which typical values for u are: 30 MPa ≤ u ≤ 50 MPa). An The principle of conservation of elastic modulus of E = 22,000 MPa energy is fundamentally important and Poisson ratio of = 0.15 are in structural analysis. This typical for concrete. In using principle, expressed as energy or concrete for analysis, the ACI code work balance, is applicable to both specifies using the gross cross rigid and deformable structures. area properties to perform Rigid structures only require analyses to determine the force multiplying the external forces by distributions in frame structures, the respective displacements. i.e., ignore the reinforcing steel Deformable structures also require and tension cracking in calculating the summation of the internal the force distributions. stresses acting through the 5 6 respective deformations. Internal Limiting attention to gradually work is called strain energy and applied forces, i.e., ignoring inertial must be accounted for in the forces caused by dynamic loads, energy balance. and linear elastic response leads The work dW of a force F acting to through a change in displacement WFdkd 11 d in the direction of F is 00 112 dW Fd (1) kF (3) 22111 Over 1, the total work is F 1 F1 WFd (2) 0 k 1 7 8 1 2 Expanding to a vector of forces where U= strain energy for the and displacements leads to element. Equation (5) is a 1 WF{} (4) homogeneous, quadratic polyno- 2 mial in terms of the local coor- The special case shown dinate element displacements {u} in the right figure: or global coordinate element displacement {v}. 1 u 1 WF0xx Fu 2 v2 Expanding (4) for a single element ({F} = [k] {u} or {F} = [K] {v}): Wu[k]{u}1 2 1 v[K]{v}U (5) 2 9 10 Principle of Virtual Displacements to constructing stiffness equations. In prior chapters we established The principle of virtual the relationships of framework displacements can be stated as analysis directly utilizing the basic If a deformable structure is in conditions of equilibrium and equilibrium and remains in displacement continuity. Hence- equilibrium while it is subject to a forth, we will use energy principles, virtual distortion, the external specifically the principle of virtual virtual work done by the external displacements since it permits forces acting on the structure is mathematical manipulations that equal to the internal virtual work are not possible with direct done by the stress resultants. procedures. We restrict our attention to virtual displacements Recall: virtual imaginary, not since this principle is applicable 11 real, or in essence but not in fact12 3 The principle of virtual displacements Equation (6) is based on the is expressed mathematically as conservation of energy principle, Wext = Wint (6) i.e. the work done by the external forces going through a virtual F displacement equals the work F1 done by the internal forces due to Wext the same virtual displacement. W The external virtual work can be generalized to a system of forces 1 as s Wqdx()P(7) where Wext = F1 = external ext i i virtual work (shaded blue area in i1 the figure) and Wint = internal 13 14 virtual work. internal virtual work (dWint) is The internal virtual work (Wint) is a function of the structure type. d( u) dW Fdx (8a) Since this course focuses on frame intdx x members, only axial and bending where u = virtual axial displace- deformations will be considered. ment and Fx = real axial force. Axial Deformation Recalling from your mechanics of Consider the axial force system materials class that axial strain ex = shown in Fig. 2. The differential du/dx and the axial force Fx = x A (axial stress times area), (8a) can be rewritten as dW int e x x Adx (8b) Integrating (8b) over the length of 15 16 Fig. 2: Axial Deformation the element and substituting 4 Hooke’s law (x = Eex) leads to work is L LL W M dx EI dx WeEAedxint x x int z z z z 0 00 L L d(v)22 dv d( u) du (10) EA dx (9) EI dx dx dx dx22 dx 0 0 For the beam bending (flexure) case (Fig. 3), the internal virtual where v = virtual transverse displacement; z = d(v)/dx = virtual rotation; Mz = real moment 2 2 about the z-axis; z = d v/dx = curvature strain about the z-axis; and Mz = EI kz. Fig. 3: Bending Deformation 17 18 Analytical Solutions Using Principle of Virtual Displacements NOTE: A difficulty in applying the Consider the simple axial force principle of virtual displacements is structure shown in Fig. 4. The real that functions must be assumed or developed for the real and virtual L 2 1 F , u displacement functions in (9) and x, u x2 2 (10). Development of these Fig. 4: Axial Deformation Structure expressions will follow finite element mechanics, which is displacement u: covered in a later section. u = x/L u2 The real strain is ex = du/dx = u2/L Imposing a virtual displacement 19 20 5 u2 results in an external virtual work We will consider various of expressions for the virtual Wext = u2 Fx2 displacement to demonstrate the In order to calculate the internal principle of virtual displacements. virtual work First, consider L d( u) du u = (x/L) u WEAdx 2 int dx dx 0 The internal virtual work: L expressions for u and u over the uuEA WdxEAuu22 length of the axial deformation intLLL 2 2 0 structure must be assumed. We Equating the external and internal will consistently assume the real virtual works gives displacement u: u2 Fx2 = u2 (EA/L) u2 u = (x/L) u2 or 21 22 u2 = Fx2 L/EA The internal virtual work: which is exact. L uxu22 Consider next: WcosdxEAint 2L 2L L u = (x/L)2 u 0 2 EA The internal virtual work: uu 22L L 2u u EA WxdxEAuu22 Which again gives the exact int2 LL 2 2 L 0 solution: Which again gives the exact u2 = Fx2 L/EA solution: These three virtual displacement u2 = Fx2 L/EA expressions all resulted in an exact Lastly, consider: solution since the real displace- ment solution was exact. If the u = u2 sin(x/2L) chosen real displacements 23 24 6 A = A (1-x/2L) correspond to stresses that 1 F 1 x2 x, u identically satisfy the conditions 2 L of equilibrium, any form of Fig. 5: Nonprismatic Axial Deformation admissible virtual displacement Structure will suffice to produce the exact Consider next the nonprismatic solution. axial deformation structure of Fig. 5. We will repeat the process Notice the adjective “admissible” in considered for Fig. 4 with front of virtual displacement. reference to the geometry of Fig. Admissible means that the 5. Considering the first case: chosen function is physically u = (x/L) u continuous and satisfies all 2 L essential boundary conditions, i.e., uu WA(1)dxE22 x is appropriately zero at all intLL 1 2L 0 supports. 25 26 3EA1 Equating the external and internal Wuint 2 u 2 4L virtual works leads to Equating the external and internal 3F L u x2 virtual works leads to 2 2EA1 4Fx2 L u2 Considering the third virtual 3EA1 displacement expression: Considering the second virtual u = u2 sin(x/2L) displacement expression: leads to 2 u = (x/L) u2 L uxxu22 leads to W1cosdxEAint 1 2L 2L 2L L L 2 0 2u 22 x u WxdxEAint 1 11EA1 L2 2L L uu22 0 2L EA 1 EA1 2u22 u u (0.818) u 3L 27 22L 28 7 Again, equating the external and The principle of virtual internal virtual works leads to displacements has its greatest 1.222Fx2 L application in producing u2 EA1 approximate solutions. NOTE: None of the three solutions The standard procedure is to match. This is because neither the adopt a virtual displacement of real or virtual displacements are the same form as the real exact. However, we produced displacement. Adopting different three good approximate solutions. forms for the real and virtual The exact solution for Fig. 5 is displacements can lead to 1.387Fx2 L unsymmetric stiffness matrices.
Load more

Recommended publications
  • Phys 140A Lecture 8–Elastic Strain, Compliance, and Stiffness
    Lecture 8 Elastic strains, compliance, and stiffness Review for exam Stress: force applied to a unit area Strain: deformation resulting from stress Purpose of today’s derivations: Generalize Hooke’s law to a 3D body that may be subjected to any arbitrary force. We imagine 3 orthogonal vectors 풙̂, 풚̂, 풛̂ embedded in a solid before we have deformed it. After we have deformed the solid, these vectors might be of different length and they might be pointing in different directions. We describe these deformed vectors 풙′, 풚′, 풛′ in the following way: ′ 풙 = (1 + 휖푥푥)풙̂ + 휖푥푦풚̂ + 휖푥푧풛̂ ′ 풚 = 휖푦푥풙̂ + (1 + 휖푦푦)풚̂ + 휖푦푧풛̂ ′ 풛 = 휖푧푥풙̂ + 휖푧푦풚̂ + (1 + 휖푧푧)풛̂ The components 휖훼훽 define the deformation. They are dimensionless and have values much smaller than 1 in most instances in solid state physics. How one ‘reads’ these vectors is (for example) 휖푥푥force along x, deformation along x; 휖푥푦shear xy-plane along x or y direction (depending which unit vector it is next to) The new axes have new lengths given by (for example): ′ ′ 2 2 2 풙 ∙ 풙 = 1 + 2휖푥푥 + 휖푥푥 + 휖푥푦 + 휖푥푧 Usually we are dealing with tiny deformations so 2nd order terms are often dropped. Deformation also changes the volume of a solid. Considering our unit cube, originally it had a volume of 1. After distortion, it has volume 1 + 휖푥푥 휖푥푦 휖푥푧 ′ ′ ′ ′ 푉 = 풙 ∙ 풚 × 풛 = | 휖푦푥 1 + 휖푦푦 휖푦푧 | ≈ 1 + 휖푥푥 + 휖푦푦 + 휖푧푧 휖푧푥 휖푧푦 1 + 휖푧푧 Dilation (훿) is given by: 푉 − 푉′ 훿 ≡ ≅ 휖 + 휖 + 휖 푉 푥푥 푦푦 푧푧 (2nd order terms have been dropped because we are working in a regime of small distortion which is almost always the appropriate one for solid state physics.
    [Show full text]
  • 19.1 Attitude Determination and Control Systems Scott R. Starin
    19.1 Attitude Determination and Control Systems Scott R. Starin, NASA Goddard Space Flight Center John Eterno, Southwest Research Institute In the year 1900, Galveston, Texas, was a bustling direct hit as Ike came ashore. Almost 200 people in the community of approximately 40,000 people. The Caribbean and the United States lost their lives; a former capital of the Republic of Texas remained a tragedy to be sure, but far less deadly than the 1900 trade center for the state and was one of the largest storm. This time, people were prepared, having cotton ports in the United States. On September 8 of received excellent warning from the GOES satellite that year, however, a powerful hurricane struck network. The Geostationary Operational Environmental Galveston island, tearing the Weather Bureau wind Satellites have been a continuous monitor of the gauge away as the winds exceeded 100 mph and world’s weather since 1975, and they have since been bringing a storm surge that flooded the entire city. The joined by other Earth-observing satellites. This weather worst natural disaster in United States’ history—even surveillance to which so many now owe their lives is today—the hurricane caused the deaths of between possible in part because of the ability to point 6000 and 8000 people. Critical in the events that led to accurately and steadily at the Earth below. The such a terrible loss of life was the lack of precise importance of accurately pointing spacecraft to our knowledge of the strength of the storm before it hit. daily lives is pervasive, yet somehow escapes the notice of most people.
    [Show full text]
  • Beam Element Stiffness Matrices
    Beam Element Stiffness Matrices CEE 421L. Matrix Structural Analysis Department of Civil and Environmental Engineering Duke University Henri P. Gavin Fall, 2014 Truss elements carry only axial forces. Beam elements carry shear forces and bending moments. Frame elements carry shear forces, bending moments, and axial forces. This document presents the development of beam element stiffness matrices in local coordinates. 1 A simply supported beam carrying end-moments Consider a simply supported beam resisting moments M1 and M2 applied at its ends. The flexibility relates the end rotations {θ1, θ2} to the end moments {M1,M2}: θ1 F11 F12 M1 = . θ2 F21 F22 M2 The flexibility coefficients, Fij, may be obtained from Castigliano’s 2nd Theo- ∗ rem, θi = ∂U (Mi)/∂Mi. First Column Second Column 2 CEE 421L. Matrix Structural Analysis – Duke University – Fall 2014 – H.P. Gavin The applied moments M1 and M2 are in equilibrium with the reactions forces V1 and V2; V1 = (M1 + M2)/L and V2 = −(M1 + M2)/L M + M x ! x V (x) = 1 2 M(x) = M − 1 + M L 1 L 2 L The total potential energy of a beam with these forces and moments is: 1Z L M 2 1Z L V 2 U = dx + dx 2 0 EI 2 0 G(A/α) By Castigliano’s Theorem, ∂U θ1 = ∂M1 ∂M(x) ∂V (x) Z L M(x) Z L V (x) = ∂M1 dx + ∂M1 dx 0 EI 0 G(A/α) x 2 x x Z L Z L Z L Z L L − 1 dx αdx L L − 1 dx αdx = + M1 + + M2 0 EI 0 GAL2 0 EI 0 GAL2 and ∂U θ2 = ∂M2 ∂M(x) ∂V (x) Z L M(x) Z L V (x) = ∂M2 dx + ∂M2 dx 0 EI 0 G(A/α) x x x 2 Z L Z L Z L Z L L L − 1 dx αdx L dx αdx = + M1 + + M2 0 EI 0 GAL2 0 EI 0 GAL2
    [Show full text]
  • Introduction to Stiffness Analysis Stiffness Analysis Procedure
    Introduction to Stiffness Analysis displacements. The number of unknowns in the stiffness method of The stiffness method of analysis is analysis is known as the degree of the basis of all commercial kinematic indeterminacy, which structural analysis programs. refers to the number of node/joint Focus of this chapter will be displacements that are unknown development of stiffness equations and are needed to describe the that only take into account bending displaced shape of the structure. deformations, i.e., ignore axial One major advantage of the member, a.k.a. slope-deflection stiffness method of analysis is that method. the kinematic degrees of freedom In the stiffness method of analysis, are well-defined. we write equilibrium equations in 1 2 terms of unknown joint (node) Definitions and Terminology Stiffness Analysis Procedure Positive Sign Convention: Counterclockwise moments and The steps to be followed in rotations along with transverse forces and displacements in the performing a stiffness analysis can positive y-axis direction. be summarized as: 1. Determine the needed displace- Fixed-End Forces: Forces at the “fixed” supports of the kinema- ment unknowns at the nodes/ tically determinate structure. joints and label them d1, d2, …, d in sequence where n = the Member-End Forces: Calculated n forces at the end of each element/ number of displacement member resulting from the unknowns or degrees of applied loading and deformation freedom. of the structure. 3 4 1 2. Modify the structure such that it fixed-end forces are vectorially is kinematically determinate or added at the nodes/joints to restrained, i.e., the identified produce the equivalent fixed-end displacements in step 1 all structure forces, which are equal zero.
    [Show full text]
  • Fundamentals of Biomechanics Duane Knudson
    Fundamentals of Biomechanics Duane Knudson Fundamentals of Biomechanics Second Edition Duane Knudson Department of Kinesiology California State University at Chico First & Normal Street Chico, CA 95929-0330 USA [email protected] Library of Congress Control Number: 2007925371 ISBN 978-0-387-49311-4 e-ISBN 978-0-387-49312-1 Printed on acid-free paper. © 2007 Springer Science+Business Media, LLC All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer Science+Business Media, LLC, 233 Spring Street, New York, NY 10013, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. 987654321 springer.com Contents Preface ix NINE FUNDAMENTALS OF BIOMECHANICS 29 Principles and Laws 29 Acknowledgments xi Nine Principles for Application of Biomechanics 30 QUALITATIVE ANALYSIS 35 PART I SUMMARY 36 INTRODUCTION REVIEW QUESTIONS 36 CHAPTER 1 KEY TERMS 37 INTRODUCTION TO BIOMECHANICS SUGGESTED READING 37 OF UMAN OVEMENT H M WEB LINKS 37 WHAT IS BIOMECHANICS?3 PART II WHY STUDY BIOMECHANICS?5 BIOLOGICAL/STRUCTURAL BASES
    [Show full text]
  • Chapter 10: Elasticity and Oscillations
    Chapter 10 Lecture Outline 1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 10: Elasticity and Oscillations •Elastic Deformations •Hooke’s Law •Stress and Strain •Shear Deformations •Volume Deformations •Simple Harmonic Motion •The Pendulum •Damped Oscillations, Forced Oscillations, and Resonance 2 §10.1 Elastic Deformation of Solids A deformation is the change in size or shape of an object. An elastic object is one that returns to its original size and shape after contact forces have been removed. If the forces acting on the object are too large, the object can be permanently distorted. 3 §10.2 Hooke’s Law F F Apply a force to both ends of a long wire. These forces will stretch the wire from length L to L+L. 4 Define: L The fractional strain L change in length F Force per unit cross- stress A sectional area 5 Hooke’s Law (Fx) can be written in terms of stress and strain (stress strain). F L Y A L YA The spring constant k is now k L Y is called Young’s modulus and is a measure of an object’s stiffness. Hooke’s Law holds for an object to a point called the proportional limit. 6 Example (text problem 10.1): A steel beam is placed vertically in the basement of a building to keep the floor above from sagging. The load on the beam is 5.8104 N and the length of the beam is 2.5 m, and the cross-sectional area of the beam is 7.5103 m2.
    [Show full text]
  • Glossary of Materials Engineering Terminology
    Glossary of Materials Engineering Terminology Adapted from: Callister, W. D.; Rethwisch, D. G. Materials Science and Engineering: An Introduction, 8th ed.; John Wiley & Sons, Inc.: Hoboken, NJ, 2010. McCrum, N. G.; Buckley, C. P.; Bucknall, C. B. Principles of Polymer Engineering, 2nd ed.; Oxford University Press: New York, NY, 1997. Brittle fracture: fracture that occurs by rapid crack formation and propagation through the material, without any appreciable deformation prior to failure. Crazing: a common response of plastics to an applied load, typically involving the formation of an opaque banded region within transparent plastic; at the microscale, the craze region is a collection of nanoscale, stress-induced voids and load-bearing fibrils within the material’s structure; craze regions commonly occur at or near a propagating crack in the material. Ductile fracture: a mode of material failure that is accompanied by extensive permanent deformation of the material. Ductility: a measure of a material’s ability to undergo appreciable permanent deformation before fracture; ductile materials (including many metals and plastics) typically display a greater amount of strain or total elongation before fracture compared to non-ductile materials (such as most ceramics). Elastic modulus: a measure of a material’s stiffness; quantified as a ratio of stress to strain prior to the yield point and reported in units of Pascals (Pa); for a material deformed in tension, this is referred to as a Young’s modulus. Engineering strain: the change in gauge length of a specimen in the direction of the applied load divided by its original gauge length; strain is typically unit-less and frequently reported as a percentage.
    [Show full text]
  • On the Relationship Between Indenation Hardness and Modulus, and the Damage Resistance of Biological Materials
    bioRxiv preprint doi: https://doi.org/10.1101/107284; this version posted February 9, 2017. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY 4.0 International license. On the relationship between indenation hardness and modulus, and the damage resistance of biological materials. David Labontea,∗, Anne-Kristin Lenzb, Michelle L. Oyena aThe NanoScience Centre, Department of Engineering, Cambridge, UK bUniversity of Applied Sciences, Bremen, Germany Abstract The remarkable mechanical performance of biological materials is based on intricate structure-function relation- ships. Nanoindentation has become the primary tool for characterising biological materials, as it allows to relate structural changes to variations in mechanical properties on small scales. However, the respective theoretical back- ground and associated interpretation of the parameters measured via indentation derives largely from research on ‘traditional’ engineering materials such as metals or ceramics. Here, we discuss the functional relevance of inden- tation hardness in biological materials by presenting a meta-analysis of its relationship with indentation modulus. Across seven orders of magnitude, indentation hardness was directly proportional to indentation modulus, illus- trating that hardness is not an independent material property. Using a lumped parameter model to deconvolute indentation hardness into components arising from reversible and irreversible deformation, we establish crite- ria which allow to interpret differences in indentation hardness across or within biological materials. The ratio between hardness and modulus arises as a key parameter, which is a proxy for the ratio between irreversible and reversible deformation during indentation, and the material’s yield strength.
    [Show full text]
  • Direct Stiffness Method: Beams
    Module 4 Analysis of Statically Indeterminate Structures by the Direct Stiffness Method Version 2 CE IIT, Kharagpur Lesson 27 The Direct Stiffness Method: Beams Version 2 CE IIT, Kharagpur Instructional Objectives After reading this chapter the student will be able to 1. Derive member stiffness matrix of a beam element. 2. Assemble member stiffness matrices to obtain the global stiffness matrix for a beam. 3. Write down global load vector for the beam problem. 4. Write the global load-displacement relation for the beam. 27.1 Introduction. In chapter 23, a few problems were solved using stiffness method from fundamentals. The procedure adopted therein is not suitable for computer implementation. In fact the load displacement relation for the entire structure was derived from fundamentals. This procedure runs into trouble when the structure is large and complex. However this can be much simplified provided we follow the procedure adopted for trusses. In the case of truss, the stiffness matrix of the entire truss was obtained by assembling the member stiffness matrices of individual members. In a similar way, one could obtain the global stiffness matrix of a continuous beam from assembling member stiffness matrix of individual beam elements. Towards this end, we break the given beam into a number of beam elements. The stiffness matrix of each individual beam element can be written very easily. For example, consider a continuous beam ABCD as shown in Fig. 27.1a. The given continuous beam is divided into three beam elements as shown in Fig. 27.1b. It is noticed that, in this case, nodes are located at the supports.
    [Show full text]
  • Introduction to the Stiffness (Displacement) Method
    MANE 4240 & CIVL 4240 Reading assignment: Introduction to Finite Elements Chapter 2: Sections 2.1-2.5 + Lecture notes Summary: Introduction to the Stiffness • Developing the finite element equations for a system of (Displacement) Method: springs using the “direct stiffness” approach • Application of boundary conditions Analysis of a system of springs • Physical significance of the stiffness matrix • Direct assembly of the global stiffness matrix Prof. Suvranu De • Problems FEM analysis scheme F1x F F 2x 3x x Step 1: Divide the problem domain into non overlapping regions (“elements”) connected to each other through special points k1 k2 (“nodes”) Step 2: Describe the behavior of each element Problem Analyze the behavior of the system composed of the two springs Step 3: Describe the behavior of the entire body by putting loaded by external forces as shown above together the behavior of each of the elements (this is a process known as “assembly”) Given F1x , F2x ,F3x are external loads. Positive directions of the forces are along the positive x-axis k1 and k2 are the stiffnesses of the two springs 1 F1x k F2x k2 F3x F F F 1 x 1x 2x 3x x 1 2 3 Element 2 k k Element 1 1 2 d1x d2x d3x Solution Node 1 Step 1: In order to analyze the system we break it up into smaller Solution parts, i.e., “elements” connected to each other through “nodes” Step 2: Analyze the behavior of a single element (spring) F1x k F2x k2 F3x 1 x 1 2 3 Element 2 Element 1 © 2002 Brooks/Cole Publishing / Thomson Learning™ d1x d2x d3x Node 1 Two nodes: 1, 2 ˆ ˆ Unknowns: nodal displacements d , d ,d , Nodal displacements: d1x d2x 1x 2x 3x ˆ ˆ Nodal forces: f1x f2x Spring constant: k Behavior of a linear spring (recap) F x k k 1 F d k d F = Force in the spring © 2002 Brooks/Cole Publishing / Thomson Learning™ d = deflection of the spring Local (xˆ , yˆ , zˆ ) and global (x,y,z) coordinate systems k = “stiffness” of the spring Hooke’s Law F = kd 2 Note T fˆ ˆ 1.
    [Show full text]
  • Analysis of the Stiffness Ratio at the Interim Layer of Frame-Supported Multi-Ribbed Lightweight Walls Under Low-Reversed Cyclic Loading
    applied sciences Article Analysis of the Stiffness Ratio at the Interim Layer of Frame-Supported Multi-Ribbed Lightweight Walls under Low-Reversed Cyclic Loading Suizi Jia 1,*, Wanlin Cao 1, Yuchen Zhang 2 and Quan Yuan 3 Received: 23 October 2015; Accepted: 11 January 2016; Published: 15 January 2016 Academic Editor: César Vasques 1 College of Architecture and Civil Engineering, Beijing University of Technology, No.100, Pingleyuan, Chaoyang District, Beijing 100124, China; [email protected] 2 Academy of Railway Sciences, Scientific & Technological Information Research Institute, No. 2 Daliushu Road, Haidian District, Beijing 100081, China; [email protected] 3 School of Civil Engineering, Beijing Jiaotong University, No.3 Shangyuancun, Haidian District, Beijing 100044, China; [email protected] * Correspondence: [email protected]; Tel.: +86-10-6739-6617; Fax: +86-10-6739-6617 Abstract: By conducting low-reversed cyclic loading tests, this paper explores the load-bearing performance of frame-supported multi-ribbed lightweight wall structures. The finite-element software (OpenSees) is used to simulate the process with the shear wall width (at the frame-supported layer) and different hole opening approaches (for multi-ribbed lightweight walls) as variables. The conclusions reflect the influence of the stiffness ratio at the interim layer on the load-bearing performance of the structure. On this basis, the paper identifies the preferable numerical range for engineering design, which provides a solid foundation for the theoretical advancement of the structures in this study. Keywords: frame-supported structure; multi-ribbed lightweight wall; OpenSees; stiffness ratio; interim layer 1. Introduction The wide application of frame-supported structures serves the increasing demand for modern buildings that are designed and constructed with multiple functions for various purposes.
    [Show full text]
  • Chapter 2 – Introduction to the Stiffness (Displacement) Method
    CIVL 7/8117 Chapter 2 - The Stiffness Method 1/32 Chapter 2 – Introduction to the Stiffness (Displacement) Method Learning Objectives • To define the stiffness matrix • To derive the stiffness matrix for a spring element • To demonstrate how to assemble stiffness matrices into a global stiffness matrix • To illustrate the concept of direct stiffness method to obtain the global stiffness matrix and solve a spring assemblage problem • To describe and apply the different kinds of boundary conditions relevant for spring assemblages • To show how the potential energy approach can be used to both derive the stiffness matrix for a spring and solve a spring assemblage problem The Stiffness (Displacement) Method This section introduces some of the basic concepts on which the direct stiffness method is based. The linear spring is simple and an instructive tool to illustrate the basic concepts. The steps to develop a finite element model for a linear spring follow our general 8 step procedure. 1. Discretize and Select Element Types - Linear spring elements 2. Select a Displacement Function - Assume a variation of the displacements over each element. 3. Define the Strain/Displacement and Stress/Strain Relationships - use elementary concepts of equilibrium and compatibility. CIVL 7/8117 Chapter 2 - The Stiffness Method 2/32 The Stiffness (Displacement) Method 4. Derive the Element Stiffness Matrix and Equations - Define the stiffness matrix for an element and then consider the derivation of the stiffness matrix for a linear- elastic spring element. 5. Assemble the Element Equations to Obtain the Global or Total Equations and Introduce Boundary Conditions - We then show how the total stiffness matrix for the problem can be obtained by superimposing the stiffness matrices of the individual elements in a direct manner.
    [Show full text]