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1 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 CIE3109 Structural Mechanics 4 Hans Welleman Module : Unsymmetrical and/or inhomogeneous cross section

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2 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 CIE3109 : Structural Mechanics 4 1-2Inhomogeneous and/or unsymmetrical cross sections Introduction General theory for extension and bending, beam theory Unsymmetrical cross sections Example curvature and loading Example normalstress distribution Deformations 3Inhomogeneous cross sections Refinement of the theory Examples 4-5Stresses and the core of the cross section Normal stress in unsymmetrical cross section and the core Shear stresses in unsymmetrical cross sections Shear centre Lectures

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3 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 Question What is the stress and strain distribution in a cross section due to extension and bending in case of a unsymmetrical and/or non-homogeneous cross section’ ? z z z y y y (a)(b)(c) concrete steel E1E1 E1E1 E2E2 unsymmetricalinhomogeneousboth

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4 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 BENDING and AXIAL LOADING RELATION BETWEEN EXTERNAL LOADS AND DISPLACEMENTS Structural level Cross sectional level uxux uzuz uyuy x z y zz xx yy FzFz FxFx FyFy F global definitions sectional definitions VzVz VyVy

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5 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 fibre in cross section x at position y,z ASSUMPTIONS FIBRE MODEL SMALL ROTATIONS OF THE CROSS SECTION UNIAXIAL STRESS SITUATION IN THE FIBRES LINEAR ELASTIC MATERIAL BEHAVIOUR Hooke’s law :

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6 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 SOLUTION PATH Determine the strain distribution due to the displacements of the cross section? Determine the stress distribution caused by these strains? Determine the resulting forces in the cross section? LoadSectional forcesStressStrainDeformationsDisplacements (F en q)(N, V, M)(fibre)(fibre)( , )(u, ) EquilibriumStatic Constitutive CompatibilityKinematische relationsrelations relations relatiesrelaties Constitutive relation (cross section)

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7 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 KINEMATIC RELATIONS Relation between deformations and displacements z x-as z-as yy uzuz uxux yy z y x-as y-as zz uyuy uxux zz y

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8 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 FIBRE MODEL Horizontal displacement z x-as z-as yy uzuz uxux yy z y x-as y-as zz uyuy zz y uxux

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9 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 RELATIVE DISPLACEMENT-STRAIN with

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10 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 STRAIN DISTRIBUTION zz yy x-axis z-axis x-axis y-axis strain z y Conclusion: Strain distribution is fully described with three deformation parameters

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11 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 STRAIN FIELD Three parameters strain in fibre which coincides with the x-axis slope of strain diagram in y-direction slope of strain diagram in z-direction

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12 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 k k CURVATURE First order tensor Curvature in x-y-plane Curvature in x-z-plane Plane of curvature k

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13 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 NEUTRAL AXIS k k is perpendicular to neutral axis neutral axis

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14 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 FROM STRAIN TO STRESS Constitutive relation : link between deformations and stresses

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15 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 STRESS AND SECTIONAL FORCES Static relations : link between stresses and sectional forces

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16 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 Elaborate … approach with “double-letter” symbols

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17 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 CONSTITUTIVE RELATION on cross sectional level INDEPENDENT OF THE ORIGIN OF THE COORDINATE SYSTEM SPECIAL LOCATION OF THE ORIGIN OF THE COORDINATE SYSTEM TO UNCOUPLE BENDING AND AXIAL LOADING

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18 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 NORMAL FORCE CENTRE Bending and axial loading are uncoupled: Axial loading Bending definition NC : if N = 0 then zero strain at the NC and the n.a. runs through the NC

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19 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 LOCATION NC y z NC

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20 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 RESULT Bending and axial loading are uncoupled Moment is first order tensor

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21 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 MOMENT M m x-axis z-axis y-axis MzMz MyMy mm MOMENT M TENSION COMPRESSION N.C. SUMMARY of formulas TENSION COMPRESSION CURVATURE k n.a. x-axis n.a. z-axis y-axis zz yy kk N.C.

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22 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 PLANE OF LOADING SAME AS PLANE OF CURVATURE ?

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23 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 PRINCIPAL DIRECTIONS

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24 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 ROTATE TO PRINCIPAL DIRECTIONS

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25 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 EXAMPLE 1 Determine the position of the plane loading m-m for the specified position of the neutral line which makes an angle of 30 o degrees with the y-axis. The rectangular cross section is homogeneous.

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26 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 EXAMPLE 2 A triangular cross section is loaded by pure bending only. The cross section is homogeneous and the Youngs modulus is E. The normal stress in point A and C is equal to 10 N/mm 2. a)Calculate the magnitude and direction of the resulting bending moment b)Compute the stress in point B

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27 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 F1 = HELP

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28 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 Equillibrium conditions

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29 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 Differential equations (structural level) Kinematics: Constitutive relations: Equilibrium relations: substitute axial loading bending

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30 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 Result modify the load in all forget-me-not’s OR solve differential equation

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31 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 EXAMPLE (see lecture notes)

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32 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 Result

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33 Unsymmetrical and/or inhomogeneous cross sections | CIE3109 SUMMARY displacements solve differential equations Use “pseudo” load for y - and z -direction and use this load in standard engineering equations Use curvature distribution in combination with moment area theoremes to obtain displacements and rotations (see notes) Use principal directions, decompose load in (1) and (2) direction, and compute displacements in (1) and (2) direction with standard engineering equations. Finally transformate the displacements back to y - and z -direction Original y-z coordinate system Principal 1-2 coordinate system

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