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# Lect8 Internal Forces

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### Lect8 Internal Forces

1. 1. Mindanao State UniversityIligan Institute of Technology College of Engineering Internal Forces a ForceGevelyn Bontilao Itao, MOE
2. 2. Internal Forces Objectives: The design of any structural or mechanical member requires an investigation of the loading acting within the member in order to be sure the material can resist the external loadings applied into it..gsbitao_2013
3. 3. Internal Forces The internal loadings ca be determined using the method of sections.  If internal loadings at the cross-section of C are to be determined an imaginary line is passed thru the beam, cutting it into two segments.gsbitao_2013
4. 4. Internal Forces Rectangular force components are developed to maintain equilibrium:  N – force component acting normal to the beam  V – force component acting tangent to the beam  M – couple moment; bending momentgsbitao_2013
5. 5. Internal Forces  N, V, and M must be equal in magnitude but opposite in directions on each segent (Newton’s 3rd Law)gsbitao_2013
6. 6. Internal Forces Vx , Vz – shear force components (tangent to the section) Ny – normal force (axial) Mx , Mz – bending moment My – tortional moment/twisting moment (motion is along the axis perpendicular to the section)gsbitao_2013
7. 7. Internal Forces Example 1: The beam is supports the loading shown. Determine the internal normal force, shear force and bending moment acting just to the left of point C and just to the right of point C.gsbitao_2013
8. 8. Internal Forces Example 2: Determine the internal normal force, shear force and bending moment acting at point B of the two-member frame shown.gsbitao_2013
9. 9. Mindanao State University Iligan Institute of Technology College of EngineeringShear and Moment Diagrams a Force Gevelyn Bontilao Itao, MOE
10. 10. Shear and Moment Diagrams Objectives: The design of beam requires an investigation of the shearing forces and bending moments produced by the load in order to be sure the beam can withstand the external loadings applied into it.gsbitao_2013
11. 11. Shear and Moment Diagrams Classification of Beams: Based on the type of supports 1. SIMPLY SUPPORTED BEAMS – pinned at one end and roller at the other end. 2. Cantilever Beam – fixed support at one end and free on the other end.gsbitao_2013
12. 12. Shear and Moment Diagrams Variation of V and M  is a function of the position x along the beam’s axis.  The function describing the variation of V and M become discontinuous where distributed load changes or where concentrated loads or couple moments are appliedgsbitao_2013
13. 13. Shear and Moment Diagrams Sign Convention: Positive directions:  V – cause clockwise rotation of the member on which it acts  M – causes compression or pushing on the upper part of the member. If the beam is elastic, M would tend to bend the member, concave upward.gsbitao_2013
14. 14. Shear and Moment Diagrams Procedure for Analysis: 1. Determine all the reactive forces and couple moments acting on the beam and resolve all the forces into components acting perpendicular and parallel to the beam’s axis. 2. Specify separate coordinates x having an origin at the beam’s left end and extending to the regions of the beams between concentrated forces and/or couple moments and draw the FBD’s of the sections. 3. Shear is obtained by summing forces perpendicular to the beam’s axis. 4. The moment is obtained by summing moments about the sectioned end of the segment.gsbitao_2013
15. 15. Shear and Moment Diagrams Example 1: Draw the shear and bending moment diagrams for the shaft shown. The support at A is a thrust bearing and the support at C is a journal bearing.gsbitao_2013
16. 16. Shear and Moment Diagrams Example 2: Draw the shear and bending moment diagrams for the beam shown.gsbitao_2013