130 likes | 362 Views
Chapter 5 Analysis and Design of Beams for Bending . 5.1 Introduction. -- Dealing with beams of different materials: steel, aluminum, wood, etc. -- Loading: transverse loads Concentrated loads Distributed loads. -- Supports Simply supported Cantilever Beam
E N D
5.1 Introduction -- Dealing with beams of different materials: steel, aluminum, wood, etc. -- Loading: transverse loads Concentrated loads Distributed loads
-- Supports Simply supported Cantilever Beam Overhanging Continuous Fixed Beam
A. Statically Determinate Beams -- Problems can be solved using Equations of Equilibrium B. Statically Indeterminate Beams -- Problems cannot be solved using Eq. of Equilibrium -- Must rely on additional deformation equations to solve the problems. FBDs are sometimes necessary:
FBDs are necessary tools to determine the internal (1) shear force V – create internal shear stress; and (2) Bending moment M – create normal stress From Ch 4: (5.1) (5.2) Where I = moment of inertia y = distance from the N. Surface c = max distance
Recalling, elastic section modulus,S = I/c, (5.3) hence For a rectangular cross-section beam, (5.4) From Eq. (5.3),max occurs at Mmax It is necessary to plot the V and M diagrams along the length of a beam. to know where Vmaxor Mmax occurs!
5.2 Shear and Bending-Moment Diagrams • Determining of V and M at selected points of the beam
Sign Conventions • The shear is positive (+) when external forces acting on the beam tend to shear off the beam at the point indicated in fig 5.7b 2. The bending moment is positive (+) when the external forces acting on the beam tend to bend the beam at the point indicated in fig 5.7c Moment
5.3 Relations among Load, Shear and Bending Moment • Relations between Load and Shear Hence, (5.5)
Integrating Eq. (5.5) between points C and D (5.6) VD – VC = area under load curve between C and D (5.6’) 1 (5.5’)
Relations between Shear and Bending Moment or (5.7)
(5.7) MD – MC = area under shear curve between points C and D
5.4 Design of Prismatic Beams for Bending -- Design of a beam is controlled by |Mmax| (5.1’,5.3’) Hence, the min allowable value of section modulus is: (5.9)