Calculating Deflection and Stress in a Tapered Cantilever Beam

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Discussion Overview

The discussion revolves around calculating deflection and stress in a tapered cantilever beam, specifically an I-section beam with a point load at the free end. Participants seek to derive the deflection formula and understand the implications of tapering on bending and shear stress calculations.

Discussion Character

  • Technical explanation
  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant expresses confusion about deriving the deflection formula for a tapered cantilever beam and questions if the bending and shear stress calculations are similar to those for a normal beam.
  • Another participant suggests that a simple deflection formula may not exist due to the varying moment of inertia along the beam's length, proposing the double integration method for calculating deflection.
  • It is noted that the shear force and bending moment diagrams are based solely on the loading of the beam, and tapering does not affect these calculations.
  • Participants mention that while bending moments and shear forces are the same as for a non-tapered beam, the bending and shear stresses depend on the geometric properties of the beam's cross-section at the specific point of interest.
  • One participant indicates that numerical integration methods may be necessary to obtain deflection values due to the complexity of the functions involved.

Areas of Agreement / Disagreement

Participants generally agree on the complexity introduced by the tapering of the beam, particularly regarding the calculation of deflection and stresses. However, there is no consensus on a specific method or formula for deriving the deflection, and multiple approaches are suggested without resolution.

Contextual Notes

Participants acknowledge that the moment of inertia varies along the length of the beam, which complicates the calculations. The discussion does not resolve the specific mathematical steps required for integration or the implications of varying geometric properties.

Timisoarian
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Hey all,
So I have this beam problem and I honestly am lost with it!
The beam is I-section cantilever, tapers in depth along its length (See picture attached) with a point load at the free end. I am trying to figure out the deflection formula and how to derive it! Also, when calculating its bending stress and shear stress, is it the same way as a normal beam?
Please guys, any help is appreciated it as I am completely lost!
 

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Timisoarian said:
Hey all,
So I have this beam problem and I honestly am lost with it!
The beam is I-section cantilever, tapers in depth along its length (See picture attached) with a point load at the free end. I am trying to figure out the deflection formula and how to derive it!
There probably won't be a simple deflection formula. Since the moment of inertia of the beam varies with length, deflections will probably best be calculated using the double integration method:

θ(x) = \int^x_0 \frac{M(x)}{EI(x)} dx + C_1

δ(x) = \int^x_0 θ(x) dx + C_2

where:

θ(x) - slope of the beam
δ(x) - deflection of the beam
I(x) - moment of inertia of the beam, as a function of the length
E - Young's modulus for the beam material

C1 and C2 - constants of integration; determined by applying the boundary conditions at the fixed end, i.e. θ(0) = δ(0) = 0.

Even if you can determine the moment of inertia I(x) as a function of x, you probably won't get simple functions for M(x)/I(x) to integrate. You may have to use a numerical integration method to obtain θ and δ.

Also, when calculating its bending stress and shear stress, is it the same way as a normal beam?

The shear force and bending moment diagrams are calculated based on the loading of the beam only. The taper does not come into play.

The regular formulas for bending stress and shear stress still apply ... you do have to calculate the section properties of the beam at the location where you want to determine the stresses. Unlike a prismatic beam, if you change the location of where the stresses are calculated, you must re-calculate the section properties at that new location.
 
Timisoarian said:
Hey all,

So I have this beam problem and I honestly am lost with it!

The beam is I-section cantilever, tapers in depth along its length (See picture attached) with a point load at the free end. I am trying to figure out the deflection formula and how to derive it! Also, when calculating its bending stress and shear stress, is it the same way as a normal beam?

Please guys, any help is appreciated it as I am completely lost!
For the statically determinate beam, bending moments and shear forces at any point along the beam are the same as a non tapered beam, but bending and shear stresses will depend upon the geometric properties of the beam cross section at the point in question. For deflection, since I is non-uniform, you'll have to do the calculus using one of those deflection equations. Like \int{( mM/EI) }dx .
 
Two threads merged, and moved to homework.
 

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