Calculating Fixed End Moments with Uneven Beam Heights?

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Discussion Overview

The discussion revolves around calculating the fixed end moments for a beam with uneven heights, specifically focusing on a member subjected to a uniformly distributed load (UDL). Participants are examining the implications of the height difference on the calculations of fixed end moments and stiffness factors.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant describes a beam configuration with a UDL and expresses uncertainty about how the height difference affects the fixed end moment calculations.
  • Another participant asserts that the fixed end moment is indeed 180, suggesting that the height does not impact the moment until stiffness factors are considered in the moment distribution method (MDM) analysis.
  • A participant questions their own calculations regarding EI (flexural rigidity) and seeks clarification on how raising the member affects the moment of inertia and stiffness.
  • It is noted that raising the member increases its moment of inertia, thereby making it stiffer, which may influence the calculations.
  • Participants reference the moment distribution method and its relevance to the problem at hand.

Areas of Agreement / Disagreement

There is no consensus on the correct fixed end moment value, as one participant claims it is 180 while another expresses uncertainty about their calculations. The discussion reflects competing views on the impact of member height on the calculations.

Contextual Notes

Participants mention potential mistakes in EI calculations and the need for clarity on how height affects stiffness, indicating that assumptions about these factors may be unresolved.

seamie
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Ok, so I have a problem as follows:

A beam is simply supported at joints A, B, C D and E.

there is a UDL acting on the BC member

The member is 6m long with a UDL of 60kn/m

However the tricky part is that this member is 1.2 times higher than the height of the members AB, CD, and DE.

So BC = 1.2h, AB = CD = DE = h

I need to calculate the FIXED END MOMENT of CB and BC - which I am taking to be WLsq./12 - however I am unsure how the height element effects the caluclations

the answer is not 180 - that does not fit with my MDM calculations - anyone got any ideas?
 
Last edited:
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seamie said:
The member is I need to calculate the FIXED END MOMENT of CB and BC - which I am taking to be WLsq./12 - however I am unsure how the height element effects the caluclations

the answer is not 180 - that does not fit with my MDM calculations - anyone got any ideas?
The answer IS 180...plus at one end and minus at the other...the height doesn't come into play until you start calculating the stiffness factors for your MDM analysis.
 
Hi there,

In that case i am making a mistake with my EI calculations - what effect does raising the member have?

the exact layout is:

Fixed End @ A -------B Simply Supported C Simply Supported D ----E @ E is a cantilever

BC to C is raised by 1.2h

Am i not still using 4EI/l at member BC and CB
 
Last edited:
seamie said:
Hi there,

In that case i am making a mistake with my EI calculations - what effect does raising the member have?
it increases its moment of inertia, which makes it stiffer
the exact layout is:

Fixed End @ A -------B Simply Supported C Simply Supported D ----E @ E is a cantilever

BC to C is raised by 1.2h

Am i not still using 4EI/l at member BC and CB
Oh heck it's been a long time...see here:

http://en.wikipedia.org/wiki/Moment_distribution_method
 
are you there?
 

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