Need a book? Engineering books recommendations...

# Re: Displaced Center of Mass Question

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Displaced Center of Mass Question
• From: Seaintonln(--nospam--at)aol.com
• Date: Fri, 30 Jul 1999 12:18:31 EDT

```Greg, I think my questions is much simpler than the answer. I believe that
there is validity in your response when dealing with a heavier mass such as
masonry or concrete walls. My question was to consider the results on
lightweight structures by considering the displaced center of mass as it
might occur on either sides of the Center of Ridgity rather than the approach
taken by Amrhein in the Reinforce Masonry Handbook that simply adds 5% of the
diaphragm dimension perpendicular to the direction of force in both the X and
Y axis. Although he does suggest that the displaced eccentricity is both
added and/or subracted from the eccentricity resulting between the CR and CM
his examples in the book use a simplified approach by only adding the
I can easily see how by considering the eliptical effect of the displaced CM
that the loads to the walls farthest from the is point will increase.
However, is if enough to make a significant difference or are we trying to be
too specific in the design?

Thanks
Dennis

In a message dated 7/29/99 7:46:30 PM Pacific Daylight Time, strusup(--nospam--at)gte.net
writes:

<<      The book by Breyer - Design of wood structures addresses "seismic
irregularity on pgs.785-794.  Re-thinking my statement on the eccentricity
defining an axis when the eccentricity is a scalar measure of how much the
structure will rotate (I can visualize what I am saying but sometimes I get
ahead of myself and put my foot in it wordwise), anyway, to explain what I
am saying in a direction away from what is leading to the center of
rotation, a very applicable analytical method would be the ellipse of
inertia which leads to the ellipse of elasticity with elastic centers and
instantaneous center.  This method orthogonalizes the oblique axis that I
mentioned which, unproven by me, relates the COM, CORig and CORotation
(instantaneous center).  The method is as powerful as any FE method and is
well suited for arches.

Greg >>

```