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Re: Displaced Center of Mass Question
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- 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 additional 5% eccentricity. 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 >>
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