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Reference needed
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- Subject: Reference needed
- From: "Dennis Wish" <dennis.wish(--nospam--at)verizon.net>
- Date: Sat, 25 Aug 2007 17:32:52 -0700
I asked this same question of a close friend, but thought I
might get a wider range of references by posting this notice on the SEAINT
List. I have a need to write my own spreadsheet tool or TEDDS
template that will allow me to design a spread footing with multiple eccentric
loads (say two or three columns that share the same pad that might be common in
custom home remodels). One of the problems stems from doweling two slab
on grades together where a room addition is added and removing a wall to allow
a pass-through. In some cases the framing is such that the reaction at each
header column exceeds the soil bearing capacity of a typical turned down
12-inch wide continuous slab on grade foundation when considering the
maximum distribution on the foundation should not exceed a 4:1 ratio. So if the
combined reaction is 6-kips and the soil bearing pressure is only 1000 psf then
the maximum bearing pressure you can distribute over the length of the slab
foundation is 4:1 or 4-kips. However, if you provide a similar turn-down edge
to the adjacent new slab on grade (rather the more common 8-inch thick slab edge
that is used to dowel the two together) then you can double the bearing
pressure by considering the width of the combined slab foundation to be 2-feet
in width and the 4:1 max ratio will allow for an 8-kip reaction. The problem is
that the column now has an eccentricity that must be considered. The second condition is if the new and the existing are independently
supported on two columns where the framing is parallel to one another. This
provides two columns on two slab edges that are doweled together or on one rectangular
(or square pad) with each column eccentric and not necessarily balanced in
loading. To be frank, after 21 years in private practice, I’ve
relied on software to do the work and while my intuition is good, I would like
to relearn my skills and go back to the basics so that I can write a
spreadsheet for up to four of six eccentric loads on one pad foundation. I’m looking for a back to basic soils or foundation
design manual to help me work out the algorithms that I need to write the
spreadsheet. I think I understand how to find the center of mass based on the
load distributions but would like to compare it against a text. My foundation
design manuals that I used in school seem more than complicated and I am
looking for something fairly straight forward. If I would prefer, I would also like the text to cover other
types of foundations; continuous wall foundations; friction piles, spread
footings that are used installed below an existing foundation (remodeling
situation); distribution of shear from eccentric loading conditions where new
foundations are doweled or added to the existing etc. Please post your favorite references for foundation design.
I think the Retaining wall reference published by Huge Brooks is the best I’ve
seen and I use this as a primer to refresh my memory on retaining wall design,
but for the other conditions I am seeking a text rather than a reference for a
computer program that will do the work for me. One of the problems with relying on computer software that I
take for granted because I write most of my own tools is writing one that you
have been used to designing by shortcut (for example a grade beam that takes
the moment from each end at the base of a moment frame). I’ve designed
these using a half page or less shortcut, but I want to restore my
understanding of the basics as I have always done with code programs such as
MultiLat™ that assisted me to understand what was in the mind of the code
writer while I was recreating the spreadsheet. At nearly sixty years old, I am not too proud to want to
return to the basics and admit that I forgot some of my elemental skills. Help
me restore my memory by suggesting the reference that you use when you need to
do an analysis manually that you have not done for a long time. Thanks Dennis Dennis S. Wish, PE California Professional Engineering – C 41250 Exp
03/31/09 Structural Engineering Consultant La Quinta California No virus found in this outgoing message. |
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