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- To: seaoc(--nospam--at)seaoc.org
- Subject: caisson footings
- From: Mark and Jessica Pemberton <jmpember(--nospam--at)softcom.net>
- Date: Thu, 19 Feb 1998 20:10:36 -0800
I have two general questions regarding 94 UBC caisson footing equations: 1) I was able to derive the constrained formula for required depth of a caisson footing using simple statics, however was not able to exactly derive the non-constrained formula. I have researched several foundation texts and have found no method of modeling a laterally loaded pile/caisson that yield any similar results. Does anyone know the general assumptions used to derive this formula? I'm sure it has something to do active verses passive pressure or bearing stress reversal, but all the attempts I have made yield a similar formula with two constants off (one by 50%!) 2) The code allows for a developed frictional force between the walls of a cast in place caisson footing and the soil equal to 1/6 the allowable bearing stress (per table). By using this value I find that the frictional resistance is several times that derived using standard skin friction equations. Why is this? The maximum the code allows is 250 psf of frictional resistance which is way more than you can achieve in any standard soil. Is this value perhaps only allowed for resistance in the downward direction, or can it be used to resist uplift as well? Any help would be greatly appreciated. So far I am getting widely varied opinion on this, and it seems different building departments are interpreting these provisions differently. I have even called ICBO directly and received an unsure at best response.
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