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Re: ACI 318 App. D[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: Re: ACI 318 App. D
- From: "S. Gordin" <mailbox(--nospam--at)sgeconsulting.com>
- Date: Sun, 8 Oct 2006 21:32:54 -0700
I also figured this much regarding the inspection, but was not sure as is did not make much sense. Oh well.
The difference in the anchor bolt pullout values is staggering. According to Ronald Cook's "Strength Design of Anchorage to Concrete" (PCA), this difference results from the "high tensile stresses that exist at the embedded head of the anchor while other approaches... assume uniform distribution of stresses over the assumed failure surface."
As a result of such "new" approach, the "old" breakout strength of concrete is supposed to be divided by a square root of the embedment depth. Say, if I have a 25" embedment depth, the "new" concrete breakout strength is 5 times lower than the "old" one. This also changes the governing case (it becomes concrete, not steel) and results in further reduction of capacity due to lower strength reduction factor (of course, the final result may be less different due to the steel-concrete strength "play").
We are used to the "new and improved" methods leading to the same decades-old results through more difficult calculations. In spite of natural frustration, this gives us confidence in the ultimate adequacy of the decades-proven design techniques. Here, one of the most basic structural engineering concepts appears to have been proven wrong. Did I miss somebody in California notifying the engineers not to use CBC/UBC Section 1923 that produces non-conservative - at best - results?
Steve Gordin SE
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