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Unit Error in Diaphragm Deflection examples
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- Subject: Unit Error in Diaphragm Deflection examples
- From: Seaintonln(--nospam--at)aol.com
- Date: Thu, 8 Jul 1999 02:04:25 EDT
- Cc: seaint(--nospam--at)seaint.org, jgs(--nospam--at)eqe.com, Mlcse(--nospam--at)aol.com, cgreenlaw(--nospam--at)speedlink.com, hoh(--nospam--at)eqe.com, hessengineering(--nospam--at)csi.com, jnairvine(--nospam--at)compuserve.com, billw4(--nospam--at)sesol.com
To all: I am not sure if this has been brought to anyone's attention. I was one of the volunteers who checked the steel design problem (example 3) in the ICBO '97 UBC Design Examples Volume II. I did not catch this problem when I sent in my comments but there appears to be an error in the diaphragm deflection calculations for the first terms dealing with beam bending. The example fails to calculate the units correctly and the deflection calculated for 5vL^3/(8EAb) should be multiplied by 12 to convert the answer to inches. The same problem exists in the example by Bill Nelson and Doug Thompson in the seminar notes from the February 21, 1998 "97 UBC Wood Provisions". Again the first term in the formula represents feet rather than inches. I would appreciate it if the appropriate people were notified of this problem so that it may be corrected in the code. There also appears to be some confusion in the third portion of the equation that deals with nail slippage and bending. In this case, the answer shown is probably correct, but can not be verified as the 0.188 term has no units applied to it. Can someone please verify publically for the seaint listservice if the 0.188 constant is a conversion factor and how it was derived. Otherwise, it appears that the units do not balance in this portion of the equation. Many of us are struggling to work with these formulas in order to complete work within our offices. I am trying to convert the methodology to a spreadsheet format and will offer this free to any engineer who wants it. I only request that when design examples are provided that they include the proper units so that the results can be verified. I found the error in the first term by using MathCad which automatically converts units. Programs such as this assume that the constants in the equation are unitless. If any of these constants are conversions, we must know this so that we can create our design tools appropriately. There are other inconsistencies in the only examples provided to practicing engineers. It is important that these issues be addressed by SEA or ICBO as soon as possible so as to protect the engineering community. The last thing we need is increased liability due to the code that we are expected to learn. Respectfully, Dennis S. Wish PE
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