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Steel Collapse Energy Ratio Calculation
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- Subject: Steel Collapse Energy Ratio Calculation
- From: Dom Dudz <ddspectra(--nospam--at)yahoo.com>
- Date: Sun, 24 Sep 2006 07:24:26 -0700 (PDT)
I'm new here and I have an important and hopefully easy structural engineering question. What is the easiest way to calculate the energy ratio Wg/Wp ? The formula comes from Bazant&Zhou 2001. I have recently read an article by structural engineer Dr. Abolhassan Astaneh-Asl which describes that the WTC twin towers may have collapsed due to architectural flaws. This is in contradiction of the NIST report which is the motivation for my question. I have calculated the energy ratio myself and I find it to be MUCH LOWER than the one mentioned in the NIST report. However, the calculations for this important energy ratio are nowhere to be found. Not in the NIST report and not in the orinal Bazant paper nor in a more recent paper june 2006 which agains states the energy ratio is 8.4. This ratio of 8.4 seems to be calculated for damaged storeys whereas NIST and others seem to mistakenly assume it applies to intact storeys. So I have been trying to track down this calculation and understand the root of this confusion. In NCSTAR 1-6 chapter 9 NIST refers to a paper by Bazant that quotes an energy ratio of 8.4 in favor of collapse (Wg/Wp) implying that the potential energy released for each storey would exceed the energy required to crush it. In NCSTAR 1-6 chapter 8 there are DCRs for the columns of the 95th storey before impact. Averaging the values for all of the columns, the implied safetyFactor is 4. The energy ratio I come up with from my simplfied formula is: energyReleased = m*g*h energyAbsorbed = m*g*safetyFactor*areaUnderLoadProfile*h (The areaUnderLoadProfile of Bazant 2001 Fig. 5d is 35%) therefore the energyReleased is LOWER than the energyAbsorbed by a factor of 1/(safetyFactor*areaUnderLoadProfile )= 1/(4 * 35%) = 0.7 I will not be surprised to see energy ratios greater than 1 if the safetyfactor or loadprofile that I have used are incorrect. However, an energy ratio of 8 seems absurd. Can anyone provide some clarification for how to calculate the energy ratio? Regards, Dom Dudz __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ******* ****** ******* ******** ******* ******* ******* *** * Read list FAQ at: http://www.seaint.org/list_FAQ.asp * * This email was sent to you via Structural Engineers * Association of Southern California (SEAOSC) server. To * subscribe (no fee) or UnSubscribe, please go to: * * http://www.seaint.org/sealist1.asp * * Questions to seaint-ad(--nospam--at)seaint.org. Remember, any email you * send to the list is public domain and may be re-posted * without your permission. Make sure you visit our web * site at: http://www.seaint.org ******* ****** ****** ****** ******* ****** ****** ********
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