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Thread: Why Buildings Respond Differently to Earthquakes

  1. #1
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    Lightbulb Why Buildings Respond Differently to Earthquakes

    I received the following email from our professional body IPENZ, that is Institution of Professional Engineers New Zealand.

    "Due to some confusion in the media, IPENZ has drawn on Membership expertise to prepare a simple fact sheet, "Why Buildings Respond Differently to Earthquakes".
    Once again we encourage you to share it with your networks."

    You will find this fact sheet here: http://www.nzgs.org/wp-content/uploa...e28Mar2011.pdf
    (It is currently not available on our IPENZ web site.)

    The examination and evaluation of the events has not been finished yet. So more fact sheets, notes and reports will surely follow.

  2. #2
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    Interesting to hear this quote from the article:

    There are three main concepts which form the basis of modern seismic design.

    The first of these was to recognise that it is not economical to design all buildings to resist the largest earthquake they will every experience and so buildings may experience larger seismic energy and forces than those they were designed to resist.

    The second concept is that the excess energy imparted to a building by an earthquake needs to be absorbed in a controlled manner. This concept involved making essential elements of the building ductile (flexible), because as ductile elements yield they absorb energy without failing completely. If the energy imparted were to be large, then parts of the building were designed to be the primary places where the energy would be absorbed and possibly distort.

    The third concept was to create a hierarchy of strength, known as “capacity design”. This is a design approach in which those elements which must be protected from yielding are given an “overstrength”. In simple terms, this results in a hierarchy of strong unyielding columns and weaker yielding beams which absorb the energy of the earthquake while preventing an undesirable collapse mechanism.


    The 1st concept is a critical one. No recognition is given to the buildings that were built under the current code and for many, imply that there isn't enough being done to make buildings and houses safer. A vast # of builders such as my uncle (who come from an old school of building) say that the way we build houses today (residential) is of poor quality and proned to earthquake damage. They feel that it's unacceptable for a house to experience Gib cracking, brick motar cracks, or other cosmetic issues.

    So the question asks, do we need to construct houses that can resist the slightest cracks inside the house? The article makes no mention that the current building code (and the way we build today) requires a major upgrade. It address that older buildings needing to be strengthen are only talking about meeting 67% of the current earthquake resistance code. Yet we have extreme people that say the current code isn't sufficient - prompting the issue of spending huge sums of $ just to meet the strongest earthquake possible.

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    Quote Originally Posted by Super_BQ View Post
    So the question asks, do we need to construct houses that can resist the slightest cracks inside the house?
    I clearly think we do not need to do so. And as such I deem it prudent that there is no requirement per Building Code.
    People who want to do so voluntarily are not prohibited or prevented of taking additional measures to those of the Building Code.


    Quote Originally Posted by Super_BQ View Post
    The article makes no mention that the current building code (and the way we build today) requires a major upgrade.
    The article cannot mention the necessity as our profession "will carefully examine the observed behaviour of all buildings to establish what types of structural design, building strengthening techniques and construction methods led to the most resilient behaviour.
    The causes of any failure, including those in above-design load conditions, will also be examined. From collegial debate amongst those with expertise, better methods to design new buildings and to seismically retrofit old buildings will emerge."
    That is why I wrote earlier that
    Quote Originally Posted by ralf-nz View Post
    The examination and evaluation of the events has not been finished yet. So more fact sheets, notes and reports will surely follow.
    Finally it will be up to the government - as the society's representatives to decide further action, if required. "The Government may also consider whether the design levels expressed in the Building Code represent the risk appetite of the New Zealand public and balance that against building and occupancy cost."


    I think these are the relevant questions: How much risk are we willing to take and able to pay? As a society and as an individual? Compulsorily or voluntarily?

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    Obviously, Christchurch is now considered as an earthquake prone area. Building designs and building codes should be likened to Japanese designs and codes.

    I don't want to blame the engineers in Christchurch but I can't imagine why they approve the WOF of those collapsed buildings. Didn't they have a mandatory WOF after the September quake?

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    Quote Originally Posted by ricktee View Post
    Obviously, Christchurch is now considered as an earthquake prone area.
    It has already been considered "prone" before these earthquakes! I pointed it out in several threads within this forum. Also the fact sheets is saying it: "In the 2008 Building Code, Wellington’s seismic hazard is approximately twice that of Christchurch and three times that of Auckland." The exact hazard factors "Z" per NZS 1170 are for Auckland 0.13, Christchurch 0.22 and Wellington 0.40. The factor of 0.13 is the lowest within this standard; the highest is 0.60 for Otira and Arthur's Pass.


    Quote Originally Posted by ricktee View Post
    Building designs and building codes should be likened to Japanese designs and codes.
    I havn't worked yet with the Japanese designs and codes yet. And as I wrote before our professional examination has not been finished yet (see fact sheet clause 6.). Could you please elaborate why you conclude already now that our design and codes should follow them. I would think it is a little premature as not all facts have been evaluated.



    Quote Originally Posted by ricktee View Post
    I don't want to blame the engineers in Christchurch but I can't imagine why they approve the WOF of those collapsed buildings. Didn't they have a mandatory WOF after the September quake?
    Thanks! WoFs are and have been issued and assessed on the basis of our current code. As far as I know WoFs became not mandatory. Another system was used - as it is now again. As I wrote here http://www.enz.org/forum/showthread.php?t=33181 there are "links to several IPENZ fact sheets on the Christchurch earthquake of February 2011 published and distributed respectively on 4th March.
    Overview: http://www.ipenz.org.nz/ipenz/forms/...s-Overview.pdf
    Building Safety Evaluation: http://www.ipenz.org.nz/ipenz/forms/...dingSafety.pdf
    Liquefaction: http://www.ipenz.org.nz/ipenz/forms/...quefaction.pdf"
    For further details on the assessment of buildings please read the fact sheet "Building Safety Evaluation".

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    Didn't they have a mandatory WOF after the September quake?
    I think there will be a lot of finger pointing and blaming of inspectors and engineers. People automatically assumed that when a building survived the Sept 4th quake and has passed all inspections, that it will be safe to handle another major earthquake. The Feb 22nd earthquake was nothing like the Sept one as expert analysis have found 2 times the gravity vertical down force in the meter readings (as mentioned in the articles posted by ralf). The public doesn't realise this and assume that 6.3 is less than 7.1 and therefore the buildings should not of had the same amount of damage.

    We all have to wait to see what the appointed earthquake commissioner report will say. Meanwhile, everything is just gossip.

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    Quote Originally Posted by ralf-nz View Post
    a simple fact sheet, "Why Buildings Respond Differently to Earthquakes".
    (It is currently not available on our IPENZ web site.)
    Now it is: http://www.ipenz.org.nz/ipenz/forms/...ifferently.pdf

    It is on the same site where the previous fact sheets are; http://www.ipenz.org.nz/ipenz/forms/pdfs/:
    Earthquake Fact Sheets
    * Christchurch Earthquake - an overview (99KB PDF)
    * Building Safety Evaluation (94 KB PDF)
    * Liquefaction (1 MB PDF)
    * Why buildings respond differently to earthquakes (152 KB PDF)

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    >I havn't worked yet with the Japanese designs and codes yet. And as I >wrote before
    >our professional examination has not been finished yet (see fact sheet >clause 6.).
    >Could you please elaborate why you conclude already now that our design >and codes
    >should follow them. I would think it is a little premature as not all facts >have been
    >evaluated.


    Japanese quake is measured at 9.0. Christchurch Quake is measured at 6.3. The big difference is Japan's tall buildings held up better than the buildings in Christchurch. That is the reason why I think NZ codes should liken Japanese building design and codes for tall buildings.

    >Thanks! WoFs are and have been issued and assessed on the basis of our >current code. As far as I know WoFs became not mandatory. Another >system was used - as it >is now again. As I wrote here >http://www.enz.org/forumshowthread.php?t=33181 there >are "links to several IPENZ fact sheets on the >Christchurch earthquake of >February 2011 published and distributed respectively on >4th March.

    If they used the current code to evaluate building safety, then that proves that they need to change the code.

    They used the same code before the Sept '10 and before Feb '11 quake.
    After seeing the damage of the Feb 22 quake, I would think engineers would be reluctant in approving a WOF using the same codes. Would you?
    Last edited by ricktee; 31st March 2011 at 03:08 AM.

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    Quote Originally Posted by Super_BQ View Post
    I think there will be a lot of finger pointing and blaming of inspectors and engineers. People automatically assumed that when a building survived the Sept 4th quake and has passed all inspections, that it will be safe to handle another major earthquake. The Feb 22nd earthquake was nothing like the Sept one as expert analysis have found 2 times the gravity vertical down force in the meter readings (as mentioned in the articles posted by ralf). The public doesn't realise this and assume that 6.3 is less than 7.1 and therefore the buildings should not of had the same amount of damage.

    We all have to wait to see what the appointed earthquake commissioner report will say. Meanwhile, everything is just gossip.
    Engineers pass inspections (using the current building code) with the knowledge that approving a WOF means the building should withstand any future major quake. That is the purpose of the inspections.

    How do you explain the damage? Either the engineer did not follow the building code or the engineer followed the code but the code needs to have higher standards.
    Last edited by ricktee; 31st March 2011 at 03:38 AM.

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    Quote Originally Posted by ricktee View Post
    Japanese quake is measured at 9.0. Christchurch Quake is measured at 6.3. The big difference is Japan's tall buildings held up better than the buildings in Christchurch. That is the reason why I think NZ codes should liken Japanese building design and codes for tall buildings.
    "The big difference" needs to take into account other differences: The location of the epicentre, and its depth, and the specific ground conditions.
    Also, did the design follow just the building code or has there been done voluntarily more?


    Quote Originally Posted by ricktee View Post
    If they used the current code to evaluate building safety, then that proves that they need to change the code.

    They used the same code before the Sept '10 and before Feb '11 quake.
    After seeing the damage of the Feb 22 quake, I would think engineers would be reluctant in approving a WOF using the same codes. Would you?
    I don't agree that it "proves" it. It is an indicator to rethink our risk assessment as a society.
    The technical evaluation is not finished yet. Currently no one can tell. How our findings will be evaluated again is also a question.
    As I wrote earlier: "Finally it will be up to the government - as the society's representatives to decide further action, if required. "The Government may also consider whether the design levels expressed in the Building Code represent the risk appetite of the New Zealand public and balance that against building and occupancy cost.""

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