Ronan Point

Fire-Induced Progressive ‘Damage’ or ‘Collapse’ ? More …

Posted by CJ Walsh

2012-05-02:  Last week, I attended joint meetings of CIB W14: ‘Fire Safety’ … and ISO Technical Committee 92: ‘Fire Safety’, Sub-Committee 3: ‘Fire Threat to People and the Environment’ & Sub-Committee 4: ‘Fire Safety Engineering’ … in Thessaloniki (Salonika), Greece.

The relationship between these two independent groups is symbiotic … ISO TC 92 develops International Fire Standards, while CIB W14 is the pre-normalization forum for discussion and action on a comprehensive approach to Fire Research and Innovation.

I should add, here, that CIB W14’s Aims & Objectives were substantially updated at our meeting in Thessaloniki … and I presented the CIB Research WG IV Reflection Document: ‘Structural Reliability & Fire-Induced Progressive Damage’ for discussion … which was lively, but far too short !

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While I was away, however, the following question was posed by Mr. Panagiotis Kotsovinos, on the Society of Fire Protection Engineers (SFPE-USA) Page of LinkedIn (http://www.linkedin.com/groups?gid=96627).

” I would like to please explain a bit more why the term ‘Fire-Induced Progressive Damage’ is preferred over ‘Fire-Induced Progressive Collapse’, and what is the confusion that exists widely as you say with the later definition ? “

Firstly, apologies for the late reply.  This was due to my absence from base … I am not continuously ‘plugged-in’ to the virtual environment while travelling.  But, I also wished to respond to this and other queries after some thought.  The issues raised are important.

Very briefly … it was NIST, in its 2005 Report, which introduced the term ‘Fire-Induced Progressive Collapse’ to a wide audience.  No definition, or elaboration, of this structural concept was provided in either the 2005 or 2008 Recommendations.  There is no confusion caused by ‘Fire-Induced’.

The reason I have been so quick to focus in on the distinction between ‘Damage’ and ‘Collapse’ is because we went through this whole debate, in Ireland … starting at the end of the 1980’s and continuing on through to the middle of 1990’s.  Because … in January 1987 … a Multi-Storey Apartment Block, called Raglan House, collapsed as a result of a gas explosion.  Two people were killed.  An examination of records at the time will reveal the same general confusion about technical terminology.  And … following the collapse, the Structural Engineering Profession was in disarray.

After a considerable amount of time witnessing, at close hand, these events … I formed the strong opinion that the proper connection of vertical and horizontal structural elements in a building was, and continues to be, a fundamental principle of all good structural engineering design … no matter what the height of the building.

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Colour photograph showing World Trade Center Building No. 7 in ruins, after 9-11 in New York City ... when Fire-Induced Progressive Damage led to Disproportionate Damage, and finally to total building failure ... a Collapse Level Event (CLE). Click to enlarge.
Colour photograph showing World Trade Center Building No. 7 in ruins, after 9-11 in New York City ... when Fire-Induced Progressive Damage led to Disproportionate Damage, and finally to total building failure ... a Collapse Level Event (CLE). Click to enlarge.

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Tackling the current confusion over technical terminology …

In 1987, Raglan House collapsed in Dublin.  In 2001, World Trade Center Building 7 collapsed in New York City.

In English … the word Collapse can have the following meanings, which are very broadly similar …

  • To fall down or cave in suddenly: the whole building collapsed ;
  • To fail completely ;
  • To break down or fall down from lack of strength ;
  • To fold (furniture, etc.) compactly or (of furniture, etc.) to be designed to fold compactly ;
  • The act or instance of suddenly falling down, caving in, or crumbling ;
  • A sudden failure or breakdown.

[from Latin, from collabi to fall in ruins, from labi to fall]

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Black and white image reproducing Figure 1-1 in NIST Report: 'Best Practices for Reducing the Potential for Progressive Collapse in Buildings' (NISTIR 7396, February 2007) ... showing a bird's eye view of the Disproportionate Damage at Ronan Point, in England, which was caused by a gas explosion in 1968. Click to enlarge.
Black and white image reproducing Figure 1-1 in NIST Report: 'Best Practices for Reducing the Potential for Progressive Collapse in Buildings' (NISTIR 7396, February 2007) ... showing a bird's eye view of the Disproportionate Damage at Ronan Point, in England, which was caused by a gas explosion in 1968. Click to enlarge.

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Please examine the photograph above.  Ronan Point (later demolished) was a 22 Storey Residential Tower Block in London, England.  In May 1968, this building suffered Disproportionate Damage as a result of a gas explosion.  As is clear from the photograph … it did not Collapse.

Disproportionate Damage

The failure of a building’s structural system:  (i) remote from the scene of an isolated overloading action;  and (ii) to an extent which is not in reasonable proportion to that action.

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Let me now return to the CIB Research WG IV Reflection Document: ‘Structural Reliability & Fire-Induced Progressive Damage’ … where I began by stating …

Fire-Induced Progressive Damage in Buildings is distinguished from Disproportionate Damage – a related but different structural concept – by the mode of damage initiation, not the final condition of building failure.  Until this phenomenon is properly understood, and unless it is impeded, or resisted, by building design … Fire-Induced Progressive Damage will result in Disproportionate Damage … and may lead to a Collapse Level Event (CLE), which is entirely unacceptable to the general population of any community or society.

… and, later in the document, provided this definition …

Fire-Induced Progressive Damage

The sequential growth and intensification of structural deformation and displacement, beyond fire engineering design parameters, and the eventual failure of elements of construction in a building – during a fire and the ‘cooling phase’ afterwards – which, if unchecked, will result in disproportionate damage, and may lead to total building collapse.

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Quickly Concluding …

‘Progressive Collapse’ is not the same as ‘Disproportionate Collapse’ … and while total building collapse may be the condition of final building failure, this will certainly not always be the case.  Therefore … ‘Damage’ is the more correct word to use than ‘Collapse’.

To go even further … it should not be necessary to have to use the word ‘total’ in the first sentence above.

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Reminder … Please Read the Reflection Document …

The purpose of the Reflection Document issued by CIB W14 Research Working Group IV is to examine the ‘hot form’ structural concept of Fire-Induced Progressive Damage, and to propose a critical update to fire engineering design practice.  It is also intended to encourage a wider discussion about some of fire engineering’s fundamental tenets, and the future direction of our profession in a rapidly evolving trans-disciplinary approach to the design, construction and operation of a Safe and Sustainable Built Environment.

Let me repeat again … and as I emphasized in Greece … ALL comments on the Reflection Document are most welcome !

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‘Fire-Induced Progressive Collapse’ – A Term Born To Confuse ?

Posted by CJ Walsh

2012-03-26:  Let me lay out the problem this way … recently, after further developing and refining the definition of the term …

‘ The sequential growth and intensification of structural deformation and displacement, beyond fire engineering design parameters, and the eventual failure of elements of construction in a building – during a fire and the ‘cooling phase’ afterwards – which, if unchecked, will result in disproportionate damage, and may lead to total building collapse ‘

… our attention, in CIB W14’s Research Working Group IV, automatically turned towards the term itself.  It didn’t sound right … it didn’t look right … and a lot of people in North America are still completely confused.

Was there anything we could do to clarify the situation ?

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BACKGROUND

The long delay in incorporating the Recommendations of the following 2 Reports …

  • NIST (National Institute of Standards and Technology).  September 2005.  Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report on the Collapse of the World Trade Center Towers.  NIST NCSTAR 1.  Gaithersburg, MD, USA.

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  • NIST (National Institute of Standards and Technology).  August 2008.  Federal Building and Fire Safety Investigation of the World Trade Center Disaster: Final Report on the Collapse of World Trade Center Building 7.  NIST NCSTAR 1A.  Gaithersburg, MD, USA.

… into building and fire codes/regulations, standards and administrative provisions at international, regional and national levels … can partly be explained by institutional inertia and the stubborn resistance of vested interests in the construction sector.  To be fair, however, although both NIST Reports made extensive reference to the term ‘Fire-Induced Progressive Collapse’ … the structural concept was not defined, or elaborated, in either document.  This was not really a task for NIST.

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WHO IS CONFUSED ?

Since the publication of the 2005 NIST Report above, there has been much confusion about the term ‘Fire-Induced Progressive Collapse’.

Refer, for example, to the Introduction – Paragraph 1.1 on Page 1 – from NIST Document: ‘Best Practices for Reducing the Potential for Progressive Collapse in Buildings’ (NISTIR 7396 – February 2007) … where a lot of people, who should know better, really screwed up … and got it so wrong …

” The term ‘progressive collapse’ has been used to describe the spread of an initial local failure in a manner analogous to a chain reaction that leads to partial or total collapse of a building.  The underlying characteristic of progressive collapse is that the final state of failure is disproportionately greater than the failure that initiated the collapse.  ASCE Standard 7-05 defines progressive collapse as ‘the spread of an initial local failure from element to element resulting, eventually, in the collapse of an entire structure or a disproportionately large part of it’ (ASCE 2005).  The disproportionality refers to the situation in which failure of one member causes a major collapse, with a magnitude disproportionate to the initial event. Thus, ‘progressive collapse’ is an incremental type of failure wherein the total damage is out of proportion to the initial cause.  In some countries, the term ‘disproportionate collapse’ is used to describe this type of failure.

Based on the above description, it is proposed that the professional community adopt the following definition, which is based largely on ASCE 7-05:

progressive collapse – the spread of local damage, from an initiating event, from element to element resulting, eventually, in the collapse of an entire structure or a disproportionately large part of it; also known as disproportionate collapse.

The concept of progressive collapse can be illustrated by the famous 1968 collapse of the Ronan Point apartment building (Fig. 1-1). “

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Colour photograph showing World Trade Center Building No. 7 in ruins after 9-11 in New York City ... when Fire-Induced Progressive Damage led to Disproportionate Damage, and finally to total building failure ... a Collapse Level Event (CLE). Click to enlarge.
Colour photograph showing World Trade Center Building No. 7 in ruins after 9-11 in New York City ... when Fire-Induced Progressive Damage led to Disproportionate Damage, and finally to total building failure ... a Collapse Level Event (CLE). Click to enlarge.

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WE NOW KNOW

Fire-Induced Progressive Damage in Buildings is distinguished from Disproportionate Damage – a related but different structural concept – by the mode of damage initiation, not the final condition of building failure.  Until this phenomenon is properly understood, and unless it is impeded, or resisted, by building design … Fire-Induced Progressive Damage will result in Disproportionate Damage … and may lead to a Collapse Level Event (CLE), which is entirely unacceptable to the general population of any community or society.

So … if unchecked, Fire-Induced Progressive Damage will lead to Disproportionate Damage.

BUT … while it may happen … which it did, when WTC Building 7 failed completely at approximately 17.21 hrs (local time) on the afternoon of 11 September 2001 in New York City … it is not necessarily always the case that Fire-Induced Progressive Damage and Disproportionate Damage will lead to Total Collapse.

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OUR SOLUTION

In order to avoid the wide confusion which the term ‘Fire-Induced Progressive Collapse’ is continuing to cause at international level … the preferred term is now Fire-Induced Progressive Damage.

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