2008 NIST WTC RECOMMENDATIONS

Upcoming CIB/NIST Workshop on Structural Reliability in Fire ?!?

2014-05-16:  Anybody with even the slightest interest in the Future Development of Fire Engineering Design, and Structural Fire Engineering in particular, should pay attention to the proceedings of an upcoming CIB/NIST Workshop, which will be held on 21-22 May 2014, at the NIST Campus in Maryland, USA …

CIB/NIST Fire Resistance/Resistant/Resisting/Resistive Structures Workshop

It is essential to read 3 White Papersproduced by three separate teams of experts, contracted by NIST, in advance of the Workshop … to get a ‘real’ flavour of how discussions may, or may not, develop next week.  All three papers are available to download from the NIST WebSite (and the links below).  I suggest that you get your hands on them … ASAP !

1.   Fire Behaviour of Steel Structures (March 2014).  20 Pages, 786 Kb.
2.   State-of-the-Art on Fire Resistance of Concrete Structures: Structure-Fire Model Validation (March 2014).  32 Pages, 1.26 Mb.
3.   Fire Resistance of Timber Structures (March 2014).  20 Pages, 998 Kb.

After reading these 3 NIST White Papers … I was not surprised by the large number of ‘unknowns’, or the enormous gaps in our ‘knowns’ …

Taken in whole and all together, however, the three documents are a public confirmation that today’s general practice of Fire Engineering is more akin to that of mid-19th Century Alchemy.  Blinkered practitioners are isolated from the building design process … because they have no understanding of that process, and have no means of effective communication with the many other design disciplines involved.  And minimal, i.e. ‘cost-effective'(?), compliance with the limited and inadequate fire safety objectives in current building codes/regulations is widely regarded as the one and only target for their efforts … a minor one compared to the fundamental, long-term target of realizing a Safe, Resilient and Sustainable Built Environment for All.  At the same time, frontline fire service personnel are forced to operate on shoestring budgets … and, when a fire emergency inevitably occurs, they are regarded as nothing more than an expendable resource.

!!  Structure … Does Not A Building Make  !!

Some comments on the 3 NIST White Papers …

A.  The Papers contain a number of important technical errors:

  • A similar Introduction in two of the Papers refers only to the 2005 NIST Report (NCSTAR 1) on the 9-11 Collapse of WTC Buildings 1 & 2 in New York City, which contained 30 Recommendations.  However, NIST published a later Report in 2008 (NCSTAR 1A) on the Collapse of WTC Building 7, which contained a further 13 Recommendations … 1 new, and 12 revised/updated from the earlier 2005 Report.
  • There is a reference in one of the Papers to a 1989 European Directive on Construction Products (89/106/EEC), and as later amended.  This Directive was repealed, in 2011, by Article 65 of the new European Union (EU) Regulation No.305/2011 on Construction Products.  Unlike a Directive, a Regulation is addressed directly to the EU Member States, and does not permit any flexibility with regard to national implementation. Annex I of Regulation 305/2011 sets out 7 Basic Requirements for Construction Works:

–  Mechanical resistance and stability ;
–  Safety in case of fire ;
–  Hygiene, health and the environment ;
–  Safety and accessibility in use ;
–  Protection against noise ;
–  Energy economy and heat retention ;
–  Sustainable use of natural resources.

Concerning fire safety in buildings … it is incorrect to state, or even suggest, that only the second Basic Requirement is relevant … a building must satisfy all of the Basic Requirements taken together, i.e. the 7 Basic Requirements are inter-dependent.

B.  Having carefully read the Papers … none of the expert teams appear to have paid any attention to any of the NIST Recommendations, in either the 2005 or the 2008 Reports !   Note well that two separate series of posts on both sets of NIST Recommendations have been carried here on this Technical Blog.

C.  If we have learned anything from the WTC 9-11 Building Collapses, it is that the Fire Engineer must be able to communicate effectively with other mainstream building design disciplines … especially ‘ambient’ structural engineers who speak the language of Structural Reliability, Limit State Design and Serviceability Limit States.  The Fire Engineer must also become an active participant in the creative, trans-disciplinary process of design.  These issues have not been seriously considered in any of the Papers.

D.  All of the Papers lack a common and precise starting point … relevant structural fire engineering concepts are either not defined or badly defined … and the ‘dynamic, complex architectural interaction between a building’s structure and fabric under conditions of fire’ requires immediate and urgent investigation …

Structural Reliability

The ability of a structural system to fulfil its design purpose, for a specified time,
under the actual environmental conditions encountered in a building.

Structural Fire Engineering

Those aspects of fire engineering concerned with structural design for fire …
and the dynamic, complex architectural interaction between a building’s structure and
fabric, i.e. non-structure … under conditions of fire and its immediate aftermath,
including but not confined to the ‘cooling phase’.

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.

[ *fire serviceability limit states ]

.

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.

[ Fire-Induced Progressive Damage and Disproportionate Damage are fundamental concepts in the Fire Engineering Design of All Buildings ! ]

.

E.  It is not acknowledged in any of the Papers that the Fire Safety Objectives in Current Building Codes/Regulations are, of necessity, limited in scope … and entirely inadequate in the context of Annex I in EU Regulation 305/2011, and the long-term goal of realizing a Safe, Resilient and Sustainable Built Environment for All.  Refer to the updated Scope, Aims & Objectives of CIB Working Commission 14: ‘Fire Safety’.

F.  Once and for all … use of the term Fire Resistance (and any number of variations thereof, e.g. resistant, resisting, resistive, etc.) in connection with any aspect of structural performance in fire … is ridiculous !   It is roughly comparable to use of the term Fire Proof during the first half of the 20th Century.

G.  Finally, for now … the current unwise focus on Crude Pass/Fail Results from the ‘standard fire’ testing of single loadbearing structural elements must evolve … must be transformed into the more detailed and precise measurement of all aspects of ‘real’ structural system performance over the full duration of a ‘design’ fire (including the cooling phase afterwards) … using a much wider range of performance monitoring equipment, e.g. short wave infra-red thermography.

.

It is no longer acceptable for Fire Engineering to exist in an isolated Twilight Zone … completely removed from the everyday realities of Mainstream Building & Construction.

.

.

END

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

‘Sustainable Fire Engineering for All’ – SDI’s Professional Service

2012-12-14 & 2012-12-30:  Further to this distressing incident … which exposed a profound lack of awareness, care and competence within the general fire safety industrial sector …

Recent Fatal Fire at a Disabled Workshop in SW Germany

… this is how we would like to help you … whether you are an individual, or an organization … whether you are located in Ireland, Italy or Turkey … some other part of Europe, the Arab Gulf Region, India, Japan, China … or wherever !

And … we can, if requested or necessary, work in collaboration with local partners in those different geographical regions.

– FireOx International is the Fire Engineering Division of Sustainable Design International Ltd. (SDI) –

.

Colour photograph showing the 2 World Trade Center Towers, in New York City, immediately after the second plane impact. The mechanical damage arising from such a plane impact had been considered in the Initial Building Design Process; incredibly, any type of Fire Incident had not ! In the case of both towers and within a short period of time, Fire-Induced Progressive Damage resulted in Disproportionate Damage, and eventual Total Building Collapse. The horror and carnage at the World Trade Center Complex, and the extensive collateral damage to everywhere south of Canal Street, caused enormous long-term damage to the economy of Manhattan ... and had a very significant adverse impact on Global Financial Markets. Click to enlarge.

Colour photograph showing the 2 World Trade Center Towers, in New York City, immediately after the second plane impact. The mechanical damage arising from such a plane impact had been considered in the Initial Building Design Process; incredibly, any type of Fire Incident had not ! In the case of both towers and within a short period of time, Fire-Induced Progressive Damage resulted in Disproportionate Damage, and eventual Total Building Collapse. The horror and carnage at the World Trade Center Complex also caused enormous long-term damage to the economy of Manhattan … and had a very significant adverse impact on Global Financial Markets. Click to enlarge.

.

Introduction

Fundamentally, the 9-11 World Trade Center Incident in New York (2001) was an Extreme ‘Real’ Fire Event.  It presented the International Fire Engineering Community with a catastrophic failure in conventional practices and procedures related to:

  • Fire Engineering, Structural Engineering, and Architectural Design ;
  • Human Building Management Systems ;
  • Emergency Response by Firefighters, Rescue Teams, and Medical Personnel ;
  • National and Local Organizations Having Authority or Jurisdiction (AHJ’s) ;

… and with the serious problem of entirely inadequate Fire Safety Objectives in the building legislation, model codes and design standards of the most economically advanced countries in the world.

Those people who understand the building design process, and have experience as construction practitioners, have long realised that the lessons from 9-11 must be applied across the full spectrum of building types … not just to tall buildings.  Right up to the present day, unfortunately, many people in the International Fire Engineering Community are either unwilling, or unable, to do this.

Furthermore … Fire Engineering, Architectural Design and Structural Engineering must, of urgent necessity, be seamlessly conjoined … with the aim of removing misunderstandings and the wide gaps in client service delivery between the different disciplines.

In 2002, a series of Long-Term 9-11 Survivor Health Studies commenced in the USA … and in 2005 and 2008, the U.S. National Institute of Standards and Technology (NIST) issued a series of Post 9-11 Critical Recommendations concerning the design, construction, management and operation of buildings.

At FireOx International … we have fully integrated this essential design guidance into our frontline fire engineering and architectural practice … we have developed unique and practical solutions for worldwide application, some of which appear in International Standard ISO 21542: ‘Building Construction – Accessibility & Usability of the Built Environment’, published in December 2011.

.

Colour photograph showing an armed assailant during the November 2008 'Hive-Attack' on Mumbai ... an extraordinarily violent, co-ordinated assault on the largest (and wealthiest) city in India, which involved the strategic targeting of built environment Places of Public Resort, Iconic Buildings, High-Rise Buildings, Buildings having a Critical Function, Transport Infrastructure and Service Utilities ... with the aim of causing widespread terror among the general population, including tourists, and disruption to the city’s important economic environment. Click to enlarge.

Colour photograph showing an armed assailant during the November 2008 ‘Hive-Attack’ on Mumbai … an extraordinarily violent, co-ordinated assault on the largest (and wealthiest) city in India, which involved the strategic targeting of built environment Places of Public Resort, Iconic Buildings, High-Rise Buildings, Buildings having a Critical Function, Transport Infrastructure and Service Utilities … with the aim of causing widespread terror among the general population, including tourists, and disruption to the city’s important economic environment. Click to enlarge.

.

FireOx International’s Commitment to You

As a necessary response to the New 21st Century Paradigm of Real Extreme Event in a Built Environment which is becoming more and more complex … is subject to climate change and severe weather events … and is vulnerable to malign and malevolent disruption –

WE are committed to … the implementation of a Sustainable Human Environment which is Fire Safe and Secure for All, meaning that an ‘appropriate project-specific fire safety level’ is our fire engineering objective, with ‘human health protection’ targeted as a priority … through the use of innovative, reliability-based and person-centred sustainable design practices and procedures.

.

What is an ‘Appropriate Fire Safety Level’ in Your Building or Facility ?

It is rarely, if ever, explained to clients/client organizations that the Minimal Fire Safety Objectives in building legislation are focused solely on protecting the ‘interests’ of society, not those of the individual …  are, quite often, inadequate and/or flawed … and are, always, revised only after the latest tragedy !

To properly protect Your Interests as a client/client organization … we strongly advise that the Appropriate Level of Fire Safety in Your Building or Facility should exceed the minimal level of safety required by building legislation.  We would also caution that, in many jurisdictions (e.g. India), compliance with national building legislation is voluntary.

Which raises the issues of whether or not you will actually get what you pay for, and whether or not the Fire Protection Measures in Your Building or Facility are reliable (in other words, will they perform as intended at the time of a ‘real’ fire, which may occur at any time in a building’s long life cycle) !?!   Competent Technical Control of Design and Construction, independent of the design and construction organization(s), is essential.

You should carefully consider the following spectrum of issues which may be directly relevant to Your Project.  Following a process of consultation with you, we then develop Project-Specific Fire Engineering Design Objectives … bearing in mind that you must also comply with safety at work, anti-discrimination, and environmental legislation, etc … maintain business continuity, etc … be energy efficient, etc … and be socially responsible, etc …

–     Protection of the Health of All Building Users … including People with Activity Limitations (2001 WHO ICF), Visitors to the building or facility who may be unfamiliar with its layout, and Contractors or Product/Service Suppliers temporarily engaged in work or business transactions on site ;

–     Protection of Property from Loss or Damage … including the Building or Facility, its Contents, and Adjoining or Adjacent Properties ;

–     Safety of Firefighters, Rescue Teams and Other Emergency Response Personnel ;

–     Ease and Reasonable Cost of ‘Effective’ Reconstruction, Refurbishment or Repair Works after a Fire ;

–     Sustainability of the Human Environment (social – built – virtual – economic) … including Fitness for Intended Use and Life Cycle Costing of fire engineering related products and systems, etc … fixed, installed or otherwise incorporated in the building or facility ;

–     Protection of the Natural Environment from Harm, i.e. Adverse or Damaging Impacts.

.

FireOx International – Our Fire Engineering Services

  • WE  will advise you on Fire Safety Policy, Fire Safety Strategy Development, Fire Safety Implementation … and, whether you are within or from outside the European Union, on CE Marking of Fire Protection Related Construction Products

  • WE  understand the process of Design, particularly the new language of Sustainable Design … and we will produce Creative Fire Engineering Solutions for Your Project

  • WE  are thoroughly familiar with the intricacies of Building Sites … and we will verify and/or validate Design Compliance during construction, and at project completion … and, if requested or necessary, as a completely Independent Technical Controller ; 

  • WE  communicate easily and effectively with other Professional Design Disciplines, including architects and structural engineers … and we will act as fully participating members of Your Project Design & Construction Team … and, if requested or necessary, as the Design Professional in Responsible Charge **

  • WE  practice in accordance with a comprehensive Professional Code of Ethics

.

Sustainable Fire Engineering Solutions ?

  1. Are adapted to Local Geography, Climate/Climate Change, Social Need, Culture, Economy … and Severe Events (e.g. earthquakes, flooding) ;
  2. Are ‘Reliability-Based’, i.e. that design process based on practical experience, competence and an examination of real extreme events, e.g. 2001 WTC 9-11 & 2008 Mumbai Attacks, and 2011 Fukushima Nuclear Incident … rather than theory alone ;
  3. Are ‘Person-Centred’, i.e. that design process which places ‘real’ people at the centre of creative endeavours and gives due consideration to their responsible needs, and their health, safety, welfare and security in the Human Environment.

.

FireOx International’s Contact Information

E-Mail:  cjwalsh@sustainable-design.ie

International Phone:  +353 1 8386078   /   National Phone:  (01) 8386078

.

.

Important Note:  This Post should be read in conjunction with an earlier Post …

Sustainable Design International Ltd. – Our Practice Philosophy

It is there, not here, that we define Sustainable Human & Social Development … and describe how our Practice is responding to this open, intricate, dynamic, and still evolving concept.  The resulting transformation in how frontline services are provided to our Clients/Client Organizations ensures a much more comfortable ‘fit’ to their needs … and a greater level of protection, safety and security for society !

.

[ ** 2005 NIST(USA) Final Report on 9-11 World Trade Center 1 & 2 Tower Collapses

– Footnote 49 –

… the Design Professional in Responsible Chargeusually the lead architect – ensures that the (Design) Team Members use consistent design data and assumptions, co-ordinates overlapping specifications, and serves as the liaison with enforcement and review officials, and with the client or client organization. ]

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

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

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 ?

.

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.

and

  • 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.

.

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). “

.

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.

.

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.

.

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.

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

2012 Review of Part B & TGD B – Irish Building Regulations

2012-03-02:  Please bear with me while I update you at the start of this post … rather than at the end, which would be more usual here … and logical.

[ In Ireland … a related problem, which continues to fester and cause a great nuisance in an everyday work environment … concerns the lack of proper, i.e. formal, recognition of electronic communications, and information in an electronic format, by public and private organizations … in spite of the following very clear legal text …

2000 Electronic Commerce Act (No. 27 of 2000)

Section 9 – Electronic Form not to Affect Legal Validity or Enforceability

Information (including information incorporated by reference) shall not be denied legal effect, validity or enforceability solely on the grounds that it is wholly or partly in electronic form, whether as an electronic communication or otherwise. ]

.

Yesterday afternoon (1 March 2012), we received the following e-mail communication from the Department of Environment, Community & Local Government (DECLG)

Folks,

Could you please send me your submissions in either Microsoft Word or Excel as it it easier to copy and paste into the format that is required , it is proving rather difficult to copy from a PDF document.

Thank You

Claire Darragh, Architecture / Building Standards, DECLG.

.

I immediately replied …

Dear Claire,

Further to your informal e-mail message, which we received just a short while ago …

Please note that this is not an acknowledgement that the FireOx International Submission was received by the Department … and we certainly do not wish that you copy and paste anything relating to its contents anywhere else.

IF this is a Proper Public Consultation Process … you must adapt internal DECLG systems to suit the Submissions !   We will be communicating with the Minister’s Office concerning this issue.

Once again, I would ask you to properly acknowledge receipt of our Submission, dated 2012-02-14.

.

In connection with the original FireOx International Submission … I would also like to take this opportunity to advise you that:

  • Due to an error in ISO (International Standards Organization) … the publication of ISO 21542: ‘Building Construction – Accessibility and Usability of the Built Environment’, on 12 December 2011, was not notified to people directly involved in its development and drafting, or to the participating national standards organizations ; 

and

  • 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.

.

I have amended our Submission accordingly.

Kind regards.

C. J. Walsh, FireOx International – Ireland, Italy & Turkey.

.

.

2012-02-18:  The following is the text of  FireOx International’s Submission, dated 14 February 2012, to the Department of the Environment, Community & Local Government (DECLG) in Dublin … concerning the current review of the Irish Building Regulations Part B & TGD B … including, for good measure, some initial and very pertinent comments on the Irish Building Control Regulations.

None of these comments will come as any surprise to regular visitors here.

It should also be noted that the same comments are just as relevant in the case of the British (England & Wales) Building Regulations, Part B and Approved Document (AD) B !

.

Ms. Claire Darragh, Architecture & Building Standards Section, DECLG.

Dear Claire,

Thank you for this opportunity to advise the Department on some urgent and necessary improvements to Part B: ‘Fire Safety’ of the 2nd Schedule to the Building Regulations in Ireland … and its supporting Technical Guidance Document (TGD) B.

1.  Some Initial Comments

  • The continuing debacle of the Priory Hall Apartment Complex, in Donaghmede Dublin 13, is just the tip of a very large iceberg in Ireland.  Yet, when we now hear that there will be a ‘risk-based’ approach to Septic Tank Inspections, instead of an approach which involves inspecting all septic tanks … independently, competently and thoroughly … it is clear that the Minister, and senior officials in his Department, have failed to learn any lessons from ‘Priory Hall’.

What was happening on Irish construction sites during the Celtic Tiger boom years … has been happening for twenty years all over the country … more precisely, since the introduction of legal national building regulations in 1991, with NO effective building control … and, before that again, in those parts of the country outside of the major urban areas having legal building bye-laws AND effective building control, i.e. mandatory inspections by competent local authority personnel at the foundation level and drainage level of ALL projects … and, depending on the type of project, occasional or frequent inspections above ground level.

Over the years, local authority officials who carried out building bye-law inspections accumulated a considerable wealth of knowledge and understanding about local construction conditions and practices.  This valuable resource, widely used by the construction industry at the time, has now been diluted and discarded.

PLEASE LEARN THE LESSONS FROM ‘PRIORY HALL’ !!

In connection with ALL Applications for Fire Safety Certificates (Part B) and Disability Access Certificates (Part M) … competent and thorough inspections must, from now on, be carried out by local authority personnel to confirm proper implementation of Part B & M, respectively, of the 2nd Schedule to the Building Regulations.

Furthermore … while on site, local authority personnel must not be discouraged, or restricted, from dealing with any other Parts of the 2nd Schedule to the Building Regulations.  Under the present dysfunctional system, important horizontal linkages between different Parts of the 2nd Schedule are being widely disregarded and ignored, e.g. between Parts B & D, between Parts B & M, and between Parts B & A … or between Parts M & D, etc., etc !

  • European Union (EU) Council Directive 89/106/EEC has been repealed … and, instead, we now have EU Regulation No 305/2011 of the European Parliament and of the Council, of 9 March 2011, laying down Harmonised Conditions for the Marketing of Construction Products.

Unlike the earlier EU Directive … this Regulation, applicable in all EU Member States, is binding in its entirety.

And although Annex I of EU Regulation 305/2011 will enter into force from 1 July 2013 … the Department should now prepare for, and slowly begin the process of, incorporating all of the Annex I Basic Requirements for Construction Works into the 2nd Schedule of the Irish Building Regulations.

SEE BELOW …

.

2.  Firefighter Safety

Fully consistent with Basic Requirement for Construction Works 2(e), in Annex I of EU Regulation No. 305/2011 … Revise Part B Requirement 5 to read as follows …

B5  Firefighter Safety, and Access and Facilities for the Fire Service

A building shall be so designed and constructed that the safety of firefighters is adequately considered and, in the event of an outbreak of fire, that there is adequate provision for access for fire appliances and such other facilities as may be required to assist the fire service in the protection of life and property.

Two examples of issues which should be highlighted in a relevant revision/addition to TGD B’s Guidance Text:

  • The incorporation, in building designs, of alternative safe means of approach towards the scene of a fire by firefighters ;
  • The provision of wider staircases in buildings in order to facilitate the recovery of an injured/impaired firefighter during the course of firefighting operations.

.

3.  Protection of Vulnerable Building Users from Fire

The European Union ratified the United Nations Convention on the Rights of Persons with Disabilities (CRPD) on 23 December 2010.  Ireland has not yet ratified the Convention.

However … fully consistent with Ireland’s legal obligation, under Article 4.3 of the Treaty on European Union (TEU), to co-operate fully with EU Institutions in their implementation of this UN Convention … Revise Part B Requirement 1 to read as follows …

B1  Means of Evacuation in the Event of an Outbreak of Fire

A building shall be so designed and constructed that the protection of vulnerable building users is adequately considered and, in the event of an outbreak of fire, that there are adequate and accessible means of evacuation from the building to a place of safety remote from the building, capable of being safely and effectively used.

[ Use of the word ‘escape’, in the context of emergencies, should be strongly discouraged at all times. ]

Concerning TGD B’s Guidance Text … reference to ISO 21542: ‘Building Construction – Accessibility and Usability of the Built Environment’ will be more than sufficient.

.

Specifically relating to Adequate Protection of Vulnerable Building Users from Fire

NOTE WELL THAT BS 9999 (AND BS 5588:PART EIGHT)  IS (ARE)  ENTIRELY UNFIT FOR PURPOSE !!

Please carefully examine the attached PDF File – My Note for the National Standards Authority of Ireland:  ‘BS 9999:2008 & BS 8300:2009 – Impacts on Accessibility Design in Ireland & Implications for ISO Accessibility & Fire Safety Standards’ , dated June 2009.

.

4.  TGD B’s Appendix A – Performance of Materials and Structures

2 Important Notes should be added to Paragraph A21 – Structural Fire Design

  • In complying with Part B, reference should also be made to Part A of the 2nd Schedule of the Building Regulations, particularly Requirement A3 – Disproportionate Collapse ;

and

  • In order to show that a Fire Protection Material/Product/System for Structural Elements properly complies with Part D … it is also necessary, besides showing that it has been adequately fire tested, to show that the material/product/system is durable over a specified, reasonably long life cycle … and that it can adequately resist mechanical damage during construction of the building and, in the event of an outbreak of fire, during the course of that fire incident.

.

Specifically relating to Steel Structural Performance in Fire

You should be aware that Table A1 and Table A2 are only appropriate for use by designers in the case of single, isolated steel structural elements.

In steel structural frame systems, no consideration is given in the Tables to adequate fire protection of connections … or limiting the thermal expansion (and other types of distortion) in fire of steel structural elements … in order to reduce the adverse effects of one steel element’s behaviour on the rest of the frame and/or adjoining non-loadbearing fire resisting elements of construction.

In the case of steel structural frame systems, therefore, the minimum fire protection to be afforded to ALL steel structural elements, including connections, should be 2 Hours.  Connections should also be designed and constructed to be sufficiently robust during the course of a fire incident.  This one small revision will contribute greatly towards preventing Fire-Induced Progressive Damage in buildings … a related, but different, structural concept to Disproportionate Damage …

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.

Fire-Induced Progressive Damage

The sequential growth and intensification of structural distortion 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.

.

With regard to the above … please carefully examine these 2 Series of Posts on FireOx International’s Technical Blog ( www.cjwalsh.ie ), beginning on the dates indicated …

  • 2011-10-25:  NIST’s (2005) Recommendations on the 9-11 WTC Building Collapses … GROUP 1. Increased Structural Integrity – Recommendations 1, 2 & 3 (out of 30) ;

and

  • 2012-01-18:  Progressive Collapse of WTC 7 – 2008 NIST Recommendations – Part 1 of 2 … GROUP 1. Increased Structural Integrity – Recommendation A … and GROUP 2. Enhanced Fire Endurance of Structures – Recommendations B, C, D & E (out of 13).

.

5.  TGD B’s Appendix F – Reference Standards

Add this Important New Standard …

  • ISO 21542 : 2011     Building Construction – Accessibility and Usability of the Built Environment

.

6.  TGD B’s Appendix G – Reference Publications

Add these Two Important Publications …

  • 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.

and

  • 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.

.

Should you wish to receive further information on any of my comments … please consult FireOx International’s Technical Blog at  www.cjwalsh.ie … or contact me directly.

Please acknowledge receipt of this e-mail communication.

.

Kind regards.

C. J. Walsh, FireOx International – Ireland, Italy & Turkey.

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Progressive Collapse of WTC 7 – 2008 NIST Recommendations – Part 2 of 2

1st Series of Posts on the 2005 NIST WTC 1 & 2 Collapse Recommendations … which began towards the end of 2011 …

2011-10-25:  NIST’s Recommendations on the 9-11 WTC Building Collapses … GROUP 1. Increased Structural Integrity – Recommendations 1, 2 & 3 (out of 30)

Previous Post in this New Series …

2012-01-18:  Progressive Collapse of WTC 7 – 2008 NIST Recommendations – Part 1 of 2 … GROUP 1. Increased Structural Integrity – Recommendation A … and GROUP 2. Enhanced Fire Endurance of Structures – Recommendations B, C, D & E (out of 13)

.

2012-01-22:  SOME PRELIMINARY COMMENTS …

  1.     Keeping my ear closely to the ground … I hear you wondering: “So … how did the fires actually start in World Trade Center Building 7 ?”

Extracts from the Executive Summary (pages xxxi – xxxv) – 2008 NIST NCSTAR 1A …

[ Refer back to the WTC 1 & 2 Collapse Damage Plan in the previous post.]

The fires in WTC Building 7 were ignited as a result of the impact of debris from the collapse of WTC Tower 1, which was approximately 110 metres to the south.  The debris also caused some structural damage to the south-west perimeter of WTC 7.  The fires were ignited on at least 10 floors;  however, only the fires on Floors 7 to 9 and 11 to 13 grew and lasted until the time of building collapse.  These uncontrolled fires had characteristics similar to those that have occurred previously in tall buildings.  Their growth and spread were consistent with ordinary building content fires.  Had a water supply for the automatic sprinkler system been available and had the sprinkler system operated as designed, it is likely that the fires in WTC 7 would have been controlled, and the collapse prevented.  However, the collapse of WTC 7 highlights the importance of designing fire resisting structures for situations where sprinklers are not present, do not function (e.g. due to disconnected or impaired water supply), or are overwhelmed.

and …

There were no serious injuries or fatalities, because the estimated 4,000 occupants of WTC 7 reacted to the airplane impacts on the two WTC Towers and began evacuating before there was significant damage to WTC 7.  The occupants were able to use both the elevators and the stairs, which were as yet not damaged, obstructed, or smoke-filled.  Evacuation of the building took just over an hour.  The potential for injuries to people leaving the building was mitigated by building management personnel holding the occupants in the lobby until they identified an exit path that was safe from the debris falling from WTC Tower 1.  The decisions not to continue evaluating the building and not to fight the fires were made hours before the building collapsed, so no emergency responders were in or near the building when the collapse occurred.

and …

The design of WTC 7 was generally consistent with the New York City Building Code of 1968 (NYCBC), with which, by policy, it was to comply.  The installed thickness of the thermal insulation on the floor beams was below that required for unsprinklered or sprinklered buildings, but it is unlikely that the collapse of WTC 7 could have been prevented even if the thickness had been consistent with building code requirements.  The stairwells were narrower than those required by the NYCBC, but, combined with the elevators, were adequate for a timely evacuation on 11 September 2001, since the number of building occupants was only about half that expected during normal business hours.

The collapse of WTC 7 could not have been prevented without controlling the fires before most of the combustible building contents were consumed.  There were two sources of water (gravity-fed overhead tanks and the city water main) for the standpipe and automatic sprinkler systems serving Floor 21 and above, and some of the early fires on those upper floors might have actually been controlled in this manner.  However, consistent with the NYCBC, both the primary and back-up source of water for the sprinkler system in the lower 20 floors of WTC 7 was the city water main.  Since the collapses of the WTC Towers had damaged the water main, there was no water available (such as the gravity-fed overhead tanks that supplied water to Floor 21 and above) to control those fires that eventually led to the building collapse.

Link to read and/or download a copy of the 2008 NIST NCSTAR 1A Report … www.fireox-international.eu/fire/structdesfire.htm 

.

  2.     On a separate subject and quite by chance … a few days ago, I was invited to review a technical paper for a reputable international fire engineering journal (which shall remain nameless).  The paper was discussing a certain aspect of steel column critical temperatures.  After three days, I replied to the journal’s editor as follows …

2012-01-18.

Most regrettably, I must decline your invitation to review Paper XYZ.

The ‘critical temperature’ approach to the fire engineering design of steel-framed structures is deeply flawed … and obsolete.

C. J. Walsh, FireOx International – Ireland, Italy & Turkey.

The ‘critical temperature’ approach is antiquated … and this nonsense has got to stop !   NOW … would be the best time !!

.

  3.     In the last post, I wrote …

Structural Fire Engineering is concerned with those aspects of fire engineering which relate to structural design for fire, and the complex architectural interaction between a building’s structure and fabric, i.e. non-structure, under conditions of fire and its immediate aftermath.

Indeed !   But, more needs to be added …

I hope it is becoming clearer now that Structural Fire Engineering is not just ambient structural engineering with a few extra ‘bells and whistles’ grafted on … in token consideration of what could happen in fire conditions, i.e. at high temperatures.

[ If, in some jurisdictions, there are no legal requirements to add even those ‘bells and whistles’ … then, typically, even they will be omitted ! ]

This brings me right back to the typical education of Civil/Structural Engineers;  because:  (i) they exit the educational system with little understanding of anything beyond ‘structure’ … in other words, a ‘real’ building, which also comprises ‘fabric’, i.e. non-structure, is a mystery to them;  and (ii) they have difficulty reading architectural drawings … which is why a walk-through inspection of a building, as it is nearing completion, is much preferred over a detailed discussion about drawings at the most appropriate stage, which is well before construction commences … when faults can be readily identified and easily rectified !

In ambient conditions … the architectural interaction between a building’s structure and fabric is difficult, not being entirely static.  Before the surface finishes have been applied, it is immediately obvious when this interaction has been properly ‘designed’, and looks neat and tidy … or, on the vast majority of construction sites, when this interaction is a ‘traffic accident’, and the results are desperately ugly … and you know that they can’t apply the surface finishes quickly enough in order to hide everything from view !

In fire conditions … this architectural interaction between building fabric and structure is complex, certainly very dynamic … and fluid !

It would be more appropriate to think of Structural Fire Engineering as ‘Design in the Hot Form’ … which is a completely different mindset.

It is essential, therefore, that Fire Engineers understand ‘real’ buildings … most importantly, the ‘design’ of real buildings … and, that they know which end is ‘up’ on a real construction site !!   See NIST WTC 7 Recommendation L below.

.

  4.     Since the collapse of WTC Building 7 on 11 September 2001, it has been generally assumed that Fire-Induced Progressive Collapse is a large-scale, macro-phenomenon only.  But, believe it or not, this phenomenon has also been observed at micro-level in small building types.

In fact … Progressive Collapse was already receiving sporadic attention, in Ireland, as far back as the 1980’s …

  • As organizer of the 1987 Dublin International Fire Conference: ‘Fire, Access & Safety in Residential Buildings’, I requested that the following Paper be presented … ‘Design against Progressive Collapse in Fire’ … by Dr. Willie Crowe, who was Head of Construction Technology, in the old Institute for Industrial Research & Standards (IIRS) in Ireland.  He later became Manager of the Irish Agrément Board (IAB).  Those were the days … and Willie really knew his stuff !

Mr. Noel C. Manning, of FireBar in Ireland (www.firebar.ie),  and I both contributed to the development of his Paper.

And now is as good a time as any to give full credit to Noel Manning for his innovative approach to Structural Fire Engineering back in the early 1980’s.  He’s a ‘hard man’ … a term that we use for some special people in Ireland !

Link to the Dublin International Fire Conferences, and a copy of this Paper … www.fireox-international.eu/fire/dublinfire.htm 

  • For approximately 12 years from the mid-1980’s, I was a Member of the National Masonry Panel – the National Standards Authority of Ireland (NSAI) Masonry Standards Advisory Committee.  A small, but substantial, text on Fire-Induced Progressive Collapse in Buildings was included, by me, in the following standard … Irish Standard 325: Code of Practice for Use in Masonry – Part 2: Masonry Construction (1995).  Appendix A – Determination of Movement in Masonry.  A.3 – Thermal Movement.  Once again … those were the days … when I was the only architect in a sea of engineers !!   Not a pretty experience.

.

  5.     What next ?   A final draft of the International CIB W14 Research WG IV Reflection Document on Fire-Induced Progressive Collapse will be completed in time for circulation to all CIB W14 members before the end of March 2012 … well in time for the next CIB W14 Meetings in Greece, near the end of April 2012.

.

2008 NIST WTC 7 RECOMMENDATIONS  (Final Report NCSTAR 1A)

5.1.3     GROUP 3.  New Methods for Fire Resisting Design of Structures

The procedures and practices used in the fire resisting design of structures should be enhanced by requiring an objective that uncontrolled fires result in burnout without partial or global (total) collapse.  Performance-based methods are an alternative to prescriptive design methods.  This effort should include the development and evaluation of new fire resisting coating materials and technologies, and evaluation of the fire performance of conventional and high-performance structural materials.

NIST WTC 7 Recommendation F  (NCSTAR 1  Recommendation 8).

NIST recommends that the fire resistance of structures be enhanced by requiring a performance objective that uncontrolled building fires result in burnout without partial or global (total) collapse.  Such a provision should recognize that sprinklers could be compromised, non-operational, or non-existent.  Current methods for determining the fire resistance of structural assemblies do not explicitly specify a performance objective.  The rating resulting from current test methods indicates that the assembly (component or sub-system) continued to support its superimposed load (simulating a maximum load condition) during the test exposure without collapse.  Model Building Codes:  This Recommendation should be included in the national model building codes as an objective, and adopted as an integral pert of the fire resistance design for structures.  The issue of non-operational sprinklers could be addressed using the existing concept of Design Scenario 8 of NFPA 5000, where such compromise is assumed and the result is required to be acceptable to the Authority Having Jurisdiction (AHJ).  Affected Standards:  ASCE-7, AISC Specifications, ACI 318, and ASCE/SFPE 29.

Relevance to WTC 7:  Large, uncontrolled fires led to failure of a critical column and consequently the complete collapse of WTC 7.  In the region of the collapse initiation (i.e. on the east side of Floor 13), the fire had consumed virtually all of the combustible building contents, yet collapse was not prevented.

.

NIST WTC 7 Recommendation G  (NCSTAR 1  Recommendation 9).

NIST recommends the development of:  (1) performance-based standards and code provisions, as an alternative to current prescriptive design methods, to enable the design and retrofit of structures to resist real building fire conditions, including their ability to achieve the performance objective of burnout without structural or local fire collapse;  and (2) the tools, guidelines, and test methods necessary to evaluate the fire performance of the structure as a whole system.  Standards development organizations, including the American Institute of Steel Construction, have already begun developing performance-based provisions to consider the effects of fire in structural design.

a.     Standard methodology, supported by performance criteria, analytical design tools, and practical design guidance;  related building standards and codes for fire resistance design and retrofit of structures, working through the consensus process for nationwide adoption;  comprehensive design rules and guidelines;  methodology for evaluating thermo-structural performance of structures;  and computational models and analysis procedures for use in routine design practice.

b.     Standard methodology for specifying multi-compartment, multi-floor fire scenarios for use in the design and analysis of structures to resist fires, accounting for building-specific conditions such as geometry, compartmentation, fuel load (e.g. building contents and any flammable fuels such as oil and gas), fire spread, and ventilation;  and methodology for rating the fire resistance of structural systems and barriers under realistic design-basis fire scenarios.

c.     Publicly available computational software to predict the effects of fires in buildings – developed, validated, and maintained through a national effort – for use in the design of fire protection systems and the analysis of building response to fires.  Improvements should include the fire behaviour and contribution of real combustibles;  the performance of openings, including door openings and window breakage, that controls the amount of oxygen available to support the growth and spread of fires and whether the fire is fuel-controlled or ventilation-controlled;  the floor-to-floor flame spread;  the temperature rise in both insulated and un-insulated structural members and fire barriers;  and the structural response of components, sub-systems, and the total building system due to the fire.

d.     Temperature-dependent thermal and mechanical property data for conventional and innovative construction materials.

e.     New test methods, together with associated conformance assessment criteria, to support the performance-based methods for fire resistance design and retrofit of structures.  The performance objective of burnout without collapse will require the development of standard fire exposures that differ from those currently used.

There is a critical gap in knowledge about how structures perform in real fires, particularly concerning: the effects of fire on the entire structural system (including thermal expansion effects at lower temperatures);  interaction between the sub-systems, elements, and connections;  and scaling of fire test results to full-scale structures (especially for structures with long-span floor systems).

Relevance to WTC 7:  A performance-based assessment of the effects of fire on WTC 7, had it considered all of the relevant thermal effects (e.g. thermal expansion effects that occur at lower temperatures), would have identified the vulnerability of the building to fire-induced progressive collapse and allowed alternative designs for the structural system.

.

5.1.4     GROUP 4.  Improved Active Fire Protection

Active fire protection systems (i.e. sprinklers, standpipes/hoses, fire alarms, and smoke management systems) should be enhanced through improvements to the design, performance, reliability, and redundancy of such systems.

NIST WTC 7 Recommendation H  (NCSTAR 1  Recommendation 12).

NIST recommends that the performance, and possibly the redundancy and reliability of active fire protection systems (sprinklers, standpipes/hoses, fire alarms, and smoke management systems), in buildings be enhanced to accommodate the greater risks associated with increasing building height and population, increased use of open spaces, high-risk building activities, fire department response limits, transient fuel loads, and higher threat profile.

Reliability is affected by (a) redundancy, such that when one water supply is out of service (usually for maintenance), the other interconnected water supply can continue to protect the building and its occupants;  (b) automatic operation of water supply systems (not only for starting fire pumps but also for testing and tank replenishment, with appropriate remote alarms to the fire department and local alarms for notifying emergency personnel);  and (c) the use of suitable equipment and techniques to regulate unusual pressure considerations.

Relevance to WTC 7:  No water was available for the automatic suppression systems on the lower 20 storeys of WTC 7, once water from street-level mains was disrupted.  This lack of reliability in the source of the primary and secondary water supplies allowed the growth and spread of fires that ultimately resulted in collapse of the building.

.

5.1.5     GROUP 6.  Improved Emergency Response

Technologies and procedures for emergency response should be improved to enable better access to buildings, response operations, emergency communications, and command and control in large-scale emergencies.

NIST WTC 7 Recommendation I  (NCSTAR 1  Recommendation 24).

NIST recommends the establishment and implementation of codes and protocols for ensuring effective and uninterrupted operation of the command and control system for large-scale building emergencies.

a.     State, local, and federal jurisdictions should implement the National Incident Management System (NIMS).  The jurisdictions should work with the Department of Homeland Security to review, test, evaluate, and implement an effective unified command and control system.  NIMS addresses interagency co-ordination and establishes a response matrix – assigning lead agency responsibilities for different types of emergencies, and functions.  At a minimum, each supporting agency should assign an individual to provide co-ordination with the lead agency at each incident command post.

b.     State, local, and federal emergency operations centres (EOC’s) should be located, designed, built, and operated with security and operational integrity as a key consideration.

c.     Command posts should be established outside the potential collapse footprint of any building which shows evidence of large multi-floor fires or has serious structural damage.  A continuous assessment of building stability and safety should be made in such emergencies to guide ongoing operations and enhance emergency responder safety.  The information necessary to make these assessments should be made available to those assigned responsibility (see related Recommendations 15 and 23 in NIST NCSTAR 1).

d.     An effective command system should be established and operating before a large number of emergency responders and apparatus are dispatched and deployed.  Through training and drills, emergency responders and ambulances should be required to await dispatch requests from the incident command system and not to self-dispatch in large-scale emergencies.

e.     Actions should be taken via training and drills to ensure a co-ordinated and effective emergency response at all levels of the incident command chain by requiring all emergency responders that are given an assignment to immediately adopt and execute the assignment objectives.

f.     Command post information and incident operations data should be managed and broadcast to command and control centres at remote locations so that information is secure and accessible by all personnel needing the information.  Methods should be developed and implemented so that any information that is available at an interior information centre is transmitted to an emergency responder vehicle or command post outside the building.

Relevance to WTC 7:  (1) The New York City Office of Emergency Management (OEM) was located in WTC 7 and was evacuated before key fire ground decisions had to be made.  The location of OEM in WTC 7, which collapsed due to ordinary building fires, contributed to the loss of robust interagency command and control on 11 September 2001.  (2) Due to the collapse of the WTC Towers and the loss of responders and fire control resources, there was an evolving site leadership during the morning and afternoon.  Key decisions (e.g. not to fight the fires in WTC 7 and to turn off power to the Con Edison substation) were reasonable and would not have changed the outcome on 11 September 2001, but were not made promptly.  Under different circumstances (e.g. if WTC 7 had collapsed sooner and firefighters were still evaluating the building condition), the outcome could have been very different.

.

5.1.6     GROUP 7.  Improved Procedures and Practices

The procedures and practices used in the design, construction, maintenance, and operation of buildings should be improved to include encouraging code compliance by non-governmental and quasi-governmental entities, adoption and application of evacuation and sprinkler requirements in codes for existing buildings, and retention and availability of building documents over the life of a building.

NIST WTC 7 Recommendation J  (NCSTAR 1  Recommendation 27).

NIST recommends that building codes incorporate a provision that requires building owners to retain documents, including supporting calculations and test data, related to building design, construction, maintenance, and modifications over the entire life of the building.*  Means should be developed for off-site storage and maintenance of the documents.  In addition, NIST recommends that relevant information be made available in suitably designed hard copy or electronic formats for use by emergency responders.  Such information should be easily accessible by responders during emergencies.

[ * F-12  The availability of inexpensive electronic storage media and tools for creating large searchable databases makes this feasible.]

Relevance to WTC 7:  The efforts required in locating and acquiring drawings, specifications, tenant layouts, and material certifications, and especially shop fabrication drawings, significantly lengthened the investigation into the collapse of WTC 7.

.

NIST WTC 7 Recommendation K  (NCSTAR 1  Recommendation 28).

NIST recommends that the role of the ‘Design Professional in Responsible Charge’* be clarified to ensure that:  (1) all appropriate design professionals (including, e.g. the fire protection engineer) are part of the design team providing the highest standard of care when designing buildings employing innovative or unusual fire safety systems;  and (2) all appropriate design professionals (including, e.g. the structural engineer and the fire protection engineer) are part of the design team providing the highest standard of care when designing the structure to resist fires, in buildings that employ innovative or unusual structural and fire safety systems.

[ * F-13  In projects involving a design team, the ‘Design Professional in Responsible Charge’ – usually the lead architect – ensures that the team members use consistent design data and assumptions, co-ordinates overlapping specifications, and serves as the liaison between the enforcement and reviewing officials and the owner.  This term is defined in the International Building Code (IBC) and in the International Code Council’s Performance Code for Buildings and Facilities (where it is the Principal Design Professional).]

Relevance to WTC 7:  Following typical practice, none of the design professionals in charge of the WTC 7 Project (i.e. architect – structural engineer – fire protection engineer) was assigned the responsibility to explicitly evaluate the fire performance of the structural system.  Holistic consideration of thermal and structural factors during the design or review stage could have identified the potential for the failure and might have prevented the collapse of the building.

.

5.1.7     GROUP 8.  Education and Training

The professional skills of building and fire safety professionals should be upgraded through a national education and training effort for fire protection engineers, structural engineers, and architects.  The skills of building regulatory and fire service personnel should also be upgraded to provide sufficient understanding and the necessary skills to conduct the review, inspection, and approval tasks for which they are responsible.

NIST WTC 7 Recommendation L  (NCSTAR 1  Recommendation 29).

NIST recommends that continuing education curricula be developed, and programmes be implemented for:  (1) training fire protection engineers and architects in structural engineering principles and design;  and (2) training structural engineers, architects, fire protection engineers, and code enforcement officials in modern fire protection principles and technologies, including the fire resisting design of structures;  and (3) training building regulatory and fire service personnel to upgrade their understanding and skills to conduct the review, inspection, and approval tasks for which they are responsible.  The outcome would further the integration of the disciplines in effective fire-safe design of buildings.

Relevance to WTC 7:  Discerning the fire-structure interactions that led to the collapse of WTC 7 required research professionals with expertise in both disciplines.  Assuring the safety of future buildings will require that participants in the design and review processes possess a combined knowledge of fire science, materials science, heat transfer, and structural engineering, and design.

.

NIST WTC 7 Recommendation M  (NCSTAR 1  Recommendation 30).

NIST recommends that academic, professional short-course, and web-based training materials in the use of computational fire dynamics and thermo-structural analysis tools be developed and delivered to strengthen the base of available technical capabilities and human resources.

Relevance to WTC 7:  NIST stretched the state-of-the-art in the computational tools needed to reconstruct a fire-induced progressive collapse.  This enabled identification of the critical processes that led to that collapse.  Making these expanded tools and derivative, validated, and simplified modelling approaches usable by practitioners could prevent future disasters.

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Progressive Collapse of WTC 7 – 2008 NIST Recommendations – Part 1 of 2

See the 1st Series of Posts on the 2005 NIST WTC 1 & 2 Collapse Recommendations … which began, here, towards the end of 2011 …

2011-10-25:  NIST’s Recommendations on the 9-11 WTC Building Collapses … GROUP 1. Increased Structural Integrity – Recommendations 1, 2 & 3 (out of 30)

.

Colour plan showing the World Trade Center Complex in New York City, and its surrounding neighbourhood in Manhattan. By means of yellow shading and annotation in red text, the extent of direct damage caused by the collapse of the 2 WTC Towers on 11 September 2001 is shown. Not shown is the much greater extent of indirect damage caused, e.g. dust and debris from the collapses clogged up and destroyed air conditioning systems and ductwork in buildings. Everywhere south of Canal Street was a disaster zone. Also not shown is the damage caused by WTC 7, at the north-eastern tip of the Complex, which collapsed late on the afternoon of 9-11. Click to enlarge.

Colour plan showing the World Trade Center Complex in New York City, and its surrounding neighbourhood in Manhattan. By means of yellow shading and annotation in red text, the extent of direct damage caused by the collapse of the 2 WTC Towers on 11 September 2001 is shown. Not shown is the much greater extent of indirect damage caused, e.g. dust and debris from the collapses clogged up and destroyed air conditioning systems and ductwork in buildings. Everywhere south of Canal Street was a disaster zone. Also not shown is the damage caused by WTC 7, at the north-eastern tip of the Complex, which collapsed late on the afternoon of 9-11. Click to enlarge.

.

2012-01-18:  SOME PRELIMINARY COMMENTS …

  1.     World Trade Center Building 7 was a 47 Storey Office Building located at the north -eastern tip of the WTC Complex in Lower Manhattan, New York City.  It had been built on top of an existing Consolidated Edison of New York electric power substation, on land owned by the Port Authority of New York and New Jersey.

On Tuesday, 11 September 2001 … WTC Building 7 was on fire for almost seven hours … from the time of the collapse of WTC Tower 1 – North Tower, just before 10.30 hrs (local time), until 17.21 hrs … when WTC 7 failed completely, collapsing progressively as a result of ‘real’ fires – as distinct from ‘standard test’ fires – on many floors. 

There were only two certainties on that fateful day (9-11) … the Fire-Induced Progressive Collapse of WTC Building 7 could no longer be ignored by the International Fire Science and Engineering Community … and the ‘reality’, which Modern Fire Engineering must now confront, was significantly altered.  Secondly, it is NEVER acceptable to a general population for buildings to collapse !

Later in 2008, the Mumbai ‘Hive’ Attacks would add a sinister new ingredient to the standard threat profile for buildings, their occupants, and emergency services.

However, long before 9-11 and Mumbai, the growing complexity of modern communities and their rapidly evolving architectural forms had left the Fire Engineer far behind, unable to respond to the new fire safety challenges posed.

.

  2.     The second of the NIST Publications being referenced in this New Series of Posts is as follows …

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.

This 2008 NIST Report contains, in Chapter 5, a list of 13 Recommendations for Action (A-M), grouped together under the same 8 Subject Headings used in the 2005 NIST Report (NCSTAR 1) …

     i)       Increased structural integrity … Recommendation A ;

     ii)      Enhanced fire endurance of structures … Recommendations B, C, D & E ;

     iii)     New methods for fire resisting design of structures … Recommendations F & G ;

     iv)     Improved active fire protection … Recommendation H ;

     v)      Improved building evacuation … Long before its collapse, all occupants/users had evacuated WTC 7 … No Recommendation ;

     vi)     Improved emergency response … Recommendation I ;

     vii)    Improved procedures and practices … Recommendations J & K ;   and

     viii)   Education and training … Recommendations L & M.

NIST has clearly stated that “the urgency of these Recommendations is substantially reinforced by their pertinence to the collapse of a tall building that was based on a structural system design that is in widespread use”.

.

  3.     The Colour Coding of Texts which I am using in this new series of posts … where NIST has presented new texts relating to WTC Building 7, these are shown in blue … where NIST has chosen to reinforce earlier texts from the 2005 Report on the WTC Towers 1 & 2 Collapses, these are shown in black.  The important new paragraphs describing the critical relevance of WTC Building 7 are shown in red.

Please pay particular attention to these Red Paragraphs.  Having carefully digested their contents … then if, by any chance, you happen to encounter somebody who still insists that the NIST 9-11 WTC Recommendations have no relevance to the design, construction, management and operation of ALL Buildings … that person is either living in Alice’s Wonderland … or he/she has never bothered to read the NIST Recommendations in the first place !!

.

  4.     While it is still essential to distinguish clearly between the two closely related structural concepts below … I would like to take this opportunity to bring to your attention a necessary and important modification … more, a refinement … to the definition of Fire-Induced Progressive 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.

Fire-Induced Progressive Collapse

The sequential growth and intensification of structural distortion 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.

This modification/refinement recognizes the following … that Fire-Induced Progressive Collapse may commence long before any breach occurs in a Fire Compartment Boundary … that, as a result of rampant commercial pressures in our societies, the tendency is for Compartment Volumes to become far too large to be any longer effective … and in the case of a Sustainable Building, for example, where natural patterns of air movement in buildings are used for either heating or cooling purposes, there may be no Compartments at all !

Restricting the application of one or both of these structural concepts, in law, to Multi-Storey Buildings, i.e. in many jurisdictions, those buildings having 5 or more storeys … is a purely arbitrary cut-off point.

CIB W14’s Research Working Group IV: ‘Structural Reliability & Fire-Induced Progressive Collapse’ would argue, rationally, that both of these concepts are fundamental to all structural fire engineering design.

.

  5.     Structural Fire Engineering is concerned with those aspects of fire engineering which relate to structural design for fire, and the complex architectural interaction between a building’s structure and fabric, i.e. non-structure, under conditions of fire and its immediate aftermath.

As Chair of CIB W14’s Research Working Group IV … I will shortly be making a Workshop Presentation in Europe, the aim of which will be to set the scene for the launch of an International CIB W14 Research WG IV Reflection Document;  the specific objective of the Presentation, however, will be to accurately describe the phenomenon that is Fire-Induced Progressive Collapse … and to outline a necessary new design approach which will fulfil future requirements, legal and otherwise, concerning adequate resistance to this phenomenon.

It will be shown that the new design approach is fully compatible with the Recommendations contained in the 2005 and 2008 NIST Reports on the 9-11 World Trade Center Buildings 1, 2 & 7 Collapses – NCSTAR 1 & NCSTAR 1A.

.

2008 NIST WTC 7 RECOMMENDATIONS  (Final Report NCSTAR 1A)

5.1  GENERAL

In its final report on the collapse of the World Trade Center Towers (NIST NCSTAR 1), NIST made 30 Recommendations for improving the safety of buildings, occupants, and emergency responders.  These encompass increased structural integrity, enhanced fire endurance of structures, new methods for fire resisting design of structures, improved active fire protection, improved building evacuation, improved emergency response, improved procedures and practices, and education and training.

WTC 7 was unlike the WTC Towers in many respects.  It was a more typical tall building in the design of its structural system.  It was not struck by an airplane.  The fires in WTC 7 were quite different from those in the Towers.  Since WTC 7 was not doused with thousands of litres of jet fuel, large areas of any floor were not ignited simultaneously.  Instead, the fires in WTC 7 were similar to those that have occurred previously in several tall buildings where the sprinklers did not function or were not present.  These other buildings did not succumb to their fires and collapse, because they were of structural designs that differed from that of WTC 7.

The Investigation Team has compiled a list of key factors that enabled ordinary fires to result in an extraordinary outcome.  In so doing, the Team recognized that there were additional aspects to be included in the content of some of the earlier 30 Recommendations.

Based on the findings of this Investigation, NIST has identified 1 New Recommendation and has reiterated 12 Recommendations from the Investigation of the WTC Towers.

The urgency of the Prior Recommendations is substantially reinforced by their pertinence to the collapse of a tall building that is based on a structural system design that is in widespread use.  A few of the Prior Recommendations have been modified to reflect the findings of this Investigation.

The partial or total collapse of a building due to fires is an infrequent event.  This is particularly true for buildings with a reliably operating active fire protection system, such as an automatic fire sprinkler system.  A properly designed and operating automatic sprinkler system will contain fires while they are small and, in most instances, prevent them from growing and spreading to threaten structural integrity.

The intent of current practice, based on prescriptive standards and codes, is to achieve life safety, not collapse prevention.  However, the key premise of NIST’s Recommendations is that buildings should not collapse in infrequent (worst-case) fires that may occur when active fire protection systems are rendered ineffective, e.g. when sprinklers do not exist, are not functional, or are overwhelmed by the fire.

Fire scenarios for structural design based on single compartment or single floor fires are not appropriate representations of infrequent fire events.  Such events have occurred in several tall buildings resulting in unexpected substantial losses.  Instead, historical data suggests that infrequent fires which should be considered in structural design have characteristics that include:  ordinary combustibles and combustible load levels, local fire origin on any given floor, no widespread use of accelerants, consecutive fire spread from combustible to combustible, fire-induced window breakage providing ventilation for continued fire spread and accelerated fire growth, concurrent fires on multiple floors, and active fire protection systems rendered ineffective.  The fires in WTC 7 had all of these characteristics.

NIST believes the Recommendations are realistic, appropriate, and achievable within a reasonable period of time.  NIST strongly urges that immediate and serious consideration be given to these Recommendations by the building and fire safety communities in order to achieve appropriate improvements in the way buildings are designed, constructed, maintained, and used – with the goal of making buildings safer in future emergencies.

A complete listing of all 13 Recommendations (Recommendations A through L) based on this Investigation follows.  Under a few of the Recommendations, the pertinent lesson from the reconstruction of the WTC 7 Collapse is reflected in the form of a modification.   For the 12 Reiterated Recommendations, the pertinent codes, standards, and organizations were listed in Table 9-1, and Tables 9-2a through 9-2c of NIST NCSTAR 1 and are not repeated here.  For the 1 New Recommendation, B, this information is provided in the text.

.

5.1.1     GROUP 1.  Increased Structural Integrity

The standards for estimating the load effects of potential hazards (e.g. progressive collapse, wind) and the design of structural systems to mitigate the effects of those hazards should be improved to enhance structural integrity.

NIST WTC 7 Recommendation A  (NCSTAR 1  Recommendation 1).

NIST recommends that:  (1) progressive collapse be prevented in buildings through the development and nationwide adoption of consensus standards and code provisions, along with the tools and guidelines needed for their use in practice;  and (2) a standard methodology be developed – supported by analytical design tools and practical design guidance – to reliably predict the potential for complex failures in structural systems subjected to multiple hazards.

Relevance to WTC 7:  Had WTC 7 been expressly designed for prevention of fire-induced progressive collapse, it would have been sufficiently robust to withstand local failure due to the fires without suffering total collapse.

.

5.1.2     GROUP 2.  Enhanced Fire Endurance of Structures

The procedures and practices used to ensure the fire endurance of structures should be enhanced by improving the technical basis for construction classifications and fire resistance ratings, improving the technical basis for standard fire resistance testing methods, use of the ‘structural frame’ approach to fire resistance ratings, and developing in-service performance requirements and conformance criteria for sprayed fire resisting materials.

NIST WTC 7 Recommendation B  (New)

NIST recommends that buildings be explicitly evaluated to ensure the adequate performance of the structural system under worst-case design fires with any active fire protection system rendered ineffective.  Of particular concern are the effects of thermal expansion in buildings with one or more of the following features:  (1) long-span floor systems* which experience significant thermal expansion and sagging effects;  (2) connection designs (especially shear connections) that cannot accommodate thermal effects;  (3) floor framing that induces asymmetric thermally-induced (i.e. net lateral) forces on girders;  (4) shear studs that could fail due to differential thermal expansion in composite floor systems;  and (5) lack of shear studs on girders.  Careful consideration should also be given to the possibility of other design features that may adversely affect the performance of the structural system under fire conditions.

[ * F-6   Typical floor span lengths in tall office buildings are in the range of 12-15 metres;  this range is considered to represent long-span systems.  Thermal effects (e.g. thermal expansion) that may be significant in long-span buildings may also be present in buildings with shorter span lengths, depending on the design of the structural system.]

Building owners, operators, and designers are strongly urged to act upon this Recommendation.  Engineers should be able to design cost-effective fixes to address any areas of concern that are identified by these evaluations.  Several existing, emerging, or even anticipated capabilities could have helped prevent the collapse of WTC 7.  The degree to which these capabilities improve performance remains to be evaluated.  Possible options for developing cost-effective fixes include:

  • More robust connections and framing systems to better resist the effects of thermal expansion on the structural system ;
  • Structural systems expressly designed to prevent progressive collapse.  The current model building codes do not require that buildings be designed to resist progressive collapse ;
  • Better thermal insulation (i.e. reduced conductivity and/or increased thickness) to limit heating of structural steel and to minimize both thermal expansion and weakening effects.  Currently, insulation is used to protect steel strength, but it could also be used to maintain a lower temperature in the steel framing to limit thermal expansion ;
  • Improved compartmentation in tenant areas to limit spread of fires ;
  • Thermally resisting window assemblies which limit breakage, reduce air supply, and retard fire growth.

Industry should partner with the research community to fill critical gaps in knowledge about how structures perform in real fires, particularly considering:  the effects of fire on the entire structural system; the interactions between sub-systems, elements, and connections; and scaling of fire test results to full-scale structures, especially for structures with long-span floor systems.

Affected Standards:  ASCE 7, ASCE/SFPE 29, AISC Specifications, and ACI 318.  Development of performance objectives, design criteria, evaluation methods, design guidance, and computational tools should begin promptly, leading to new standards.

Model Building Codes:  The new standard should be adopted in model building codes (IBC, NFPA 5000) by mandatory reference to, or incorporation of, the latest edition of the standard.

Relevance to WTC 7:  The effects of restraint of free thermal expansion on the steel framing systems, especially for the long spans on the east side of WTC 7, were not considered in the structural design and led to the initiation of the building collapse.

.

NIST WTC 7 Recommendation C  (NCSTAR 1  Recommendation 4).

NIST recommends evaluating, and where needed improving, the technical basis for determining appropriate construction classifications and fire rating requirements (especially for tall buildings) – and making related code changes now, as much as possible – by explicitly considering factors including:*

[ * F-7  The construction classification and fire rating requirements should be risk-consistent with respect to the design-basis hazards and the consequences of those hazards.  The fire rating requirements, which were originally developed based on experience with buildings less than 20 storeys in height, have generally decreased over the past 80 years since historical fire data for buildings suggest considerable conservatism in those requirements.  For tall buildings, the likely consequences of a given threat to an occupant on the upper floors are more severe than the consequences to an occupant on the first floor or the lower floors.  For example, with non-functioning elevators, both of the time requirements are much greater for full building evacuation from upper floors and emergency responder access to those floors.  The current height and areas tables in building codes do not provide the technical basis for the progressively increasing risk to an occupant on the upper floors of tall buildings that are much greater than 20 storeys in height.]

  • timely access by emergency responders and full evacuation of occupants, or the time required for burnout without partial collapse ;
  • the extent to which redundancy in active fire protection systems (sprinklers and standpipe, fire alarm, and smoke management) should be credited for occupant life safety ;*

[ * F-8  Occupant life safety, prevention of fire spread, and structural integrity are considered separate safety objectives.]

  • the need for redundancy in fire protection systems that are critical to structural integrity ;*

[ * F-9  The passive fire protection system (including the application of fire protection insulation, compartmentation, and fire stopping) and the active sprinkler system each provide redundancy for maintaining structural integrity in a building fire, should one of the systems fail to perform its intended function.]

  • the ability of the structure and local floor systems to withstand a maximum credible fire scenario* without collapse, recognizing that sprinklers could be compromised, not operational, or non-existent ;

[ * F-10  A maximum credible fire scenario includes conditions that are severe, but reasonable to anticipate, conditions related to building construction, occupancy, fire loads, ignition sources, compartment geometry, fire control methods, etc., as well as adverse, but reasonable to anticipate operating conditions.]

  • compartmentation requirements (e.g. 1,200 sq.m*) to protect the structure, including fire rated doorsets and automatic enclosures, and limiting air supply (e.g. thermally resisting window assemblies) to retard fire spread in buildings with large, open floor plans ;

[ * F-11  Or a more appropriate limit, which represents a reasonable area for active fire fighting operations.]

  • the effect of spaces containing unusually large fuel concentrations for the expected occupancy of the building ;   and
  • the extent to which fire control systems, including suppression by automatic or manual means, should be credited as part of the prevention of fire spread.

Relevance to WTC 7:  The floor systems in WTC 7 failed at lower temperatures because thermal effects within the structural system, especially thermal expansion, were not considered in setting the fire rating requirements in the construction classification, which are determined using the ASTM E 119 or equivalent testing standard.

.

NIST WTC 7 Recommendation D  (NCSTAR 1  Recommendation 5).

NIST recommends that the technical basis for the century-old standard for fire resistance testing of components, assemblies and systems be improved through a national effort.  Necessary guidance also should be developed for extrapolating the results of tested assemblies to prototypical building systems.  A key step in fulfilling this Recommendation is to establish a capability for studying and testing components, assemblies, and systems under realistic fire and load conditions.

Of particular concern is that the Standard Fire Resistance Test does not adequately capture important thermally-induced interactions between structural sub-systems, elements, and connections that are critical to structural integrity.  System-level interactions, especially due to thermal expansion, are not considered in the standard test method since columns, girders, and floor sub-assemblies are tested separately.  Also, the performance of connections under both gravity and thermal effects is not considered.  The United States currently does not have the capability for studying and testing these important fire-induced phenomena critical to structural safety.

Relevance to WTC 7:  The floor systems failed in WTC 7 at shorter fire exposure times than the specified fire rating (two hours) and at lower temperatures because thermal effects within the structural system, especially thermal expansion, were not considered in setting the endpoint criteria when using the ASTM E 110 or equivalent testing standard.  The structural breakdowns that led to the initiating event, and the eventual collapse of WTC 7, occurred at temperatures that were hundreds of degrees below the criteria that determine structural fire resistance ratings.

.

NIST WTC 7 Recommendation E  (NCSTAR 1  Recommendation 7).

NIST recommends the adoption and use of the ‘structural frame’ approach to fire resistance ratings.  This approach requires all members that comprise the primary structural frame (such as columns, girders, beams, trusses, and spandrels) be fire protected to the higher fire resistance rating required for the columns.  The definition of the primary structural frame should be expanded to include bracing members that are essential to the vertical stability of the primary structural frame under gravity loading (e.g. girders, diagonal bracing, composite floor systems that provide lateral bracing to the girders) whether or not the bracing members carry gravity loads.  Some of these bracing members may not have direct connections to the columns, but provide stability to those members directly connected to the columns.  This Recommendation modifies the definition of the primary structural frame adopted in the 2007 supplement to the International Building Code (IBC).  The IBC considers members of floor or roof construction that are not connected to the columns not to be part of the primary structural frame.  This Recommendation ensures consistency in the fire protection provided to all of the structural elements that contribute to overall structural stability.  State and local jurisdictions should adopt and enforce this requirement.

Relevance to WTC 7:  Thermally-induced breakdown of the floor system in WTC 7 was a determining step in causing failure initiation and progressive collapse.  Therefore, the floor system should be considered as an integral part of the primary structural frame.

.

.

END

Enhanced by Zemanta

Tags: , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , ,

Search

 

December 2017
S M T W T F S
« Oct    
 12
3456789
10111213141516
17181920212223
24252627282930
31  

Links