earthquakes

2015 Paris Hive Attacks & Fire Engineering for Urban Resilience !

2015-01-31:  The beginning of this 21st Century is deeply unsettling … history is catching up on us, and old certainties are crumbling before our eyes …

The recent, extremely violent Paris Hive Attacks … which occurred between Wednesday and Friday (7-9 January 2015) … have again shown that co-ordinated attacks on a small number of carefully chosen, low-level targets can be just as effective in causing widespread social and economic disruption in a City as a single attack on a high-level target.  Search for our previous detailed discussion, here, on the 2008 Mumbai ‘Hive’ Attacks.

On this tragic occasion, the attacks happened in Europe … not, as before, in far-off India.

Following the 2001 WTC 9-11 Attacks in New York City … the U.S. National Institute of Standards and Technology (NIST), in 2005 and 2008, recommended that these Building Types should be treated as ‘Risk Priorities’ …

• Tall / High-Rise Buildings ;
• Iconic Buildings ;
• Buildings Having a Critical Function ;
• Buildings Having an Innovative Design.

However, a typical medium-rise office building (in Paris) and off-street supermarket do not fall into the above categories … another indication that the NIST Recommendations must soon undergo a thorough international review and updating.

In the real world, the whole urban and sub-urban infrastructure of a City is at risk from Extreme Man-Made Events … one more risk among significant others, i.e. Hybrid Disasters (e.g. 2011 Fukushima Nuclear Incident), Severe Natural Events (e.g. earthquakes, typhoons, tsunamis) and Complex Humanitarian Emergencies (e.g. mass human migrations, regional famines).  And with 50% of the world’s population already living in Cities, and substantial urban population growth projected over the coming decades … it is clear that, in the short to medium term, Cities must become much more resilient.  Search for our continuing discussion, here, about Sustainable Urban Resilience.

In this context, compliance solely with the minimal and limited fire safety objectives in current national legislation – from whatever source around the world – is so far from being either adequate or acceptable … that it is no longer worth a moment’s consideration.

A Fire Engineering which is ‘fit for purpose’, i.e. is both ethical and professional, in today’s complex and dynamic Human Environment … has an essential and critical part to play in the realization of a Safe, Resilient and Sustainable Built Environment for All !

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Sustainable Human & Social Development – Reloaded !

2014-04-13:  Further to the Post, dated 2013-01-13

There are many essential qualities and features belonging to and representative of a Sustainable Human Environment (including the Social, Built, Virtual and Economic Environments).  As discussed here many times before … Accessibility-for-All is one fundamental attribute, under Social and Legal Aspects of Sustainable Human and Social Development.

Another fundamental attribute … Urban Resilience … is now moving centre stage in the world of International Construction Research & Practice.  WHEN, not if … this concept is fully elaborated and understood, it will have a profound impact on All Tasks, Activities and Types of Performance in the Human Environment … under All Aspects of Sustainable Human and Social Development.

After working for many years on Climate Change, particularly Adaptation … it was quite natural for me to encounter the concept of Resilience.  But the aim of a newly established Core Task Group within CIB (International Council for Research & Innovation in Building & Construction) is to widen out this concept to also include Severe Natural Events (e.g. earthquakes, typhoons, tsunamis), Complex Humanitarian Emergencies, (e.g. regional famines, mass human migrations), Extreme Man-Made Events (e.g. 2001 WTC 9-11 Attack, 2008 Mumbai ‘Hive’ Attacks), and Hybrid Disasters (e.g. 2011 Fukushima Nuclear Incident) … to set down Resilience Benchmarks … and to produce Resilience Performance Indicators.  An imposing challenge !

AND … as Urbanization is proceeding at such a rapid pace in the BRICS Countries (Brazil, Russia, India, China & South Africa) and throughout the rest of the Southern Hemisphere … ‘practical’ and ‘easily assimilated’ trans-disciplinary output from this CIB Task Group is urgently required.  In other words, the work of the Task Group must not be permitted to become an exercise in long drawn out pure academic research … the clear focus must be on ‘real’ implementation … As Soon As Is Practicable !!

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A New and Updated Groundwork …

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SUSTAINABLE DESIGN

The ethical design response, in resilient built and/or wrought form, to the concept of Sustainable Human & Social Development.

SUSTAINABLE HUMAN & SOCIAL DEVELOPMENT

Development which meets the responsible needs, i.e. the human and social rights*, of this generation – without stealing the life and living resources from the next seven future generations.

*As defined in the 1948 Universal Declaration of Human Rights … and augmented by UN OHCHR Letter, dated 6 June 2013, on the Post-2015 Development Agenda.

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The CITY (as Region)

A geographical region, with open and flexible boundaries, consisting of:

(a)              An interwoven, densely constructed core (built environment) ;

(b)              A large resident population of more than 500,000 people (social environment) ;

(c)              A supporting hinterland of lands, waters and other natural resources (cultivated landscape) ;

together functioning as …

(i)                 a complex living system (analogous to, yet different from, other living systems such as ecosystems and organisms) ;     and

(ii)               a synergetic community capable of providing a high level of individual welfare, and social wellbeing for all of its inhabitants.

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SOCIAL WELLBEING

A general condition – in a community, society or culture – of health, happiness, creativity, responsible fulfilment, and sustainable development.

INDIVIDUAL WELFARE

A person’s general feeling of health, happiness and fulfilment.

HUMAN HEALTH

A state of complete physical, mental and social wellbeing, and not merely the absence of disease or infirmity.     [World Health Organization]

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SOCIAL ENVIRONMENT

The complex network of real and virtual human interaction – at a communal or larger group level – which operates for reasons of tradition, culture, business, pleasure, information exchange, institutional organization, legal procedure, governance, human betterment, social progress and spiritual enlightenment, etc.

The social environment shapes, binds together, and directs the future development of the built and virtual environments.

BUILT ENVIRONMENT

Anywhere there is, or has been, a man-made or wrought (worked) intervention by humans in the natural environment, e.g. cities, towns, villages, rural settlements, service utilities, transport systems, roads, bridges, tunnels, and cultivated lands, lakes, rivers, coasts, seas, etc … including the virtual environment.

VIRTUAL ENVIRONMENT

A designed environment, electronically generated from within the built environment, which may have the appearance, form, functionality and impact – to the person perceiving and actually experiencing it – of a real, imagined and/or utopian world.

The virtual and built environments continue to merge into a new augmented reality.

ECONOMIC ENVIRONMENT

The intricate web of real and virtual human commercial activity – operating at micro and macro-economic levels – which facilitates, supports, but sometimes hampers or disrupts, human interaction in the social environment.

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And So To Work !!

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SDI Practice Announcement – New 32 Storey Hotel in China

2013-04-02:  Sustainable Design International Ltd. (SDI) is pleased to announce that its Managing Director, C.J. Walsh, has been invited to be ‘Project Design Architect’ / ‘Design Professional in Responsible Charge’ for a New 32 Storey Hotel in Yunnan Province, People’s Republic of China (PRC).

He will have responsibility for the Project’s Architectural Concept Design and General Schematic Design … including the overall architectural character and profile of primary exterior surfaces.

Project Approximate Value = € 65 Million (Euros) … excluding interior design, finishes and furnishing (which could end up doubling, or even tripling, the overall project value).

Sustainable Design International Ltd.  maintains a strict practice policy of Client Confidentiality.

[ If this Type of Professional Design Service Appeals to You, or Your Organization – Contact Us Immediately ! ]

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2012 ‘Understanding China’ Policy Briefing Friends of Europe & EuroChambres

An estimated One Billion People will be living in China’s cities by 2030.  This large-scale and very rapid urbanization demands that a sustainable transformation of their urban built, social, economic and institutional environments commences Today – not at some notional point in a far distant future.

Furthermore … replicating a European approach to sustainable design and construction in other regions of the world is doomed to failure.  Urban Transformation in China must be adapted to Local Geography, Climate, Climate Change, Social Needs, Cultures, Economy, and Local Severe Events (e.g. earthquakes, flooding).  With European support and collaboration … China must, and will, find its own way.

Greening China's Cities of Tomorrow (2012) - Report CoverGreening China’s Cities of Tomorrow (Spring 2012)

Click the Link Above to read and/or download a PDF File (4.42 Mb)

Report on a One-Day China Advisory Council Roundtable, co-organized by Friends of Europe and EuroChambres, which was held in Brussels on 8 March 2012.  This event was part of an ‘Understanding China’ Programme (mid-2009 to mid-2012), co-funded by the European Commission.

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2013 Asian Development Bank (ADB) Guidebook: ‘Increasing Climate Change Resilience of Urban Water Infrastructure’ 

This Guide describes a practical approach to bridge the gap between theoretical analyses of climate change impacts and the planning decisions that need to be made by city authorities and utility managers to increase climate change resilience of the water sector in the city of  Wuhan, Hubei Province, People’s Republic of China (PRC).  It focuses on answering the questions currently being asked by city planners and managers all over the world, as follows:

  • What changes might be caused by climate change ?
  • How will these changes affect services and utilities ?
  • What can we do now to prepare for them ?

The long lead time required to plan, finance, build, and commission city infrastructure facilities means that decision makers cannot wait for more detailed data on the effects of future climate change, especially those relating to local circumstances, but must make investment decisions based on what is known now and what can be readily predicted.  An important principle in this kind of ‘robust’ decision-making is provided by the  Intergovernmental Panel on Climate Change (IPCC)  tenet that adaptation investments, which move a city’s infrastructure toward sustainable development (such as providing safe drinking water and better sanitary conditions), are justifiable even without climate change.

This Guide is arranged in clear steps to provide direction and information for similar exercises in other areas.  Having grown out of a specific locality and its needs, the principles and solutions developed in this guide are founded on real world situations and problems …

ADB Guidebook: 'Increasing Climate Change Resilience of Urban Water Infrastructure' (2013) - Cover PageIncreasing Climate Change Resilience of Urban Water Infrastructure (ADB, 2013)

Click the Link Above to read and/or download a PDF File (2.31 Mb)

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***  THIS TALL BUILDING IN YUNNAN PROVINCE  &  SIMILAR COMPLEX ARCHITECTURAL PROJECTS  ***

Working within the professional constraints of ‘client confidentiality’ … it is possible to have a general discussion about current building design, construction and operation issues in an international sector which is operating, more and more, beyond national borders … without adequate, or very often any, national and local regulation.  By ‘regulation’, I mean a flexible system of building-related legislation which is operated in conjunction with mandatory and effective technical control.

In order to cope with today’s complex built environment and the enormous variation in the size and scale of construction projects … a ‘flexible’ mix of functional, performance and prescriptive legal requirements is the sharpest and most appropriate instrument.

And you can forget the hype about performance-based building codes coming out of the USA … hot air, and much ado about little !

Of course, the biggest issue of all is the competence of those individuals who work in Authorities Having Jurisdiction (AHJ’s), i.e. technical controllers.  Even in the most developed economies of the world … there are many occasions when the level of individual incompetence in an AHJ is astounding … and institutional arrangements within the AHJ itself are a mess, i.e. the AHJ is not fit for purpose.

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1.  Sustainable Design – Design Process Efficiency & Proper Preparation for Construction

A tremendous amount of waste is associated with and generated by the processes of conventional building design, construction and operation.  There is a more up-to-date and efficient way of doing things … an essential way for Sustainable Design … and it’s called Building Information Modelling (BIM) !

Furthermore … consider, for a moment, just the initial list of Specialist Consultants who will be engaged directly by the Chinese Client when the project’s conceptual design has reached a sufficiently developed stage.  How can all of these individuals and organizations – listed in the revised and agreed Project Design Agreement – obtain accurate and reliable ‘real time’ information about the rapidly evolving project from a central design library / information database … then feed their new work back into the centre without unnecessary delay ?   How, next, can everyone else who needs to know, be updated with the new design input … again, without delay ?   And perhaps, these consultants may also be based in different countries … working in very different time zones …

  • Building Information Modelling (BIM) Consultant
  • Local Design Institute (LDI) … a local architectural practice which will produce the project’s working drawings, handle local spatial planning and building code approvals, carry out site inspections, and deal directly with construction organization(s), etc., etc.
  • Interior Design Consultant
  • Traffic / Parking Analysis Consultant
  • Curtain Wall Consultant (Curtain Wall, Skylights & Special Roof Structures)
  • Retail Market Analysis Consultant
  • Landscape Design Consultant
  • Quantity Surveying & Cost Estimating Consultant
  • Furniture Design Consultant
  • Geotechnical, Civil Engineering & Structural Engineering Consultant (including structural performance under fire and earthquake conditions, resistance to fire-induced progressive damage and disproportionate damage … and also including climate resilience)
  • Acoustic & Audio-Visual Design Consultant
  • Mechanical, Electrical & Plumbing (MEP) Engineering Consultant
  • Integrated Building Automation & Management / Telecom / Security / Networking Consultant
  • Fire & Life-Safety Engineering Consultant
  • Water Feature Consultant
  • Wind Tunnel Test Consultant
  • Kitchen Equipment and Layout Design Consultant
  • Art, Artefact and Accessories Consultant & Procurement Services for Art, Artefacts, and Accessories
  • Tenant Storefront Design Consultant
  • Helicopter Landing Pad Design Consultant
  • Universal Design / Accessibility for All Consultant [including access to the building, electronic, information and communication technologies (EICT’s), and services offered at the hotel … and including fire safety, protection and evacuation for all]

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2.  The ‘Design Professional in Responsible Charge’ !

The Project Design Agreement requests that the Client receive advice on who might be the different Specialist Consultants listed above.  In addition, it will be necessary to demarcate the boundaries within which each Consultant will operate … and, where appropriate, to prescribe a design performance target (see below) for each speciality … which must be ‘realized’ in the completed and occupied building !

Recalling the many previous posts, here on this Technical Blog, concerning NIST’s 2005 & 2008 Recommendations on the 9-11 World Trade Centre Building Collapses in New York City‘somebody’ must ensure that the many individuals and organizations listed above – members of the Larger (2nd Stage) Design Team – use consistent design data and assumptions … must co-ordinate design documents and specifications to identify overlaps and eliminate gaps … must serve as ultimate liaison between the Client, the Local Design Institute, AHJ officials, and the Construction Organization(s) … and must ensure that everybody is on the same communication wavelength, and working towards the same objective in a trans-disciplinary manner.

That ‘Somebody’ … the Design Professional in Responsible Charge … must be the Project Design Architect !

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3.  Some Sustainable Design Performance Targets

Actual construction and building user performance shall be carefully (i.e. reliably and precisely) monitored … and independently verified …

A.   Basic Functional Requirements … the Building shall comply with the Basic Requirements for Construction Works – elaborated in Annex I of European Union (EU) Regulation No.305/2011 of the European Parliament and of the Council, of 9 March 2011, laying down Harmonized Conditions for the Marketing of Construction Products and Repealing Council Directive 89/106/EEC.

See my Post, dated 2011-09-13 … https://cjwalsh.ie/2011/09/new-eu-construction-product-regulation-3052011-halleluiah/

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B.   Good Indoor Air Quality (IAQ) … Two high-level performance indicators have been developed with the aim of protecting Human Health, and are both now referenced in International Standard ISO 21542: ‘Building Construction – Accessibility & Usability of the Built Environment’

      –   Radon Activity (incl. Rn-222, Rn-220, RnD) in a building should, on average, fall within the range of 10 Bq/m3 to 40 Bq/m3, but shall at no time exceed 60 Bq/m3 ;

      –   Carbon Dioxide (CO2) Concentrations in a building should not significantly exceed average external levels – typically within the range of 300 parts per million (ppm) to 500 ppm – and shall at no time exceed 800 ppm.

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C.   Energy Conservation & Efficiency + A ‘Positive Energy’ Return + Assured Building User Thermal Comfort

See my Post, dated 2013-09-10 … https://cjwalsh.ie/2013/09/passivhaus-standard-is-not-enough-in-new-building-projects/

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D.   Project-Specific Sustainable Fire Engineering Design Objectives

See my Post, dated 2014-04-20 … https://cjwalsh.ie/2014/04/sustainable-fire-engineering-design-targeting-mrv/

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NIST’s Recommendations on the 9-11 WTC Building Collapses

2011-10-25:  Since shortly after my visit to Lower Manhattan in mid-October 2001 … we have maintained an Archive Page on Structural Fire Engineering, World Trade Center Incident (9-11) & Fire Serviceability Limit States … at SDI’s Corporate WebSite.  And I have referenced here … many, many times … the Recommendations contained in the 2005 & 2008 Final Reports of the U.S. National Institute of Standards & Technology (NIST) on the 9-11 World Trade Center Building 1, 2 & 7 Collapses.

In this post (and a series of future posts) … I find it most necessary that the 2005 & 2008 NIST Recommendations now be presented for everyone to read.  Yes, some of Recommendations apply specifically to Tall and Very Tall Buildings … and Building Designers in India, China, Brazil, Russia & South Africa (BRICS), the Arab Gulf RegionEurope and North America, etc., should be fully aware of their contents.

BUT … I am also strongly convinced … precisely because I am an Architect, a Fire Engineer and a Technical Controller … that most of the NIST Recommendations apply to ALL Buildings … so catastrophic was the failure exposed on that fateful day (11 September 2001) … in all of our common design and construction practices … and our operation, maintenance and emergency response procedures !

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PRELIMINARY COMMENTS

  1.     Extract from Paragraph #9.2, Chapter 9, NIST Final Report on the Collapse of the World Trade Center Towers – Report Reference NIST NCSTAR 1 (2005) …

  • NIST believes  that these Recommendations are both realistic and achievable within a reasonable period of time, and that their implementation would make buildings safer for occupants and emergency responders in future emergencies.
  • NIST strongly urges  that immediate and serious consideration be given to these Recommendations by the building and fire safety communities – especially designers, owners, developers, codes and standards development organizations, regulators, fire safety professionals, and emergency responders.
  • NIST also strongly urges  building owners and public officials to:  (i) evaluate the safety implications of these Recommendations for their existing inventory of buildings;  and (ii) take the steps necessary to mitigate any unwarranted risks without waiting for changes to occur in codes, standards, and practices.

  2.     At the time of writing … it is important to point out that although they are related Structural Concepts … and there is still, to this day, a lot of confusion about these concepts in the USA … it is important to clearly distinguish between …

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 distortion, displacement and 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.

  3.     Recommendation 2, below, would certainly need to be understood and implemented within today’s additional design constraints of Sustainable Climate Change Adaptation and Resilience to Severe Weather Events.  Therefore … Design Wind Speeds must be increased, accordingly, for ALL Buildings.

  4.     As such a high level of performance is expected … indeed demanded … of a Sustainable BuildingSustainable Fire Engineering must be ‘reliability-based’.  In other words, it must have a rational, empirical and scientifically robust basis … unlike conventional fire engineering, which is yet aimlessly wandering around in pre-historic caves !

  5.     Finally … there is no use trying to hide the fact that progress on implementing the NIST Recommendations, within the USA, has been lamentably slow.  Outside that jurisdiction, the response has ranged from mild interest, to complete apathy, and even to vehement antipathy.  The implications arising from implementation are much too hard to digest … for long established fire safety professionals and researchers who are unswervingly committed to the flawed and out-of-date practices and procedures of conventional fire engineering and, especially, for vested interests !

However … is it either in society’s interest, or in the interests of our clients/client organizations … that, to give you a simple example which is relevant close to home, British Standard 9999 (published on 31 October 2008): ‘Code of Practice for Fire Safety in the Design, Management and Use of Buildings’ takes absolutely no account of any of the NIST Recommendations ?   As far as the British Standards Institution is concerned … 9-11 never happened … which I think is an inexcusable and unforgivable technical oversight !

For this reason, the General Public in ALL of our societies and Clients/Client Organizations in ALL countries should also be fully aware of the contents of these Recommendations …

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Colour photograph showing the two World Trade Center Towers immediately after the impact of the second plane. At a fundamental level, this was a very serious 'real' fire incident ... which was extensively, and very thoroughly, investigated by the U.S. National Institute of Standards & Technology (NIST) ... and resulted in the important 2005 & 2008 NIST Recommendations. Click to enlarge.

Colour photograph showing the two World Trade Center Towers immediately after the impact of the second plane. At a fundamental level, this was a very serious 'real' fire incident ... which was extensively, and very thoroughly, investigated by the U.S. National Institute of Standards & Technology (NIST) ... and resulted in the important 2005 & 2008 NIST Recommendations. Click to enlarge.

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2005 NIST WTC RECOMMENDATIONS

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 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.

a.   Progressive collapse* should be prevented in buildings.

[ * F-19  Progressive collapse (or disproportionate damage) occurs when an initial local failure spreads from structural element to structural element resulting in the collapse of an entire structure or a disproportionately large part of it.]

The primary structural systems should provide alternate paths for carrying loads in case certain components fail (e.g. transfer girders or columns).  This is especially important in buildings where structural components (e.g. columns, girders) support unusually large floor areas.*

[ * F-20  While the WTC towers eventually collapsed, they had the capacity to redistribute loads from impact and fire damaged structural components and sub-systems to undamaged components and sub-systems.  However, the core columns in the WTC towers lacked sufficient redundant (alternative) paths for carrying gravity loads.]

Progressive collapse is addressed only in a very limited way in practice and by codes and standards.  For example, the initiating event in design to prevent progressive collapse may be removal of one or two columns at the bottom of the structure.  Initiating events at multiple locations within the structure, or involving other key components and sub-systems, should be analyzed commensurate with the risks considered in the design.  The effectiveness of mitigation approaches involving new system and sub-system design concepts should be evaluated with conventional approaches based on indirect design (continuity, strength and ductility of connections), direct design (local hardening), and redundant (alternate) load paths.  The capability to prevent progressive collapse due to abnormal loads should include:  (i) comprehensive design rules and practice guides;  (ii) evaluation criteria, methodology, and tools for assessing the vulnerability of structures to progressive collapse;  (iii) performance-based criteria for abnormal loads and load combinations;  (iv) analytical tools to predict potential collapse mechanisms;  and (v) computer models and analysis procedures for use in routine design practice.  The federal government should co-ordinate the existing programmes that address this need:  those in the Department of Defence;  the General Services Administration;  the Defence Threat Reduction Agency;  and NIST.  Affected Standards:  ASCE-7, AISC Specifications, and ACI 318.  These standards and other relevant committees should draw on expertise from ASCE/SFPE 29 for issues concerning progressive collapse under fire conditions.  Model Building Codes:  The consensus standards should be adopted in model building codes (i.e. the International Building Code and NFPA 5000) by mandatory reference to, or incorporation of, the latest edition of the standard.  State and local jurisdictions should adopt and enforce the improved model building codes and national standards based on all 30 WTC Recommendations (2005).  The codes and standards may vary from the WTC Recommendations, but satisfy their intent.

b.   A robust, integrated predictive capability should be developed, validated, and maintained to routinely assess the vulnerability of whole structures to the effects of credible hazards.  This capability to evaluate the performance and reserve capacity of structures does not exist and is a significant cause for concern.  This capability would also assist in investigations of building failure – as demonstrated by the analyses of the WTC building collapses carried out in this Investigation.  The failure analysis capability should include all possible complex failure phenomena that may occur under multiple hazards (e.g. bomb blasts, fires, impacts, gas explosions, earthquakes, and hurricane winds), experimentally validated models, and robust tools for routine analysis to predict such failures and their consequences.  This capability should be developed via a co-ordinated effort involving federal, private sector, and academic research organizations in close partnership with practicing engineers.

NIST WTC Recommendation 2.

NIST recommends that nationally accepted performance standards be developed for:  (1) conducting wind tunnel testing of prototype structures based on sound technical methods that result in repeatable and reproducible results among testing laboratories;  and (2) estimating wind loads and their effects on tall buildings for use in design, based on wind tunnel testing data and directional wind speed data.  Wind loads specified in current prescriptive codes may not be appropriate for the design of very tall buildings since they do not account for building-specific aerodynamic effects.  Further, a review of wind load estimates for the WTC towers indicated differences by as much as 40 % from wind tunnel studies conducted in 2002 by two independent commercial laboratories.  Major sources of differences in estimation methods currently used in practice occur in the selection of design wind speeds and directionality, the nature of hurricane wind profiles, the estimation of ‘component’ wind effects by integrating wind tunnel data with wind speed and direction information, and the estimation of ‘resultant’ wind effects using load combination methods.  Wind loads were a major factor in the design of the WTC tower structures and were relevant to evaluating the baseline capacity of the structures to withstand abnormal events such as major fires or impact damage.  Yet, there is lack of consensus on how to evaluate and estimate winds and their load effects on buildings.

a.   Nationally accepted standards should be developed and implemented for conducting wind tunnel tests, estimating site-specific wind speed and directionality based on available data, and estimating wind loads associated with specific design probabilities from wind tunnel test results and directional wind speed data.

b.   Nationally accepted standards should be developed for estimating wind loads in the design of tall buildings.  The development of performance standards for estimating wind loads should consider:  (1) appropriate load combinations and load factors, including performance criteria for static and dynamic behaviour, based on both ultimate and serviceability limit states;  and (2) validation of wind load provisions in prescriptive design standards for tall buildings, given the universally acknowledged use of wind tunnel testing and associated performance criteria.  Limitations to the use of prescriptive wind load provisions should be clearly identified in codes and standards.

The standards development work can begin immediately to address many of the above needs.  The results of those efforts should be adopted in practice as soon as they become available.  The research that will be required to address the remaining needs also should begin immediately and results should be made available for standards development and use in practice.  Affected National Standard:  ASCE-7.  Model Building Codes:  The standard should be adopted in model building codes by mandatory reference to, or incorporation of, the latest edition of the standard.

NIST WTC Recommendation 3.

NIST recommends that an appropriate criterion be developed and implemented to enhance the performance of tall buildings by limiting how much they sway under lateral load design conditions (e.g. winds and earthquakes).  The stability and safety of tall buildings depend upon, among other factors, the magnitude of building sway or deflection, which tends to increase with building height.  Conventional strength-based methods, such as those used in the design of the WTC towers, do not limit deflections.  The deflection limit state criterion, which is proposed here is in addition to the stress limit state and serviceability requirement;  it should be adopted either to complement the safety provided by conventional strength-based design or independently as an alternate deflection-based approach to the design of tall buildings for life safety.  The recommended deflection limit state criterion is independent of the criterion used to ensure occupant comfort, which is met in current practice by limiting accelerations (e.g. in the 15 to 20 milli-g range). Lateral deflections, which already are limited in the design of tall buildings to control damage in earthquake-prone regions, should also be limited in non-seismic areas.*

[ * F-22  Analysis of baseline performance under the original design wind loads indicated that the WTC towers would need to have been between 50 % and 90 % stiffer to achieve a typical drift ratio used in current practice for non-seismic regions, though not required by building codes.  Limiting drift would have required increasing exterior column areas in lower stories and/or significant additional damping.]

Affected National standards:  ASCE-7, AISC Specifications, and ACI 318.  Model Building Codes:  The standard should be adopted in model building codes by mandatory reference to, or incorporation of, the latest edition of the standard.

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