1.At last, we arrive at the Group 8 Recommendations ! At this stage … my impression is that the NIST Team began to run out of steam, because these two short Recommendations barely scratch the surface with regard to the significant education and training needs of the many different design, construction, management, operation, maintenance and emergency response disciplines engaged with, and confronted by, the Built Environment … every day of every week.
After a careful reading of all 30 NIST WTC Recommendations, I hope that you have satisfied yourself/yourselves that these Recommendations must be applied to ALL Buildings … not just Tall Buildings. At various times … Iconic Buildings, and Buildings having a Critical Function or an Innovative Design have been specifically mentioned. And look back to Recommendation 22a … tunnels and subways also made an appearance ! The proper focus for the International Fire Science and Engineering Community must be on the Built Environment as a whole.
At All Levels in a Typical Construction Project … there are also pressing education and training needs. It is of little use if the Project Design Documentation is 100% … and the people actually installing the passive fire protection measures or the active fire protection systems on site don’t know which end is ‘up’ ! The Project Design Documentation, in whatever format, is merely a means to an end … a fully realized and occupied Building, which is fire-safe.
Preferably … we should be discussing the mandatory Re-education and Re-training of Practitioners in the different Disciplines … [CPD (Continuing Professional/Personal Development) is not at all sufficient !] … accompanied by a very necessary Re-engineering of the Stakeholder Professional and Educational Institutions … and other related Organizations, particularly National Authorities Having Jurisdiction (AHJ’s).
Our Best Hope for Transformation … lies with the current crop of third-level undergraduate students in the different disciplines. And, as we are discovering with the introduction of the Structural EuroCodes in the European Union, it will take perhaps 5-8 years of continuous student output to transform pre-9/11 conventional fire engineering … into a post-9/11 and post-Mumbai fire engineering which is properly ‘reliability-based’ and ‘person-centred’, i.e. Sustainable Fire Engineering !
As for the Future, and Some Conclusions to this Series … coming shortly to a computer monitor screen near you !
2005 NIST WTC RECOMMENDATIONS
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 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. Affected Organizations: AIA, SFPE, ASCE, ASME, AISC, ACI, and state licensing boards. Model Building Codes: Detailed criteria and requirements should be incorporated into the model building codes under the topic ‘Design Professional in Responsible Charge’.
NIST WTC 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.Affected Organizations: AIA, SFPE, ASCE, ASME, AISC, ACI, ICC, and NFPA.
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 Region, Europe 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 !
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 …
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 Building … Sustainable 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 …
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.