Web Exclusive Feature! Performance-Based Design: From Local Needs to Global Needs
As you stand on the Brooklyn Bridge at dawn and look out on the city, the first light of day catches the Empire State Building, then the gleaming Chrysler Building. As the sun rises further, its rays lead your eye down the boulevard, stopping at one architectural and cultural marvel after another. On your right stands a 36-story pyramid with a sphinx guarding the entrance. On your left, there's the Doges' Palace, the Rialto Bridge and St. Mark's Basilica. Across the street, the Eiffel Tower begins to glint above the Arc de Triomphe. The Eiffel Tower? Yes, you guessed it; this is Las Vegas, NV, a living monument to American fantasy, ingenuity and excess. It's also a prime example of performance-based design in action.
The unique world-unto-themselves hotel theme parks that make the Las Vegas Strip one of America's favorite vacation and gambling locations have all required performance-based design to some degree. Prescriptive codes alone cannot tell you how many exits it takes to make a restaurant safe on the 11th floor of a half-size Eiffel Tower replica.
While Las Vegas may overflow with performance-based designs, most areas of the United States still rely on building codes and fire safety standards that are prescriptive in nature. Unlike performance codes or guidelines that are based on design objectives and goals, prescriptive building codes tell you the exact requirements that must be met in order to make a structure safe for building occupants. This level of detail, while easy to enforce, also limits design options, say critics. In addition, many of these prescriptive codes have been instituted on a regional basis across the U.S. in reaction to catastrophic fires, earthquakes and windstorms, resulting in a patchwork of standards.
Many are familiar with the common U.S. residential building standard that calls for wooden studs and beams to be located 16 inches-on-center. This is a simple example of a prescriptive code. In the United States, we do not yet have a single building code or set of unified standards that are used in every state. Building construction and fire safety design in the U.S. is primarily governed on a regional basis by four code models issued by nonprofit organizations. These include: BOCA National Building Code from Building Officials and Code Administrators International (BOCA), Uniform Building Code from the International Conference of Building Officials (ICBO); Standard Building Code from the Southern Building Code Congress International (SBCCI); and Life Safety Code from the National Fire Protection Associations (NFPA).
International Code CouncilMost states and municipalities in the U.S. have adopted one or more of these codes and typically add their own modifications and amendments to cover local needs or concerns. In 1994, BOCA, ICBO and SBCCI together founded a nonprofit organization known as the International Code Council (ICC) with the mission to develop a single set of codes. One of the goals of the ICC from the outset was to incorporate the concepts of performance-based design.
In August 2000, the ICC completed the final draft of the ICC Performance Code for Buildings and Facilities. This document was the result of four years of work by the ICC Performance Building and Fire Committees. The ICC is careful to point out that its performance-based code does not replace its prescriptive codes.
According to the ICC Code Preface, "The ICC Performance Code for Buildings and Facilities clearly defines the objectives for achieving the intended levels of occupant safety, property protection and community welfare. This code is distinctly different from the prescriptive code, which directs the user to a single solution to address a safety concern for a building or facility. The performance code allows the user to systematically achieve various solutions...this code provides a procedure to help address design and review issues associated with the alternate materials and methods section of the prescriptive code."
While a typical prescriptive building code may encompass hundreds of pages, the ICC performance code consists of just 60 pages of actual performance-based code, followed by about 20 pages of appendices.
NFPA Moves AheadAt the National Fire Protection Association (NFPA), performance-based design options have been or are being added to many of the codes produced by the organization. For instance, an effort is underway now to add an appendix to the Life Safety Code, NFPA 101, which would detail performance-based criteria and definitions.
In addition, the NFPA is working towards its own building code that, while primarily prescriptive, will include a chapter on performance-based design as a code option. As part of an overall effort to create a complete set of consensus codes "for the built environment," the NFPA has decided to use Disneyworld's EPCOT Building Code as a starting point for its own code. According to the NFPA, the EPCOT Building Code already references NFPA codes and standards, making it easier to achieve harmonization.
Most important, perhaps, is the fact that the EPCOT Building Code is performance-based in nature and adaptable to innovative and challenging construction. Under its safety guidelines, buildings such as a fiberglass castle, an 18-story geosphere, and windowless assembly buildings containing hundreds of thousands of square feet of public attractions have been built.
SFPE GuideAnother organization that has taken a lead role in developing performance-based guidelines is the Society of Fire Protection Engineers (SFPE). The SFPE has released an engineering guide, the SFPE Performance-based Analysis and Design Guide, intended for anyone who will apply, approve, or be affected by performance-based codes and standards. This group includes engineers, authorities having jurisdiction (AHJs), architects, building code officials, fire code developers, building owners, fire officials, and legislators.
The SFPE Guide covers topics such as:
- Defining your project scope and identifying goals
- Specifying stakeholders and design objectives
- Developing performance criteria
- Creating design fire scenarios and trial designs
- Evaluating trial designs
- Documentations and specifications
Dr. Ron Alpert, manager of Factory Mutual Research's flammability technology research program, noted that the SFPE Guide is similar to guides published in other countries where performance-based building codes and standards are used extensively, including Japan, Australia, New Zealand and the United Kingdom. However, the SFPE Guide is not a building code, but rather a guide to performance-based structure design.
International Electrotechnical Commission (IEC)In the process industries, rapid technological developments in processes, materials and equipment have led to a demand for performance-based standards that can provide industry with greater flexibility in implementing practical and cost-effective safety solutions. Factory Mutual Research has assisted in the development of several standards in this area, including the performance-based standard IEC 61508 from the International Electrotechnical Commission (IEC), and IECd61511 for the process industries.
Paris Stavrianidis, director of Risk Engineering Methodologies at Factory Mutual Research, participated in the development of IEC 61508. "In the past, most of the process industry ran hard-wired safety systems," he explains. "Today, however, almost everything is microprocessor based. Processes have changed as well. The pace is faster with more potential danger. Monitoring and safety systems must have the ability to respond much faster."
"The IEC 61508 standard requires the process owner to identify the level of risk they currently have in their process(es) and define the level of risk they wish to achieve," Stavrianidis says. "The standard gives you the flexibility to reduce process risk in a number of different ways. For instance, you could use a microprocessor-based safety solution such as a programmable controller, a mechanical device such as a relief valve, or a passive system such as a dike. You also have to consider many other factors such as regulations, good engineering practice(s), your insurance carrier recommendations, and concerns of other stakeholders."
Stavrianidis notes that while prescriptive standards have served the process industries well for many years, the time to embrace change was obvious. "Our old standard on instrumentation and control was prescriptive," he says. "It was based on many years of loss experience and has worked very well. However, the process industries in particular had clearly moved down a path that required a new way of thinking. We could either fight the trend or get on board early and influence the development of new performance-based standards. That's what we chose to do."
Why the Sudden Interest?While it may seem as though U.S.-based code making bodies have suddenly discovered performance-based concepts, in fact, the U.S. has employed performance-based design for many years, particularly in the area of structural engineering. Performance-based design has always been an option, even with prescriptive codes, as long as you could prove or validate your design.
With the evolution and advances in engineering tools, fire testing, and fire safety systems, there is evidence that new technologies and building techniques could significantly reduce fire losses in the U.S. According to one report, the per capita fire loss record in the U.S. is still among the worst in the industrialized world.
"I believe that code issues are in fact cyclical in nature," notes Dr. Paul Croce, vice president and manager of the research division for Factory Mutual Research. "When there is new knowledge available, which is where we find ourselves now, then performance-based codes are viewed as superior to prescriptive codes. It's believed that state-of-the-art technology and tools will result in the development of superior designs and protective schemes. This was true with structural design some years ago.
"As new techniques and technologies become more widely understood, codes tend to again become prescriptive as consistency is sought. Then as prescriptive codes take root, they tend to be viewed as unchanging and out-of-date, particularly as new knowledge arises," he adds.
Benefits CitedWhile the jury is still out on whether performance-based codes have been effective in areas of the world where they are widely used, advocates attribute the following benefits to performance-based design:
- Increased design flexibility
- Greater cost efficiency
- Better structural and fire performance
- Increased safety
- Improved global competitiveness
Barriers to OvercomeWhile the potential benefits of performance-based standards and codes may be many, the road to performance rewards can be a long one. According to a white paper released by Worcester Polytechnic Institute (WPI) in conjunction with its "Second Conference on Fire Safety Design in the 21st Century," the barriers that stand in the way of the widespread adoption of performance-based codes include social, legal, political, attitudinal, economic and institutional changes.
The WPI white paper noted that "the transition from prescriptive to performance-based codes and design practices is not an easy one. An entirely new way of thinking must be instilled in the minds and practices of designers, AHJs and others. And new tools must be evaluated for their validity and adopted by reference in the model codes and standards."
According to Dr. Alpert, there seems to be reluctance on the part of engineering firms to participate in the effort to standardize performance-based methodologies for fire protection engineering. "Unlike some of the more fundamental standards, such as those defining concrete or fire resistance materials, there is not a strong financial incentive for engineering firms to help standardize engineering and design methodologies," he stressed. "These firms succeed because of their unique approaches to design and they don't want to give that up or reveal their approach in detail. I believe it will take the influence of AHJs and others to convince many design firms to participate."
For additional information on work being conducted by Factory Mutual Research, visit www.fmglobal.com.