Diseño Prestacional y Diseño Sostenible 2 mayo 2010Posted by pbdfire in diseño prestacional, fire safety, performance based, simulacion de incendios.
Sin más, os presentamos un extracto de un artículo muy interesante y completo sobre como el diseño prestacional, la ingeniería de incendios y las simulaciones CFD, pueden y deben ayudar al diseño de edificios sostenibles, y complementar a los códigos prescriptivos tradicionales.
El artículo incluye un par de ejemplos de aplicación de simulación de incendios en edificios singulares con atrios, utilizados para el diseño de los sistemas de ventilación y control de humos.
Prescriptive to Performance-Based Design in Green Buildings.
By: Craig E. Hofmeister, P.E.
“…this article will focus on how the fire protection engineer (FPE) can participate in and support the building design process for a sustainable design. The solutions to the prescriptive code challenges can range from relatively simple common-sense alternatives to more detailed performance-based design analyses. The code compliance issues are often similar to those which the FPE has developed solutions for in the past; they are now just put in a green wrapper.
The sustainable building design concept is a focus on increasing the efficiency of resource use while reducing impact on human health and the environment throughout the building’s lifecycle. In general, this includes optimizing and reducing natural resource use, integrating the building within the local landscape, and a focus on building siting and operation, and optimizing transportation and similar community infrastructure use. As such, green building certification processes, such as the USGBC LEED certification, typically utilize several categories to evaluate the overall building design and operation. The LEED certification process includes points based upon categories including site sustainability, water efficiency, energy and atmosphere, materials and resources, indoor environment and quality, and innovation and design. The building can then be certified at various levels, including certified, silver, gold or platinum, based upon the number of points gained in the evaluation process.
In support of the green building certification processes, the FPE has often been asked the question, “What points can fire protection gain the project for green building certification?” Unfortunately, the simple answer is usually “none,” or perhaps more accurately “none directly.” However, the same concepts and design elements that are used to meet the building’s sustainable design goals are often in conflict with prescriptive code requirements. Therefore, the FPE can develop alternative or performance-based options to help the architect and design team meet the sustainable design goals for the project, and in turn, influence the certification process. The following will outline several areas of potential prescriptive code issues and/or general fire protection and life safety concerns and discuss some potential analysis options to maintain a consistent level of fire protection and life safety for the building design.
In general, the fire resistance construction requirements for a building are dictated by the building’s size, use and protection features to determine the basic construction type in accordance with the applicable building code. Larger commercial buildings typically require a fire resistance rated structural frame as well as additional fire resistance rated assemblies for separation of different use groups or specific building features (such as atriums, exit components, etc.).
This basic design premise results in large, open building spaces, which span multiple floor levels, often classified as atriums, and a desired use of materials such as glass and unprotected steel for assemblies that are required by prescriptive codes to maintain a fire resistance rating. A notable example of this design concept is the MASDAR Corporate Headquarters Building in Abu Dhabi, United Arab Emirates as seen in Figure 1.
The striking design includes several integral cone building elements intended to moderate natural ventilation for the space as well as provide natural light transfer throughout many levels of the building. The cone elements are part of the structural frame of the building, which would require a fire resistance rating based upon the applicable building code. Several of the cone elements also constitute atrium spaces, which would also require fire resistance rated separation on several levels.
Traditional methods of providing the required fire resistance rating would clearly mitigate the intent of the design, and therefore a performance-based approach was deemed appropriate. In this case, a specific review of the use, fuel loading and potential fire hazards was conducted to develop conservative severe-case fire scenarios for the spaces, and working with the project structural engineer, an analysis incorporating the design fire exposures, materials and structural loading conditions was conducted to develop an appropriate protection scheme for the specific building elements.
While the above building design is certainly distinctive, the more common use of traditionally non-rated materials in applications that may require a fire resistance rated assembly in accordance with the applicable code is be coming commonplace in green building designs. Further, more innovative ideas, ranging from undulating concrete floor/ceiling assemblies to optimize radiant heating/cooling systems, to encapsulating landfill waste (such as plastic bottles) within structural elements are being proposed to further the sustainable design principles. It likely will be incumbent on the FPE to develop methods to analyze and assess these unique design ideas.
FIRE PROTECTION SYSTEMS DESIGN AND INSTALLATION
Another challenge in green building designs can often include the design and installation of fire protection systems, such as automatic sprinklers, fire alarm and smoke control. When discussing sustainable design and fire protection systems, many thoughts jump immediately to whether reclaimed water, such as stormwater or pumped groundwater, can be used for a sprinkler/standpipe system or whether the use of alternative suppression agents, such as “clean agent” systems, will have an impact on the design goals.
While each of these are valid areas of analysis and come with their individual benefits and causes of concern, an often more basic challenge can be the design and installation of the systems based on the green building design features. The challenge can range from the performance-based design of atrium smoke control systems to the placement of sprinklers and/or devices based upon obstructions, local temperature conditions, and even simply affixing devices to glazing.
Many green building designs include atrium spaces to enhance light transfer and natural ventilation throughout the building areas. Further, the atrium spaces are often of a unique design configuration as opposed to more traditional “box” type atrium spaces to optimize the design goals. The use of fire modeling and performance-based design techniques can be of direct benefit to provide a detailed assessment of simulated smoke movement and the potential impact on egress and tenability conditions within and surrounding the unique space configurations.
Additionally, such detailed analysis can also be of benefit to review the potential for natural smoke venting schemes, in support of the sustainable design concept of reducing mechanical equipment and energy usage.
The MASDAR Corporate Headquarters Building is again an example of the potential benefit of a detailed performance-based smoke control analysis. Several of the large cone elements are classified as atrium spaces, requiring smoke control based upon the applicable code requirements. The unique cone design offered an opportunity to review a natural smoke ventilation design for the spaces. Similar to the fire rated construction analysis, conservative fire scenarios were developed for the atrium and surrounding spaces. A detailed smoke modeling analysis was conducted considering such parameters as interior and exterior temperature conditions, exterior wind conditions, etc. Figure 2 shows an example of the design and a fire model simulation of the cone temperature conditions.
The fire modeling simulations allowed a detailed assessment of smoke movement and occupant tenability within the spaces and ultimately a workable natural ventilation scheme that resulted in the elimination of much of the mechanical smoke control equipment for the project.
Another example outlining several more basic fire protection systems installation issues was the design of the Sara Lee Knit Products Corporate Headquarters Building. A design sketch of one of the atrium spaces is shown in Figure 3.
In this case, the use of automatic extending and retracting sunshades created dynamic obstructions to sprinklers and detection devices, both for roof configurations as well as along curtain walls. The shades could potentially cause obstructions in the extended, partially extended, and even the closed configurations, due to the shade support equipment.
In addition, the project originally included unique undulating poured concrete floor/ceiling assemblies, intended to maximize radiant heating and cooling surface areas, which could potentially obstruct sprinkler spray patterns based on the depth of the “waves.”
In effect, the sprinkler and fire alarm detection device placements needed to be reviewed on a location-by-location basis to assess the potential obstruction under a number of different conditions. The fire alarm device locations also needed to be reviewed based upon simple issues such as affixing the devices to glazing and the potential impact of strobe flash through or reflection from the glazing.
Lastly, the abundance of glazing and the use of natural ventilation panels in the design warranted a detailed review to assess whether specific local areas could result in elevated temperatures approaching sprinkler or device activation or decreased temperatures approaching freezing for the typical and potential extreme local weather conditions.
While none of the discussed fire protection systems design and installation challenges are necessarily specific to green building design, or even items that have not been encountered on past building designs, each can be attributed to specific green building design concepts and thus will likely continue to surface in the future.
In addition, the FPE can impact building operation efficiency items, such as life cycle water conservation. As an example, the development of a specific test plan in combination with the design and installation of equipment to allow recirculated water to be used for periodic fire pump testing can result in a significant water usage savings over the life of the building. Many items are derived from simply thinking about the conservation goals for the building….”