This language permits the designer to use an approach outside the prescriptive requirements of the code, provided the building official deems it in compliance with the intent of the code.
At its core, performance-based design is about alleviating some of the prescriptive requirements of codes and standards and allowing for design flexibility. Generally, the designer is obligated to demonstrate how the proposed alternative is equal to certain aspects of the code, which can include fire safety compliance and structural integrity. The fire protection engineer will encounter many potential practical applications for performance-based design, whether as a result of prescriptive codes being impractical to the situation or a better solution existing outside the constraints of the code.
One of the more common applications is smoke control system design, specifically for large voluminous spaces. IBC Section details requirements for smoke control design. One of the potential methods of smoke control is the exhaust method. Criteria for the exhaust method includes exhausting the smoke from the space at a rate to maintain a tenable environment for building occupants.
Prescriptively, the smoke layer is required to be maintained at least 6 ft above the highest walking surface within the zone.
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This could prove to be problematic, as large volumes or occupied areas above the ground floor that are open to below can require significant smoke-exhaust rates on the order of magnitude of a million cubic feet per minute cfm. This is where performance-based design could come in. With the help of a computer model—a computational fluid dynamics model—reducing the quantity of exhaust is achievable. Various factors contribute to the final quantity, as evidenced above. Provided the engineer uses sound judgment and documents his or her thought process along the way, significant savings can be achieved through not only the reduction in fan size, but also the associated equipment that would go along with it and the ongoing maintenance and testing associated with smoke control systems.
Other applications of performance-based design may include the use of a clean agent suppression system for a data center or high-value commodity space, such as a museum. The IBC requires buildings over a certain square footage to be provided with an automatic sprinkler system. For unique hazards, such as a data center or museum, IBC Section allows for alternative suppression systems.
It is important to note that the use of an alternative suppression system does not allow the designer to use the exceptions located throughout the code for a fully sprinklered building. This is another instance within a prescriptive code that allows the designer to use a different approach, as the prescriptive approach—in this case, water—is not desirable to be applied to computers, servers, and invaluable pieces of art.
Clean agent systems are intended to extinguish the fire without the use of water and without damaging the contents of the space. Another area where alternative methods are used in fire protection is the application of interior finishes and unique interior designs. The code has specific design criteria for application of interior finishes that often conflict with the interior design criteria.
Performance-based design of structural steel for fire conditions: a calculation methodology
Using an alternative method to reduce the impact of interior finish applications can be of a benefit to the design while also maintaining fire safety measures. The main concern with interior finishes is the spread of fire and smoke should the finish ignite. Alternative measures to mitigate these concerns could include increased sprinkler protection for the space. Cost savings is not the only reason to consider performance-based design, although this can be a significant driving factor, especially in the case of smoke control system design.
Historical renovations may cost more when using performance-based design to maintain the integrity of the structure. However, when considering what the goals of the project are, a higher priority may be placed on the aesthetics of the building over cost. Structures built in the 17 th century were commonly constructed of heavy timber and masonry. Structures built in the 21 st century are mostly steel and concrete. How do you compare what was built several centuries ago to the prescriptive codes of today?
The normal yield strength grades available are , , , , , and , although some grades are more commonly used than others e. Higher grades are available in quenched and tempered material , , , , and - although grades above receive little if any use in construction at present. A set of Euronorms define the shape of a set of standard structural profiles:. These steels have an alloy identification beginning with A and then two, three, or four numbers. The four-number AISI steel grades commonly used for mechanical engineering, machines, and vehicles are a completely different specification series.
The standard commonly used structural steels are: .
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Because steel components are "safety critical", CE Marking is not allowed unless the Factory Production Control FPC system under which they are produced has been assessed by a suitable certification body that has been approved to the European Commission. In the case of steel products such as sections, bolts and fabricated steelwork the CE Marking demonstrates that the product complies with the relevant harmonized standard. The standard has come into force in late After a transition period of two years, CE Marking will become mandatory in most European Countries sometime early in Most construction projects require the use of hundreds of different materials.
These range from concrete of all different specifications, structural steel of different specifications, clay, mortar, ceramics, wood, etc. Most commercial and industrial structures are primarily constructed using either structural steel or reinforced concrete. When designing a structure, an engineer must decide which, if not both, material is most suitable for the design. There are many factors considered when choosing a construction material. Cost is commonly the controlling element; however, other considerations such as weight, strength, constructability, availability, sustainability, and fire resistance will be taken into account before a final decision is made.
The tallest structures today commonly called " skyscrapers " or high-rise are constructed using structural steel due to its constructability, as well as its high strength-to-weight ratio. In comparison, concrete, while being less dense than steel, has a much lower strength-to-weight ratio.
Designing Steel Structures for Fire Safety
This is due to the much larger volume required for a structural concrete member to support the same load; steel, though denser, does not require as much material to carry a load. However, this advantage becomes insignificant for low-rise buildings, or those with several stories or less. Low-rise buildings distribute much smaller loads than high-rise structures, making concrete the economical choice. This is especially true for simple structures, such as parking garages, or any building that is a simple, rectilinear shape. Structural steel and reinforced concrete are not always chosen solely because they are the most ideal material for the structure.
Companies rely on the ability to turn a profit for any construction project, as do the designers. The price of raw materials steel, cement, coarse aggregate, fine aggregate, lumber for form-work, etc. If a structure could be constructed using either material, the cheapest of the two will likely control.
Another significant variable is the location of the project. The closest steel fabrication facility may be much further from the construction site than the nearest concrete supplier. The high cost of energy and transportation will control the selection of the material as well. All of these costs will be taken into consideration before the conceptual design of a construction project is begun.
Structures consisting of both materials utilize the benefits of structural steel and reinforced concrete. This is already common practice in reinforced concrete in that the steel reinforcement is used to provide steel's tensile strength capacity to a structural concrete member. A commonly seen example would be parking garages. Some parking garages are constructed using structural steel columns and reinforced concrete slabs.
The concrete will be poured for the foundational footings, giving the parking garage a surface to be built on. Pre-cast concrete beams may be delivered on site to be installed for the second floor, after which a concrete slab may be poured for the pavement area.
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