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Fire Protection of Structural Steel in High Rise Buildings

Quiz Questions


1.In addition to ordinary concrete encasement, autoclaved aerated concrete (AAC) is a concrete material that uses widely available concrete constituents (sand, cement, lime, gypsum and water) with an expansion agent that after heat treating under pressure results in a finished product that is up to five times the volume of the raw materials and has an air content up to 80 percent in a closed cell structure1.

This type of material has achieved up to ___________ UL fire resistance ratings in the ASTM E-119 furnace test. It is lightweight and has high strength and can be made in slabs that could be used for enclosure of structural elements or possibly applied directly to steel prior to the autoclaving process.

2. One of the most important advantages of this method is its durability. Concrete encasement performs very well in environments where resistance to impact, abrasion, weather exposure, and corrosive agents is important. Applications can include interior or exterior components. Typical applications therefore include car parks, external structures, oil drilling platforms, and warehouses.
3.Advantages of insulating board systems include:
Aesthetics – board systems provide a clean appearance and can be finished/decorated as appropriate.
Steel preparation – boards can be attached directly to bare steel elements with little or no preparation.
Installation – installation is dry versus ‘wet’, boards are relatively easy to install, and they can be installed with limited impact on other trades. They are also relatively easy to finish off once applied. Off-site fabrication is often difficult.
Quality control – the boards are manufactured off-site where thickness, composition, etc. can be monitored.
4.Disadvantages of insulating board systems include:
Installation time – board products are often slower to install than some other types of systems.
Cost – board products may be more expensive, particularly where a ‘decorative’ finish is needed.
Installation – installing around elements and complex details may be difficult.
Maintenance – damage, service penetrations, etc., need to be fixed as they will compromise fire rating.
5.Man made mineral fiber (MMMF) type systems include those made of mineral wool. These are typically made from fibers of melted rock (97-99% by weight), organic binders and oils. It is often used as _____________, and as fire protection to structural steelwork when bound into higher density slabs using a thermosetting resin. The board systems can be installed by various means, although the use of stud-welded pins seems to offer the best mechanical properties.
Thermal insulation
Structural support
6.Spray applied fireproofing materials are typically cement-based products or gypsum with a light weight aggregate (vermiculite, perlite, or expanded polystyrene beads) that have some type of cellulosic or glass fiber reinforcement. Some of the earliest spray applied fireproofing materials contained ______________, which is no longer allowed due to health issues. Spray applied fireproofing is typically one of the more inexpensive means to protect structural elements. Thicknesses required to achieve various ratings may be found on a generic basis in some publications, but typically are provided by the manufacturer.
7.Advantages of spray include:
Application – it is easy to protect detailed features including connections, bolts, etc.
Installation – spray applied materials are quick to apply.
Durability – some spray applied materials may be used for exterior application, most though are used for interiors.
Preparation – some spray applied materials can be applied to unpainted steel.
8.Disadvantages of spray include:
Installation – the process is wet and often can be messy, and this can also impact the construction schedule and potentially the overall costs of using this method if it impacts other trades.
Preparation – steel typically needs to be prepared.
Over spraying – protecting on-site areas from overspray is typically required.
Aesthetics – it produces a rough surface finish and cannot be easily finished to meet aesthetic requirements.
Durability – the material is relatively soft and should be protected when in a vulnerable area where contact could damage the product.
Quality control – sometimes difficult, labor intensive and time consuming to adequately control quality of installation in the field.
9.Intumescent paints have been available in Europe for over 25 years, although these materials have been known for centuries. Over approximately the last 10 years, they have seen increased application in the United States and in the UK. The products are broadly similar in terms of testing, performance and applicability among manufacturers. Intumescent paints have two key components: a resin binder and a mixture of chemicals that decomposes and releases a gas when _______________.
10.During a fire, the material melts. A gas-producing reaction is triggered at a temperature corresponding to an appropriate resin melt viscosity, and the release of gas causes the resin melt to foam developing an insulating layer. This then produces a thick char, which insulates the steel from fire. Intumescents may typically expand approximately 15 times to 30 times their initial thickness during a standard fire test.
11.Advantages of intumescents include:
Installation – intumescent paints do not require a significant thickness relative to other materials.
Durability – intumescent coating are typically quite durable, and do not readily flake off when struck. Also, they can be fairly easily repaired.
Application – intumescents are relatively quick to apply. They are good at covering complex structural details. They can be applied on-site or off-site. Being applied off site can lead to decreased construction time.
Aesthetics – the relatively thin coating is often aesthetically acceptable and can be left exposed to show the shape of the structure, and also can be given a colored finish.
Maintenance – post installation repairs are relatively easy. Also, intumescent coatings are relatively easy to clean.
12.Disadvantages of intumescents include:
Cost – high relative cost when compared to spray on systems, particularly for higher fire ratings.
Application – goes on wet and hence suitable environment is needed. Also, protection of adjacent areas from overspray is necessary. Solvent-based paints need to be applied in well ventilated areas.
Installation – mechanical damage during installation of off-site prepared materials will need to be made.
Identification – it can be difficult to verify the existence of intumescents at later dates.
Maintenance/Inspections – regular inspections needed. Difficult to assess applied thickness without damaging material.
Fire ratings – coatings typically provide 30 to 120 minutes of protection.
Quality control – important that steel surfaces be appropriately prepared, paint properly applied, etc. and that proper thicknesses are applied.
13.Sprinklers can be used to protect structural elements. The water is sprayed onto the structural member at a given density to cool the structure. NFPA 15-Standard for Water Spray Fixed Systems for Fire Protection20 addresses this type of protection technology for both horizontal and vertical structural steel. This technology appears to be more prevalent in the US, and not an option typically used in the UK.
14.In many instances, particularly in tall buildings or massive structures, the mass of steel required to support the loads and resist moments is very large and thus the thermal mass of the steel itself provides inherent resistance to weakening by fire exposure for periods of time that can be determined by engineering analysis. Such time periods can exceed those required by the building code. It is suggested that by __________ the mass of steel in the basic design of the structure, the need for fire resisting assemblies or spray-applied coverings could be eliminated. It is also suggested that the incremental cost of the additional steel may be less than the cost of the additional fire resistant materials and installation. Such an approach should be investigated as a performance-based alternative solution.
15.It should also be remembered that bare steel has some degree of fire resistance. As temperatures increase, steel’s yield stress decreases. It approaches 50% of its room temperature yield stress at approximately 550 °C. Depending on fire conditions, loading, connections, end restraints, geometry of the space, etc. bare steel may be shown to provide sufficient resistance to the design fire(s) deemed credible for that space. Common applications of structures with bare steel include low-rise buildings, open car parks and external structural elements.
It approaches 50% of its room temperature yield stress at approximately 550 °C
It approaches 50% of its room temperature yield stress at approximately 1000 °C
It approaches 50% of its room temperature yield stress at approximately 2000 °C
16.Ablative coatings are those that gradually erode during exposure to a fire due to the absorbed heat energy input that changes the virgin solid coating into a gas composite. This action prevents heat transmission to the material that the ablative coating is applied to. These coatings are similar to intumescent paints, as they possess a resistance to mechanical damage. However, the application procedure is complex and this results in ___________________ for application.
relatively high costs
relatively low costs
17.Subliming compounds have an active ingredient that absorbs heat as it changes from the solid to a gas phase (i.e. sublimation). Similar to ablative coatings, subliming compounds are added to provide an additional layer for insulation. The effectiveness of subliming compounds is a function of various elements including the coating material thickness, compounds’ sublimation temperature and enthalpy at sublimation, heat capacity of the substrate, and fire exposure. The fire depletes the subliming compounds. Therefore once exposed, the protection provided by the compound is reduced or eliminated. This can be a major disadvantage during long fires that exceed the design exposure period.
18.Aerogels are solid materials with nano-meter scale pores. These are typically made of silica, and are basically “puffed up” sand possessing a 99% open porosity. This material is almost transparent. Aerogels make very good insulators due to their lattice structure. Aerogels have been in existence since the 1930’s, however until recently have been cost prohibitive for production. In the 1990’s, a new fast and more efficient solvent extraction process was developed that allowed faster production. When exposed to heat it does not thermally degrade or generate toxic fumes. A version of this with a ¼ inch thickness was tested at 1000o C for over 5 hours with limited physical and performance deterioration.