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Products and solutions, 2004-01-16, 01:00 AM

Greater safety and freedom in building with steel: FRB 90 from ThyssenKrupp Stahl

Structural components of multi-story and high-rise buildings often have to meet the requirements of fire resistance class 90 (F 90), i.e. withstand a fire for 90 minutes. In the past, if these components were made of steel, they had to be protected either with boards or by spray coating with special cement. That was expensive, time-consuming and destroyed the special advantages of steel. The filigree structures and transparent glass/steel designs typical of steel buildings were impossible to achieve with elaborately protected structural members. Two other key advantages, short construction times and low structural weights, were also impossible to achieve in this way.

ThyssenKrupp Stahl AG has now developed a new solution for building with steel in the shape of the fire-resistant structural steel system FRB 90. It is based on the innovative structural steel FR 30 from ThyssenKrupp Stahl AG, which has been approved for general use for fire resistance class F 30 since February 2001. Containing chromium, molybdenum and vanadium, this material displays significantly better elevated-temperature strength than the standard structural steel S235. Its critical failure temperature is 140 degrees Kelvin higher than that of S235. FR 30 has been patented for ThyssenKrupp Stahl AG.

The new FRB 90 system consists of FR 30 with an additional intumescent coating. The coating is only a few millimeters thick. Because the steel itself already has a 30 minute fire rating, a relatively low-cost 60-minute intumescent coating can be used. If the fire resistance requirements are lower, e.g. F 60, an F 30 coating is also sufficient. FRB 90 uses the intumescent material pyroplast Stahl D plus from Rütgers Organics. It is applied simply and quickly on site after the steel structure is erected. General approval for building use has been requested for the new system from Deutsches Institut für Bautechnik (German Institute for Structural Engineering) and is expected to be granted shortly.

The FRB 90 system gives architects and building owners new freedom in building with steel: A single coating is enough to meet the requirements of Germany`s third-highest fire protection class and the one most frequently specified in multi-story and high-rise construction. The system also offers wider structural possibilities: The load-bearing ability of the fire-resistant steel is 15 percent higher than that of S235, meaning that FRB 90 beams can be used to bridge much wider spans than standard structural steel. For the same length of span, smaller sections can be used, saving material, weight and money.

Finally, FRB 90 also offers greater safety and freedom in design: As a rule, a standard design complying with DIN 18800 or EUROCODE 3 is sufficient for the system. The intumescent coating applied to the section is classified as a listed fire protection measure and so no further fire design needs to be carried out.

FRB 90 beams are welded together from heavy plates to form structural sections, and so any desired cross section can be produced so long as the ratio of perimeter to cross sectional area per meter does not exceed 200 m-1. FRB 90 sections can be tailored exactly to actual loads from the outset and can be designed to produce special architectural effects. Standard sections are naturally also possible. The beams are delivered to the site ready-welded, with ThyssenKrupp Stahl organizing the logistics. With a suitable top coat applied on top of the intumescent coating, steel structures can also be provided with special color effects.

Dietmar Stamm
Tel.: +49 203 / 52 - 2 62 67
Fax: +49 203 / 52 - 2 57 07

Bernd Overmaat
Tel.: +49 203 / 52 - 4 51 85
Fax: +49 203 / 52 - 2 57 07

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