1.3 Fire Engineering Analysis and Design

1.3.1 Design of Steel Members Exposed to Fire

Each of the structural members in a steel building are expected to supply the basic fire resistance requirements. Naturally, each building product is classified with its fire rating value which shows the limit time in which the product can bear the structural loads under fire safely. Therefore, the designer must take into account the fire resistance values for each building material used in building construction and ensure that the fire-related properties of these members matches the required fire performance of the whole building system.

1.3.2 Design of Steel Member Assemblies Exposed to Fire

Related code regulations necessitate structural members to have a sufficient fire resistance. There are two approaches used for a fire resistant building design: prescriptive and performance-based systems. The prescriptive approach defines a fire resistant design by using the materials and geometric shape of the building members, composition and the thickness of the protective materials, the member assembly details and so on. In general, the design code recommendations are prepared in relation to previously performed fire tests which work very well for most of the cases concerning static building loads. However, this approach has some restrictions regarding some detailed architectural applications. On the other hand, performance-based applications are effectively used, especially concerning the lateral loads caused by wind and earthquakes. Regarding this method, structural performance of the building members are tested and measured under the effect of a fire in order to observe the capacity of the structure to resist the acting loads during the fire. Although it is primarily aimed to have a well-done structural fire design that will enable the whole structure to resist flames, it is not possible to isolate a fire-exposed, and thus excessively heated, structural member from the other building parts with which it is interconnected. Therefore, it is an important issue to evaluate the fire resistance of a structural building assembly correctly. Fire resistance tests, heat simulation models, critical temperature methods, approximate calculation models and use of design tables and empirical approaches are examples of the evaluation methods used for steel building fire design. Standard fire resistance tests are conducted over the structural assemblies, while loaded with design building loads. It is an observed fact that a critical temperature can be reached between 450 ⁰C to 650 ⁰C. Various software programs also can be supplied and used in fire related structural design that conduct thermal and physical simulations which consider different failure modes in relation to various fire scenarios.

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