Structual fire design

Author: Design of fire resistance buildings

Structual fire design

Fire Resistance is governed by two basic models:
 

• Heat model
• Structural model

which normally have three to four levels of sophistication. Traditional methods of assessment are based on the standard fire curve as far as heat models are concerned, but more quantitive methods are available based on natural fires. F-required and F-element are usually graded in catalogues or by calculation in fire resistances classes starting with 15 and 30 minutes and continuing by steps of 30/60/90 minutes.

The term "Current Fire Resistance Requirements" is taken generally to mean the values fixed by codes. They always use Fire Resistance classes which represent the time an isolated element will resist the action of a standard fire as defined by the heat exposure given by ISO-834. The level of requirements is a function of the number of storeys, and depending on the country, can be a function of the occupancy of the building and of the fire load.

The concept of equivalent or effective fire duration provides a first but important step towards a more differentiated approach. The equivalent fire duration is a quantity which relates a non-standard or natural fire exposure to the standard fire, and can be calculated if the fire load density and the ventilation conditions of the fire compartment are known.

In more advanced concepts of the equivalent fire duration, the effects of the thermal properties of the building components surrounding the fire compartment are accounted for. For current occupancies and their types of fire compartments, the T-equivalent concept gives a reasonable approach to the reality of fire. Basically the value of the required fire resistance (Frequired) should be: Frequired = g . Te where g is a partial safety factor for model uncertainties. For normal cases g is often taken equal to one, due to the fact that a part of the fire load burns outside the fire compartment and that the combustion is never a total one.

There is a growing belief that there is a need to move away from the Building Codes approach to structural fire design. Structural fire design; BS EN 1997. The minimum legislative level of safety for structural fire design aims to provide an acceptable risk associated with the safety of building occupants. In structural fire design, the concern must be that the structure will fulfil its purpose, both during the fire - and for a minimum period afterwards. Structural fire design codes: BS5268: Part 4 (timber), BS5950: Part 8 (steel), BS5628: Part 3(masonry). Design of Concrete Structures Part 1.2: General Rules-Structural Fire Design," Eurocode 2.  Eurocode 1, Part 1-2: Structural fire design.

The real behaviour of different steel grades at fire temperatures in order to provide a good basis for the structural fire design of steel structures. Fire Safety Engineering Design of Structures. substantial heat capacity, structural fire design, free thermal strain, fire test performance, unprotected steelwork. Educate designers in the use of structural fire design codes. Structural fire design of steel and composite structures. General rules and rules for buildings and structural fire design. Advanced Structural Fire Design of Offshore Structures.