BRE IP9/12 PDF

INTRODUCTION

Fire performance for elements of structure is traditionally assessed in relation to performance in a standard fire test[1, 2], where structural elements are placed in a standard furnace under prescribed boundary and loading conditions and subjected to a thermal exposure corresponding to the standard time–temperature fire curve. Performance is assessed in relation to the ability of the structure to maintain loadbearing capacity, prevent the passage of flames or hot gases and restrict the temperature rise on the unexposed face of the specimen for a specified duration of time. The fire performance of structural elements of reinforced concrete is generally assessed by reference to tabulated values as set out in national codes[3] and design guides[4]. This generally involves checking that minimum dimensions and minimum cover from the exposed face of the concrete to the reinforcement are provided to achieve the specified period of fire resistance. In many cases the requirements for durability and strength under normal conditions will mean that such a check is unnecessary. With the advent of the structural Eurocodes, national standards have been withdrawn. In the first instance for new buildings, recourse should now be made to the fire part of the Eurocode for concrete design[5] to see if the structural element has the fire resistance required. For floors, the Eurocode presents tabulated data to cover simply supported and continuous solid and ribbed slabs. Such information should be used to determine the fire resistance of new forms of construction or to assess the anticipated performance of an in-situ floor system where it conforms to the provisions of the code. However, in many instances when dealing with existing structures the floor system may bear little relation to the forms of construction covered in the tabulated data. There is therefore a need for additional guidance to cover those forms of construction with which the current generation of designers, contractors and building control officers may be unfamiliar.