Calculation of the heating rate of an unprotected steel member in a standard fire resistance test

ENV.1991-2-7 is the new ‘European standard code of practice for actions on structures exposed to fire’. The document recommends a standardized procedure for the calculation of the fire resistance of a structural member. For each member state of the EU, a national application document (NAD) is being drafted to provide values of those parameters used in the calculations described in the code of practice. The first part of this paper provides a justification o f the values recommended for test piece surface and furnace emissivities as well as the safety factors in the UK version of the NAD.

ENV.1991-2-7 is designed to have a working life of only three years, after which its contents will be reviewed in the light of the experience gained during its use, before being issued as a final EN standard. The second part of this paper attempts to identify the most important developments needed during this three year period. There is an urgent need to develop a reliable means of measuring and controlling the total heat flux incident on a specimen during a standard fire resistance test. The availability o f total heat flux control would allow modification of EN. 1363-1 (the standard fire resistance test) to achieve harmonization of fire test results across the whole EU.

A method has been developed by which existing fire resistance test data can be used to calculate the total heat flux incident on the specimen at any instant during the test. The method has been used to compare the total incident heat flux/time characteristics of beam testing. furnaces at the Warrington Fire Research Centre (WFRC) and TNO (Delft) as well as the column furnace at the Borehamwood laboratory of the Loss Prevention Council (LPC). These characteristics have then been compared with those implied in the draft UK-NAD for ENV.1991-2-7. The latter has been shown to use heat flux/time characteristics very similar to those derived from standard test data.