Fire resistance of a civil engineering structure
This is the time from the beginning of the thermal impact on the structure to the occurrence of one or several limit states in terms of fire resistance, taking into account the functional purpose of the structure. The limit state of the structure in terms of fire resistance is characterised by the fact that the structure loses the ability to fulfil one of its fire resistance functions, namely: the load-bearing capacity is defined by R, and the separating functions are defined by I (insulation), E (integrity).
The R criterion
It is considered to be fulfilled when the load-bearing function is maintained for the required time of fire exposure.
The I criterion
It is considered to be fulfilled if the average temperature rise over the entire unheated surface is limited to 140 K, and the maximum temperature rise at any point on that surface does not exceed 180 K.
The E criterion
It is considered to be fulfilled if the penetration of flames and hot gases through a part of the structure is prevented.
Unloaded (non-bearing) walls should meet criteria E and I, and loaded (structural) walls R, E, I.
Autoclaved aerated concrete is a non-combustible material which is classed as a material with the highest Euroclass reaction to fire – A1.
Thanks to its raw materials and porous structure, autoclaved aerated concrete displays exceptional resistance to fire and heat. It releases no harmful or toxic substances in the event of a fire. Autoclaved aerated concrete precision blocks and other masonry components are not involved in a possible fire and will keep out the spread of flames. When directly exposed to fire, it retains its load-bearing properties for a long time. In addition, properly built partitions made of this material show high stiffness.
Autoclaved aerated concrete has another very important property: it does not heat up when exposed to high temperatures. A large temperature increase in the surroundings does not lead to the same temperature changes in the material. Owing to the high resistance to high temperatures, autoclaved aerated concrete is used to construct chambers in which fire tests on other building materials are carried out.
Fire classification of walls made from autoclaved aerated concrete on the basis of the test report (03032.2/18/Z00NZP) of the Institute of Building Technology
Wall thickness *) [cm] | Load level | |||
0 | 0,2 | 0,6 | 1,0 | |
10 | EI 120 | – | – | – |
12 | EI 120 | – | – | – |
18 | EI 240 | REI 240 | REI 240 | REI 240 |
24 | EI 240 | REI 240 | REI 240 | REI 240 |
30 | EI 240 | REI 240 | REI 240 | REI 240 |
36 | EI 240 | REI 240 | REI 240 | REI 240 |
42 | EI 240 | REI 240 | REI 240 | REI 240 |
*) – applies to non-plastered walls
The column corresponding to load level “0” gives the fire classification for curtain and partition walls (unloaded)
Comment on the above table:
- Fire resistance tests are performed on models of walls that are not plastered, so the above fire resistance applies to non-plastered walls.
- The above fire resistance is for walls made with mortar for thin joints or traditional mortar.
- The EI criterion means that the wall retains the fire resistance class as an unloaded (self-supporting) wall.
- The 10 and 12 cm blocks are not used for load-bearing (structural) walls, so only the EI criterion is given for these walls.
- Walls made of SOLBET blocks, i.e. 60 and 80 mm wide elements, were not tested because partition walls should not be made of these elements.
