Loads under fire exposure refer to forces and/or reactions caused by an exceptional situation such as fire and the high temperature accompanying this phenomenon. These loads are quite important during the design and analysis of buildings, construction objects and other structures exposed to the risk of fire or subject to fire protection conditions. They can act in any direction, which is why the greatest emphasis in fire resistance calculations is placed on longitudinal and transverse forces. From the point of view of their effect on a given building, they are unpredictable not only in terms of direction, but also strength and duration.
In order to ensure adequate fire protection, it is important to design structural elements properly, including fixings in load-bearing building elements, in order to ensure the required behaviour of the entire structure in fire conditions. Models of structures should be adopted that allow for determining the behaviour of the structure with acceptable accuracy. It is also recommended that they are suitable for the considered limit states. Models of structures should be established in accordance with recognised engineering theory and practice. If necessary, these models should be verified experimentally.
Fire resistance calculations according to EN 1991-1-2
The calculation of the fire resistance of the structure should be based on the fire design scenario and take into account the temperature change models inside the structure, as well as the behavior of the mechanical structure exposed to high temperatures. It is recommended that the required behavior of the structure in fire conditions be verified: by analyzing the entire structure, a subassembly of the structure or a structural element – or by using data from tables or test results. The behavior of the structure in fire conditions should be assessed taking into account the following conditions, as well as accompanying actions.
- nominal fire conditions, or
- fire conditions models.
The behaviour of the structure subjected to high temperatures shall be assessed in accordance with EN 1992 to EN 1996 and EN 1999, which provide calculation models for temperatures and structures. If appropriate to the specific material and assessment method, then:
- temperature models can be established assuming uniform or non-uniform temperature across the cross-section and along the length of the structural element;
- structural models may be limited to the analysis of single structural elements or may take into account the interaction of structural elements under fire conditions.
Additionally, it is recommended that models of the mechanical behaviour of structures under fire conditions are non-linear.
The properties of fasteners subjected to fire loading are divided into categories according to fire resistance:
- R30
- R60
- R90
- R120
R30 lub R60,… – fire resistance class for the load-bearing criterion for 30, or 60,… minutes in standard fire exposure
Fire attack acc. to “Annex D” in EN 1992-4 standard
The design method for anchors and fixings covers fasteners with a fire exposure from one side only. For fire exposure from more than one side, the design method may be used only, if the edge distance of the fastener is both:
- c ≥ 300 mm
- c ≥ 2hef
The above-described parameters (fire exposure and fire attack) can be defined in the EasyFix program in the “Loads” tab using drop-down lists – as shown in the graphic below.
The EasyFix program allows loads under fire exposure to be taken into account in fastener design cases in following modules: Concrete, Balustrade and Post-installed rebar. For the first two modules, calculations under fire conditions are carried out for mechanical anchors: R-HLX, R-HPTII, R-HPTIII, R-RB and taking into account data outside ETA, chemical anchor: R-KERII. For the Post-installed rebar module, calculations can be made using R-KEXII epoxy resin, R-KERII-S hybrid resin and R-KER vinylester resin.
Author: Eng Jakub Oleksy (Technical Support Engineer)
If you have any additional questions, please contact us – Rawlplug Technical Helpdesk
Download and check the program EasyFix
Find out more at rawlplug.com
Comment section
Share this article: