Behaviour of reinforced concrete members under fire conditions
Within the scope of the revision of EN 1992-1-2, this project dealt with various topics for the design of reinforced concrete members in the event of fire: (i) the simplified design methods for bending as well as bending and normal action, (ii) the rotation capacity and (iii) explosive spalling of concrete.
Currently, EN 1992-1-2 provides several methods for verifying the fire resistance of reinforced concrete structures. In Switzerland, only one model is recommended for the design of columns, but its range of application is limited. In this research project, existing and new models are verified using, inter alia, results from extensive experimental test series carried out by the Swiss precast industry over the past five years. Furthermore, the range of application of simplified design methods is studied beyond their existing limitations.
In the event of a fire, hyperstatic systems can be subject to very large restraint moments due to temperature gradients within the cross-section. In many cases, these restraint moments can partially be re-distributed, however, EN 1992-1-2 does not provide a basis for this verification. The rotation capacity under fire conditions was last dealt with scientifically in the late 70s. With the help of these test results and the more recent fundamentals on material behaviour in the event of fire, the rotation capacity of reinforced concrete is examined with today's state of knowledge (at ambient temperature) for the verification of the load deformation behaviour of reinforced concrete.
The distinction for concrete, which can be regarded as safe with regard to explosive spalling, defined in the current EN 1992-1-2, is based on old principles – the development of concrete as a material over the last 50 years is not taken into account. Regardless of this, of the three influencing factors specified in the current EN 1992-1-2 – concrete strength, concrete moisture content and silica fume content of the concrete –, the two latter are both unusable for designing in engineering practice. The aim of the research and standardisation work on the explosive spalling of concrete is (i) to develop simple and safe provisions taking into account the current (limited) state of scientific knowledge on the material behaviour when explosive spalling occurs and (ii) to incorporate it into the standards commonly used in Switzerland (SIA 262 and EN 1992-1-2).