Systematic analysis of RC Members under fire conditions
Author: Ken Zumstein
Language: English
Abstract
Generally, concrete offers good protection against high temperatures caused by fire thanks to its low thermal conductivity and its high specific heat. Therefore, the fire design is in very most cases very simple by using tabulated design data. Tabulated design data defines minimum dimensions depending on required fire resistance classes.
In Switzerland, reinforced concrete columns are usually precast with high performance concrete and a rather high degree of reinforcement (often ρ > 4%). However, for the definition of values given in tabulated design data from current standards, normal strength concrete as well as degrees of reinforcement ρ < 4% were generally used.
Since 2013, Swiss precast companies have been carrying out extensive experimental campaigns on high strength precast columns subjected to fire. After developing high performance concrete (HPC) recipes in order to avoid spalling, both numerous column stumps (more than 84 at MPFA Leipzig) and loaded full scale columns were tested under fire loading for various configurations. These tests were evaluated by using tabulated design data included in the Swiss code «SIA 262:2013» and in the European Standard «SN EN 1992-1-2:2004», as well as by using advanced design methods implemented in a commercial software from the Cubus AG. It was shown that under design assumptions, namely, long-term effects and minimum eccentricities defined in current codes, the calculated ultimate normal force resistance mostly yield conservative results when compared to the test results.
In further parameter studies by using advanced design calculations, based on the results of the above mentioned experimental campaign, supplemented with older tests results and with fictitious columns, different column configurations were examined to check their sensitivity to explosive spalling. Assuming a spalled layer, the decisive parameters and limitations of tabulated design data given in SIA 262 were identified for high performance concrete.
