Numerical Investigation on the Fire Performance of Concrete Encased Steel Composite Columns with High Strength Materials

Abstract Concrete Encased Steel (CES) composite columns exhibit excellent mechanical properties at room temperature, owing to the confining effects that the stirrups and the steel profile provide to the encased concrete. These columns show a good bearing capacity/cost ratio, besides an inherent advantage in case of fire related to the thermal protection offered by the concrete mass, which delays the degradation of the inner steel profile under the thermal action. However, the fire performance of these columns may be compromised by the occurrence of spalling, since the concrete mass remains directly exposed to the fire source. Additionally, the development of high‐performance materials opens a new range of possibilities for their application in composite columns with embedded steel profiles, where they can be very useful for substantially improving their fire resistance in the case of slender columns, while contributing to reduce the associated carbon footprint through the more rational use of materials. The benefits of using high‐strength steel and concrete in CES composite columns have already been proven for room temperature design, showing a significant enhancement of their load‐bearing capacity and, consequently, a reduction on the sectional dimensions and volume of material used. By using the appropriate combination of steel and concrete grades, it may also be possible to obtain an enhanced fire resistance without the need for external protection, with the consequent savings in costs and execution times. In this investigation, a finite element model is developed and validated against the fire test results on CES composite columns available in the literature. Based on this numerical model, parametric analyses varying the concrete strength, steel strength, load ratio and slenderness of the column specimens are conducted, to investigate the influence of these parameters over the fire performance of this typology and derive practical recommendations for the fire design of CES composite columns.