Hybrid Fire Following Earthquake Testing of a Steel Braced Frame

The paper presents the results of an experimental-numerical analysis aimed at investigating the performance of passive fire protections applied to steel columns under fires following earthquake (FFE) scenarios. In particular, five FFE tests on columns belonging to a steel braced frame were performed at the Bundesanstalt für Materialforschung und -prüfung (BAM, Federal Institute for Materials Research and Testing)a by means of hybrid fire testing technique. In particular, an internal steel column of the ground floor belonging to a three-bay, four-storey concentrically braced steel building was tested, whilst the effect of the remainder of the structure was numerically simulated by means of an equivalent axial stiffness. Since the structure has a low degree of redundancy, the loss of a column can trigger global structural collapse. Two FFE tests were performed without any fire protection system and the other FFE tests were performed with three different fire protection solutions, i.e. conventional and seismic-resistant calcium silicate boards as well as vermiculite spray-based protection. Each column was firstly subjected to horizontal and vertical displacements resulting from seismic nonlinear time-history analysis performed on the numerical model of the case study. Then, the furnace was switched on and the ISO 834 standard fire curve was applied to the specimen. Numerical models were developed and calibrated on experimental data using different types of finite elements. The calibrated models with the presence of axial and rotational springs accurately captured the transition from pre- to post-buckling behavior. These findings highlight the importance of accurate modelling of the boundary conditions. Despite the fact, that seismic intensity was at life safety limit state, it was also found that the seismic damage of the fire protections was not high enough to hinder the fire performance of the fire protections.