Experimental Study of Braced Steel Frames Subjected to Fire After Earthquake

The EQUFIRE project aims to study the post-earthquake fire performance of steel frame structures and is part of the Transnational Access activities of the SERA project (www.sera-eu.org) at the ELSA Reaction Wall of the European Commission - Joint Research Centre. As it has happened in many historical occasions, after an earthquake, earthquake-induced rupture of gas piping, failure of electrical systems, etc. may trigger fire. The structural fire performance can deteriorate because the fire acts on a previously damaged structure. In addition, the earthquake may have damaged fire protection elements and the fire can spread more rapidly if compartmentation walls have failed. This is particularly relevant for steel structures as the high thermal conductivity of elements with small thickness entails quick temperature rise with consequent fast loss of strength and stiffness. EQUFIRE studied a four-storey three-bay steel frame with concentric bracings in the central bay. The structure was designed for reference peak ground acceleration equal to 0.186g, soil type B and type 1 elastic response spectrum according to Eurocode 8. Tests were performed at the ELSA Reaction Wall and at the furnace of the Federal Institute for Materials Research and Testing (BAM). The experimental activities at the ELSA Reaction Wall comprise pseudo-dynamic tests on a full-scale specimen of the first storey of the building, while the upper three storeys are numerically simulated. The aim is to study the response of the structure and fire protection elements with their interaction, under the design earthquake and for different configurations: bare frame without fire protection, specimen with three fire protection solutions (conventional and seismic-resistant boards, and vermiculite spray). Fire protection are applied on the bracing and one column, and with conventional and seismic-resistant fire barrier walls built in the two external bays of the specimen. The testing programme at BAM included fire tests of four columns (without fire protection elements and with the three types of fire protection mentioned above). Before the fire test, each column was subjected to a horizontal and vertical displacement history resulting from the seismic action. During the fire tests, the effect of the surrounding structure was simulated by limiting axial thermal expansion. The experimental results will serve to study the response of structural and non-structural components to fire following earthquake scenarios, with a view to improving existing design guidelines and future standards.