Post earthquake fire and seismic performance of welded steel-concrete composite beam-to-column joints

The performance of steel-concrete composite full strength joints endowed with concrete
filled tubes, designed with a multi-objective methodology dealing with seismic actions followed by fire is presented in this paper. In detail, instead of a traditional single-objective design where fire safety and seismic safety are independently achieved and the sequence of seismic and fire loading are not taken into account, the proposed design approach guarantees: i) both seismic safety and fire safety with regard to accidental actions; ii) fire safety for at least 15 min fire exposure on a joint characterised by stiffness deterioration and strength degradation due to seismic loading.
In order to achieve the multi-objective design, full strength beam-to-composite tubular column joints were designed by means of the component method of Eurocode 4 Part 1-1 and Eurocode 3 Part 1-8, while Eurocode 4 Part 1-2 was considered for fire design. Moreover, to face seismic-induced fire, they were enhanced with specific joint components which will be detailed.
Both the experimental program and the results provided by seismic tests, pre-damaged tests and fire tests carried out on beam-to-column joints are presented and discussed. The results emonstrate their adequacy in terms of design and performance. Moreover, non-linear numerical simulations clearly show that these joints can be deemed adequate for moment resisting frames of medium ductility class characterized by a behaviour factor of about 4.