Experimental behaviour of heated composite steel–concrete joints subject to variable bending moments and axial forces

This paper presents the results of seven experimental tests performed at the University of Coimbra on a two dimensional composite steel–concrete beam-to-column sub-frame. These experimental tests were part of a global study of the robustness of composite steel–concrete open car park buildings under localised fire. The tested sub-frame was extracted from a composite open car park building, using the real cross-section dimensions of the beams (IPE 550) and the columns (HEB 300), and using bolts M30 grade 10.9 in the composite connection, and was subject to mechanical (bending and axial forces) and thermal loadings (constant temperature equal to 20 °C, 500 °C or 700 °C; or linear increase up to 800 °C). The interaction between the bending moment and axial load in the heated internal joint, after the loss of the column, is the objective of the tests. In order to reach this goal, the effect of the axial restraint to the beam was simulated: three tests were performed without any restraint to the beam, two tests with total axial restraint to the beam and two tests with a realistic axial restraint to the beam (spring restraint). The results of the seven tests are analysed and the behaviour of the joint is investigated and discussed in detail.

► Seven experimental fire tests were performed on a beam-to-column sub-frame.
► The heated joints were subject to combined bending moment and axial loads.
► The sub-frame showed sufficient robustness provision thanks to the ductility of the joint.
► A well designed joint is able to behave in a ductile manner under fire conditions.