Effects of strain-hardening of structural steel and limited damage of joints on the seismic design of moment-resisting steel frames

The responses of four different steel moment-resisting frames are analysed in the seismic context defined by Eurocode 8-1. In particular, the q-factor and the evaluation of the inelastic displacements are examined thoroughly considering three assumptions successively: perfectly-plastic behaviour of structural steel, plastic behaviour with strain-hardening, and use of partial-strength beam-to-column joints. The q-factor appears clearly depending on the rotation capacity of the dissipative elements. The present specifications of Eurocode 8-1 on the required rotation capacity are deemed generally optimistic and even too unsafe when partial-strength joints are used. However, Eurocode procedure to determine the inelastic displacements appears conservative provided the rotation capacity of the dissipative elements is not too low.