Cyclic behaviour of semi-rigid partial-strength steel joints: Assessment by large-scale testing

The paper presents the results of an experimental investigation into the seismic performance of full-scale steel moment-resisting frames incorporating semi-rigid, partial-strength bolted joints. Three two-bay, one-storey specimens were tested under cyclic lateral loading: a reference frame, a frame subjected to concurrent gravity loads, and a frame with thinner end-plates. Complementary vibration tests were performed using an electrodynamic shaker to investigate the correlation between structural damage and variations in natural frequency. The test campaign employed extensive instrumentation, and the use of the AISC-341 loading protocol with additional cycles, enabling detailed assessment of both global and local behaviour. All specimens exhibited ductile global responses, with plastic rotation capacities exceeding 30 mrad, thus satisfying Eurocode 8 requirements for structures of moderate ductility. The inelastic behaviour was primarily governed by flexural yielding of the end-plates. Limited participation from beam ends and panel zones was evidenced, as well. While gravity loads had negligible influence on global frame performance, they affected the local hysteretic behaviour of the end-plate connections by reducing their energy dissipation capacity. Decreasing the end-plate thickness from 20 to 16 mm lowered flexural resistance and accelerated onset of plastic deformation and connection fracture. The results confirm the feasibility of using semi-rigid, partial-strength joints in frames for moderate seismic regions. The study provides empirical evidence supporting the advancement of design methodologies and performance-based assessment of steel joints in seismic applications. • Full-scale tests on MRF with semi-rigid joints extending state-of-the-art. • Experimentally validates ductile seismic energy dissipation in end-plates. • System- and local-level effects of gravity loads and thinner end-plates shown. • Links stiffness loss from structural damage to reduction in natural frequency. • Offers evidence to advance design of steel structures for moderate ductility.