Development and experimental seismic study of bearing-two-level yielding energy dissipation beam-column-slab joints for precast concrete frames

Precast concrete (PC) structures always collapsed under strong earthquakes causing unpredictable damage and difficult post-earthquake repair. To achieve fast assembly and seismic resilience, a new type of damage-controllable beam-column-slab joint with a bearing-two-level yielding energy dissipation (BTED) connector for fully PC frames was proposed. The BTED mechanism was achieved by the successive yielding of low- and high-strength steel in BTED connector to dissipate energy in stages under different earthquake levels. Meanwhile, the limited-slip components were arranged above the BTED connector to control the cracking damage of the PC slab. To comprehensively understand the seismic performance and the replaceability of the proposed joint, cyclic loading tests were carried out on five specimens, including three PC joints, one post-repaired PC specimen, and one monolithic joint. The failure modes, load-displacement curves, strength and stiffness, and energy dissipation capacity were investigated. Test results showed that the monolithic joint exhibited flexural failure with serious concrete crushing and reinforcement fracture, while the PC joint achieved the PC beam, column, and slab remaining elastic and concentrated the damage at the BTED connector, whose two-level-stage yield mechanism was effectively realized. The PC joint with BTED connector exhibited improved post-yield stiffness, enhanced seismic performance, and excellent post-earthquake repairability. The repaired joint behaved highly similar damage development and seismic performance to the previous joint. Moreover, the design methods of the first- and second-stage yield bending moments of the joint with BTED connector were proposed and verified to be in good agreement with the experimental results.