Xu, Guo, Li, 2022
In this study, a new approach to steel moment resisting frame was proposed which comprises a new self-centering rotational joint (SCRJ), aiming to improve energy dissipation and minimize main frame yielding during earthquakes. The proposed system with different sets of friction components and spring devices was investigated under a series of quasi-static cyclic tests. The study found that SCRJ generates a flag-shaped hysteresis curve with satisfactory energy dissipation and self-centering capacity and achieves the plastic state more easily compared to traditional plastic hinges.
System Concept
The SCRJ consists of a pin rod, two rotational parts and coupling plates, each with a right helicoid surface known as friction surface, and prestressed string devices. When the system is subjected to rotation, the coupling plates shift upwards causing greater compressive forces, which generate friction among the helicoid surface and dissipate energy. When the load causing this rotation is removed, the device self-centers and static friction in a reverse direction is created followed by kinetic friction. The joint then reaches its initial state after the completion of the half-cycle and friction dissipates. The moment bearing capacity during the rotation, self-centering capacity, and energy dissipation capacity depends on the precompressive force, stiffness and slope angle of the right helicoid surfaces and the proposed design can be modified considering these parameters. As the system achieves yielding by geometric nonlinearity rather than material plasticity, the SCRJs reach the plastic state more readily, allowing greater deformation.
Experimental Study, Results and Discussion
Pseudo-static cyclic compression tests were conducted on the disc springs to investigate their performance such as their elasticity and stability followed by 12 quasi-static cyclic tests on the proposed SCRJs, tested on four sets of different steel friction devices. The setup includes a loading arm, a pin rod, gaskets, and a pressure sensor to monitor the force applied during the tests. A displacement-controlled loading protocol was carried out on all test cases applying a force loading arm through the pin rod that caused a bending moment on the joint. This allowed analyses on energy dissipation and self-centering capacity of the components portrayed by the hysteresis curves. Numerical models were also tested on different parameters such as initial stiffness and pre compressive displacements to observe the effect on the overall seismic performance.
Test results verified the ability of SCRJ to generate a typical hysteresis curve with great energy dissipation, moment bearing and self-centering capacity, despite a slight nonlinear response due to some loss of compressive force during loading. The results concluded that the SCRJ represents a promising alternative to plastic hinges when designing earthquake resilient frame structures.
Reference
Xu, G., Guo, T., & Li, A. (2023). Self-Centering Rotational Joints for Seismic Resilient Steel Moment Resisting Frame. Journal of Structural Engineering, 149(2), 04022245. https://doi.org/10.1061/JSENDH.STENG-11475