Self-Centering Rotational Joints for Seismic Resilient Steel Moment Resisting Frame

Steel Moment Resisting Frame (SMRF) is a type of structural system used in building construction to resist lateral loads such as wind or earthquake forces. It consists of a series of steel beams and columns that are connected together using moment connections, which allow for the transfer of forces between members. The moment connections are designed to be strong enough to transfer forces between the beams and columns without significant deformation, allowing the frame to resist lateral forces without collapsing. The design of moment connections is critical to the performance of the SMRF, as they must be able to withstand significant forces without failure. SMRFs are commonly used in high-rise buildings and other structures where lateral loads are a concern. They are often preferred over other structural systems because they offer good resistance to lateral forces while still allowing for flexibility in the design of the building. SMRFs are typically designed using a combination of analytical calculations and computer simulations to ensure that they meet the required safety and performance standards. The design process also takes into account the specific site conditions, such as the location and severity of potential earthquakes or wind events.

The conventional steel moment-resisting frame structures have always adopted capacity-based design strategy, in which plastic hinges are expected to provide adequate ductility and dissipate seismic energy during significant earthquakes. However, such structures are prone to severe plastic damage and residual deformations during seismic events, resulting in significant repair and rebuilding costs. Consequently, researchers focus has switched to seismic resilience instead of seismic resistance, seismic mitigation, and isolation. Several studies are being carried out to enhance seismic resilience in steel moment resistant frame buildings. Self-centering structures are robust structural systems that utilize dampers and other self-centering mechanisms to effectively absorb seismic energy and provide sufficient self-centering capability. Self-centering steel moment resistant frame structures have been constructed using methods including self-centering bracing, rocking frame systems, and self-centering joints.

In a new study published in the peer-reviewed Journal of Structural Engineering, Assistant Research Fellow Gang Xu and Professor Tong Guo from Southeast University along with Professor Aiqun Li from Beijing University of Civil Engineering and Architecture introduced the new concept self-centering rotational joint to allow for controlled rotation and self-centering of the beam during seismic events, thereby reducing damage to the structure. In the newly developed concept two rotational components are coupled together by a hinged pin rod, and two coupling plates are positioned on the exterior of the rotational parts to form the self-centering rotational joint. Pinholes are present in the center of the coupling plates and rotatable components. The right helicoid surfaces, also referred to as the friction surfaces of the rotational part and the friction surfaces of the coupling plate, are positioned at the interfaces of the rotational parts and coupling plates. Several right helicoid surfaces are arranged in rotational symmetry and with the adjacent slopes in alternate directions to provide a compressive force. To supply the compressive force, prestressed components such as spiral springs, disc springs, and ring springs are positioned outside the coupling plates. The total of the resistance moments produced by the rotational part’s friction surfaces and the coupling plate’s friction surfaces on both sides determines the self-centering rotational joint’s moment carrying capacity.

The authors developed the mathematical model to calculate the maximum moment that a self-centering rotational joint can withstand before failure. Additionally, the performance of steel moment-resisting frame structures during seismic occurrences was examined using numerical modelling. To investigate the mechanical and hysteresis behavior of self-centering rotational joint under various loading circumstances, the system was tested in quasi-static settings. The self-centering rotational joint was subjected to cyclic loads throughout the testing, and the responses were recorded. To investigate their impact on hysteresis behavior, the compressive force, compressive force stiffness, and slope angle of right helicoid surfaces were modified. The results of these tests showed that the compressive force, stiffness of compressive force, and slope angle of right helicoid surfaces significantly affect hysteresis behavior.

The research team conducted a nonlinear dynamic analysis to assess the effect of the proposed self-centering rotational joint on the seismic performance of a six-story steel moment resisting frame structure. The results showed that by lowering residual drift and inter-story drift ratio, the self-centering rotational joint considerably enhanced the seismic performance of the structure. Peak floor acceleration and base shear force, which are significant indications of structural safety during seismic occurrences, were significantly lowered by the self-centering rotational joint.

Overall, the self-centering rotational joint for seismic resilient steel moment resisting frames has benefits for both structural engineering practice and research. Future research may entail practical testing of full-scale steel moment resistant frame constructions with self-centering rotational joint to confirm their performance under realistic circumstances. As a result, engineers might better understand how self-centering rotational joint function in real-world situations and improve the seismic resilience of their designs.