Min Fan, Hongchao Guo, Shen Li, Zhenshan Wang, Yunhe Lui 2024
The seismic performance of a self-centering linked beam equipped with SMA bars is studied. The rotational behavior of the linked beam about its connection to the frame beam is investigated in its response to seismic loads. The connection includes energy-dissipating steel angles with shear keys and SMA bars, which are tested and verified with theoretical calculation and finite element analysis. Permanent deformation was concentrated in the steel angle, which can be replaced after the event of an earthquake. LY160 steel angles are tested against Q235 steel angles to study their respective self-centering capacity and energy dissipation capacity in relation to the linked beam. Additionally, a SMA bar of full length configuration and a partition-type SMA bar was studied. Quasi static cyclic loading test are conducted on four specimens, which comprised of the two SMA bar arrangement and the two materials for steel angles. It was found that the full length SMA bars had better self-centering and energy dissipating capacity than that of the partition type SMA bars. Theoretical calculation and finite element result were consistent with testing results. Ultimately, self-centering linked beams system equipped with SMA bars was effective in reducing residual deformation and allows for repairability after an earthquake by replacing the steel angles.
System Concept
A linked beam is secured to frame beams on both ends with high-strength bolts and steel angle. SMA bars are either secured along the linked beam at full length or partition type SMA bars are secured by anchor plates welded to the linked beam with stiffening ribs. The end plates between the linked beam and the frame beam are designed with slotted holes and shear keys are included between the steel angle attaching the linked beam to the frame beam. The shear key and slotted end plates compensate for the low shear-carrying capacity of the SMA bars which are prone to fracture under shear loading. While the linked beam provides the self-centering capacity of the system, the steel angles and high-strength bolts provide energy dissipation capacity. Under seismic loading, the steel angles undergo permanent deformation and can be replaced with new energy-dissipating steel angles.
Analytical Study, Results, and Discussion
The linked beam and steel angles were primarily tested for energy dissipating capacity, while the SMA bars are tested for self-centering capacity. The two connection types of the SMA bars – full length and partition type – along with material type of the steel angles are studied for their effect on self-centering and energy dissipation capacity. Experimental testing of the systems included a quasi-static cyclic loading test. The test setup employs a rigid frame sliding horizontally with a constant force from an actuator. Lateral supports prevent out of plane deformation and the link beam is position vertically with the force applied to one end of the linked beam. During initial stages of testing, cyclic loading was applied with increasing inter-story drift amplitudes followed by incrementally increasing displacements. A maximum loading rate was set to prevent fractures of the SMA bars. Results showed that the maximum rotation angle of the self-centering link beam was determined to meet seismic resitance requirement. The hysteresis curve indicated a clear flag shape and therefore exceptional energy dissipation capacity was established. Residual rotation about the connection was also determined to meet seismic requirements. The steel angles was found to significantly impact the self-centering performance and enegry dissipating capacity of the linked beams. Specifically, when the rotation angle exceeded 0.4 rads, the self-centering rate of the linked using LY160 angles was higher than that of using Q235 angles. Additionally, it was found that the SMA bars at full length provided higher self-centering and energy dissipation than that of partition type SMA bars. Improved designs were made outlined by the results of the test and was verified using finite element analysis. The system showed promising designs that allowed by appropriate self-centering and energy dissipating capacity, along with the ability to replace steel angles at the end of its lifecycle.
Reference
Min Fan, Hongchao Guo, Shen Li, Zhenshan Wang, Yunhe Lui (2024). “Seismic Performance of vertex-rotation type self-centering link beam equipped with SMA bars,” Journal of Construction Steel Research