Damage-free self-centering steel columns incorporating SMA bolts and replaceable steel angles

Abstract

Steel moment-resisting frames (MRFs) are one lateral force-resistant structural system commonly used in high seismicity areas. The current seismic design practice for MRFs expects to develop plastic hinges at the beam ends to dissipate earthquake input energy. Meanwhile, plastic hinges also form almost unavoidably at the column bases of the first story due to the strong-base-weak-column design philosophy. However, concentrated deformation in the predetermined plastic hinges may lead to considerable damage in structural components. The accompanying large residual drifts can substantially compromise post-earthquake reparability and normal functionality. Hence, this paper presents a novel type of self-centering (SC) steel column base incorporating shape memory alloy (SMA) bolts and replaceable steel angles as a damage-free solution. First, the working principle of the column bases is described. Subsequently, the seismic performance of the steel columns is experimentally evaluated by considering the influences of the steel angles and repeated loading scenarios, and the replaceability of steel angles. Results show the novel steel column bases exhibit satisfactory flag-shaped hysteresis loops with excellent SC capability and stable energy dissipation, whereas almost all the damage is concentrated in the steel angles that can be replaced rapidly after the cyclic loading if required. The deformed columns are restored to their upright positions instantaneously with negligible residual deformation after unloading. More importantly, the steel column stays damage-free, and the SMA bolts with prestrain remain tightened. This enables the steel columns to maintain high functionality to withstand immediate aftershocks or future earthquakes, explicitly achieving seismic resilient design.