Conventional seismic-resistant moment-resisting frames (MRFs) designed to Eurocode 8 develop inelastic deformations in beams and column bases that result in residual drifts and structural damage. Self-centering MRFs (SC-MRFs) with post-tensioned beam-column connections have been proposed to address these problems. However, SC-MRFs cannot avoid plastic hinges in their column bases, resulting in difficult-to-repair damage and first-storey residual drifts. Therefore, a damage-free self-centering column base connection (referred to as column base) is needed to further enhance the earthquake resilience of SC-MRFs.
A novel column base is proposed in this study. The column base uses post-tensioning technology to achieve self-centering behaviour and replaceable web-hourglass shape steel pins (WHPs) to dissipate seismic energy, while the rest of its components remain damage-free. The column base requires no field welding, it is easy to construct, deconstruct and rehabilitate, and thus facilitates sustainable (green) construction. The study develops an analytical model to predict the column base hysteretic behaviour and identify its limit states. A performance-based design procedure is developed for the column base which ensures self-centering and damage-free behaviour and designs its main components.
A high-fidelity nonlinear finite element method (FEM) model for the column base is developed in software Abaqus. The Abaqus model verifies the accuracy of the analytical model and identifies failure modes that cannot be predicted analytically. A FEM model for the column base is also developed in software OpenSees. The model validates the accuracy of the previous models and facilitates the seismic assessment of the novel column base.
Design recommendations for practical application to real buildings are also provided. The conventional MRF of a prototype steel building is redesigned as: (a) SC-MRF with conventional column bases; and (b) as SC-MRF with the novel column bases. The two design cases are modelled in OpenSees and nonlinear analyses are performed to compare their seismic response. The results of the analyses demonstrate the resilient performance of the novel column base under strong earthquakes, achieving self-centering and damage-free behaviour.
The beneficial effect of the novel column base on the seismic response of SC-MRFs is demonstrated by reducing their peak and residual drifts in the upper storeys, eliminating the latter in the first storey, and pushing their critical structural limit states to higher seismic intensities. Recommendations for future research are also provided.