Seismic damage characteristics and evaluation of aboveground-underground coupled structures

Aboveground-underground coupled structures (AUCSs) integrate aboveground multitowers, podiums, and large underground structures. The complex structural composition and connection forms enhance structure-structure and soil-structure interactions and result in a complicated structural seismic damage condition. The different dynamic characteristics of aboveground and underground structures make it difficult to select optimal seismic intensity measures (IMs) for the seismic damage evaluation of the AUCS. A refined nonlinear finite element model of the AUCS considering soil-structure interactions is established in this paper. Near-fault pulse-type and far-field ground motions are selected as seismic inputs. The structural seismic failure and its influencing factors, including ground motion characteristics and structural coupling interactions, are thoroughly examined. Nu-merical results demonstrated that structural seismic damage and weak positions are associated with the embedded effects induced by the podium and the underground structure. The structural failure begins at the column of the podium, and the failure modes are associated with the ground motion characteristics. The coupling interactions between towers are beneficial for reducing the seismic response of the AUCS. The wave scattering caused by the underground structure amplifies the seismic response of the aboveground structure as seismic intensity increases. A stability criterion for optimal IM selection is proposed, which evaluates changes in seismic response dispersion after the structure enters the plastic stage and can reflect the influence of dynamic char-acteristics of the AUCS on IM selection. Statistical results showed that the peak ground velocity and the root mean square velocity are optimal IMs for the evaluation of seismic damage of the AUCS.