Inelastic dynamic response and fragility analysis of arched hydraulic tunnels under as-recorded far-fault and near-fault ground motions

Abstract

Despite the significant differences in the inelastic dynamic responses of aboveground structures to near-fault (NF) and far-fault (FF) ground motions, the impacts of such ground motions on underground structures, especially arched hydraulic tunnels, are still insufficiently understood. In addition, the current seismic design code for arched hydraulic tunnels generally ignores the effects of NF ground motions because of the considerable uncertainty of the damage caused by such ground motions. Thus, it remains a topic of debate whether the effects of NF ground motions should be considered in the performance-based seismic design (PBSD) of arched hydraulic tunnels. This paper presents a fragility analysis based on the seismic response of arched hydraulic tunnels and an in-depth comparison of the effects of FF and NF ground motions (including directivity and fling-step effects) on the probabilistic seismic responses. Additionally, the peak ground velocity (PGV) to peak ground acceleration (PGA) ratio of NF ground motions with directivity is also considered as a ground motion parameter to illustrate the effect of the frequency components on the structural inelastic dynamic response. An arched hydraulic tunnel is modeled in the commercial software ABAQUS based on the inelastic dynamic damage analysis model for fluid-structure-rock interaction systems. Then, the incremental dynamic analysis (IDA) methodology is used to generate various sets of fragility curves for arched hydraulic tunnels based on probabilistic seismic demand models (PSDMs). The findings from this study reveal that NF ground motions with the fling-step effect can cause larger deformations and a higher probability of exceedance (POE) for an arched hydraulic tunnel than other types of ground motions. In addition, more severe accumulated damage to the arched hydraulic tunnel and a correspondingly higher POE are generated under NF ground motion with a high PGV/PGA ratio compared with a low PGV/PGA ratio. In summary, the findings of this study highlight the significance of distinguishing different frequency components and ground motions when evaluating the seismic performance of arched hydraulic tunnels.