Optimal intensity measures for longitudinal seismic response of tunnels
To study the ground motion intensity measures(IMs)suitable for the design of seismic performance with a focus on longitudinal resistance in tunnel structures,21 different seismic intensity parameters are selected for nonlinear calculation and analysis of tunnel structures,in order to determine the optimal IM for the longitudinal seismic performance of tunnel structures under different site conditions.An improved nonlinear beam-spring model is developed to calculate the longitudinal seismic response of tunnels.The PQ-Fiber model is used to simulate the longitudinal nonlinear behavior of tunnel structures and the tangential interactions between the tunnel and the soil is realized by load in the form of moment.Five different site types are considered and 21 IMs is evaluated against four criteria:effectiveness,practicality,usefulness,and sufficiency.The results indicate that the optimal IMs are significantly influenced by the site conditions.Specifically,sustained maximum velocity(VSM)emerges as the optimal IM for circular tunnels in soft soil conditions(Case Ⅰ sites),peak ground velocity(VPG)is best suited for Case Ⅱ sites,sustained maximum acceleration(ASM)is ideal for both Case Ⅲ and Case Ⅴ sites,and peak ground acceleration(APG)for Case Ⅳ sites.As site conditions transition from Case Ⅰ to Case Ⅴ,from soft to hard,the applicability of acceleration-type intensity parameters gradually decreases,while the applicability of velocity-type intensity parameters gradually increases.
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