基于等效单自由度模型的高桩码头地震位移需求分析

Seismic displacement demand analyses for pile-supported wharves based on equivalent single-degree-of-freedom models

在基于位移的高桩码头抗震设计方法中,准确合理地确定码头地震位移需求是关键。在位移需求分析方法中,非线性时程分析方法可以很好地考虑地震动的不确定性,但由于复杂的桩-土相互作用,使得直接对码头结构进行时程分析的计算量较大。为简便确定码头地震位移需求,提出了一种可用于码头非线性时程分析的等效单自由度模型。该模型可以很好地模拟码头的承载力和刚度退化以及土体耗能,并可通过对码头结构进行往复加载分析来确定模型的恢复力特性。为验证所提出的等效单自由度模型的合理性和准确性,以两个高桩码头为例,选取60条地震波,分别对码头及其等效单自由度模型进行非线性时程分析,结果表明二者的最大位移相关性很好,位移比的均值接近于1,且变异性很小。

In the displacement-based seismic design method for the pile-supported wharves, the key is to determine seismic displacement demand accurately and reasonably. In the displacement demand analysis methods, the nonlinear time-history analysis method can address the uncertainty of the ground motion well. However, due to the complex pile-soil interaction, the computation cost will be huge when the time-history analysis is carried out directly on the wharf structures. In order to estimate the seismic displacement demands of the pile-supported wharves with simplicity, an equivalent single-degree-of-freedom （SDOF） model for nonlinear time history analysis is proposed in this study. The simplified model is able to represent the deterioration of strength and stiffness for the wharf, as well as the dissipated energy of soil, whose restoring force is determined by the cyclically lateral loading analysis. To validate the applicability and accuracy of the proposed SDOF model, the nonlinear time history analyses of two typical wharves and counterpart SDOF models are carried out to compute the maximum displacements with an ensemble of 60 earthquake wave records, respectively. The validation process reveals that the displacements from the SDOF models correlate well with those of wharves, and the average values of their displacement ratios are close to unity with relatively low variability.