水平循环荷载下海上大直径单桩累积变形特性

Accumulated response of offshore large-diameter monopile under lateral cyclic loading

受风、波浪等荷载作用海上大直径单桩的水平循环受荷特性在其设计中更为关键。基于有限差分程序,通过开发用户子程序实现土体刚度衰减模型的嵌入,分析循环次数和荷载特征对桩基累积变形的影响规律,并讨论累积变形预测模型的适用性与可靠性。研究结果表明,密砂地基中荷载值的增加将导致累积变形发展加快,设计最大循环荷载值应控制在0.58倍的桩基静承载力内;对数模型能较好地预测小循环荷载值作用下桩基累积变形,而低估较大荷载值引起的累积变形;幂函数模型较好地反映不同荷载作用下的桩基累积变形发展规律,且模型参数α的取值随着荷载幅值的增加呈线性增大,并给出了不同荷载下幂函数模型的设计参数。

The design of offshore monopile is generally governed by its accumulated response to lateral cyclic load, e.g. loads induced by winds and waves. In order to investigate the characteristic of this accumulated response, a user subroutine of degradation stiffness model (DSM) is developed and incorporated into a commercial finite difference program. Based on this program, the effect of load cycle number and load character on the displacement development of monopile is quantified; and the applicability and reliability of two mostly used models for prediction of accumulated displacement are evaluated. The results show that: In dense sand ground, cyclic loading with larger load amplitude leads to a continuous increase in monopile displacement as the number of loading cycles increasing; and the maximum load in each load cycle is suggested to be less than 0.58 times its static load capacity to produce a plateau of accumulated displacement after a certain number of load cycles; logarithmic model is capable of predicting accumulated displacement induced by smaller load and underestimates the displacements for larger load levels; the power model shows its advantage over the logarithmic model for its validity under various load levels; and the value of model parameter α increases linearly with increase in the load levels. Finally, parameter values of power model are given for various load conditions. © 2016, Science Press. All right reserved.