摘要
Bridge foundations located in deep water are usually subjected to horizontal dynamic loads and moments which may be caused by the wind, waves, earthquake, and the possibility of boat crashing or vehicle braking. Caisson foundations based on gravel or sand cushions are a new type of deep-water foundation for bridges, suitable for meizoseismal areas. In this paper, harmonic horizontal excitation tests for the study of the lateral dynamic response of caisson foundations based on cushion layers are described. Different lateral loads and two different cushion types are considered. The results show that the lateral dynamic responses of caisson foundations based on sand and gravel cushions both show strong nonlinear characteristics, and the resonant frequency of the foundation decreases with the increase of the excitation force. The dynamic displacement of a foundation based on a sand cushion is far less than that based on a gravel cushion, and the rate of decrease of the resonant frequency of a foundation based on a gravel cushion is faster than that of a foundation based on a sand cushion under the same conditions. Under dynamic loading the gravel cushion can more effectively dissipate vibration energy and isolate the vibration, than the sand cushion can. A simplified nonlinear analysis method is proposed to simulate the lateral dynamic response of caisson foundations, and the predicted response shows a reasonable match with the results observed in laboratory tests. Scaling laws have also been applied in this small-scale vibration model test to predict the dynamic behavior of the prototype foundation.
目的:沉箱底部垫层型式对基础的水平振动特性有重要影响。本文旨在探讨不同垫层型式(砂垫层或碎石垫层)对沉箱基础水平动力响应的影响规律,并提出简化的沉箱垫层基础水平动力的非线性分析计算方法。创新点:1.针对不同垫层下的沉箱基础开展室内水平稳态振动模型的试验研究;2.建立沉箱垫层基础的非线性分析计算模型;3.建立沉箱垫层基础模型的动力特性与原型沉箱垫层基础动力特性之间的关系。方法:1.通过室内水平稳态振动模型试验研究,得出不同垫层型式对沉箱基础动力特性的影响规律(图11和12);2.通过理论推导,构建激振力大小与基础振动位移幅值及共振频率之间的关系,并建立相应分析模型(公式(3)和(12));3.通过相似理论,分析模型基础与原型基础之间的动力特性关系(表5)。结论:1.静荷载作用下,基础水平荷载-位移曲线近似于刚塑性发展过程,且基础置于砂垫层时的极限荷载比置于碎石垫层的更大;2.沉箱置于砂垫层或碎石垫层上时,随着激振力幅值的增大,由于土体非线性特性的产生,基础振动响应幅值明显增大,且基础的共振频率呈衰减趋势;3.相对于砂垫层,碎石垫层在动力荷载作用下更易产生塑性变形,从而消耗并阻隔部分能量的传递,进而表现出比砂垫层更好的隔震效应。
基金
supported by the National Natural Science Foundation of China(Nos.51808220 and 51822809)
the Natural Science Foundation of Jiangxi Province(Nos.20192BAB216036 and 20181BCB24011)
the Science and Technology Research Project of the Education Department of Jiangxi Province(No.GJJ180340),China。
