On Stability of Submerged Floating Foundation

近年来对桥梁的许多要求仍然存在，但塔与塔之间的距离越来越长，获得牢固基础的海床深度越来越大。为了在这样条件恶劣的地方建造桥梁，人们可能需要更轻，同时更坚固的新材料。或者可以使用浮动基础来支撑至少一部分恒载。这种浮动基础通常由锚泊在海床上的电缆系泊。索结构的主要缺点是索内张力必须高到足以支撑结构，而且总性能表现出高度非线性。在考虑浮式基础时，海面波动是影响浮式基础支护性能的最恶劣条件之一。这种通过缆索作用在柔性结构上的振荡力要求具有抗疲劳能力。为了避免这一困难，这里的浮动基础被淹没在海中，因此除了上部结构的荷载外，最大的力是潮汐力，可以认为是准静力。此外，为了在电缆内引入足够大的张力来支持负载，一个大的浮体附着在电缆结构的顶部，它的浮力就像一个预张紧机制，以及支持负载。该系统的数值模拟得到如下结果。该系统在实际载荷条件范围内表现出良好的线性抗力，可以将整个系统估计为线性弹簧系统，从而使设计方法变得非常简单。在限制沉降角和旋转角的情况下，其性能表现为线性和稳定，模型简单，易于设计。

Recently many demands of bridges still exist, but the distance between towers becomes much longer and the depth of the sea bed to obtain firm foundation becomes larger. In order to build bridges in such bad-conditioned sites, one may need new materials which is much lighter and at the same time much stronger. Or one can use floating foundations to support at least some part of dead loads. Such floating foundations are usually moored by cables anchored at the sea bed. Cable structures have essential disadvantage that the tension within cables must be high enough to support structures and that the total performance show highly non-linear behavior.In considering floating foundation, oneof the worst conditions to affect its supporting function is wave of sea surface. Such oscillating forces on flexible structures by cables require fatigue resistance. In order to avoid this difficulty, the floating foundation here is sub-merged in the sea, so that the largest force except the load from upper structures is the tidal force which may be considered quasi-static. Furthermore to introduce tension forces within cables large enough to support loads, a big floating body is attached at the top of the cable structuresand its buoyancy acts just like a pre-tensioning mechanism as well as for supporting loadings. Numerical simulation of such system yields following results. Such system shows quite linear resisting behavior in the range of the actual loading conditions and thus the designing method may become very easy because the total system can be estimated as alinear-spring systme. As far as the sinkage and rotating angles are restricted, the behavior shows linear and stable to make its design easy enough with simple model.