Studies on Method of Limit States Design for Underground RC Frame Structures

为了建立“地下钢筋混凝土框架结构极限状态设计”方法，对作用在结构上的地震力进行估计是最重要的。地震力的主要部分是水平土压力。在日本现行的抗震设计标准中，规定用Mononobe和Okabe的公式来确定上动土压力，而这些公式最初是为了挡土墙的抗震设计而提出的，因此并不一定适用于地下管道等柔性墙的地下结构。因此，首先要建立动土压力产生的机理和公式，才能合理地预测动土压力。在剪切试验装置上压实的气干岐阜砂模型地基和在同一模型地基上埋设不同刚度的模型管道的3个复合模型，在振动台上水平激励共振频率的正弦运动。沿管道侧壁的响应动土压力观测结果表明，随着管道剪切刚度由低到高的变化，其在基振同一阶段的分布方向相反。在低刚度情况下，管道底部的响应加速度远小于自由地面情况。用有限元数值模型对上述试验进行了模拟，结果与上述试验结果一致。综合实验和数值结果，阐明了作用于地下水管侧壁的动土压力的发展机理，并推导了动土压力的预测公式。阐明了钢筋混凝土框架延性的特点，并建立了一种估算框架延性的方法。通过以上结果，可以说建立了一种估算地下钢筋混凝土管道极限状态承载力的方法。少

In order to establish the method of "Limit States Design for Underground RC Frame Structures" it is most important for us to estimate the seismic forces acting on the structures. Main part of the seismic forces are horizontal earth pressures. In Japanese current aseismatic design standard it is specified to determine above dynamic earth pressures by Mononobe and Okabe's formulae which were, however, originally proposed for the purpose of the earthquake resistant design of retaning wall, so that they are not necessarily fit to such underground structure of flexible walls as underground conduit. Thus, we must establish an idea of mechanism of generating dynamic earth pressures for the first as well as the formula to be able to predict them reasonably.A model ground of air dried Gifu sand compacted in a shear testing apparatus and three composite models at each of which the model conduit of different rigidity was buried in the above same model ground were excited horizontally with sinusoi … More dal motions of resonant frequencies on a shaking table.The observed response dynamic earth pressures along a side wall of conduit show that the distribution of them at the same phase of base motion reverses in its direction as the shearing rigidity of conduit changes from lower to higher than the oneof surrounding soil layer. In the case of lower rigidity of conduit the response acceleration at its bottom is much lower than the one in free ground case. The simulations of above tests with FEM numerical models show the same behavior as mentioned above. Synthesizing both experimental and numerical results the mechanism of development of dynamic earth pressures acting on side walls of underground conduit has been clarified and a formula predicting them has been derived.Besides, the characteristics of the ductility of reinforced concrete frames have been clarified and a method of estimation of it has been established too. With all the results obtained above it may be said that a method to estimate the limit states bearing capacity of underground RC conduit has been established. Less