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

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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