AN INVESTIGATION ON THE DYNAMIC BEHAVIOR OF SUBMERGED FLOATING TUNNELS

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The purpose of this study is to investigate the characteristics of the dynamic behavior of submerged floating tunnels under wave and seismic action, which are critical forces in design. Moreover, effective beam model for discussion on the design of structure is also presented.The most important findings under wave force are summarized as follows;For leg arrangement Type-A :1. Although lateral displacement is great, slack is least likely to occur with this arrangement.2. The rigidity of the joints between tunnel elements has a major effect on the lateral displacement of the tunnel as a whole. The ideal type of joint for Type-A would be a pin joint. Lateral displacement and the maximum bending moment in rigid joints increases with the angle of wave incidence.For leg arrangement Type-C :1. Lateral displacement is much less than in type A, but slack is more likely to occur.2. No significant variations in lateral displacement are found with different joint rigidities.The results of analysis under seismic wave can be summarized as follows:1. If the natural period of the structures is long enough comparing to the predominant period of seismic wave, maximum response of displacement or bending moment for design are approximately predictable by an analysis with simultaneous excitation. When the natural period of the structure is close to the predominant period of seismic wave, propagation velocity plays an important role for dynamic response and it should be taken into account.2. For prediction of sectional force like the bending moment at the joints, propagation velocity should be carefully decided.In order to discuss the global behavior of the structure, a beam model on elastic foundation is developed for submerged floating tunnel with tension legs spaced at equal interval. It Is shown that the approximation of a uniform continuous elastic foundation is reasonable whenever kィイD2vィエD2hィイD13ィエD1/(6EI)≦0.2.