Nonlinear Dynamic Response Characteristics of Submerged Floating Tunnels

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Nonlinear dynamic response characteristics of submerged floating tunnels (SFT) are investigated for different arrangements of tension leg. The main results obtained in this study are summarized as follows :(1)The tension acting on the leg is qualitatively classified into three regions :1)Region-A : A leg is stable .2)Region-B : A leg is slacking .3)Fegion-C : Snap loading takes place .(2)In the case of tension leg arrangements (Type A) with a constant inclination (alpha=90ﾟ) with respect to the horizontal plane, the non-linearity of the lateral restoring force bcomes a problem. The features of this type are :1)Although lateral displacement is great, slack is least likely to occur with this arrangement.2)Lateral displacement increased with the angle of wave incidence.(3)In the case of tension leg arrangements (Type B) with a constant inclination (alpha*0ﾟ) the stiffness in the horizontal direction is superior to others in terms of moderating the response of SFT.The features of this typeare :1)Lateral displacement is much less thanin type A,but slackis more likely to occur.2)No significant variations in lateral displacement are found with different joint rigidities between tunnel elements.(4)The magnitude of the fluctuating tension is strongly influenced by the wave height.(5)The higher initial tension and smaller wave hight are indispensable for avoidance of slacking phenomena.