Study On The Influence Of Inconsistencies Of Ground Motions On A Semi-floating Cable-stayed Bridge

Superior span capacity,remarkable economy,and progressive theory and technology make cable-stayed Bridges the first choice for long-span bridges.However,because of the characteristics of large span,flexibility and dense frequency,cable-stayed bridges have multiple paths of force transmission mechanism and complex interaction of components.Under dynamic actions such as earthquakes and wind loads,cable-stayed bridges are vulnerable to multiple modes of vibration failure.Among them,the asymmetric dynamic response caused by the inconsistent effect of ground motion amplifies the seismic demand of local components,which does great harm to cable-stayed Bridges.At present,this problem is not sufficiently studied.Taking Hunkou Yangtze River Highway Bridge,a semi-floating cable-stayed bridge with the main span of 780 m,as the prototype,this paper studied the influence law of non-consistent characteristics of ground motion on the dynamic response of cable-stayed bridge.Firstly,the ground motion synthesis and multi-point input methods for soft soil,medium-hard soil and hard soil sites are introduced,as well as the ground motion synthesis methods considering incoherent effect,traveling wave effect and local field effect,and the acceleration time histories of the bridge site under the two methods are respectively synthesized.Then,a 3D finite element model of the bridge was established in Midas Civil to obtain the dynamic characteristics of the structure,and the response distribution law of the cable-stayed bridge under single site and uniform excitation was analyzed.On this basis,the coherence effect,traveling wave effect and site effect of the single element of the non-uniform dynamic response of the cable-stayed bridge are further analyzed,and the response of the bridge under the uniform excitation is compared.Finally,the influence of various non-consistent characteristics on the response distribution of cable-stayed bridge is studied.The results show that the internal force and displacement responses of the structure are large in hard and soft soil sites,but small in medium and hard soil sites.When the coherence effect is considered alone,the dynamic response of the structure generally increases.when traveling wave effect is considered alone,it cannot be concluded that the influence of lower apparent wave velocity on structural dynamic response is more obvious.Whether the internal force response at the bottom of the main tower is related to the site of the main tower is determined by whether the site is symmetrical about the longitudinal axis of the structure,and the internal force at the bottom of the bridge tower is not affected by the site change during the seismic wave.When the non-uniform characteristics of ground motion exist at the same time,the action law of coherence effect on the structure is quite different from that in a single site,which no longer increases the internal force at the bottom of the tower,and the traveling wave effect weakens the non-uniform phenomenon of longitudinal displacement of the main tower in the asymmetric site where the bridge tower is located.The spatial variation characteristics of seismic waves have little effect on the vibration state of longitudinal,but it will increase the vertical displacement response of the main beam.In this study,the three main characteristics of non-consistent ground motion are fully considered,and various working conditions such as apparent wave velocity,correlation function,single site soil and different site soil combination are constructed.The time history of displacement and internal force,peak distribution envelope and frequency domain are analyzed from the key parts of cable-stayed bridge such as cable-beam-tower.The spatial dynamic response of semi-floating cable-stayed bridge under non-uniform ground motion is systematically analyzed and summarized.