Dynamic Performance Of Cable-stayed-suspension Bridges

The cable-stayed-suspension bridge is a new form of bridge structures with strong spanning capability, and combines the advantages of cable-stayed and suspension bridges and to some extent overcomes their shortcomings, and therefore has a broad application prospect. At present, the domestic and foreign researches on the dynamic performance of cable-stayed suspension bridge is not much. By taking a1400m main span cable-stayed-suspension bridge as example, with summarizing the domestic and foreign literature, from the aspect of design parameters, dynamic characteristics and seismic performance of the cable-stayed-suspension bridge are investigated, which are also compared to the cable-stayed bridge and suspension bridge with the same main span.Firstly, by using finite element analysis software MIDAS/Civil, a3D finite element model of a1,400m main span cable-stayed-suspension bridge is established, and the dynamic characteristics is analyzed and compared to the cable-stayed bridge and suspension bridge with the same main span. Effects of structural parameters such as the sag to span ratio of main cables, the suspension to span ratio, the side span length, the subsidiary piers in side spans, the constraint condition of the girder and the deck form etc on the dynamic characteristics of the cable-stayed-suspension bridge are investigated.Secondly, by using the response spectrum method and time history analysis, seismic responses of the cable-stayed-suspension bridge are analyzed, and the differences between the two methods are revealed and discussed. At the same time, the seismic responses of the cable-stayed bridge and suspension bridge with the same main span are analyzed and compared to that of the cable-stayed-suspension bridge. By changing structural design parameters such as the sag to span ratio of main cables, the suspension to span ratio, the side span length, the subsidiary piers in side spans, the constraint condition of the girder and the deck form etc, the seismic responses of the bridge are analyzed, the key design parameters and also their reasonable value are proposed.It can be concluded from the above analysis that:(1) the cable-stayed-suspension bridge is a kind of flexible structures, the modal frequencies are small, and the modal coupling is strong;(2) the dynamic characteristics of cable-stayed-suspension bridge is between the cable-stayed bridge and suspension bridge, and are more close to the suspension bridge. In general, its dynamic performance is better than the cable-stayed bridge and suspension bridge with the same main span;(3) compared to the response spectrum method, the time history analysis method can consider some nonlinear factors, and can predict the seismic performance of the bridge more accurately;(4) better dynamic characteristics and seismic performance are achieved for the cable-stayed-suspension bridge with the sag to span ratio of1/10, the suspension to span ratio between0.4to0.5, short side spans and subsidiary piers, semi-floating system and the hybrid deck form.