Elastic-plastic Seismic Responses Analysis Of Multi-tower Cable-stayed Bridge

Multi-tower cable-stayed is one of the most important structure systems in cross-sea engineering at home and abroad,and it is an urgent need for social progress and traffic development to study it's seismic performance and damping control.However,compared with the conventional cable stayed bridge,the seismic theory and damping control technology of multi-tower cable-stayed bridge are relatively weak,so the mechanical characteristics of multi-tower cable-stayed bridge should be fullly considered in the research process.It is a serious challenge for bridge engineering research scholars at home and abroad,that in-depth analysis of the seismic performance of multi-tower cable-stayed bridge longitudinal structure system,the formation of a more substantial seismic theoretical system,and the establishment of practical damping control measures to enhance the safe operation of the structure and the ability to resist earthquakes.The paper focuses on the seismic safety of multi-tower cable-stayed bridge under elastic-plastic earthquake,taking Jiashao bridge as the engineering background,and studying the dynamic characteristics of Jiashao bridge that under earthquake,and the seismic response characteristics of multi-tower cable-stayed bridge under different tower-beam constraints are investigated,finally,comparing and analyzing the influence laws of rare and frequent earthquake on internal force and displacement of multi-tower cable-stayed bridge.The main contents and achievements of this paper are as follows:1.The development process and present situation of multi-tower cable-stayed bridge structure are described in detail,and the research progress of earthquake resistance and shock absorption of multi-tower cable-stayed bridge is introduced.And the characteristics of four common structural systems are analyzed,and three basic theories of earthquake response anslysis are expounded and relevant conclusions are drawn;The multi-tower cable-stayed bridge with full floating system is simple in stress and small in internal force,but easy to produce large deformation and displacement;The mechanical behavior of semi-floating structure system is similar to that of full-floating structure system,but the peak calue of negative bending moment is easily generated at the support of tower pier;The fully consolidated system can effectively limit the displacement and deformation of structural members,but it often causes problems such as excessive internal force;Partial consolidation system takes into account the advantages of both fully floating and fully consolidated structuralsystems,so the internal force,displacement and deformation of the structure under this system are moderate.With the progress of science and technology,the theory of seismic response analysis is becoming more and more perfect,and dynamic time history analysis method is widely used in the process of response analysis because of it's more comprehensive,more accurate and more stable analysis characteristics.2.Based on the large-scale finite element software platform ANSYS,and taking Jiashao bridge as the engineering background,the spatial nonlinear simulation model of multi-tower cable-stayed bridge structure is established,and the dyanmic characteristics of the longitudinal structure system of multi-tower cable-stayed bridge,including vibration mode,frequency,period and other information are studied and analyzed.The results show that:the main girder of multi-tower cable-stayed bridge has higher torsional stiffness and stronger torsional capacity,which is beneficial to the overall wind resistance stability of the bridge;The lateral stiffness of the main girder of the multi-tower cable-stayed bridge is larger than that of the main tower,and the out-of-plane stiffness of the main girder is larger than that of the in-plane stiffness;In the first 10 vibration modes of Jiashao bridge,the main girder of the first two vibration modes and the second two vibration modes are changed from symmetric vertical bending to anti-symmetric vertical bending,and the main tower is changed from symmetric longitudinal bending to anti-symmetric longitudinal bending,and the periodic change is the largest.3.Based on the finite element software ANSYS and the incremental theory of elasto-plastic constitutive relation,the seismic response analysis of multi-tower cable-stayed bridge under strong earthquake is carried out,the longitudinal full floating system and longitudinal partial consolidation system are selected,and the influence laws of key structural components such as pylon and girder of multi-tower cable-stayed bridge under elastic-plastic earthquake damage are compared.The results show that: the longitudinal internal forces of the multi-tower cable-stayed bridge under the longitudinal floating system,such as the bottom shear force and bending moment,are relatively small,and the longitudinal displacement of the tower top,the longitudinal relative displacement of the tower beam and pier beam are relatively large.In the longitudinal partial consolidation system,the displacement response is relatively small,but in the internal force response,there are two kinds of reactions between the tower and the beam due to the different forms of longitudinal constraints: the longitudinal internal force response between the middle tower withlongitudinal consolidation and the bottom of the side tower is larger,while the longitudinal internal force of the bottom of the secondary tower with longitudinal freedom at the tower beam is relatively small.4.The seismic response characteristics of multi-tower cable-stayed bridge under rare earthquake and frequent earthquake are compared and analyzed.The results show that: the longitudinal shear force,bending moment amplitude and the longitudinal relative displacement between pylon and pier under rare earthquake are obviously increased compared with those under frequent earthquake.