Preliminary Study On The Unseating Prevention Minimum Seat Length Of Girder Bridge

The unseating of bridge superstructure is one of the most serious earthquake damage of girder bridges. It is one of the most important topics to study the unseating prevention seismic measures for seismic design of girder bridges. Experts and scholars at home and abroad have payed much attention to this problem during recent years, and many achivements have been obtained.. The beam seat length as a part of unseating prevention systems was revised in the Guidelines for Seismic Design of Highway Bridges(JTG/T B02-01-2008) . But many problems still exist in the seat length calculation method of simplely supported girder bridges and continuous girder bridges, it is still lack of systematic study in this area in China until now.The main purpose of this paper is to study the simplified calculation formula of the seat length of simplely supported girder bridges and continuous girder bridges. The main contents and achievements of this dissertation are described as follows:â‘ Because the beam seat length was impacted by more than one factors(the effection of span, pier height and skew angle were mainly considered in this paper), ten levels were selected for each factor, if we do comprehensive tests or orthogonal tests, the number of required tests would be very large. The uniform design method was used in the multi-factors and multi-levels'tests for the purpose of reducing tests'number.â‘¡According to uniform design table, Standard Drawing of Highway Bridges (JT/GQB 008-96) and Comman Drawing of Highway Bridges(36-31), simplely supported girder bridges'dynamic models were established by SAP2000 finite element software; according to the seismic design process of Guidelines for Seismic Design of Highway Bridges(JTG/T B02-01-2008), the response spectrum analysis and the time-history response analysis were conducted. The piers and the beams'relative displacement of simplely supported girder bridges were calculated under longitudinal earthquake action E2. The formulas of the beam seat length were derivated by using least squares regression method.â‘¢In order to maintain the consistency of the calculation formulas, the adoption of continuous girder bridges'span and height value was researched. â‘£From the calculations of girder bridges, the effection of the ratio of periods, effective stiffness and mass of the adjacent frames were further studied, and the seismic conceptual design for girder bridges were given.