Seismic Response Analysis Of Skew Highway Girder Bridges

With the improvement of China's comprehensive national strength, a new upsurge in building skew bridge is up to a climax since the 1980s. Due to the development history and design theory is relatively later than that of right bridge, the seismic response analysis on skew bridge is immature. The sensitivity and complexity of seismic response in skew bridge, resulted from these space mechanical properties of bending-torsion coupling, unbalanced distribution of reaction force, in-plane crawl displacement effect, slope effect etc. makes it earthquake-vulnerability. Current codes of seismic design for expressway bridges in main earthquake countries have not given a utility seismic design method for skew expressway bridges. By studying on seismic design theory for skew highway bridges, this paper proposes a simplified seismic response calculation theory for skew expressway bridges to solve difficult problem met in seismic design. Firstly, this paper summarize current status of the seismic response research on skew bridge; secondly, based on overseas and domestic research achievements, this paper take slope angle, support stiffness, span, pier highness and span number as five variable parameters to study the impact on seismic response as changing these parameters. The main conclusions drawn from the analysis are as follows:1. Basing on response spectrum method and time history method, the effects of single-span simple-supported skew expressway girder bridges skew angle, span and support stiffness of bearing on seismic response of the structures are discussed. The results fit with the achievements of foreign researches satisfactorily. It is concluded that seismic design force and displacement of single-span expressway skewed girder bridges can be calculated according to relative straight bridges.2. Basing on response spectrum method and time history method, the effects of two and three-span skew expressway continues skew bridges skew angle, height of pier and span on seismic response of the structure are thoroughly discussed.(1)The impact on seismic response of continuous skew bridge as changing slope angle. When the earthquake motion is inputted in normal direction of supporting bead(x direction or vertical axis of bent column) and skew angle is less than 25 degree, skew angle has little effects on the seismic internal forces at the feet of piers and the displacements of girders, But if skew angle exceeds 25 degree, then seismic internal forces at the feet of piers and displacements of girders are increasing with the skew angles. Furthermore, the higher the piers are, the larger increasing effects are. When the earthquake motion is inputted in tangential direction of supporting bead (y direction or parallel axis of bent column),skew angle has little effects on the seismic internal forces at the feet of piers and the displacements of girders.(2)The impact on seismic response of continuous skew bridge as changing pier highness. When the earthquake motion is inputted in x direction, the internal forces at the feet of piers and displacements of girders are increasing with the height of piers. Moreover, the higher these piers are, the more obviously effect is. At the case of skew expressway bridges with higher piers and larger skew angles, the displacements of superstructures can be two times as large as the displacements of relative straight bridges. When the earthquake motion is inputted in y direction, the higher the piers are, the larger the seismic internal forces at the effect of piers and displacements of girders are.(3)The impact on seismic response of continuous skew bridge as changing span. When earthquake motion are inputted in x direction or y direction respectively, seismic internal forces at the feet of piers and displacements of girders are both increasing with the span, and the changing of the span is not alter the regulation of slope angle parameter's impact on seismic interior force.3. For the study of expressway continues skew bridges with more than three spans, the effects of the number of span on seismic response of the structure are discussed. If the earthquake motion is inputted in x direction, the internal forces at the feet of piers of middle span are increasing with the number of span, but the internal forces at the feet of piers of side spans are decreasing with the number of span. Furthermore, the displacement of the girder of middle span doesn't change obviously with the number of span, but the displacements of girders of side-spans are decreasing with the number of span. The number of span has little effect on displacements of the girders and internal forces at the feet of piers when the earthquake motion is inputted in y direction.