Stability Analysis Of High Pier During Construction Phase Of Long-span Rigid Frame Bridge

Long-span rigid frame bridge with high piers is built widely in mountain areas as high-grade highway spreads over this country. This type of bridge uses continuous beam system structure, with hollow and thin-wall piers. As the piers' height is so large, the problem of instability is of great concern, especially when in the stage of cantilever construction. Engineers need more acquaintance with the stability of high piers, and less complicated method to design safe piers. For this reason, this article searches to find easier approaches for calculating the critical load of the commonly used hollow and thin-wall piers, and examine how some nonlinear factors influence the stability of high piers through nonlinear analysis.Some analytic method was used to derive the formula for calculating the elastic buckling load, such as static equilibrium method, energy method and dynamic method, etc. The result of each method was compared to make sure the results are all right. For nonlinear stability problems, a Finite element analyzing program VFEAP with a special element type "degenerated solid element" is introduced. Nonlinear Analysis implemented on degenerated solid element model is much more efficient than on solid element model.By a large amount of calculation and summarization, a simple method using "variable cross-section reduction factor" is proposed for single-limb pier's buckling load calculating purpose. Similar suggestions were also given on double-limbs pier. Results of nonlinear analysis show that nonlinear factors greatly harm the stability of piers. Therefore, assurance coefficient should be increased when buckling critical load being calculated in elastic condition, and the strength of piers should draw the same attention.Elastic stability problems of high piers have been well solved, but nonlinear stability problems still need further research as theory on degenerated solid element is still under development.