The Stability Research On High-pier Large-span Continuous Rigid Frame Bridge

Throughout the bridge construction history, there have been accidents of bridges losing carrying capacity due to structure instability. When it comes to continuous rigid frame bridges, mostly of which adopt tall piers and thin-walled cross section, the stability of structure, as well as strength capacity of structure, is considered as one of the key issues that can't be ignored in structure design and stress calculation. Meanwhile, safety factor of continuous rigid frame bridge isn't specifically set in the domestic bridge design specifications, so further study of the stability issues is needed in time for such type of bridges. This article analyze the developing process and current situation of structure stability theory at home and abroad, carrying extensive researches on structural stability of high-pier, large-span continuous rigid frame bridge.First, according to energy method, the article derivates calculation formula of critical load of high-pier bridges, and it introduces the resolve of jumping instability of compression-bending member applying catastrophe theory.Then, the article sets an extra-large continuous rigid frame bridge (Shandian River Bridge), that locates in a highway (RuCheng to Chenzhou) with its tallest pier of 127.5m, as the practical analysis material for the research of the first type structure stability analysis, adopting the finite element analysis software MIDAS-CIVIL, while using ANSYS, another finite element analysis software, for the second type structure stability analysis.The first type analysis results reach the conclusion that maximum cantilever construction stage is the most unfavorable stage during bridge construction stage and service stage.The second type analysis targets on the most unfavorable stage of maximum cantilever construction , adopting beam element model and solid entity element model for stability analysis, and the results show that:1).When taking the geometric nonlinearity and material nonlinearity into consideration, the structure ultimate bearing capacity of the two types models is far less in comparation to the linear analysis, which indicates that the outcome of the linear stability analysis is quite conservative, and should not be the criterion for analysis. 2).the ultimate bearing capacity of double nonlinearity is less than that of geometric nonlinearity, which indicates that it is neccesary to evaluate the elastic-plasticity of the structure for the nonlinear stability analysis.After that, the article studies the influential factors on structural stability of tall-pier, large-span continuous rigid frame bridges, and the results demonstrate that:1) The variation of the cross-section has a great influence on the stability. 2) The structure acts more unstable as the slenderness ratio of high pier increase gradually. The member acts as a slender one when the slenderness ratio increases to 30, which is very unfavorable for structure stability, and should be avoided. 3) The number of diaphragm of double-limb pier could cast certain impacts to structure stability. The analysis results of Shandian River Bridge show that it is the most favorable to set one diaphragm at the 1/2 height of the pier. 4) The distance between the limbs of double-limb pier is of little influence on the structure stability. 5) The structure stability is also affected by the concrete strength grade. Studies find that by upgrading 4 levels of concrete grade, structure stability factor wasn't significantly improved, which indicated that it's not an efficient method to increase structure stability factor by leveling up concrete strength grade.At last, the article uses Wenming River Highway Bridge as the construction background case, stimulates three closing sequences, and then analyzes the affects of the closing sequences of on multi-span continuous rigid frame bridges on the structure stress, cumulative displacement and stability. The results show that: 1) All three closing methods is acceptable, but the first kind results in slightly less maximum tensile and compressive stress. 2) Different closing sequences lead to different cumulative displacements in finished bridge state. 3) All three closing methods can meet with the structure stability in disguise.