Application And Research Of Concrete-filled Steel Bridge Piers In Long Span And Low Pier Continuous Rigid Frame Bridge

In recent decades, multi-span continuous rigid frame bridge with its own advantages hasbeen widely used in our country, it uses the flexibility of the pier to adapt to the longitudinaldeformation of the superstructure. As a result of pier girder consolidation, structure is verysensitive to the secondary internal force which is caused by temperature change, concreteshrinkage and creep, automobile braking force, and horizontal seismic force, etc.. The longercontinuous span and the lower pier will lead to the greater secondary internal force, it isextremely unfavorable to the pier and even leads to the structural form is not established.Therefore, the application of continuous rigid frame bridge has been constrained by thecontinuous length and pier height in a certain extent. The concrete-filled steel tubularstructure is formed by a combination of plain concrete filled steel tube structure. It combinestwo materials of steel and concrete to mutually compensate for each other’s shortcomings andgive full play their respective advantages, is a relatively ideal type of combination.Thestructure has the advantages of high capacity, small cross-section size, easy construction, goodeconomic returns, good ductility and toughness, strong energy consumption ability, goodseismic performance, etc. At present, in bridge engineering, the concrete-filled steel tubularstructure mostly used for arch rib of the arch bridge and few examples for the bridge piers.For the mechanical characteristics of low pier in long span and low pier continuous rigidframe bridge, combined with the advantages of concrete filled steel tubular structure, it wasproposed as pier column of such rigid frame bridge in this paper, to solve the technicalproblems of low pier and to further expand the application scope of the continuous rigid framebridge. So corresponding researches were carried out in this paper, the main contents are asfollows:1、Stiffness calculation methods of the concrete-filled steel tubular structure that areconversion stiffness based on the superposition theory and combined stiffness based on theunified theory were introduced. Calculation of the error between the two stiffness for roundand square section with different steel grade, concrete grade, steel ratio, and analysis of theimpact of these parameters on the error were completed, so to get the error range between the two stiffness with the commonly steel grade and concrete grade."Critical steel ratio" was putforward in this paper, according to the relationship between actual steel ratio and critical steelratio, the designers can easily and quickly determine the relationship between the twostiffness and the deviation of calculation results due to using conversion stiffness, they canaccomplish know fairly well and shoot the arrow at the target.2、In the hypothetical mechanical mode that the end of the pier and foundation areconsolidated, the top of the pier is only allowed to produce horizontal displacement withoutangular displacement. Based on the energy method and the parallel stiffness integration theory,the theory formula of thrust stiffness of the four-columns steel tube concrete piers wasproposed, then by the formula thrust stiffness between round and square section wascompared.3、Taking Weihe bridge as the engineering background, by the finite element softwareMidas civil, the static behaviors of the steel tube concrete piers and reinforced concrete pierswere comparatively analyzed，the two piers were compared in adapting to the upper structuraldeformation, the internal force distribution, the amount of material and other differences.Concluded that compared with the reinforced concrete piers under the same conditions, thesteel tube concrete piers had smaller thrust stiffness, better ability to adapt to the upperstructural deformation, more balanced structure force, less material consumption, and lowerproject cost, it is suggested that steel tube concrete pier can be used as reasonable pier formfor long span and low pier continuous rigid frame bridge to promote.The reasonableapplication scope of the steel tube concrete piers was discussed, and some suggestions forcombination of continuous rigid frame bridge piers under the conditions of different pierheights were proposed.4、According to elastic response spectrum analysis and dynamic time-history analysis bythe finite element software Midas civil, the seismic performances of steel tube concrete piersand reinforced concrete piers were compared. The moment-curvature curves in plastic hingezone of two kinds of bridge piers under different ratio of axial compression stress to strengthwere calculated by XTRACT program, then the curvature ductility factors were obtained,combined with the moment-rotation hysteretic curves calculated by the time-history analysis, ductility and energy dissipation capability of two kinds of piers were comparatively analyzed.The results show that steel tube concrete piers can greatly reduce the seismic response ofstructure, and have better ductility and energy absorbing capability, they are conducive toaseismic structure and can be used as the ideal pier form in high earthquake intensity zone.