Study On Some Key Technologies In The Design Of A Large Span Continuous Rigid Frame Bridge

With the rapid development of transportation engineering, the single-chest and single-room box girders which meet the requirements of wide bridge decks have been widely used in continuous girder bridges and continuous rigid-frame bridges. Technologies of balanceable cantilever construction without falsework, with the use of high-strength materials have made large span, thin-wall and light weight a tendency for bridges. Problems of structural stability, distribution of temperature field, thermal effect as well as shear lag effect have thereby become more and more critical. Study on these areas owns large significance for practical engineering. The relevant research has been carried out here on a real case of the large-span continuous rigid frame bridges which is a south approach of Tianxingzhou bridge in Wuhan, includeing the following works.On the object of stability analysis, two kinds of numerical methodologies for structural stability as well as the corresponding analyzing criterions are discussed. The linear-elastic formulations for safety coefficients of both self stability and cantilever construction of continuous high-pier rigid-frame bridges are derived. Comparison is made between results of self stability analysis on both constant and varying sections by finite element method and energy method. Meanwhile, the first type stability of bridge in different constructing period under various working cases is also analyzed. In the stability analysis during the critical cantilever constructing period by arc-length method, initial deficiency, geometrical nonlinearity, as well as the dual nonlinearity are considered. On this basis, the constructing safety for the whole bridge is evaluated.Based on the theory of minimum potential energy, the variational solution of the basic differential equations for the shear lag effect on the box beam is obtained. The displacement function is assumed as cubical and biquadratic parabolas respectively. Furthermore, the formulation of variational solution for the shear lag effect coefficient of constant-section cantilever box beam under evenly distributed load is derived. Hence, through analyzing the corresponding influencing factors, the theoretical solution of the shear lag coefficient of the box beam with reduced section is obtained with improved equivalent section method. Meanwhile, the shear lag effects of reduced-section box beam as well as the whole bridge under different working cases are also discussed. Comparison between the results from finite element method and energy method identifies that the method presented here can calculate the shear lag effect of the box beam with reduced section accurately. The influence of the width-span ratio, stiffness of flange as well as the stiffness of the section on the shear lag effect of reduced-section cantilever box beam is analyzed. The influence of the form of displacement function on the calculating accuracy of shear lag coefficient, together with the influence of lateral prestress on the shear lag effect of box beam is also discussed.On the respect of temperature field of sunlight, the temperature filed in the prestressed concrete box beam is set on the assumption that there is no internal thermal source in planar transient state. Based on the planar finite element equations for thermal conduction being set up, the finite element formulation for the planar temperature field without internal thermal source and that for the mixed-edge element are derived. On this basis, the 2nd edge condition is integrated into the 3rd edge condition. Edge conditions that influence the analysis of temperature field of concrete box beam are represented. The least favorable temperature field of structures is obtained based on analyzing the influence factors on temperature distribution, such as orientation, trend, material properties, cross section, as well as the environment condition of the bridge. Thus, two kinds of gradient temperature distribution forms are proposed for this real case. The principles of stress distribution on sections are got by solving the temperature stress distribution of the spatial continuous rigid-frame bridge through coupling heat-transient state and heat-structure. Its comparison with the two kinds of gradient temperature distribution forms proposed here shows it has offered a simplified formulation for the calculation of gradient temperature distribution form.