Research On The Mechanical Behavior And Design Method Of Trapezoidal Stiffened Plate In Steel Box Girder

On the basis of previous research and design code of some countries and combining China's construction experiences of long span steel box girder cable-stayed bridge, the dissertation presented systematical study of orthotropic trapezoidal rib stiffened plate mechanical behavior in steel box girder through theoretical derivation, finite element analysis, model test and on-site test. The main works involved in this research are as follows.As the trapezoidal closed stiffener is the most common type applied in orthotropic stiffened plate of steel box girder cable-stayed bridge in China, considering the torsional strain energy of the closed stiffener and calculating the flexural strain energy through the location of the sectional center, the critical buckling stress functions for the stiffened rectangular plate with four edges simple supported under various loading conditions were derived based on the energy method and quasi-orthotropic plate method, which is the main contribution of this paper. Through the comparison of the existent methods (Timoshenko method, Ichiro Konishi method, orthogonal anisotropic method and finite element method) with the method proposed by this dissertation, it is proved that the result from the method proposed by this dissertation is the closest to the finite element method's for the critical stress of typical stiffened plate.Further, as a main creative point of this paper, through the analyzing of the torisonal strain energy for the closed trapezoidal rib stiffened plate by the energy method proposed by the author and the finite element method, the contribution of the torsional strain engery on the critical buckling stress of stiffened plate varies from 42 percent to 77 percent, which cannot be neglected, especially for the plate with larger length-width ratio.Based on the energy function derived in Chapter 2, the parameter analysis for the critical buckling stress of the simple-supported stiffened rectangular plate with one couple edges under uniform compression were performed. The important factors considered in the parameter analysis includes the width-height ratio of the parent plate, the length-width ratio of the stiffened plate, the area ratio and the flexural stiffness ratio of the stiffener to the parent plate, the torsional stiffness-flexural stiffness ratio of the stiffened plate. Then, the reasonable stiffness ratio for the open or closed stiffeners and the maximum allowed height-width ratio of the web have been derived.Next, the codes regarding the initial imperfections from different countries have been compared. In this dissertation, the ultimate bearing capacity for the parent and stiffened plates of typical steel box girder were studied, taking account of the geometrical and material non-linearility. After that, the significant parameter analysis on the ultimate bearing capacity was performed.Subsequently, the author summarized the existent research on the residual stress distribution of the section of typical steel member and the open or closed rib stiffened plate, as well as the residual stress among the specifications from different countries. The blind-hole method was chosen to measure the residual stress for 309 measuring points of the actual steel box girder, and the principal stress and the normal stress were obtained. Besides, the simplified modes of residual stress distribution of the trapezoidal rib stiffened plates were proposed according to the test results, which is the main contribution of this paper.Then, nine specimens of stiffened plate were designed with the scale of 1:3 of the prototype of the steel box girder of the South Navigable Bridge of Hang-Zhou Bay Bridge. The differences of those specimens were the width of the parent plate, the width, the height of the stiffener, and the distance between the stiffeners. Before the test, the material properties of specimens were obtained through the tensile testing. The ultimate bearing loads, the load-displacement curve and the load-strain curve of specimens were procured through the ultimate bearing test. The test results verify that the failure modes of specimens under the axial loading can be categoried into three types, i.e. the failure of the parent plate, the failure of the parent plate and the stiffener and the failure of the stiffener. The finite element analysis was carried out to calculate the ultimate bearing capacity of those specimens considering the geometric and material non-linearility. The results from finite element analysis agree well with the test as the mean value is 0.992, the standard deviation is 0.071 and the variance coefficient is 0.072.Finally, the author summarized and compared different specifications on the local stability of the flange plate under compression, the layout of the stiffeners, the calculation and the applicable scope. Based on the research of this dissertation, the design method of the stiffener of the orthotropic stiffened plate in steel box girder was proposed, which is the main contribution of this paper.