The Theoretical And Experimental Investigations On The Local Distortion Effects Of Twin-cell Box Girder Under Symmetrical Load

In recent years, as an important research subject, the distortion effects in thin-walled boxgirder is not allowed to neglect during design and analysis of bridge construction. This paperstudies under the Natural Science Foundation of China which are Space Mechanics and FiniteSegment Method of Thin-Walled Multi-cell Box Girders and Shear Lag Effect ofThin-Walled Multi-cell Box Girders Supported by Cables framework. For the local distortioneffects of twin-cell box girder under symmetrical load, based on closed thin-walled bar theory,the theoretical derivation, theoretical calculations, numerical simulation and organic glassmodel test research and comparative analysis, the mail work and achievements are as follows.(1) For the twin-cell box girder under symmetrical load, proposed combination of thesectional deformation mode decomposition of the shear lag and torsion and distortion. Fromtorsion and distortion mode can know the twin-cell box girder under symmetrical load whilegenerating vertical bending deformation also have certain local torsion and distortion. In thispaper, based on thin-walled bar theory and general beam theory, for the middle web underconcentrated loads of the twin-cell box girder section, cutting it open symmetrical from theload position. According to section bending shear flow balance, the equivalent load formulaof the single box section that has been cut open is derived. Using load decomposition methodto isolate twisting loads and distortion loads from equivalent loads, so as to establish thedistortion differential equation and the constraint torsion differential of the half beam, thenthrough the beam on elastic foundation method to calculate the local distortional stress.(2) For the case of the twin-cell box simple beam girder in the cross section and thecantilever beam girder in the free section in middle web under concentrated load. UsingANSYS finite element software SHELL63unit to establish a space shell finite elementnumerical model. From the stress of the ANSYS software, the output value by using theprinciple of superposition of load to extract the ANSYS numerical solution, and comparedwith theoretical solution in this paper, through a large number of contrast analysis shows that,the theoretical solution and the ANSYS numerical solution both the variation and thenumerical size are basic approach. Confirmed the theoretical derivation is correct and hasgood accuracy in this paper.(3) For concentrated load is symmetric function in twin-cell box girder on both sides ofsection on the web, first using the load decomposition method to turn it into a equivalent form,that only in the middle web under load recycle in this paper. Then using the proposed theoryto calculate the single box twin-cell box girder local distortional stress and compared with theANSYS finite element numerical solution, the analysis results show that the theoreticalsolution in good agreement with the ANSYS finite element numerical solution, the resultsshow that the role of the two forms symmetrical load by using the load decomposition method to a equivalent form is feasible, aslo confirmed the theoretical derivation is correct in thispaper.(4) For the ratio of distortion stress and bending stress, introduced the concept ofdistortion ratio. Through the analysis of distortion ratio can be obtained, the cantilever roofparts of the twin-cell box section have the greatest distortion ratio, while the roof and side ofthe web site of the transfer have the minimum distortion ratio. Only when the middle web isloaded, the simple beam midspan sectional maximum distortion ratio is32.16%and minimumdistortion ratio is8.94%,the cantilever beam eighth cross-sectional maximum distortion ratiois56.36%and minimum distortion ratio is18.89%.When both sides of the web aresymmetrical loaded, the simple beam midspan sectional maximum distortion ratio is16.08%and minimum distortion ratio is4.47%,the cantilever beam eighth cross-sectional maximumdistortion ratio is56.36%and minimum distortion ratio is28.18%.The results show that thelocal distortion stress of the twin-cell box girder under symmetrical load account for a largeproportion of the bending stresses which can not be ignored in the structure calculation, butalso can get, being symmetrical load distribution is more uniform in cross-section, the localdistortion effects more obvious.(5) To further understand the local distortion of the twin-cell box girder, the model of thetwin-cell box simple beam girder was established by plexiglass. For the three forms of themiddle section under the symmetrical concentrated load, also using the load superpositionprinciple to extract the test value of local distortional stress from the total stress and comparedwith the ANSYS finite element numerical solution and the theoretical solution, the analysisresults show that both the variation and the numerical size are in good agreement.