Study On The Main Tensile Stress Of Continuous Span Beam Webs In Shear Span

Continuous box girder bridges have been widely built because of their excellent performance.However,many continuous box girder bridges suffered from web cracking problems after long-term service.Therefore,it is necessary to make a detailed analysis of the main tensile stress of the web in the shear span of the beam.The main research work includes:(1)Based on the bending theory of thin-walled box girder and the geometric equations of strain and displacement,a stress analysis method of thin-walled box girder considering the in-plane shear deformation of wings and webs is proposed.The variational principle method is used to solve the equation to analyze the distribution of the stress of the box girder.And the solid finite element calculation results verified the rationality of the theoretical calculation results.(2)The calculation results of the cubic deflection displacement function and the secondary deflection displacement function are compared with the ANSYS finite element calculation results respectively.The result shows that both displacement function can be in good agreement with the ANSYS finite element calculation results.But the cubic deflection displacement function is relatively better in calculating the normal stress,the secondary deflection displacement function is relatively better in calculating the shear stress.(3)Theoretical deduction found that the positive-negative shear lag effect conversion position was just the zero position of g’(z).And the zero position of g’(z)is only related to the shear parameter k and the span l.The transition position moves to the fixed end with the increase of the value of k,and moves to the free end with the increase of the span.The function between them is obtained through numerical fitting method.(4)Based on the principle of superposition method,the calculation method of various stresses of variable-section continuous box girder bridge considering the construction process is proposed,and the stress evolution behavior of control section during cantilever construction is analyzed.The study found that before the closure of the bridge,the principal tensile stress of web gradually decreases from top to bottom,from the fixed end to the free end.After the closure of the bridge,the stress distribution of the box girder web became more complicated,the lower part of the web is compressed before1/4 span,the principal tensile stress gradually decreases from top to bottom.But after 1/4span,the stress distribution of the web changed,the upper part is compressed and the lower part is tensioned,and the principal tensile stress gradually increases from top to bottom.(5)Based on the Huanghe bridge in Zhongwei,a solid finite element model considering the construction process is established by the finite element analysis software MIDAS/FEA.Rely on the measured stress data,the distribution of the stress and its changing trend during construction was explored while the spatial model was verified.The analysis results show that the intersection of the web with the top and the bottom plate are two main locations where the tensile stress is greater.For the intersection of the web and the bottom plate the tensile stress is at a high level in each section,which has a greater impact on the safety of the structure.For the intersection of the web and the top plate while the tensile stress is only larger at the fixed end section,and at a lower level in the other sections.