Research On The Elastic Stiffness And Failure Mechanism Of Open-web Beams

The open-web girder is the basic component of the open-web sandwich plate,which has the advantages of light-weight,reasonable steel,reasonable section form,high load-carrying capacity,beautiful economy and so on.However,the study on the stiffness of open-web girder is not comprehensive and has no research on its failure mechanism,so it is of great significance to further study its elastic stiffness and damage mechanism.In this paper,the main research work on the elastic stiffness and failure mechanism of open-web girder covers the following aspects:(1)According to the domestic and overseas references,this article summarizes the stiffness calculation method of sandwich beam,castelled beam,open-web truss and open-web girder,for open-web girder laid a theoretical basis for the derivation of elastic stiffness.(2)In this paper,the calculation formula of shear key strain energy is established by means of energy principle,and the influence of shear span ratio on strain energy of shear key is analyzed.The calculation formulas for the shear,bending and axial continuous adjustment coefficient of the open-web girder are obtained.The influence factors of the continuous adjustment coefficient of the open-web girder are analyzed by using the control variable method.The basic control equation of the open-web girder is obtained by analyzing the force of the open-web girder subjected to vertical load.(3)Based on the assumption of the same bending angles of the top and bottom ribs,the general formulas for the internal force,deformation and elastic stiffness of the open-web girder are established.The calculation formulas of internal force,deformation and elastic stiffness of open-web girder subjected to uniformly distributed load and mid-span load are obtained.Using the control variable method,this paper analyzes the beam on an empty stomach reduction coefficient of stiffness,deflection and the ratio of the shear deformation influence factors,the proper grid spacing,shear key value scope of shear span ratio,Cross-height ratio.Comparing the theoretical results with the finite element results,the study shows that the formula is not only suitable for the hollow beam,but also can be applied to the hollow truss.Compared with the current calculation formula,the calculation results are more accurate.(4)For studying the effects of shear key inflection point hypothesis calculation error,to subjected to uniformly distributed load of simply supported open-web girder as an example,established the shear key inflection point is out of the middle hollow beam internal force,deformation,and the calculation formula of the deflection difference and elastic stiffness.Additional reduction using the control variable method,the paper analyzes the stiffness coefficient and the influence factors of top and bottom rib deflection difference,the result shows that only when the ratio of high to the grid spacing or across great hours,to consider the influence of shear key inflection point is not in the middle,at this point,the rib deflection difference and additional reduction stiffness coefficients is larger.(5)Destruction mechanism of open-web girder under vertical load,the analysis results show that the reinforced concrete open-web girder failure mechanism similar to ordinary plain girder of the bending,can be divided into three stages: the concrete crack are not crack before and after concrete cracking and reinforcement yield cracks in front of the stage,began to yield to the destruction of concrete section damage stage.The whole failure process of reinforced concrete open-web girder starts from the longitudinal tensile reinforcement of the bottom ribs and is finally crushed by the top rib concrete.