Analysis On Distortion Effect Of Single Box Twin-cell Box Girder

With the development of Chinese economy and infrastructure construction,bridge construction accounts for an increasing proportion.And box girder is widely used for its torsional stiffness and construction adaptability.In recent years,many scholars have devoted themselves to the research on the distortion effect of box girders and have achieved great progress.But there still some problems in the distortion effect of concrete box girder,especially the single-box double-chamber box girder.This paper takes the single-box and double-chamber box girder as the main research object,conducts in-depth studies from the following aspects:(1)Revise the traditional theory: Plate-beam frame method.And a new method for calculating the stiffness of transverse frame of single-chamber box girder by means of structural mechanics force method is presented.Compared with the existing literature,it is found that the proposed method is feasible.In the following chapters,this method is applied to the distortion analysis of double-chamber box girder to verify its feasibility in the distortion analysis of double-chamber box girder.(2)In order to analyze the distortion effect of single-box double-chamber box girder,the distortion load is composed form the eccentric load according to the method of load decomposition.In view of the double-chamber box girder under symmetrical load,according to the existing thin-walled theory and general beam theory,this paper cut the box girder open symmetrically from the middle web,then derive the equivalent formula according to the theory of shear flow balance.Using load decomposition method to isolate distortion loads form equivalent loads,then through the beam on elastic foundation method to calculate the local distortional stress.(3)Aiming to the distortion effect of single-box double-chamber box girder under eccentric load.This paper select the typical distortion angle as distortion displacement,and forces on double-room box girder are decomposed into internal force causing longitudinal warpage and external force causing transverse deformation.Establish the relationship between the distortional angle and the displacement,and deduce the distortion control of single-box double-chamber box girder differential equation.A matlab program is compiled according to the steps of solving linear equation in the process of derivation.Taking distortional angle,distortion warping displacement as initial parameters,and deduce the special solution of simply supported beam under concentrated load and uniformly distributed load in mid-span.According to the calculation of distortion warping stress of simply supported double chamber box girder,it is shown that the theoretical analytical solution is in good agreement with the numerical solution of ANSYS model,which proves the correctness of the method in this paper.Combining with the trend analysis of longitudinal distortion warping stress,distortion angle,distortion double moment and distortion moment,it is found that the distortion warping stress of double-chamber box girder reaches its maximum value in mid-span,then decreases rapidly,and finally tends to zero at the support.The maximum distortion moment occurs in the mid-span and mutation in a cross.(4)Building ANSYS model of single-box double-chamber box girder,Analyzing three parameters of mid-web thickness,width-span ratio and number of diaphragms.Finding that with the increase of web thickness in double-chamber box girder,the torsional stiffness of cross-section increases,and the distortion warping stress at the corner of box girder decreases as a whole.But when a critical value is reached,the influence of the middle web thickness on the distortion of double-chamber box girder is reduced.Keeping the width unchanged,the ratio of width to span decreases gradually with the increase of span,and the distortion warping stress of corner points of double-chamber box girder decreases linearly with the variation of width to span ratio.Increasing diaphragm can effectively limit the distortion of double-chamber box girder,but the influence of diaphragm spacing on distortion is reduced when it reaches the critical spacing.