Study On Shear Lag Effect Of Box Girder And Analysis Of Affect Factors

Shear lag effect of box girder is important problem in bridge structure designing and construction, however, the experiment calculation method of effective distribution width of flange plate of model T is not accordance with engineering. So, the factor of shear lag of box girder is researched by using the principle of the stationary value of the total potential energy, FEM and model test. In this paper, the main contents are as follows.1 Shear lag effect of box girder is reviewed in the paper.2 The reason of shear lag effect of box girder is analyzed. Differential governing equations of trapeziform box girder is yielded by using the principle of the stationary value of total potential energy. Taking shear lag into consideration, a program in FORTRAN language is revealed that the normal stress distribution is uneven markedly.3 Energy theory, model test and FEM are utilized to analysis shear lag effect of box girder. It is shown that width /span ratio and width/height ratio are the main factors, however, load styles are important factor.4 Basing on the theory of separate model for coupled method, 3-D spar element with initial stress is utilized to simulated prestressed cable. APDL program based on the ANSYS software for calculating prestressed concrete construction is designed. It is shown that the method is suitable for analysizing prestressed concrete construction for its precision.5 Prestressing is important factor for shear lag. Through parameters analysis, it is shown that the angle of prestressed cable is most important factor for shear lag effect of box girder, however, the placement of prestressed cable is insensitive. Shear lag is reduced for prestress in serviceability limit state.6 The deficiencies of the State Design Specification is discussed, furthermore, some advice is given in the paper.