Study On Influence Of Different Loading Methods On Shear Lag Effect Of Twin-cell Box Girder

With the development of the railway and highway construction of china, bridge construction will develop to long span and wide and thin-walled, researches had found box-section beam exhibit excellent mechanical characteristics.When long span and wide and thin-walled Box girder Under vertical load, due to the shear lag effect of flange plate shear deformation in the transverse uneven distribution, flat section is assumed not established, the longitudinal normal stress derived by the elementary beam theory cannot performance the actual stress state box beam.The reason of the cracks in box-section beam is that the shear lag effect is not considered in the design, it causes the design stress is not consistent with the actual stress state, it also risks the security and durable operation of box section beam. This phenomenon is proved to be true with lots of experiment and theoretical Demonstration. The shear lag effect of box section beam has caused the attention of the researchers.Through the principle of minimum potential energy and energy differential method, a formula was derived to calculate the concentrated load and uniformly distributed load of the double room with the flange of the rectangle] beam under the condition of simply supported, cantilever system.This paper introduced a concept of additional bending moment, considered the axial force balance condition, concluded the vertical deflection calculation formula. There are two parts of vertical deflection of double chamber rectangular box girder under the influence of shear lag effect, one is primary beam bending deflection, the other is additional deflection of shear lag effect.The mathematical model is established by using the finite element analysis software Midas/FEA plate unit structure, compare the calculated results with the theoretical analysis, and also compare the calculated results with the elementary beam bending theory.Different loading ways and structure have different impact on box beam shear lag effect, differently selected concentrated load and uniformly distributed load of double chamber box beam which is rolled by simply-supported structure and the cantilever structure, consider each load has three kinds of load condition, establish the mathematical model of six kinds of structure using the finite element analysis software, compute the longitudinal normal stress value of the most unfavorable section.The ratio of the longitudinal normal stress value and the longitudinal normal stress calculated by elementary beam bending theory is the box beam shear lag coefficient.To systematically analysis and summary the shear lag coefficient, conclude the factors of different load influence on shear lag of box girder, and longitudinal transverse normal stress distribution, In order to find the most unfavorable point and the most unfavorable load condition of box girder dangerous section as the control points of structure design.Select 40 m span reinforced concrete double chamber with rectangular cantilever plate girders as the calculating examples, by using the finite element analysis software Midas/FEA establish a mathematical unit model of box beam bridge, analysis lateral distribution and deflection law of simply supported, cantilever beam under different loads.