A Study Thesis About The Effction Width Of Reinforced Concrete Continuous Box Beam Section

The box beam have been widely used in the bridge engineering because their beautiful external shapes, good behaviors and structural functions, but they show the shear lag or negative shear lag effect when symmetry bending loads act longitudinally .If the effect of shear lag is neglected ,high risks up to collapse of bridges may take place .As a classic subject, shear lag effect has been studied by scholars all over the world past several decades, some conclusions have been achieved. The bridge codes and specifications in many countries have taken shear lag effect into account, but many problems with shear lag stay continuously. The bridge engineering disasters in the middle last century made the scholars pay more attention to shear lag effect again and farther research restarted.The theory about the effectual width of the box beam section is the same as the T beam. When T beam is bent because of shear lag on section, The limb fringe vertical stress closed with costal girder is same . However the limb fringe vertical stress far away costal girder is changed , that change plus or negative shear lag . The vertical stress which change along limb fringe width in a same fiber layer need solve with high material mechanics . We introduce a conception of limb fringe effectual width or limb fringe calculative width , for using primary material mechanics . The stress asymmetrical phenomena in limb fringe is produced by the infection of cut distortion of limb fringe . The shear lag comes into additive moment and outside moment .This text with a reinforced concrete continuous box beam bridge from Jilin to Caoshi for the engineering background , analyse the effectual width and the modulus of shear lag on the middle fulcrum section and the middle section of second span which use ANSYS program . Some suggestions to the effectual width are given to the design of the box girders.