Analysis of box-girder bridges by grillage and orthotropic plate methods

Abstract

The paper deals with the calculation of longitudinal moments and transverse shear in multi-spine box-girder bridges. Results from three-dimensional analyses by the well tested finite strip method are used to establish the limits of validity of the grillage analogy method and the orthotropic plate method. These methods are shown to give accurate results provided that, for the orthotropic plate method, the number of spines is not less than three.Since transverse shear is mainly responsible for transferring loads from one spine to another, the flexural ridigity of the deck slab, and hence the slab thickness, has little influence on the distribution characteristics of a bridge; this is demonstrated with specific examples. Thus it is shown that a multi-spine bridge with at least three spines can be idealized as an articulated plate, i.e., a specific orthotropic plate in which the transverse flexural rigidity is assumed to be negligible.The behaviour of multi-spine box-girder bridges can be characterized by a single dimensionless parameter, with the help of which a simplified method can be developed to calculate longitudinal moments and transverse shear.