New extended grillage methods for the practical and precise modeling of concrete box-girder bridges

The Hambly plane grillage method has been regarded as one of the classic numerical methods in the design field for modeling wide box-girder bridge structures. However, when it comes to the in-depth design applications, its strict division rules and insufficient mechanical explanations often make engineers inconvenient or puzzled at bridge modeling. This article investigates whether this method may be extended to become more adaptable for the design of current concrete box-girder bridge structures in consideration of both convenience and precision. To this end, the defects of Hambly plane grillage method are recognized, and new extended grillage methods, including the single-layer folding surface grillage and spatial grillage, are proposed respectively, to deal with different bridge design objects completely in a beam-oriented environment. The former allows freer cross-sectional division by breaking the basic rule of Hambly plane grillage method to include longitudinal separate-type beam components for a better exhibition of shear lag effects. The latter emphasizes a complete consideration of spatial behavior, including the easily missed in-plane effects of the top and bottom plates. The effectiveness of the methods are demonstrated by comparison case studies in some benchmark models and by a discussion of their applications.

INFLUENCE OF SPAN LENGTH AND CROSSBEAM ON LOAD DISTRIBUTION FACTOR FOR GIRDER BRIDGES

Load distribution factor at concrete girder bridges and steel girder bridges are analyzed with finite element method to see effect of span length and cross beam to load distribution factor. Span lengths of analyzed bridge models are 30m, 40m, 50m and 60m. The number of intermediate cross beam is increased from one to until distance between cross beams becomes 5m. The finite element analysis results show that concrete girder and steel girder can use same load distribution factor and span length doesn’t affect to load distribution factor. Even though load distribution factor in interior girders is not influenced by cross beam, in exterior girders it is influenced by cross beam. Effect of cross beam in exterior girder is influenced by the number of lanes and distance from exterior girder to curb. Since design code introduces conservative load distribution factor, economically improved load distribution factor is proposed. The proposed load distribution factor includes cross beam effect with the number of lanes and distance from exterior girder to curb. The proposed equation is compared with AASHTO code and grillage method which is well-known method to calculate load distribution. The comparison results showed that the proposed equation is more efficient and useful than AASHTO and safer than the grillage method.

The Meticulous Analysis of Skew Beam Based on the Space Skew Beam Element Method

When a skew bridge is analyzed, it is difficult to treat skew boundary conditions with general space beam element in single beam calculation of skew beam bridge. The stiffness of skew bridge cannot be simulated efficiently. In order to improve the accuracy of skew bridge, the stiffness matrix of the space skew beam element is derived based on the principle of minimum potential in this paper, this element is suitable for single beam of skew bridge and grillage method. A corresponding program is completed by Visual C++, the calculated results of different finite element models are compared, so the validity of the proposed model in this paper is validated. This paper can provide reference for plane and space calculation of the skew bridge design.