Behavior of link slab for highway girders

Abstract

A Link slab of continuous bridge deck over its adjacent span of simply supported precast girders is desirable for smooth riding due to jointless construction. Since end movements of the girders have become restraints of the slab associated with some other actions, the movements of typical highway girders of I, T, U and Box sections with different span length and their construction sequences have been investigated. The interaction behavior of end restraints; axial, rotational and translational with mid-span loading, will be determined in the study. The finite element method of the microplane model (MASA) will be a tool for the structural analyses of crack patterns, crack width, modes of failure and structural responses of each action with different details and thickness-to-span ratios. Full-scale experimental investigation of 3 specimens of different reinforcing details of hinge, semi-continuity and full continuity with mid-span loading has been conducted to verify the results of the analyses. Monitoring of actual behaviors of real structures has also been done for comparison of some essential behaviors. End movements of typical girders have shown to be less significant on the cross-section and its construction sequences. Span length has played a major role on axial deformation and the rotation, as the translation is influenced by vertical stiffness of the support. Long-term effects due to creep, shrinkage and relaxation have shown indication of the extreme cases of 20% increase. The interaction behaviors for axial deformation and end rotation due to end movements of the girders have shown some influences of support conditions. However, the effects of the support level (x/H) in roller support (R-R) and centroid of girders (Cb/H) in hinged support (H-H) is less significant. For elastomeric bearing support, axial deformation is controlled by the number of spans and girder span length and show that rotation is less influenced by the relative stiffness of girders and link slabs of more than 10 and the location of the link slab in the structural system. Translation is subjected to shear and moment to be controlled by vertical stiffness, the slab thickness and its length. To design a link slab, span length and the number of girder spans are required for interaction of restraints to determine forces and displacement of the extreme cases. Then design for strengths can be carried out by means of tension, flexure, and shear while design for serviceability would be governed by stiffness of elastomeric bearing and crack distribution as per reinforcing details. Design example has illustrated the concept and procedure of the real practice.