Analytical Study on Seismic Behavior of Multi-Span Concrete Girder-Slab Bridges with Link Slabs

Multi-span concrete girder bridges with simple supports are the most common highway bridges in Iran. In these bridges, expansion joints are usually installed at each end of simple spans to provide for deck longitudinal movement due to temperature, shrinkage, and creep. The presence of expansion joints causes many problems with regard to bridge maintenance. These problems include filling of the joint with debris, vertical misalignment of the deck, and loss of concrete cover and corrosion of cap beam reinforcement caused by water leakage through the joint. These damages in many multi-span bridges of the country are mainly due to improper maintenance. Elimination of expansion joints at the interior bents has been the subject of recent studies. These studies have led to development of a design concept for jointless bridges. In this approach, the bridge girders are simply supported but the expansion joints are replaced by constructing continuous slabs over the interior bends. The continuous portion of the slab is called the "link slab" and its presence changes the dynamic characteristics and seismic behavior of the bridge. In this paper, the results of seismic analyses of four-span and seven-span concrete girder bridges with and without the link slabs are presented. The analytical study was performed by spectral analysis in both longitudinal and transverse directions of the bridges. Seismic behavior of the bridges was investigated by comparing seismic demands in bridge substructures for various configurations and layout of link slab and expansion joint. The results of this study show that link slabs significantly affect the seismic behavior of the bridges. The total length of the bridge and the arrangement of expansion joints and link slabs on the bridge deck are the dominating parameters affecting the seismic behavior of the bridge and the distribution of the base shear to the substructure elements.