Concrete frame viaduct over national road no. S3 occurred to be to week under the dead load just after construction. Several investigations and concept works were done to develop a final way of strengthening. Finally span was reinforced by additional steel plates bolted to the bottom part and two concrete ribs placed instead of crash barriers on the road. Designed strengthening was fully implemented and several tests were performed to proof a final capacity of viaduct. Results of testing and conclusions are included.
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The paper presents two examples of frame viaducts with extensive cracks which occurred already at the stage of construction, after the dismantling of formwork. In the viaduct WD 1 the crack opening in the middle of span reached to 0,4mm. These cracks occurred at approximately 1,70m long of the middle part of frame transom and reached roughly to the width of the % of this element of frame. The average spacing of cracks was approximately 24cm. Besides the cracks on the frame transom of viaduct, some additional cracks were found on the inclined supports (legs) of frame. These cracks begun next to the foundation plate and disappeared at about 2,0m from the top edge of this foundation plate. In the second viaduct, WD3, cracks were located on the frame transom, on the side of eastern abutment, and so on the side, where there were poorer soil conditions (soil stratified, with less degree of consolidation). These cracks reached roughly to half the width of the transom. Measured cracks widths ranged from 0,05 to 0,1mm. These two analyzed viaducts should be classified as so-called integrated bridges. From the viewpoint of statics they are frame structures. Both viaducts are founded di-rectly, using continuous footings. In the ground, below the level of the foundation, the substrate was stratified with interbeds of substrates with different capacity. Additionally in both cases relatively high groundwater level was identified
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