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Strengthening is an important procedure for bridges in case of increased traffic, changes in code provisions, design or constructional mistakes, etc. A proper strengthening of a concrete-concrete composite bridge requires a detailed inspection of an existing structure before, during and after strengthening. The authors present a general algorithm of necessary steps, which are followed by an example of strengthening by external prestressing for a six-span simply supported (6 × 40 m) road bridge. The authors present results of tests carried out before, during and after strengthening as well as a brief description of external prestressing design. Tests before the design stage allowed to estimate the structure’s stiffness and to calculate the required prestressing force. The objective of tests during prestressing was to measure strains and deflections in the middle of the girders. After prestressing the bridge was tested under load again to estimate the effectiveness of the strengthening. Tests confirmed that external prestressing was an efficient method of increasing the stiffness of the structure.
Madaj et al. (Wed,) studied this question.