The article contains the method of reconstruction of an emergency bridge structure by installing a new span construction without stopping its operation taking into account difficult engineering and geological conditions of construction site on the example of bridge which is situated at the state significance road M-21, near the village Pultovtsy of Vinnitsa region. Have been reviewed the technical condition of short and medium-length beam bridges, which span structures are a system of string-concrete prestressed bridge beams which are often operated in Ukraine. Have been described methods for increasing the capacity of bridges, which were used in Soviet times. Have been proved the systemic nature of defects and damages of prefabricated string-concrete spans and bridge structures after widening. Have been described the rational ways to strengthen such bridges. Have been proved the low efficiency of their reinforcement by standard methods due to the critical corrosive wear of the reinforcing prestressed fibers of the main beams. Have been chosen the optimal method by replacing the superstructure from the considered methods. Have been proposed a precast-monolithic structural scheme of the bridge with increased carrying capacity according to modern requirements.Have been developed an analytical and finite element model of the stress-strain state of reinforced precast-monolithic bridge structure, taking into account the difficult engineering and geological conditions of the construction site. Have been proven the needed to strengthen existing pile foundations. Have been developed a constructive scheme for strengthening the bridge supported by installing additional rows of piles. Have been planned to be erected the construction of a new superstructure and additional rows of piles to strengthen the foundations of bridge supports in two stages without stopping of bridge structures exploitation but only with partial blockage of traffic. Have been proposed an effective technological installing diagram for this.