The article examines the effect of dynamic loads on crack width of decks of prestressed reinforced concrete frame (box-girder) viaducts. The experimental measurement of the changes in width of vertical cracks of Pareizgupis viaduct resulting from the loads of moving heavy weight vehicles was made. During testing, four-axle vehicles with weights of around 40 tonnes were used and they were driven over the viaduct deck at the speed of 20 – 40 km/h. The stresses in prestressed reinforcement were analysed, calculated and compared to the results obtained during testing. Having evaluated theoretically the elastoplastic operation of concrete, the width of a vertical crack was measured in the middle part of the viaduct.
