The changes of bridge loads during the long-term period

The aim of the paper is an analysis of bridge loads changes in the 20th century. The Polish bridge load standards issued in the 20th century are considered here. The two static approaches are adopted on the basis of the model of the real composite of a steel and concrete bridge carrying-deck. The first of them, the traditional simplified Courbon method which was in use up to the 1970s, gives bending moment results. The other one is the analysis by the ABAQUS FEM. The dynamic response of the structure is performed for the set of velocities starting from 10 km/h to 90 km/h. Basing on the obtained results, it is concluded that the load increase is essential for bridge sustainability in all phases i.e. for design, maintenance and optional rebuilding. Having in mind that, in general, the indicative service life of a bridge is intended for 100 years approximately, i.e. for three generations, the prognosis of load changes is crucial. The bridge load effects increase over the past century is estimated at 60% to 85%, it being at least 30%.