Cracks and damage frequently occur in RC slabs of highway bridges due to the characteristics of the road surface, difference in the level of expansion joints, and other dynamic effects of running vehicles. In this research, the effect of running loads on the flexural loadcarrying capacity of RC beams and the dynamic effects of running loads are experimentally evaluated. The conclusions are as follows: (1) A constant running load reduces the flexural loadcarrying capacity of the RC beam by 10% compared to the case of a static load. (2) Both strain and deflection of reinforcement for a 10%-running vibration load and a 20%-running vibration load increase by 17%-19% and 33%-35%, respectively, compared to a constant running load. (3) The impact coefficients for a 10%-running vibration load and a 20%-running vibration load are 0.239 and 0.374, respectively, indicating values which are higher than the amplitude of the load applied on the beam.

Cracking damage occurs in the reinforced concrete (RC) slabs of highway bridges due to the passage of heavy vehicles. Tests were conducted to determine the ultimate flexural capacity and failure mechanism of two types of RC beam with different effective depths (Type A: d=17.2cm/Type B: d=21.2 cm) modeled on RC slabs and subjected to running wheel-loads. The flexural load-carrying capacity for beams subjected to running wheel-loads decreased 16% for both Type A and Type B, as compared to beams subjected to static loads. The failure configuration for static loads and following running wheel-loads was a diagonal tension failure with a spread of approximately 50-55 deg. starting from directly beneath the wheels. For running wheel-loads of a constant strength and running wheel-loads that included vibrations, the crack that occurred at the lower edge progressed to the compression bars due to increased load strength and repeated running and became flexural tension failure. In the case of running vibration-loads, it was learned that the frequency greatly affected the cracking interval and the reduction in bending rigidity.