The reinforced concrete (RC) slabs of steel road bridges suffer crack damage caused by load variations when large trucks pass over the expansion joints of the slabs. To cope with this problem, the authors conducted a test on slab test specimens under running vibration loads and proposed an experimental formula for calculating the coefficient of impact as a function of load amplitude. In this study, the authors prepared RC slab test specimens based on the bending moment due to live load to which a dynamic influence coefficient as a function of load amplitude was applied, and conducted a test on the specimens under running vibration loads with a load amplitude of ±20% and ±30% to verify the improvement effect of RC slabs. The RC beams and slabs with increased cross-sectional area of reinforcing bars based on the bending moment were improved by approximately 39% and 35%, respectively, and the coefficients of impact were below those prescribed in the Specifications for Highway Bridges of Japan.
