Fatigue Design Method for Reinforced Concrete Slabs of Highway Bridges

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In Japan, the design of reinforced concrete slabs of highway bridges has been done by the allowable design method. However, since about 1970, the slabs were suffered from cracking damages inducing punching shear failures. These damages have been recognized an fatigue phenomenon due to heavy wheel loads. From the original experimental tests under running wheel loads, the author has explained that the fatigue failure depends mainly to alternation of shearing stresses acting on cracked surfaces in the slab under running wheel loads. Therefore, the author has recognized that the design should be chanced by considering the shearing stresses. In the case, the experimental data by the author seen to be the most suitable. The research was carried out to establish the design method.To complete the research, wheel load characteristics should be prepared. However, it was very difficult to find out the existing data. Therefore, the author has developed a new method to measure wheel loads under running which is based on measuring crack opening due to wheel load. Through 24 hours measuring for main load, we prepared a suitable data. Using the existing fatigue data and the wheel load characteristics, a new design method based on shearing stress amplitudes was derived.