Safety of bridges and breakwaters estimated through general principles for limit state design by Japan Society of Civil Engineers

Although the specifications for Japanese highway bridges are currently under revision in the format of performance-based design, the degree of safety of the designed bridges is not easy to understand. Thus, this paper attempts to disclose the safety and the underlying reliability indices of roadway bridges designed in accordance with the Japanese Specifications for Highway Bridges in the light of a proposal of general principles for the limit state design. The reliability indices and the probability of failure are numerically evaluated assuming the Normal distributions both for the resistance and for the load effect based on the Advanced First-order Second-Moment Method focusing on the relationship between the probability of failure and the factor of safety. Further special reference is made regarding tsunami breakwaters in view of a low frequency but high consequence damages by the Great Eastern Japan Earthquake of March 11, 2011. It was found from the comparison that great discrepancy of the design philosophy and thus the factor of safety exists between the designs of bridges and breakwaters.