The Correction of a Commonly Used Formula for Calculating the Reliability Index of Bridge

A formula for calculating the reliability index in the American Bridges Design Specifications is widely applied in China.Its error cause is analyzed in terms of probability distribution and variation coefficient.It is pointed out that the formula is an approximate formula no matter whether the load effect follows lognormal distribution.The reliability indices are calculated by using this formula and the Monte Carlo Method under eight typical conditions.The results show that the error of the formula is normally around 30% and up to 46%,and the reliability indices obtained by the formula are always less than those by Monte Carlo Method.Finally,both methods of theoretical analysis and numerical analysis are put forward to revise the formula.The reliability indices under eight conditions are calculated with the revised formula.Results indicate that the calculation accuracy has been obviously improved and the error is usually controlled less than 11%.