Computation of Stable Riprap Size Stone Around A Bridge Pier using first Order Reliability Method

The failure of bridge is mainly due to local scouring around the piers. The scouring around the bridge pier can be reduce by adopting various method. The placement of riprap stone around pier has been found the most common method to protect the pier scouring. A deterministic riprap stone size prediction method has been proposed in present analysis by using the data available in the literatures. The deterministic approach method is only based on the mean values of basic variables and do not include the various types uncertainties present in basic variables. A reliability-based assessment of riprap stone size prediction method is required to incorporate these uncertainties. A reliability-based design riprap stone size around the bridge piers has been carried out in the present study using first order reliability method. A methodology developed by Low and Tang (2007) based on object oriented constrained optimization technique has been used for the reliability analysis in this study. A factor of safety value has been proposed corresponding to the target reliability index using the present approach. The effect of mean values, uncertainties and distribution pattern of basic variables on reliability of riprap size have been studied in detail. The sensitivity analysis has also been performed to study the active and reactive random variables on reliability of riprap size around a bridge pier.