Local Scour in Bridge Piers: A Reliability-Based Approach

As a vital structure in civil engineering, the performance assessment of bridges becomes very imperative in view of several bridge failures around the globe. Scouring is one of the major causes of the failure of bridges that needs to be taken care of during design. Therefore, the present study aims to investigate scouring in bridge piers under the probabilistic framework. The required pier diameters in achieving three levels of target reliability indices (beta T = 3.0, 4.0, and 5.0) are estimated for different foundation depths and angles of attack of the flow considered in the study. The load and resistance factors corresponding to the same target reliability indices are also back-calculated from the design points obtained from the First Order Reliability Method. The influence of variabilities of the input parameters on the computed pier diameters and load and resistance factors is also examined. The parametric study shows that the foundation depth is the most influencing parameter in determining the required pier diameter, followed by the coefficient for streambed conditions and flow velocity. From the analysis, it is found that for beta T = 3.0, the pier diameter is increased by around 41.5% for an increase in the mean foundation depth of 1.0 m (from 4 to 5 m). Further, the study suggests that the effect of flow angles on the estimated pier diameter is also significant. For example, keeping the target reliability index and coefficient of variation (COV) of input variables at a constant value, the required pier diameter is reduced by around 60%, as the angle of attack of the flow is increased by four times. Finally, one design problem is presented to ensure the efficiency of the present approach, and recommendations for the current practice followed in India are provided.