Reliability-based sensitivity analysis for prestressed concrete girder bridges

Structural performance of bridges depends on the applied loads and the load-carrying capacity, both of which are random in nature. Therefore, probabilistic methods are needed to quantify safety. It has been widely agreed to measure structural reliability in terms of a reliability index. Material properties have changed over the last 30 years. The new material test data include compressive strength of concrete, yield strength of reinforcing steel, and tensile strength of prestressing strands. Average daily truck traffic and gross vehicle weight have also changed. The updated statistical parameters for prestressed concrete girders and live load affect the reliability indices. The objective of this paper is to present the results of the reliability analysis for prestressed concrete girders using the most recent live load and resistance (flexure) models. Several types of American Association of State Highway and Transportation Officials girders and Nebraska University (NU) girders are considered with spans ranging from 80 to 200 ft (24 to 61 m) and girder spacings from 8 to 10 ft (2.4 to 3 m). An important part of the research presented is derivation of sensitivity functions for various parameters that affect performance of prestressed concrete girders. The focus is on strength limit states, in particular bending capacity. The contribution of several resistance parameters, such as reinforcement area and yield stress, is considered. The procedure is demonstrated on representative girder bridges.