Calibration of fixed partial factors based on sensitivity factors adjustment for a cluster of structures

The adjustment of partial factors is a major lever that can be used when assessing an existing structure, avoiding unnecessary repairs and increasing the structural service life. A method to calibrate sensitivity factors, then fixed partial factors for a cluster of bridges is proposed herein. Different geometric configurations and uncertainties related to materials and loads are considered to create a collection of bridge samples. A probabilistic sensitivity analysis associated with a first order reliability method (FORM) is then performed to create a collection of most probable failure point (MPFP) coordinates. The objective is to align an assessment point with the MPFP as it is considered for design, though applying the approach to a particular cluster of bridges and including the ability to get some additional information on these structures and choices about target reliability level. Two approaches are compared to fit this new assessment point: (i) an averaged fixed sensitivity factor set matching some target reliability level and (ii) an optimization procedure enforcing reliability constraints for the whole collection of MPFP that provides fixed sensitivity factors associated with a bounded optimized failure point. Both approaches are applied to the generated samples of reinforced concrete frame bridges for illustration purpose.