Determination of load combination factors for the assessment of existing bridges

Abstract

There is a difference between the calibration of partial factors of safety for a new code of practice intended for design, and the development of factors for assessment. In particular, the treatment of load combination factors for code calibration is often a source of conservatism, as is reasonable. However, for the assessment of an existing structure, this conservatism is not desirable. Consequently a means of deriving load combination factors that simultaneously satisfy several limit states is sought. This paper examines the various methods used for load combination factors in the literature and assesses them for use in the assessment of bridges. A simple formula is proposed and demonstrated using several case studies, and compared with the results from the usual heuristic practice. It is shown that the proposed method offers a valuable means of deriving load combination factors for bridge assessment.