Bridges

RTA’s bridge design engineers have identified that the current capacity reduction factors for cast iron specified in AS 5100.6 are inordinately low compared to those for other engineering metals such as structural steels and wrought iron. The suitability of using these factors was questioned as they were derived from an older bridge design code that used working stress design without a reliability calibration carried out during the conversion to limit states design. This paper investigates the adequacy of the currently specified capacity reduction factors for ductile cast iron structural grade components in AS 5100.6 and the possibility of adopting higher factors. The paper summarises the findings of a reliability analysis carried out using test data from local foundries, assuming adoption of the specified levels of inspection and testing in the relevant RTA QC specification. The paper proposes higher capacity reduction factors than the current values in AS 5100.6 for the design of ductile cast iron components for timber bridges, provided the specified quality control provisions are followed.