Bridges

The Australian Standard for Bridge Design Part 2 (AS 5100.2) specifies requirements for the dynamic load allowance to be applied to vehicle loads to account for the interaction of moving loads with the structure. The code makes specific provision for the application of this factor to buried structures, but does not differentiate between rectangular and arch structures, or take account of the relative differences in stiffness of structures, such as between concrete and soil-steel structures. In addition, buried arch structures are often subject to very high vehicle loads in non-highway situations such as mine haul roads where typical axle loads are much higher, but vehicle speeds are significantly lower than for highway bridges, and vary for different vehicle types.

In this paper the behaviour of typical concrete buried arch structures has been analysed using a non-linear dynamic finite element analysis taking account of soil-structure interaction effects and the non-linear flexural behaviour of the concrete section. The analysis was carried out for two different arch spans with typical minimum depth of fill over the arch and varying vehicle speeds. For the vehicle speeds resulting in the greatest dynamic loads, the effect of increased fill height and increased fill elastic modulus was also investigated. Each analysis considered the AS 5100.2 standard M1600 vehicle, and a typical fully loaded mine truck.

The paper compares the critical design actions from the dynamic analyses with static analyses under the same conditions and provides recommendations for appropriate dynamic load allowance factors and comparison with the factors defined in AS 5100.2.