Developing a new bridge live load model for South Africa

South Africa's bridge design code, TMH7, was first introduced in 1981. The code was found to be unconservative for narrow and short span bridges and revisions were issued in 1988. In 1991 it was proposed to increase the axle load by 25 % to 180 kN, but the code was not amended. In 1996 the legal limits for GVW and axle loads in South Africa were increased, but TMH7 loading was not updated. One year of WIM data was used to calculate hogging and sagging moments as well as shear forces for span lengths up to 50 m. The forces and axle weights were extrapolated normally to a return period of 975.3 years. The extrapolation resulted in a characteristic axle weight of 170 kN which was applied as a double axle. The extrapolated load effects and the tandem axle were used to calculate a characteristic distributed load of 15 kPa.