 Concrete decks were added to the upstream and downstream bridges in 1972 and 1980 respectively, to minimise rot, control termites, and distribute loads on the bridge more evenly.Steel girders were also retrofitted, replacing wooden half-caps.Karri used for half-caps was particularly prone to termite attack; while the outside had been treated with sodium fluoride and arsenic trioxide, the inside was susceptible to being hollowed out, and was the cause of a partial collapse of the upstream bridge in 1987.