Follow the plan Replacing non-renewable bearings on a 96- year-old bridge by Max Willison

Abstract

Detailed condition assessments of a 96 year old continuous, 5 span, reinforced concrete road bridge showed that the bearings on one abutment were at risk of failure. Over the course of 2 years assessments and designs were developed including a very detailed methodology based on site samples and lab testing to determine how these bearings could be replaced. They were not designed to be replaced. Multiple deviations and special allowance needed to be made when compared to traditional modern remediation works to ensure the work was compatible with the old construction and materials and to preserve the original design function of the bridge. The materials encountered included, 18MPa concrete, 230MPa reinforcing, fully carbonated concrete, cast iron bearing retainers and bronze phosphor bearings. Perhaps unsurprisingly this work may have been avoided had the local drainage and road water been managed more efficiently during the bridge younger years. This is unsurprising because while working in council much of my work managing existing assets revolves around managing moisture and water to maintain the asset. Regarding the title of following instructions, the bearing replacement and jacking was performed twice as insufficient curing time was allowed for one of the components and there was no engineering solution available other than starting again and following the design procedure. The lead up work and investigations proved correct however a slight change during construction following a delay proved the method must be followed. Cutting corners and making changes based on theory sometimes does not work out.