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AUS-13 Dislodged finger plate on highway bridge
Report ID: 879
Report Overview
A correspondent received a report about a 1.5m long section of a steel finger plate expansion joint on a highway bridge that had been inadequately fixed and became dislodged.
Report Content
A correspondent received a report about a 1.5m long section of a steel finger plate expansion joint on a highway bridge that had become dislodged. The dislodged finger plate was found to have been secured with only one of the two intended fixing bolts. According to the correspondent, the missing bolt was not fitted as it clashed with a drainage channel/gulley immediately below its intended position, and no alternative fixing was provided.
The finger plate was dislodged by a passing large vehicle travelling at speed, which suffered some damage. It is very fortunate that the plate did not strike another vehicle or anyone in the area. However, the damage was sufficient to disrupt traffic for an extended period while emergency repairs were carried out.
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Bridge expansion joints are subject to very concentrated wheel loading, and fatigue failures of the joint components are common. For example, Roads and Maritime Services (NSW) Bridge Technical Direction BTD2008/10 provides valuable guidance on the selection, design, installation, assessment, maintenance and rehabilitation of bridge expansion joints. To quote from this document: “bridge deck joints can be very costly if not properly designed, installed and maintained. The replacement and rehabilitation of joints invariably involves costly traffic management and personnel working under hazardous conditions, often at night. The better the joint, the more money saved over the life of the bridge and less disruption to traffic.”
Although the age of the bridge is not specified, the incorrect fixings should have been identified either in commissioning or at ongoing condition inspections. It is vital that all bridge inspectors are adequately trained to identify such problems, and that this training and performance is subject to periodic review.
This serves as an example of a poorly designed and executed detail where only 50% of fixings were installed. Coordination of proprietary and post-fixed products with base structures always requires specific attention during both design and construction.
This was a near miss that could have had serious consequences considering the size of the component and the speed with which it must have been ejected.