CROSS Safety Report
Dislodged finger plate on highway bridge
This report is over 2 years old
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.
This was a near miss of a potentially fatal incident caused by poor detailing and installation, and inadequate inspection.
Key Learning Outcomes
For civil and structural design engineers:
Ensure that fixings of items in decks of highway structures are correctly detailed and installed without being compromised by underlying cavities, e.g., drainage channels
Consider benefit from providing additional fixings to provide redundancy if one fixing should fail
Ensure rigorous and regular inspection of items in highway structures subject to loads from passing traffic
For construction personnel:
Ensure all fixings of items into supports are as intended and that none is compromised by issues with underlying material or structure
For highway authorities:
Ensure inspections of running surfaces of highways and highway structures are regular and rigorous, especially at the time of commissioning
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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.
Near miss – public danger
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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The report AUS-13 about a dislodged finger plate reminded me that I have noted broken finger joints on an expansion joint in a bridge structure and that this could lead to a blown tire and the potential for a serious crash of the vehcles involved.
Expert Panel Comments
An Expert Panel comment on the reports we receive. They use their experience to help you understand what can be learned from the reports. If you would like to know more, please visit the CROSS-AUS Expert Panel page.
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.”
Defect not identified by inspections
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.
Poor detailing and installation
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.