Investigation of bridge bearing condition at Mollison Avenue and Lea Valley Road
By collecting detailed information from inspection, measurements and monitoring data, JFTS provided the asset owner with defined actions for bearing life management
Enfield Council had proactively identified that bearings supporting bridges were of a limited life and that maintenance or even replacement might be needed for certain aged structures. By acting ahead of any major fault, it was hoped that minor maintenance could be identified and acted upon to maximise the remaining life and to intervene ahead of any urgent matters.
The Mollison Avenue Bridge is a single span formed of pre-cast pre-tensioned concrete beams supported on abutments with pad foundations. Laminated elastomeric bearings had been identified in Principal Inspection as over-displaced and subsequent General Inspection identified concrete spalling at the interface between bridge and one wing wall. James Fisher Testing Services (JFTS) were brought to the scheme to consider the need for a Special Inspection.
JFTS conducted inspections, measurements and short duration monitoring to evaluate the present displacement of bearings and the variation with changes in temperature. By collecting this, analysing for patterns and interpreting in conjunction with previously known information, JFTS were able to suggest which bearings and zones were functioning as intended and those which were suffering undesirable effects.
JFTS’ Datanodes were the ideal monitoring solution. Discrete data acquisition units collect measurements at very high sample rates from local sensor groups without the need for long cable runs. Each Datanode can be installed individually and set running while inspections and other tasks continue.
Conclusions included evidence of foundation differential settlements causing the bearings to be forced to displace beyond their intended range. JFTS gave suggested actions for both the permanent resolves and the temporary measures to ensure safety until those works could be completed.
Lea Valley Road
The Lea Valley Road Bridge carries a major local road over the navigable River Lea. A high skew single span superstructure is formed of steel plate girders and a composite concrete deck. Bearings are steel rockers at the fixed end and laminated elastomeric at the opposite.
Previous maintenance had included painting over the bearings both steel and elastomeric, which had caused bridge inspectors to query their condition.
JFTS were brought to consider a Special Inspection and proposed a regime of investigations including detailed inspections and measurements. Analysis and interpretation of the bearings in relation to each other and the structure as a whole led to conclusions and an actions list suggested in JFTS’ report. Minor maintenance actions conducted in the near future are recommended to prolong the life of bearings and the bridge. Bearing replacements might be delayed for a further 10 years.
The asset owner and manager is provided with detailed factual and interpretive reports, which show the current condition of bearings. Causes of defects are suggested based on all evidence collected and an extensive knowledge of bridge structural behaviours. Actions are recommended for maintenance and safety measures. Bearing replacements can be delayed and limited to only those which are necessary.
By combining inspection, measurements and monitoring, along with interpretive analysis, a detailed understanding of the bridge and its faults are presented to the asset manager leading to recommended actions.