Monitoring of a bascule bridge during rehabilitation

摘要

The risk of member/connection distress or even overall collapse of bridge structures under significant rehabilitation efforts is generally greater than when subject to normal operating conditions and hazards. This is particularly evident for movable structures. Currently, visual inspection during construction is the most common source of assurance a bridge owner has that the structure is functioning properly. Complex structures like movable bridges may benefit from additional oversight beyond visual inspection because of the elevated risks. Structural health monitoring of critical elements can help reduce these risks. A case study is presented for the first monitoring effort of a rolling lift bascule bridge under rehabilitation. During an opening of the span for ship traffic, a 460με (92 MPa or 13.3 ksi) shift in strain response was measured in the truss lower chord. To identify the root cause of this behavior, a detailed investigation was performed including field studies, interviews and model-experiment correlation. It was concluded that a connection slip occurred at a partially completed repair. Fortunately the structural system utilized on this bascule span includes a partially redundant truss which allowed for redistribution of forces. In this scenario, the primary impact of the monitoring was a change to the construction sequence allowed by the contractor. This investigation shows the potential benefit of instrumentation and monitoring in conjunction with traditional visual assessment methods, specifically during construction and retrofit of a movable bascule bridge.