Technical Proposals
Provided multiple technical design options and associated costs for installation of remotely accessed strain and temperature monitoring system
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The Challenge
- Gold Star Bridge features rocker bearing support
- Stuck bearings pose risk of stress buildup
- Fiber optic system enhances sensor durability
The Gold Star Bridge’s design uses a rocker bearing support system. When functioning normally, each bearing allows a limited amount of rotational movement at each pier to accommodate for thermal expansion and contraction across the bridge’s superstructure. This helps to relieve potential stress incurred by thermal deformation. Immobilized rocker bearings, however, can cause thermal and load induced stresses to build up in key structural components, leading to potentially unsafe conditions.
During a routine maintenance inspection, it was discovered that a set of rocker bearings had become stuck at one of the piers. Ultimately, a fiber optic system was put in place which increases the durability of the sensor array and allows for in-house quality assessment testing and assured sensor reliability during and after the installation.
The Solution
Geocomp designed the final monitoring package to include temperature and strain fiber optics as the primary sensor elements; both the “restrained” and a companion “free-moving” span were chosen as sensor installation sites for taking comparative response measurements across the bridge structure. In addition, a gusset plate was selected to evaluate stress incurred from load paths on adjoining structural members. Fiber optic accelerometers were utilized at each pier to detect potential static friction slippage or movement – a possible result of built up stresses suddenly overcoming the static friction forces between the frozen rocker bearings and the pier.
Since measured stresses primarily are induced thermally, the overall system was designed to compensate for temperature fluctuations and differentiate between separate types of thermal strains.
