This fall, we will complete the arches for the new Interstate 5 northbound bridge, following the same construction process used to build the southbound bridge arches.
One of the final steps is to raise each arch section about two to three inches off the falsework by pushing the arches apart with four large 965-ton hydraulic jacks. The jacks are positioned in the gap at the top of the arch and simultaneously separate and lift each so crews can pour the concrete closure that completes each arch and allows them to stand on their own. .
Similar to a jack you would use to lift your car, a single hydraulic pump applies pressure to each of the four jack rams, which separate the arches. Each ram has its own pressure gauge. Close calibration ensures that the rams and the gauges provide uniform and accurate information so equal pressure is applied and the arches aren’t damaged.
The calibration process pressurizes the rams up to 95 percent of their maximum capacity while individual gauge readings are recorded. Once the calibration is complete, crews must set up the system identically when moving the arch sections, using the same gauge and ram combinations they used during testing.
Only a few facilities on the West Coast can test such large hydraulic rams. The
The university provides written certification of the calibration along with a copy of the data collected during the tests to help ensure accuracy during this critical process.
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