Load Capacity, Failure Mode and Design Criteria Investigation of Sand Jacks: Full Scale Load Testing of Sand Jacks

摘要

A sand-jack is a sand filled container used as a component of cast-in-place bridge false-work. The sand filler facilitates the removal of the false-work by allowing slow and controlled lowering of the bracing that has become wedged beneath the new bridge structure. A circular sand-jack made of steel was tested to isolate the response of the two different sand fillers and the effects of the gap between the sides of the sand-jack and the application of the load. It was shown that the finer sand and a larger plunger both caused a stiffer response in the steel cylinder. Several configurations of wood sand-jacks were also tested in a second phase. In a range of vertical displacement of less than 1-inch, the number of bands, the spacing of the base nails, location of the banding, and the number of crimp connections on each band had little or no effect on the response. In that range of displacement it was shown that a sand-jack with no banding had a stiffness of half that of a sand-jack with banding. Additionally, test results demonstrated no benefit to lining the sand-jack with plastic. The use of a 12-inch wide corbel under a 15-inch wide sand-jack resulted in no adverse effects. The ultimate capacity was found to be significantly affected by the number of steel bands and the spacing of the base nails.