Full-Scale Load Test of a Sand-Jack

Abstract

The results of a laboratory load test performed on a particular type of steel sand-jack are presented. A sand-jack is a sand-filled containment frame placed atop falsework to temporarily support abutting concrete bridge-girder segments prior to posttensioning. The girder segments bear directly on a timber “plunger,” which in turn is supported on the sand bed. After construction, the sand is removed, causing the timber plunger to drop, thereby removing support from beneath the finished girder. The falsework may then be easily disassembled. Also presented are the results of a finite-element analysis performed to determine the lateral pressure exerted by the sand bed corresponding to the experimentally obtained displacements of the containment frame. The results provide insight into the capacity and performance of the sand-jack assembly, and guidance to the engineer in determining appropriate design pressures.