Jack posts are telescopic tubular steel props consisting of two primary parts, the main part of the post, and the jack screw or other adjustable fitting on one or both ends. Both ends are normally fitted with flat metal plates on the end, providing additional support area. A recent improvement to Acrow props was to shape this base-plate with notches, allowing pallet loads of horizontal props to be stacked neatly, rather than randomly piled.
Most jack posts are split in two near the middle, with the upper end carrying the jack designed to slide within the lower portion. Gross adjustment for length is first made by pulling a pin and sliding the two sections within each other until they almost fill the gap, inserting the pin to lock them, then using the screw to close any remaining gap. Other designs used two threaded pipes instead of sliding sections, ratechetting or clamping sections, or other similar concepts to lock the system at a specific length.
Jack posts are mostly used for shoring: temporary supports during building repair or alteration work. A typical use is to support an existing horizontal beam while its original masonry supports are removed or repaired. When masonry itself is to be supported, holes are first knocked through the brickwork and a strong ‘needle’ or ‘strong boy’ is placed through the hole. A pair of props are then used, one under each end. Existing windows or doorways may also be supported directly, or via needles. As the plates on the end of the posts are typically small, they offer little sideways support. If there is any sideways force, props should be strutted or ‘laced’ with scaffolding poles.
Post time: May-15-2020