Components of Column-Mounted Shoring
The system consists of two major components, a deck panel and a column – or wall-mounted bracket jack system. The deck panel consists of a plywood sheathing supported by a system of wood joists (headers), and a nailer-type open-web stringer that allows a 2 X 4 in. (50.8 X 101.6 mm) wood section to be inserted into the open web. A truss system supports both the joists and stringers. For smaller spans, a steel section can be used instead of the truss system. The truss system is supported by heavy steel I beams that run on all the sides of the deck panel. The I beam rests on the column-mounted jacks bolted in the concrete columns or bearing walls. Figure 4.7 shows a cross section of the column-mounted shoring system.
The second component of the column-mounted shoring system is the bracket jack system. The function of the bracket jack system is to support the deck panel. The weight of the freshly
Figure 4.7 Components of column-mounted shoring systems. (Courtesy of Formwork Exchange Ltd.)
placed concrete and the dead weight of the deck panel are transferred from the deck through the bracket jack system and then to the concrete column or wall; thus no shores are required to support the deck panel. The bracket jack system has three major features:
1. A double steel roller at the top of the bracket jack where the deck’s I beams rest, allowing the formwork deck panel to slide in and out with minimum effort. The steel roller unit can be adjusted and extended horizontally for up to approximately 10 in. (254 mm) by using an adjusting screw.
2. An adjustable screw to adjust the jack bracket and, consequently, the deck panel vertically. Maximum screw drop is 36 in. (914.4 mm) and standard screw drop is 18 in. (457.2 mm). There are two purposes for the vertical adjustment of the jack system: (a) to adjust the deck panel in its exact vertical position without needing to remove the bracket system, and (b) to lower the deck panel away from the slab during stripping.
3. A steel plate that contacts the concrete column or wall and is attached to the column or wall by two or four 1in. (25.4-mm) through bolts.
Figure 4.8 shows the major components of the bracket jack system. It should be noted that the bracket jack weighs approximately 40 to 50 lbs and can be handled by one worker during installation and removal.