Formwork Shore Post Load and Spacing (ACI 347)
The vertical load path of an elevated pour: design pressure = max(slab_in/12 x unit weight + form load + construction live load, 100 psf floor), and the load on any one shore is that pressure times its tributary area. An 8 in slab on a 4 ft grid carries over 2,500 lb per post. Motorized buggies raise the live load to 75 psf and the floor to 125 psf. The rated capacity is the manufacturer's allowable for the extended height and bracing; reshoring and the slab below are separate analyses. A design aid, not a stamped shoring plan.
Formula and source
slab_load = slab_in / 12 x unit_weight; design_psf = max(slab_load + form_load + live_load, 100); shore_load = design_psf x spacing_x x spacing_y; utilization = shore_load / shore_capacity.
ACI 347 (Guide to Formwork for Concrete), by name; the tributary-area load path is first-principles statics.
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