Collapsed or Damaged Floor Load for Shoring

ScopeHow many pounds per square foot are sitting on the damaged floor above -- its own weight, the rubble piled on it, and the rescuers who will work under it. The US&R guides publish the unit weights a structures specialist adds up in the field: normal concrete at 150 pcf, which is 12.5 psf for every inch of slab; concrete and masonry rubble at 10 psf per inch of depth; 10 psf for furniture and 10 to 15 psf per floor for partitions; wood, steel-deck, and precast floor weights by construction; and 10 to 15 psf for the rescuers. A 6 in slab under 18 in of masonry rubble with a 15 psf rescuer allowance carries 75 + 180 + 15 = 270 psf. Shored with 3-post shores at 8 ft centers and a 4 ft tributary width, that is 8,640 lb per shore and 2,880 lb per post -- within the 5,000 lb of a 4x4 in a 10 ft shore, and two-thirds of it is rubble. An 8 in slab under 36 in of rubble with furniture reaches 485 psf, about twice a heavy-storage design live load, which is why debris comes off before shores are relied on for long. Several collapsed floors bearing on one shore are added floor by floor. This is a field load estimate from typical unit weights; wet materials, storage, and equipment can be much heavier, and a measured weight governs. It does not assess the damaged floor's remaining capacity, punching shear, the load path below the shore, or dynamic effects, and it does not size posts, cribs, or rakers. The US&R Structures Specialist and the incident's structural engineer govern.

Formula or tablefloor self-weight (concrete 12.5 psf per inch of thickness, or the published wood, steel-deck, and precast weights, or entered) + contents + partitions, per collapsed floor; + rubble at 10 psf per inch of depth; + rescuer live load 10 to 15 psf = total psf; load per shore = total x shore spacing x tributary width; load per post = load per shore / posts.

Source and editionUSACE US&R Shoring Operations Guide, Ed. 5.0 (October 2021), Disaster Site Reference Data: Design Dead Loads for Building Materials and Rescue Live Loads; USACE US&R Structures Specialist Field Operations Guide (2006) weight tables, cited by figure and named as the method.

Free accessAdditions and multiplications on the guides' published unit weights; the SOG is distributed free by USACE and state fire marshals.

What governsEstimate. AHJ and licensed structural engineer govern.

API field namesfloor_type, slab_thickness_in, floor_self_weight_psf, rubble_depth_in, contents_psf, partitions_psf, rescuer_psf, floors_bearing, shore_spacing_ft, tributary_width_ft, posts_per_shore, floor_psf, rubble_psf, total_psf, tributary_area_sqft, load_per_shore_lb, load_per_post_lb, rubble_share_pct

• Rubble is weighed by depth 10 psf per inch of concrete and masonry rubble, so 18 in of rubble outweighs two 6 in slabsUSACE US&R Shoring Operations Guide (2021)
• Rescuers are a live load in every calculation 10 to 15 psf (four 250 lb rescuers in 100 sq ft is 10 psf)USACE US&R Shoring Operations Guide (2021)
• Tributary area is half the span to each neighbor load per shore = total psf x shore spacing x tributary widthstatics