US&R Vertical Shore Post Capacity

ScopeTaken on the shore's height rather than the post's cut length: the allowable stress is 480,000 psi divided by the square of L/D, capped at 1,100 psi for short posts, times the post's actual area, times a species factor on the whole shore (1.00 for No. 1 Douglas Fir, 0.85 for Southern Yellow Pine, Hem-Fir, and Spruce-Pine-Fir, 0.75 for Eastern softwoods and Western woods). A 3-post shore of Douglas Fir 4x4s at 10 ft has an L/D of 34.3, an allowable stress of 408 psi, and 5,002 lb per post -- the guide's 5,000 -- so 15,006 lb of capacity against a 12,000 lb load, a ratio of 0.80. In Hem-Fir the ratio rises to 0.94. Cut to 6 ft, the same post is below the 20.9 crossover, the cap governs, and it carries 13,475 lb, 2.7 times as much. The L/D of 25 is a warning limit, not a strength limit: past it a post can buckle before its ends crush and creak, and the calculator flags it -- including at the guide's own headline 4x4 in an 8 ft shore, which sits at 27.4. Beyond 50 the post is refused. Lateral bracing is reported at 2% of the vertical capacity and 10% where aftershocks are expected. It overlaps the Wood Column Capacity (Slenderness) calculator, which applies the NDS method to one member; this is the distinct US&R field procedure. It does not design headers, check bearing across the grain, cover laced posts or proprietary struts, or evaluate the ground under the sole. The US&R guides, the US&R Structures Specialist, and the incident's structural engineer govern.

Formula or tableL/D = shore height (in) / post least actual width (in); Fa = 480,000 psi / (L/D)^2, capped at Fc = 1,100 psi (cap governs below L/D 20.9); P = Fa x post area; shore capacity = posts x P x species factor (1.00 / 0.85 / 0.75); L/D over 25 flagged, over 50 refused; lateral bracing = 2% of vertical capacity, 10% where aftershocks are expected.

Source and editionUSACE US&R Structures Specialist Field Operations Guide (2006), Structural Calculations -- Material Properties; USACE US&R Shoring Operations Guide, Ed. 5.0 (2021), vertical shore design loads (8,000 / 5,000 / 3,500 lb for 4x4 at 8 / 10 / 12 ft; 20,000 / 12,000 / 7,500 lb for 6x6 at 12 / 16 / 20 ft), L/D 25 limit, and species factors; DHS BIPS 08 (2011) lateral strength of 2% of vertical load, 10% desirable with aftershocks.

Free accessA closed-form expression and published factors; the SOG and BIPS 08 are free federal publications.

What governsEstimate. AHJ and licensed structural engineer govern.

API field namesshore_height_ft, post_size, post_width_in, post_depth_in, posts, species, load_per_shore_lb, aftershock_expected, slenderness_ld, fa_psi, load_per_post_lb, shore_capacity_lb, load_ratio, bracing_min_lb, bracing_aftershock_lb

• Slenderness is taken on shore height sole to top of header, divided by the post's least actual widthUSACE US&R Structures Specialist FOG (2006)
• L/D 25 is the no-warning line past it a post may buckle before its ends visibly crush; 50 is the maximumUSACE US&R Shoring Operations Guide (2021)
• Bracing is a fraction of capacity 2% of vertical capacity minimum, 10% where aftershocks are expectedDHS BIPS 08 (2011)