Also in: Disaster Response and Recovery
Steel Picket Anchor Lateral Capacity and Count
Raker soles, rope anchors, and guy lines in the field are held by steel pickets driven into the ground.
Example
You enter
- Required lateral force (lb) 1520
- Picket 1
- Soil type and class cohesive_average
- Embedment depth (in; table basis 36) 36
You get
- Design load per picket 750 lb
- Pickets required 3
- Group capacity (lb) 2250
- Standard 6-picket pattern (2021 guide, cohesive soil) 4,500 lb
No published worked example is on file for this calculation. It is checked against a hand-worked derivation of its method and an independent reference test.
Details, formula, and sources
ScopeRaker soles, rope anchors, and guy lines in the field are held by steel pickets driven into the ground, and a picket's capacity depends on the soil far more than on the picket. The US&R Structures Specialist Field Operations Guide tabulates design loads from the Federal Highway Administration's lateral-load handbook at about half the ultimate capacity, for a 48 in picket driven 36 in: a 1 in pin holds 500, 750, or 1,000 lb in poor, average, or good cohesive soil and only 50, 55, or 63 lb in loose, medium, or dense sand; a 3 in pin holds 1,000 to 2,000 lb and 150 to 190 lb. Restraining the 1,520 lb horizontal force of a raker in average clay with 1 in pickets takes ceil(1,520 / 750) = 3 pickets, a 2,250 lb group; the 2021 Shoring Operations Guide's six-picket pattern for cohesive soil gives 4,500 lb. In medium sand the same force needs 28 pickets, or 9 of the 3 in pins -- the signal to use a deadman, a buried timber, or a connection to paving rather than more steel. The table's basis has to match the field: the 2021 Shoring Operations Guide allows a 1 in x 36 in picket driven 24 in for its standard patterns, which does not earn the tabulated load, and the calculator flags any embedment under 36 in and any cohesionless soil. It does not model tandem or tied-back groups beyond simple addition, uplift, frozen, saturated, or disturbed ground, rock, or pickets in paving, and it does not design deadmen or earth anchors. The US&R guides, the US&R Structures Specialist, and the rigging competent person govern.
Formula or tabledesign load per picket from the FOG table (1 in x 48 in pin: 500 / 750 / 1,000 lb in poor / average / good cohesive soil, 50 / 55 / 63 lb in loose / medium / dense cohesionless; 3 in pin: 1,000 / 1,500 / 2,000 and 150 / 180 / 190 lb), driven 36 in; count = ceil(required force / design load); group = count x design load; embedment under 36 in and cohesionless soil flagged.
Source and editionUSACE US&R Structures Specialist Field Operations Guide (2006), Approximate Design Load of Pickets (Pins) in Soils, based on FHWA-IP-84-11, Handbook on Design of Piles and Drilled Shafts Under Lateral Load (1984), at about 50% of capacity; USACE US&R Shoring Operations Guide, Ed. 5.0 (2021), minimum picket 1 in x 36 in driven 24 in.
Free accessA table lookup from a federal field guide and a ceiling division.
What governsEstimate. Head rigger and manufacturer working-load-limit charts govern. Inspect every piece of hardware before the show.
API field namesrequired_force_lb, picket_dia, soil, embedment_in, design_load_per_picket_lb, pickets_required, group_capacity_lb, standard_pattern_capacity_lb
- Soil governs, not steel a 1 in picket holds 1,000 lb in good cohesive soil and 50 lb in loose sandUSACE US&R Structures Specialist FOG (2006), after FHWA-IP-84-11
- Table basis is 36 in of embedment a shallower picket does not earn the tabulated load and is flaggedUSACE US&R Structures Specialist FOG (2006)
- Design load is about half of capacity about 50% of the lateral capacity from the FHWA handbookFHWA-IP-84-11 (1984)