Crane Ground Bearing Pressure & Outrigger Pad report

Example project · Rev A

2026-09-02 04:38:26 UTC

SI (m · kN · kPa)

Path A - declared reactions + declared allowables

Basis

Manufacturer's chart

The crane manufacturer's outrigger load chart is authoritative. This tool does not replace it. All statics here are a cross-check and a pad/ground workup, never an operating margin.

Reaction basis

Path A - reactions DECLARED from the manufacturer's chart / lift-planning software

Support arrangement

4 outriggers - footprint 6.00 m × 5.00 m, floats 0.50 m × 0.50 m

Declared gross load

1000.0 kN over 1 reaction set(s)

Pad

timber, 1.50 m × 1.50 m × 150 mm, spread ψ = 0°

Ground capacity route

R1 - declared allowable 250.0 kPa ÷ FoS 1.00 (provenance: the project's geotechnical report)

Schematic

front ↑FL 350 kNFR 350 kNRL 150 kNRR 150 kNmargin 1.80 m

θ: 0° (over front); reactions declared set at slew 0°

True-to-scale plan, front up. The silhouette is generic - it carries no machine identity. Dashed polygon: tipping hull; filled dot: vertical resultant; its leader to the hull edge is the tipping margin.

frontleftrearright200 kNworst: FL at 0°

FLfront-leftFRfront-rightRLrear-leftRRrear-rightcapacity - Ground bearing - declared allowable (route R1)

Support reaction against slew angle - the bearing the boom is over, front at 0°; the scale starts at zero. One point per declared reaction set. Segments beyond the dashed capacity limit are the forbidden slew band.

RR/A_ftψ = 0R/A_eff on groundψ = 0 - no loaded cantilever to bend

R: 350.0 kN (governing)
a_f: 0.50 m
a_p: 1.50 m
t: 150 mm
ψ: 0° - no spread credit taken (default)
a_eff: 0.50 m
R/A_f: 1.40 MPa
R/A_eff: 1400.0 kPa
q_allow: 250.0 kPa ÷ FoS 1.00 - geotechnical report

Two levels, one drawing: the float presses on the pad over A_f (pad structure), the pad presses on the ground over A_eff (bearing). With ψ = 0 the spread lines are vertical: A_eff = A_f and the pad's plan area earns no bearing credit until a spread angle is declared.

Governing summary

Governing check

Pad bearing pressure on ground

Utilisation

5.600 (560.0%)

Overall status

fail

FEA recommended

Yes

Checks

Check	Demand	Capacity	U	Status
Support equilibrium	0.0000	0.0200	-	Pass
1 declared reaction set, each validated independently against the declared gross load; worst relative mismatch δ = 0.00% against the 2% chart-rounding threshold.
Equations used $δ = \frac{∣Σ R - P _{d ec l} ∣}{max ( Σ R , P _{d ec l} )} \leq 0.02$ (relative mismatch (dimensionless))
Support liftoff	-	-	0.400	Pass
Worst liftoff margin 0.400 at declared set 1 (slew 0.0°) - defined as 1 - n R_min/P, so 0 is perfectly even sharing and 1.0 is a support at zero reaction.
Tipping cross-check (chart governs)	-	-	0.400	Pass
The manufacturer's rated-capacity chart already embeds the stability margin required by the applicable design standard, and THE CHART GOVERNS. This utilisation is a geometric cross-check of the resultant against the support polygon - not an operating margin. Worst geometric utilisation e_res/e_edge = 0.400 at declared set 1 (slew 0.0°) (resultant 1.20 m from the footprint centre against 3.00 m to the polygon edge along its bearing). Declared tipping margin FoS_tip = 1.00 (default - pure geometry; any other default would be an invented safety factor). On declared reactions this ratio is reconstructed from the reaction set itself, so the resultant lies inside the support polygon by construction and the value cannot exceed 1.00 (unless a set declares tension). It reads how one-sidedly the declared set is distributed - a consistency reading, not an independent stability margin. The rated-capacity chart is the stability answer; the machine-model path derives the resultant from the weights instead and can place it outside the polygon.
Equations used $U_{t i p} = F o S_{t i p} \cdot \frac{e _{r es}}{e _{e d g e}} \leq 1$
Crawler track contact	-	-	-	Info
Support type is outriggers - there is no track contact to check.
Worst slew angle - found, not assumed	-	-	-	Info
Single declared reaction set - the degenerate one-row table. No slew dependence was declared; if the manufacturer's software can export reactions at several slew angles, enter them all and the worst set will be found.
Float bearing on pad	1.40 MPa	2.50 MPa	0.560	Pass
Governing reaction 350.0 kN on FL at declared set 1 (slew 0.0°) over the float area 0.250 m². This is level 1 of the two-level pad problem: the crane's float on the PAD. A pad can pass the ground check and still fail here.
Equations used $q_{f l o a t} = \frac{R}{A _{f}} \leq q_{a l l o w, p a d}$
Pad bearing pressure on ground	1400.0 kPa	250.0 kPa	5.600	Fail
Governing reaction 350.0 kN on FL at declared set 1 (slew 0.0°). ψ = 0° (default): NO spread credit, so the effective bearing area equals the float area (0.250 m²) and the ground sees the full float pressure. Declare a spread angle to credit the mat; the declaration is yours. Declared FoS on bearing = 1.00 (none declared). CIRIA C703 guidance (NOT HELD - unimplemented here): HSE-recommended FoS 1.5–3.0 on outrigger loading, scaled to how well the bearing capacity is evidenced.
Equations used $A_{e f f} = min (a_{f} + 2 t tan ψ, a_{p}) \times min (b_{f} + 2 t tan ψ, b_{p})$ (spread capped at the physical pad) $q = \frac{R}{A _{e f f}} \leq \frac{q _{a l l o w}}{F o S}$
Pad cantilever bending	0.00 MPa	16.00 MPa	0.000	Pass
ψ = 0: no spread claimed, so the pad carries no cantilever bending in this model - the ground check sees the full float pressure instead. Claiming spread credit moves demand into this check.
Equations used $M = \frac{q _{g r o u n d} s ^{2}}{2}, σ_{b} = \frac{6 M}{t ^{2}} \leq σ_{a l l o w}$
Pad shear (one-way / punching)	0.00 MPa	1.60 MPa	0.000	Pass
ψ = 0: no spread claimed, so no shear transfers through the pad in this model - the ground check sees the full float pressure instead.
Equations used $τ_{1 w} = \frac{1.5 q _{g r o u n d} s}{t}$ $τ_{p u n} = \frac{R ( 1 - A _{f} / A _{e f f} )}{2 ( a _{f} + b _{f} ) t}$
Steel pad bending - AISC 360-22	-	-	-	Info
Pad material is timber - the AISC 360-22 route applies to steel pads. Timber and composite mats use declared allowables or the coded EN 1995-1-1 route when selected.
Steel pad bending - EN 1993-1-1:2005 (superseded edition)	-	-	-	Info
Pad material is timber - the EN 1993-1-1 route applies to steel pads. Timber and composite mats use declared allowables or the coded EN 1995-1-1 route when selected.
Timber mat bending - EN 1995-1-1	-	-	-	Info
Declared-allowable timber route is selected - switch to the coded EN 1995-1-1 route to run this check.
Timber mat shear - EN 1995-1-1	-	-	-	Info
Declared-allowable timber route is selected - switch to the coded EN 1995-1-1 route to run this check.
Timber mat bearing (float contact) - EN 1995-1-1	-	-	-	Info
Declared-allowable timber route is selected - switch to the coded EN 1995-1-1 route to run this check.
Ground bearing - declared allowable (route R1)	1400.0 kPa	250.0 kPa	5.600	Fail
Route R1 - DECLARED allowable bearing pressure. Provenance: the user's geotechnical report; this tool applies the value, it does not derive it. A site-specific geotechnical investigation supersedes any capacity number here. Governing demand: pad-on-ground pressure under FL at declared set 1 (slew 0.0°) (the pad bearing check carries the same number - this card is the capacity route it runs against). Declared FoS on bearing = 1.00 (none declared). CIRIA C703 guidance (NOT HELD - unimplemented): HSE-recommended FoS 1.5–3.0 on outrigger loading, scaled to how well the hardstand bearing capacity is evidenced or validated. This band is guidance text only; declare your own value. OSHA 29 CFR 1926.1402(b): equipment must not be assembled or used unless ground conditions are firm, drained and graded so that, with supporting materials if necessary, the manufacturer's specifications for adequate support and degree of level are met.
Equations used $q_{g r o u n d} \leq \frac{q _{a l l o w}}{F o S}$
Ground bearing - classical theory (route R3, ultimate ÷ declared FoS)	-	-	-	Info
Route R3 is not selected. Classical bearing-capacity theory (Vesić / Meyerhof / Skempton, all named) is opt-in through the ground capacity route selector; route R1 - the declared allowable - is the default and the recommended basis.
Ground bearing - EN 1997-1 Annex D (route R2)	-	-	-	Info
Route R2 is not selected. EN 1997-1 Annex D is opt-in through the ground capacity route selector.
Proximity - declared excavation	-	-	-	Info
No excavation declared.
Proximity - declared slope	-	-	-	Info
No slope declared.
Proximity - declared buried structure	-	-	-	Info
No buried structure declared.

Support reactions

Peak reaction 350.0 kN on FL at the governing case. Values are the declared chart figures.

Support reactions at the governing case - declared set 1 (slew 0.0°)
Support	Reaction	State
FL	350.0 kN	bearing
FR	350.0 kN	bearing
RL	150.0 kN	bearing
RR	150.0 kN	bearing

Two-level pad verdict

Two-level pad verdict: the pad is strong enough for the float (U = 0.56) but NOT big enough for the ground (U = 5.60) - the ground check governs.

Float on pad

1.40 MPa over 0.250 m²

Pad on ground

1400.0 kPa over 0.250 m² effective

Factor ledger

Every factor between the load and the reported pressures, each with the side it acts on. Nothing in this calculation multiplies outside this table.

Factor	Value	Acts on
Reaction basis	Path A - reactions declared from the manufacturer's chart / planning software (1 set); any dynamic or out-of-level provision embedded in the chart is the chart's and is not restated here	info
Declared gross load	1000.0 kN - every reaction set is equilibrium-validated against it	demand
Load spread through the pad (ψ)	ψ = 0° - NO spread credit (default): the ground sees the full float pressure. Declare a spread angle to credit the mat; the declaration is yours.	demand
Ground capacity route	R1 - declared allowable bearing pressure; provenance: the project's geotechnical report	info
Factor of safety on ground bearing	÷ 1.00 - none declared (default). CIRIA C703 guidance (NOT HELD - unimplemented): HSE-recommended FoS 1.5–3.0 on outrigger loading, scaled to how well the bearing capacity is evidenced. Declare your own value.	resistance
Declared tipping margin (FoS_tip)	1.00 - pure geometry (default). The manufacturer's rated-capacity chart embeds the governing stability margin and ALWAYS governs.	resistance

Regulatory context (US construction)

OSHA 29 CFR 1926.1402(b): “The equipment must not be assembled or used unless ground conditions are firm, drained, and graded to a sufficient extent so that, in conjunction (if necessary) with the use of supporting materials, the equipment manufacturer's specifications for adequate support and degree of level of the equipment are met. The requirement for the ground to be drained does not apply to marshes/wetlands.” 1926.1402(a)(1) defines ground conditions as the ability of the ground to support the equipment (including slope, compaction, and firmness); 1926.1404(h)(1) carries the equivalent duty for assembly/disassembly. Responsibility for ground preparation rests with the controlling entity (1926.1402(c), paraphrased).

Warnings & scope flags

Governing utilisation is 560.0% - at this level the result should be independently verified.

Assumptions

The crane manufacturer's outrigger load chart and rated-capacity chart are authoritative. This tool does not replace them; its statics are a cross-check and a pad/ground workup, never an operating margin.
Estimated reactions (Path B) assume equal outrigger stiffness unless a per-support relative stiffness is declared. Real stiffness varies with beam extension; the equal default is an assumption, not a fact.
The machine is treated as a rigid body, level and static. Dynamics enter only through the declared dynamic allowance; out-of-level enters only through the declared allowance; wind is not modelled.
Crawler lateral distribution follows the rigid body on two elastic line supports: per-track load P/2 ± P·ȳ/s with the longitudinal moment split equally between tracks; each track is then treated independently after the split. The tipping polygon uses the track CENTRELINES, not the outer edges of the shoes - the conventional and conservative fulcrum. Partial contact is reported only while at least L/6 of the track still bears: the triangular peak 2·P_t/(b·L′) diverges as the contact closes, so beyond that the state is INDETERMINATE rather than an ever-larger number.
Contact pressures are uniform over their bearing areas (float on pad, effective area on ground), with the float centred on the pad. Local pressure peaks from pad flexibility are not modelled.
Every capacity on the declared routes - allowable ground bearing pressure, pad contact/bending/shear allowables - is a user-declared value (geotechnical report, manufacturer rating). Its provenance and validity are the user's responsibility; this tool applies it, it does not derive it.
Load spread through the pad is credited ONLY at the declared angle ψ (default 0 - no credit), capped at the physical pad edge. The declaration and its justification are the user's.
Outside scope by design: settlement (bearing capacity is not serviceability), dynamic and impact effects beyond the declared allowance, wind on the crane and load, slope stability and global site stability, and any crane machine database.
Route R3 soil parameters (φ′, c′/c_u, γ, embedment, groundwater) are user-declared values from the site's geotechnical information. The computed ultimate resistance is a named classical formulation, not a code check, and a site-specific geotechnical investigation SUPERSEDES it.
Proximity checks are geometric zone-of-influence FLAGS built from the declared geometry only (the 45° load-dispersion construction). They do not analyse the excavation face, its support, surcharge on a retaining structure, slope stability, or the buried structure's capacity - a fired flag means a temporary works design is required.
LIMITATIONS - outside this calculation by design: settlement (bearing capacity is not serviceability), dynamic and impact effects beyond the declared allowance, wind on the crane and load, slope stability and global site stability. A site-specific geotechnical investigation supersedes every capacity number here.

Source traceability

MECH_RIGID_STATICSRigid-body statics
Force/moment balance of a rigid body on point supports: equilibrium validation of declared reaction sets, the elastic estimate with unilateral (compression-only) supports and active-set liftoff, the resultant-versus-support-polygon tipping cross-check, and the parametric slew sweep over those statics. Public-domain mechanics identities; no code coefficients anywhere.
MECH_ECC_BEARINGEccentric bearing on a rectangle
Trapezoidal full-contact and triangular partial-contact pressure distributions under an eccentric resultant, with the middle-third (kern, e = L/6) transition - the crawler track longitudinal distribution and its contact-length flag. Public-domain mechanics.
MECH_CONTACT_STRIPContact pressure and cantilever strip identities
Uniform contact pressure q = R/A; load spread through the pad thickness at the DECLARED angle ψ, A_eff capped at the physical pad area (ψ = 0 default - no credit unless declared); cantilever strip from the float edge (M = q·s²/2, V = q·s), elastic strip bending σ = 6M/t², peak parabolic shear τ = 1.5V/t, punching on the plain float perimeter. Public-domain mechanics against declared allowables.
AISC360_22_F1AISC 360-22 · 2022 · §F1(a)
Flexural design basis: φ_b = 0.90 (LRFD), Ω_b = 1.67 (ASD), with M_n per §F2–F13. The steel-pad check uses the ASD form (M_n/Ω_b) because crane chart reactions are service-level loads. Verified against the licensed PDF 2026-08-10.
AISC360_22_F11AISC 360-22 · 2022 · §F11.1 eq. (F11-1); §F11.2(a)
Rectangular bars: M_n = M_p = F_y·Z ≤ 1.5·F_y·S_x (yielding); lateral-torsional buckling does not apply to rectangular bars bent about their minor axis - the pad plate strip's case. For a unit-width strip Z = t²/4 = 1.5·S, so M_n = F_y·t²/4 exactly at the cap. Verified against the licensed PDF 2026-08-10.
EN1993_1_1_BENDINGEN 1993-1-1 · 2005 (+AC) - SUPERSEDED (2022 second generation not held) · §6.2.5 eqs (6.12)/(6.13); §6.1(1) + NOTE 2B (γ_M0 = 1.00 recommended); §5.5.2(3); §6.2.9.1(3); §6.3.2.1(1)
Cross-section bending resistance M_c,Rd = M_pl,Rd = W_pl·f_y/γ_M0 for class 1/2 (eq 6.13); γ_M0 = 1.00 recommended for buildings, National Annex may alter (§6.1 NOTE 2B). A solid rectangular strip bent about its minor axis has no Table 5.2 compression part (§5.5.2(3): classification concerns width-to-thickness of compression parts), and §6.2.9.1(3) gives the solid rectangle's plastic resistance directly - the plastic modulus t²/4 per unit width applies. §6.3.2.1(1) scopes lateral-torsional buckling to MAJOR-axis bending, so the strip is outside it. Verified against the held PDF 2026-08-11. This edition is SUPERSEDED by the 2022 second generation, which is not held - labelled wherever the check surfaces.
EN1990_ACTIONSEN 1990 · 2002 (+A1:2005) - SUPERSEDED (EN 1990:2023 second generation not held) · Annex A1, Table A1.2(B) NOTE 2
Recommended action-side partial factors for STR verifications: γ_G,sup = 1.35, γ_Q,1 = 1.50 (National Annex may alter). The EN steel-pad route multiplies the whole service-level strip moment by γ_F = 1.50: a chart reaction is a characteristic total that this pack cannot decompose into permanent and variable shares, so the whole of it takes the HIGHER recommended factor - the conservative envelope of the recommended set whenever both shares act unfavourably on the reaction (the normal case for a bearing reaction). A configuration whose self-weight RELIEVES the governing support (net favourable permanent share, γ_G,inf = 1.00) is outside this envelope and needs a decomposed EN 1990 combination. This edition is superseded by the 2023 second generation, which is not held. Verified against the held PDF 2026-08-11.
EN1995_1_1_BENDINGEN 1995-1-1 · 2004+A1:2008 (BS EN) · §6.1.6 eqs (6.11)/(6.12); §3.2 eq (3.1); §3.3 eq (3.2)
Uniaxial strip bending σ_m,d ≤ f_m,d; size factor k_h. Verified against the held PDF 2026-08-11.
EN1995_1_1_MODFACTORSEN 1995-1-1 · 2004+A1:2008 (BS EN) · §2.4.1 eq (2.14); Table 2.3; §3.1.3, Table 3.1
Design value X_d = k_mod·X_k/γ_M; recommended γ_M and k_mod tables. Verified against the held PDF 2026-08-11.
EN1995_1_1_SHEAREN 1995-1-1 · 2004+A1:2008 (BS EN) · §6.1.7 eq (6.13); eq (6.13a); A1:2008 k_cr
Shear τ_d ≤ f_v,d with effective width b_ef = k_cr·b. k_cr = 0.67 solid and glulam (A1 NDP). Verified against the held PDF 2026-08-11.
EN1995_1_1_COMP90EN 1995-1-1 · 2004+A1:2008 (BS EN) · §6.1.5(1)–(2), eqs (6.3)/(6.4); Figure 6.2
Compression ⊥ grain with the 30 mm contact extension of Figure 6.2. k_c,90 is held at the clause (2) default of 1.0 - the (3)/(4) uplifts need l₁ (the clear distance between bearing areas), a declared support condition and softwood, none of which this model establishes. Verified against the held PDF 2026-08-11.
SOIL_VESICVesić (1973) bearing capacity · JSMFD 99(SM1), ASCE
Drained ultimate bearing capacity, closed form: N_q = e^{π·tanφ}·tan²(45°+φ/2) (Reissner), N_c = (N_q−1)·cotφ (Prandtl; π+2 at φ=0), N_γ = 2(N_q+1)·tanφ (Vesić); De Beer shape factors s_c = 1+(B/L)(N_q/N_c), s_q = 1+(B/L)tanφ, s_γ = 1−0.4(B/L); Hansen/Vesić depth factors d_c = 1+0.4k, d_q = 1+2tanφ(1−sinφ)²k with k = D/B for D/B ≤ 1 and the published deep form k = tan⁻¹(D/B) (radians) beyond, d_γ = 1. BENCHMARK-DERIVED: verified against the published factor tables reprinted in the standard foundation texts (φ=30°: N_q 18.40, N_c 30.14, N_γ 22.40), with full hand-worked compositions locked in the validation register.
SOIL_MEYERHOFMeyerhof (1963) bearing capacity · Can. Geotech. J. 1(1)
Drained ultimate bearing capacity, closed form: N_q and N_c as Reissner/Prandtl, N_γ = (N_q−1)·tan(1.4φ); shape factors via K_p = tan²(45°+φ/2): s_c = 1+0.2K_p(B/L), s_q = s_γ = 1+0.1K_p(B/L) for φ ≥ 10°; depth factors d_c = 1+0.2√K_p(D/B), d_q = d_γ = 1+0.1√K_p(D/B) for φ ≥ 10° - a shallow-footing method (D ≤ B), so the depth factors are held at their D/B = 1 value for deeper embedment, never extrapolated. BENCHMARK-DERIVED: verified against the published factor tables (φ=25°: N_q 10.66, N_c 20.72, N_γ 6.77; φ=30°: N_γ 15.67), with a full hand-worked composition locked in the validation register.
SOIL_SKEMPTONSkempton (1951) undrained bearing capacity · Building Research Congress
Undrained (total-stress) capacity of a footing on clay: q_ult = c_u·N_c + q₀ with N_c = 5(1+0.2·B/L)(1+0.2·D/B), the depth term capped at D/B = 2.5 (N_c ≤ 7.5 strip, ≤ 9.0 square) - the standard rendering in the soil mechanics texts. BENCHMARK-DERIVED: surface square N_c = 6.0, caps as published, with a full hand-worked composition locked in the validation register.
MECH_EFFECTIVE_STRESSEffective stress (groundwater correction)
Terzaghi's effective-stress principle applied to the drained bearing terms, γ_w = 9.81 kN/m³: effective surcharge above the base; buoyant unit weight in the N_γ term for water at/above the base, full weight beyond B below it, linear interpolation between (the standard textbook treatment). Public-domain mechanics.
EN1997_1_ANNEX_DEN 1997-1 · 2004 incl. corrigendum Feb 2009 (BS EN) · Annex D (informative), eqs (D.1)–(D.2)
Sample analytical bearing-resistance method - drained eq (D.2) and undrained eq (D.1) with N, s, i, b factors. INFORMATIVE: may be used but is not mandatory. No depth factors. tan φ′ factoring per Table A.4 footnote. Verified against the held PDF 2026-08-11.
EN1997_1_ANNEX_AEN 1997-1 · 2004 incl. corrigendum Feb 2009 (BS EN) · Annex A, Tables A.3–A.5; §2.4.7.3.4
Recommended partial factors and Design Approaches 1–3 for spread foundations. Values are Nationally Determined Parameters - the National Annex may override every number. Verified against the held PDF 2026-08-11.
EN1997_1_6_5EN 1997-1 · 2004 incl. corrigendum Feb 2009 (BS EN) · §6.5.2.1 eq (6.1); §6.5.4(1)P
Spread-foundation bearing limit state V_d ≤ R_d. Verified against the held PDF 2026-08-11. §6.5.4(1)P: special precautions when eccentricity exceeds B/3 of a rectangular footing.
MECH_DISPERSION_ZONE45° load-dispersion zone geometry
Zone-of-influence FLAG geometry: the 45° (1H:1V) load-dispersion wedge from the edge of the bearing area. Excavation (vertical face, depth H): inside when the clear distance to the face is under H - the classic stay-back-the-depth site rule. Slope (height H, angle β): reach H·(1 − 1/tanβ) behind the crest, ZERO for β ≤ 45° (a 45° line cannot daylight on a gentler face). Buried structure (top at depth d): inside when the horizontal clearance is under d. Pure public-domain geometry - a flag that temporary works design is required, NEVER a face-support, surcharge or slope-stability analysis.

The crane manufacturer's outrigger load chart and rated-capacity chart are authoritative. Declared allowables are the user's own values; the engine does not source them. A lift plan is outside this scope.