ASME BTH-1 Lifting Lug Design: Complete Engineer's Guide

What Is ASME BTH-1?

ASME BTH-1 (Design of Below-the-Hook Lifting Devices) is an ASME consensus standard referenced by ASME B30.20 and widely adopted by US-regulated facilities and North American EPC contractors for below-the-hook lifting device design. ASME BTH-1-2023 is the latest published edition; this guide implements the 2020 edition — verify your project specification before use.

The standard governs any device attached to a crane hook for the purpose of lifting a load — including spreader beams, lifting beams, C-hooks, coil lifters, and the single-plate lifting lugs this calculator focuses on. For lifting lugs specifically, the relevant clauses are §3-3.3 (lug body checks) and §3-3.4.3 (weld checks, cross-referenced to AISC 360).

Unlike EN 1993-1-8 or DNV-ST-N001, BTH-1 uses a single design factor N_d applied uniformly across all resistance checks. There are no separate partial factors for material properties, geometric tolerances, or fracture vs. yield modes — instead, the factor of safety is embedded in the capacity formulas themselves.

Standard Scope and Applicability

BTH-1 applies to devices that are attached to a crane hook and used to grip or contain the load being lifted. This explicitly includes welded lifting lugs and padeyes on structural packages, vessels, and equipment. It does not govern:

Rigging hardware (slings, shackles, hooks) — covered by ASME B30.9 and B30.10
Crane structure above the hook — covered by ASME B30.2/B30.3 and AISC
Permanently embedded lifting inserts in concrete — governed by ACI/project-specific precast design standards
Offshore marine operations — DNV-ST-N001 or NORSOK R-003 applies

For most industrial and construction projects in North America, BTH-1 is the de facto standard for lifting lug design. When a project specification says "design lifting attachments to ASME B30.20," verifying the lug body to BTH-1 §3-3.3 satisfies that requirement.

Scope note:This calculator targets single-plate lug bodies under in-plane loading. Out-of-plane loading, cheek-plate configurations, and non-standard hole geometries fall outside its implemented scope — see the limitations section below.

Design Categories: A vs B

BTH-1 §2-1.2 divides lifting devices into two categories based on how they are used. The category directly determines the design factor $N_{d}$ applied in every capacity formula.

BTH-1 Design Category determines

N_{d}

. Category B (

N_{d} = 3.0

) is the correct choice for the vast majority of structural and industrial lifting lugs.

CATEGORY AN_d = 2.0

Precision or controlled lifting environments where loads are well-defined, personnel are not at risk from dropped load, and the device operates in a controlled manner. Equipment is typically purpose-built and not subject to variable or shock loading.

· Assembly-line fixtures, jigs & tooling

· Dedicated machine tool handling

· Laboratory & test equipment lifts

· Lifts where load is precisely known and repeatable

CATEGORY BN_d = 3.0

General industrial lifting where loads may vary, personnel could be exposed below the lift path, or load calculations carry inherent uncertainty. This is the default category for structural steel packages, pressure vessels, and offshore modules.

· Structural steel packages & modules

· Pressure vessels & heat exchangers

· General construction lifts

· Lifts over or near personnel

Rule of thumb: When in doubt, use Category B (

N_{d} = 3.0

). Most engineering project specifications and client standards default to Category B for structural lifting lugs. The calculator defaults to Category B; you can switch to Category A where your project specification explicitly permits it.

Service Classes 0–4

In addition to the Design Category, BTH-1 §2-1.3 requires classifying the lifting device by its Service Class — the number of load cycles anticipated over the device's design life. Service Class affects the pin bearing coefficient only (SC 0 uses 1.25; SC ≥ 1 uses 0.63), but it is also the classification engine for fatigue-relevant equipment.

Service Class affects only the pin bearing check. All other BTH-1 checks are unaffected by SC selection.

SC 0

Static; < 20,000 cycles

One-time lifts, construction picks, vessel erection

Bearing coeff: 1.25

SC 1

< 100,000 cycles

Regular maintenance lifts, seasonal equipment moves

Bearing coeff: 0.63

SC 2

< 500,000 cycles

Daily repetitive lifts in a manufacturing environment

Bearing coeff: 0.63

SC 3

< 2,000,000 cycles

High-cycle crane operations, shift-work repetitive picks

Bearing coeff: 0.63

SC 4

> 2,000,000 cycles

Very high-cycle magnet, grab, or continuous process lifts

Bearing coeff: 0.63

Important: Service Class does not produce an S-N fatigue life estimate. A SC 4 lug still passes the BTH-1 bearing check if utilisation ≤ 1.0 with the 0.63 coefficient — it does not predict crack initiation or remaining cycles. For fatigue life prediction use IIW Recommendations, DNV-RP-C203, or ASME VIII fatigue methods.

Free calculator

Set your Design Category and Service Class instantly

Select Category A or B and Service Class 0–4 in the calculator — all five BTH-1 checks update in real time with the correct N_d and bearing coefficient.

Open the calculator Sample BTH-1 report

The Strength Checks: Three BTH-1 Lug Body Checks + Weld + Pin Shear

ASME BTH-1-2020 §3-3.3 prescribes three lug body checks: net-section tension (§3-3.3.1), shear-out (§3-3.3.3), and pin bearing (§3-3.3.4). The weld check follows §3-3.4.3 (cross-referenced to AISC 360-22 §J2.4). Pin double shear is supplementary mechanics — BTH-1 does not prescribe a specific pin shear formula, treating the pin as a separately designed fastener. The calculator runs all five simultaneously and flags which governs.

1Net-Section Tension — §3-3.3.1

The pin bearing on the hole boundary creates a non-uniform tensile stress distribution across the net section — the portion of the plate remaining after the hole is cut. Rather than assuming uniform stress (as plain mechanics does), BTH-1 introduces a stress concentration factor $C_{r}$ and an effective bearing width $b_{eff}$ to account for the contact geometry and pin-to-hole clearance.

The result is a force capacity $P_{t}$ (not a stress): the maximum design load the net section can resist. The check is simply $F_{d} \leq P_{t}$ .

BTH-1-2020 §3-3.3.1 — Net-section tension capacity (eqs 3-45 to 3-48)

C_{r} = 1 - 0.275 1 - (\frac{D _{p}}{D _{h}})^{2}

b_{e} = \frac{w - D _{h}}{2}, b_{eff} = min (4 t, 0.6 b_{e} \frac{F _{u} D _{h}}{F _{y} b _{e}})

P_{t} = \frac{2 C _{r} F _{u} b _{eff} t}{1.20 N _{d}}

C_{r}

radial stress correction factor (accounts for pin contact geometry)

D_{p}

pin diameter (mm)

D_{h}

hole diameter (mm)

b_{e}

half net width — one side of the hole (mm)

b_{eff}

effective bearing width, limited by plate thickness and slenderness

F_{u}

lug plate ultimate tensile strength (MPa)

F_{y}

lug plate yield strength (MPa)

t

plate thickness (mm)

N_{d}

design factor (2.0 Cat A, 3.0 Cat B)

Check:

F_{d} \leq P_{t}

How much more conservative is BTH-1 than plain mechanics?

For typical clearances ( $D_{p} / D_{h} \approx 0.95$ ), the $C_{r}$ factor reduces net-section capacity by 8–15% compared to the simple stress identity $σ = F_{d} / ((w - D_{h}) \cdot t)$ . Additionally, $b_{eff}$ is typically less than $b_{e}$ , further reducing the calculated capacity. The net effect is that a lug that just passes a plain mechanics check may fail BTH-1 §3-3.3.1 by 10–20%.

2Double-Plane Shear-Out — §3-3.3.3

When the pin pushes upward against the hole bore, two shear planes running from the hole surface to the plate's free edge may fail simultaneously — a punching or tear-out mode. Plain mechanics assumes straight vertical shear planes; BTH-1 §3-3.3.3 uses a curved shear plane whose sweep angle $φ$ depends on the pin-to-hole fit.

The curved plane gives a slightly larger shear area than the straight-plane identity (typically 5–10% more), making BTH-1 less conservative than mechanics for shear-out when the pin fits well. This is one of the few places where the code formula is more permissive than the simple identity.

BTH-1-2020 §3-3.3.3 — Double-plane shear-out capacity (eqs 3-50 to 3-52)

φ = 5 5^{\circ} \cdot \frac{D _{p}}{D _{h}}

A_{v} = 2 t [a_{BTH} + \frac{D _{p}}{2} (1 - cos φ)]

P_{v} = \frac{0.70 F _{u} A _{v}}{1.20 N _{d}}

φ

curved shear-plane sweep angle (proportional to pin-to-hole fit ratio)

a_{BTH}

edge distance from hole edge to free edge: a − D_h / 2 (mm)

A_{v}

total curved shear area across both planes (mm²)

F_{u}

ultimate tensile strength of lug plate (MPa)

N_{d}

design factor

Check:

F_{d} \leq P_{v}

Edge distance sensitivity:

A_{v}

is directly proportional to

a_{BTH}

. Reducing edge distance from 120 mm to 80 mm on a 75 mm hole cuts shear-out capacity by ~33%. Designers should check shear-out first when iterating on geometry — it is typically the most sensitive check to edge distance.

3Pin Bearing on the Lug Plate — §3-3.3.4

The pin applies compressive contact pressure to the bore of the pin hole. BTH-1 models the contact area as the projected rectangle $D_{p} \times t$ and expresses the check as a force capacity $P_{p}$ . The key BTH-1 distinction from mechanics is the Service Class coefficient: SC 0 (static lifts) uses 1.25; SC ≥ 1 (rotating or repetitive picks) uses 0.63 — a 50% penalty that reflects pin-bore wear under repeated cycling.

The 1.25 coefficient with $F_{y}$ (yield) in the numerator and $N_{d}$ in the denominator makes bearing the most often-governing check for typical lug geometries with small pins relative to the plate. The EN 1993-1-8 bearing formula (using $1.5 F_{y} / γ_{M 0}$ ) is broadly similar for static service, though slightly higher capacity for S355 material.

BTH-1-2020 §3-3.3.4 — Pin bearing capacity (eqs 3-53 & 3-54)

P_{p} = \frac{1.25 F _{y} D _{p} t}{N _{d}} (SC 0 — static service)

P_{p} = \frac{0.63 F _{y} D _{p} t}{N _{d}} (SC \geq 1 — rotating/repetitive)

F_{y}

lug plate yield strength (MPa)

D_{p}

pin diameter (mm)

t

plate thickness (mm)

N_{d}

design factor (2.0 Cat A / 3.0 Cat B)

Check:

F_{d} \leq P_{p}

Standard comparison — bearing on S355, D_p = 75 mm, t = 25 mm

BTH-1 Cat B SC 01.25×355×75×25/3.0 = 277 kN

BTH-1 Cat B SC≥10.63×355×75×25/3.0 = 140 kN

EC3 §3.13 (γ_M0=1.0)1.5×355×75×25/1.0 = 998 kN

Note: EC3 uses resistance format (load side carries load factor ≈1.35); BTH-1 uses allowable format. The absolute capacity numbers are not directly comparable — compare utilisation ratios with factored demands.

Bearing is the most common governing check.

For typical S355 lug geometry with Category B and SC 0, the 1.25/3.0 = 0.417 effective coefficient against $F_{y}$ is relatively tight. Increasing pin diameter, plate thickness, or upgrading to Category A ( $N_{d} = 2.0$ ) are the most effective levers when bearing governs.

4Pin Double Shear

In a standard clevis/shackle arrangement the lug plate sits between two jaw plates, so the pin spans the gap and is loaded in double shear — two shear planes, each carrying $F_{d} /2$ . BTH-1 §3-3.3 does not prescribe a separate pin shear formula; the pin itself is designed as a structural element per AISC 360 or the relevant equipment standard. The mechanics check below is the baseline.

Pin shear seldom governs for standard pin materials (Grade 8 bolts, ASTM A193-B7, or equivalent). It becomes relevant when pin diameter is constrained by the shackle selection rather than the lug geometry, or when the pin material is significantly weaker than the lug plate.

Pin double shear — mechanics identity (BTH-1 lug body check uses pin as given)

A_{pin} = \frac{π D _{p}^{2}}{4}

τ_{pin} = \frac{F _{d}}{2 A _{pin}}

D_{p}

pin diameter (mm)

A_{pin}

pin cross-sectional area (mm²)

F_{d}

design load (N)

Check:

τ_{pin} \leq τ_{allow, pin}

5Fillet Weld Group — BTH-1 §3-3.4.3 / AISC 360-22 §J2.4

BTH-1 §3-3.4.3 cross-references AISC 360 for weld design — the same standard used for all structural steel weld checks in North America. AISC 360-22 §J2.4 provides a directional strength increase for fillet welds loaded at an angle to their longitudinal axis: a weld loaded transversely (perpendicular to its axis) is 50% stronger than one loaded in pure shear.

For a lifting lug welded with two parallel side welds, the design load resolves into an axial component $N = F_{d} cos θ$ and a shear component $V = F_{d} sin θ$ . At zero lifting angle the weld sees pure tension on the throat; at larger angles a bending moment $M = V \cdot h$ is superimposed.

AISC 360-22 §J2.4 — Fillet weld nominal strength with directional increase

F_{n w} = 0.60 F_{E X X} (1 + 0.50 sin^{1.5} θ_{w})

F_{a l l o w} = \frac{F _{n w}}{Ω}, Ω = 2.0 (ASD)

f_{w} = f_{z}^{2} + f_{v}^{2}, f_{z} = \frac{N}{A _{w}} + \frac{M}{S _{w}}, f_{v} = \frac{V}{A _{w}}

F_{E X X}

electrode classification strength (MPa) — E70 = 480 MPa

θ_{w}

angle between resultant weld throat force and weld axis

Ω

ASD safety factor (2.0 for welds)

f_{z}

normal component of throat stress (tension + bending)

f_{v}

shear component of throat stress (lateral force)

A_{w}

total effective weld throat area: 2 × 0.707s × L (mm²)

S_{w}

weld group section modulus about strong axis: aL²/3 for two side welds (mm³)

Check:

f_{w} \leq F_{a l l o w}

At θ = 0° (pure vertical lift):

The two side welds run vertically along the lug plate. At zero lifting angle the applied load is also vertical — parallel to the weld axis. In AISC J2.4 terms this is longitudinal loading ( $θ_{w} = 0°$ ). The directional factor equals 1.0, giving $F_{n w} = 0.60 F_{E X X}$ and $F_{a l l o w} = 0.60 \times 480/2.0 = 144 MPa$ for E70XX — matching the worked example.

The transverse (perpendicular) case — $θ_{w} = 90°$ , giving $F_{n w} = 0.90 F_{E X X}$ and a 50% strength gain — applies when the weld is loaded across its length, such as horizontal flange welds under a vertical pull. Vertical side welds under a vertical load do not benefit from the directional increase.

What ASME BTH-1 Doesn't Cover

Understanding the boundaries of BTH-1 is as important as understanding what it checks. Engineers frequently assume BTH-1 is a complete lifting lug standard — it is not. The six gaps below are real design issues that require supplementary analysis when they arise.

✗

Out-of-plane loading and plate dishing

BTH-1 §3-3.3 applies to in-plane loading only. A sling at more than ~5° out of the plate plane introduces plate bending and prying effects that the 2D plane-stress model cannot capture. DNV-ST-N001 §16 and API RP 2A both require a 5% out-of-plane design load minimum — BTH-1 is silent on this. Use shell FEA or an explicit out-of-plane check when lateral sling forces are present.

✗

Cheek-plate / doubler-plate configurations

BTH-1 does not address multi-layer lug plates with welded cheek reinforcements. Load sharing between main plate and cheeks depends on plate thicknesses and the circumferential weld sizing, neither of which BTH-1 covers. Cheek-plate sizing requires supplementary analysis per project-specific guidelines (Shell DEP, DNV, etc.).

✗

Pin bending under eccentric loading

When shackle jaw geometry creates a moment arm on the pin, bending stress supplements shear. EN 1993-1-8 §3.13.2 has an explicit pin-bending check and combined shear + bending interaction diagram (Figure 3.11). BTH-1 does not. For custom pin designs or non-standard shackle/clevis geometry, pin bending should be checked separately to EC3 or ASME VIII rules.

✗

Fatigue life estimation

Service Class 0–4 selects the bearing coefficient but does not produce a cycle life prediction. For lifting devices subjected to high-cycle operation (cranes, traversing trolleys, permanent offshore attachments), fatigue verification requires a dedicated S-N analysis: ASME VIII Appendix 2, IIW Fatigue Design Recommendations, or DNV-RP-C203.

✗

Block shear (tearing out combined block)

EN 1993-1-8 §3.10.2 and AISC 360 §J4.3 address block shear (combined tension + shear failure of a rectangular block of material). BTH-1 §3-3.3 does not. For compact lug geometries with short edge distances, block shear may be the governing failure mode — check per AISC or EC3 as applicable.

✗

Offshore and marine dynamic amplification

BTH-1 does not prescribe Dynamic Amplification Factor (DAF) or Skew Load Factor (SKL). These demand-side multipliers are governed by DNV-ST-N001 §16. For offshore lifts from vessels, DNV governs the load chain; BTH-1 may be used for the resistance side only, with DNV-amplified loads as input.

All five BTH-1 checks in one tool

Stop juggling clause references

Enter geometry, load, and material — the calculator runs §3-3.3.1, §3-3.3.3, §3-3.3.4, pin shear, and AISC weld simultaneously. The governing check is flagged automatically.

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Worked Numerical Example

A structural steel package with a total hook load of approximately 400 kN (≈ 40.8 t) is lifted symmetrically from two padeyes, giving 200 kN static load per lug. The following example works through all BTH-1 checks for a single lug, fully computed to 3 significant figures. Design Category B, Service Class 0.

Design InputsCategory B · SC 0 · N_d = 3.0

Design CategoryB

Design factor N_d3.0

Service Class0 (static)

Static load (per lug)200 kN

Dynamic factor (DF)1.10

Factored design load F_d200 × 1.10 = 220 kN

Lifting angle θ0° (vertical)

Lug materialS355 / A572-Gr50

Yield strength F_y355 MPa

Ultimate strength F_u490 MPa

Plate width w250 mm

Plate thickness t25 mm

Hole diameter D_h80 mm

Pin diameter D_p75 mm

Edge distance a110 mm (hole centre to free edge)

Weld leg s12 mm (E70XX, F_EXX = 480 MPa)

Weld length L2 × 270 mm parallel side welds

Corrosion allowance0 mm (protected environment)

Check 1 — Net-Section Tension §3-3.3.1

0.615pass

C_r = 1 − 0.275 × √(1 − (75/80)²) = 1 − 0.275 × 0.348 = 0.904

b_e = (250 − 80) / 2 = 85.0 mm

b_eff = min(4×25, 0.6×85×√(490×80/(355×85))) = min(100, 51.0×1.140) = 58.1 mm

P_t = 2×0.904×490×58.1×25 / (1.20×3.0) = 1,287,700 / 3.6 = 357.7 kN

U = 220 / 357.7 = 0.615 ✓ PASS

Check 2 — Double-Plane Shear-Out §3-3.3.3

0.553pass

a_BTH = a − D_h/2 = 110 − 40 = 70.0 mm (hole edge to plate edge)

φ = 55° × (75/80) = 51.6° → cos(51.6°) = 0.623

A_v = 2×25×[70.0 + (75/2)×(1−0.623)] = 50×[70.0 + 14.1] = 4,207 mm²

P_v = 0.70×490×4,207 / (1.20×3.0) = 1,443,003 / 3.6 = 400.8 kN

U = 220 / 400.8 = 0.549 ✓ PASS

Check 3 — Pin Bearing §3-3.3.4GOVERNING

0.793pass

SC 0 → bearing coefficient = 1.25

P_p = 1.25 × 355 × 75 × 25 / 3.0 = 832,031 / 3.0 = 277.3 kN

U = 220 / 277.3 = 0.793 ✓ PASS — governing check

Check 4 — Pin Double Shear

0.175pass

A_pin = π × 75² / 4 = 4,418 mm²

τ_pin = 220,000 / (2 × 4,418) = 24.9 MPa

Allow. shear (pin, S355) = 0.40 × F_y = 142.0 MPa

U = 24.9 / 142.0 = 0.175 ✓ PASS

Check 5 — Fillet Weld §J2.4 (AISC 360-22)

0.333pass

θ = 0° → vertical load parallel to vertical weld axis → longitudinal shear (θ_w = 0°)

a_throat = 0.707 × 12 = 8.48 mm → A_w = 2 × 8.48 × 270 = 4,581 mm²

f_w = 220,000 / 4,581 = 48.0 MPa

F_nw = 0.60 × 480 × (1 + 0.5 × sin^1.5(0°)) = 288.0 MPa → F_allow = 288 / 2.0 = 144.0 MPa

U = 48.0 / 144.0 = 0.333 ✓ PASS

Results Summary

Check	Demand	Capacity	U	Status
Net-section tension §3-3.3.1	220 kN	357.7 kN	0.615	PASS
Double-plane shear-out §3-3.3.3	220 kN	400.8 kN	0.549	PASS
Pin bearing §3-3.3.4 (SC 0)governs	220 kN	277.3 kN	0.793	PASS
Pin double shear	24.9 MPa	142.0 MPa	0.175	PASS
Fillet weld AISC §J2.4	48.0 MPa	144.0 MPa	0.333	PASS
Overall — governing check: pin bearing at 79.3%			0.793	PASS

The bearing check governs at 79.3% utilisation. To reduce utilisation: increase pin diameter (most effective — bearing scales as $D_{p}$ ), increase plate thickness, or switch to Category A ( $N_{d} = 2.0$ ) if the application qualifies. Switching to SC≥1 would drop bearing capacity to 140 kN and increase utilisation to 1.57 — a failure, which is expected for a pick designed as static (SC 0).

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BTH-1 vs EN 1993-1-8 vs DNV-ST-N001

All three standards check the same physical failure modes, but they use fundamentally different philosophies to determine capacity. Running all three on the same lug geometry frequently produces different utilisations — and occasionally different governing checks. The calculator runs all four methodology routes simultaneously so you can see every result without switching tools.

Topic	ASME BTH-1-2020	EN 1993-1-8:2005	DNV-ST-N001*
Philosophy	Allowable Stress Design — single N_d applied to all capacity terms	Limit State Design — separate γ_M0 (yield) and γ_M2 (fracture) partial factors	Load combination + demand-side amplification; resistance per companion standard
Safety factor / margin	N_d = 2.0 (Cat A) or 3.0 (Cat B)	γ_M0 = 1.00, γ_M2 = 1.25 (pin/weld fracture)	Load factor γ_f × design factor; resides on demand side
Geographic scope	North America, OSHA-regulated lifts, US EPC projects	Europe, Middle East, CE-marked structures, NORSOK projects	Offshore / marine operations worldwide
Net-section tension	Cr stress concentration + b_eff effective width limit (eqs 3-45 to 3-48)	Table 3.10: F_t,Rd = 2·t·a·(fu/γ_M2) — uses ultimate strength	Follows companion structural standard (EC3 or AISC/ASME)
Shear-out	Curved shear plane (φ = 55°·Dp/Dh), uses 0.70 Fu (eq 3-50 to 3-52)	Not explicitly in §3.13; usually checked to AISC or as a bearing-adjacent check	Follows companion structural standard
Pin bearing	1.25 Fy × Dp × t / N_d (SC 0); 0.63 for SC≥1	Table 3.10: F_b,Rd = 1.5·t·d·fy/γ_M0 — uses yield, no SC distinction	Follows companion structural standard
Pin bending	Not explicitly covered — pin sized by equipment standard	§3.13.2 Figure 3.11 — explicit combined shear + bending interaction	Not prescribed; reference to companion standard
Weld check	AISC 360-22 §J2.4 (cross-referenced) — directional increase factor	§4.5.3 — von Mises throat stress with correlation factor β_w (grade-dependent: 0.80–1.00)	Follows AISC or EC3
Dynamic loads	Not prescribed — engineer applies own dynamic factor	Not prescribed — project-specific load combination	DAF (1.05–2.00+) and SKL (1.00–1.25+) explicitly tabulated in §16
Cheek plates	Not addressed	Not addressed explicitly — proportional thickness method from guidelines	Referenced in DNV offshore lifting guidelines; load sharing by thickness

Worked example — same lug, three standards: For the 220 kN design in the example above (S355, 250×25 mm plate, 80 mm hole, 75 mm pin), the governing utilisation under BTH-1 Cat B is 0.793 (bearing). Under EN 1993-1-8 the net-section tends to govern at a lower utilisation because EC3 uses ultimate strength without

C_{r}

. Under DNV, the design load would first be amplified by DAF×SKL, so the same lug geometry could easily fail for an offshore lift that passes onshore. Run all three simultaneously in the calculator.

* Edition notes: The calculator implements ASME BTH-1-2020; the current published edition is BTH-1-2023. DNV column reflects DNV-ST-N001 Edition 2021; the current edition is 2023-12. EN 1993-1-8:2005 column reflects the base Eurocode edition (EN 1993-1-8:2024 revision is in adoption).

BTH-1 Verification Workflow — Step by Step

1
Classify the application: Category A or B
Determine whether the lifting device is used in a controlled, precision environment (Cat A, N_d = 2.0) or in general industrial service (Cat B, N_d = 3.0). When in doubt — or when the contract specification is silent — default to Category B.
2
Select Service Class 0–4
Estimate the total number of load cycles over the device's design life. Single-use construction picks and vessel erection lugs are SC 0. Permanent crane attachments for daily operation may be SC 2 or higher. SC affects the pin bearing coefficient.
3
Define the factored design load F_d
F_d is the maximum hook load multiplied by the dynamic factor (DF). BTH-1 does not prescribe DF — it is engineer-supplied. For onshore lifts, DF = 1.10–1.30 is typical. For offshore lifts via DNV, apply DAF and SKL per §16 and enter the amplified load as F_d.
4
Check all five lug body checks §3-3.3
Net-section tension (§3-3.3.1), double-plane shear-out (§3-3.3.3), pin bearing (§3-3.3.4), pin double shear, and the weld group (§3-3.4.3 / AISC §J2.4). All five must pass. Identify the governing check (highest utilisation) and iterate on that parameter first.
5
Apply out-of-scope supplements if required
If sling geometry causes lateral loading, add a 5% out-of-plane check per API RP 2A or project guidelines. If cheek plates are used, add supplementary cheek-weld and load-sharing checks. If the pin is non-standard, add a pin-bending check per AISC 360 or EC3 §3.13.2.
6
Generate the traceable calculation record
The calculation record must identify: the BTH-1 edition used, Design Category, Service Class, all five check results (demand, capacity, utilisation), the governing check, and the N_d value. The calculator's $5 PDF report includes clause references, assumptions, and a revision stamp — ready for client or MWS submission.

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Also runs EN 1993-1-8 and DNV-ST-N001 in parallel — compare all three standards at once.