Tool · Engineering calculator

Monorail Bottom Flange Stress Calculator

Required bottom flange thickness of a monorail or underslung beam under the hoist trolley wheels, to AS 1418.18:2024 Clause 5.12.3.1 — from the wheel centres, the dynamic wheel load (AS 5221.1 factors), the beam's yield stress and the bending stress already in the flange — plus the Clause 5.12.3.3 web check for beams hung from their top flange. Indicative only — see the disclaimer.

Engineering disclaimer — read before using this tool

This calculator is not a substitute for professional engineering advice. It is provided by Sorian Holdings Pty Ltd (trading as Sorian Cranes) for general information and preliminary sizing only. It is not engineering advice, not a design verification or certification, and not a design to AS 1418, AS 4100 or any other standard.

Results depend entirely on the values you enter and on the simplified, published methods described on this page, which may not apply to your crane, beam, structure, materials, duty or site. The tool cannot see your installation and does not check fatigue, global beam strength, deflection, lateral-torsional buckling, connections, runway alignment, wear, corrosion or existing damage.

Any crane, monorail, runway or structural design must be prepared or verified by an appropriately qualified professional engineer who has reviewed your actual conditions — and, where state law requires it (for example Queensland's RPEQ scheme and Victoria's Professional Engineers Registration Act), a registered professional engineer — before fabrication, installation, modification, load testing or use.

To the maximum extent permitted by law, Sorian Holdings Pty Ltd and its directors, employees and partners accept no liability for any loss, damage, injury or death arising from use of, or reliance on, this tool or its output. Nothing on this page excludes, restricts or modifies any consumer guarantee or other right under the Australian Consumer Law that cannot lawfully be excluded. By using the calculator you accept these terms and our website terms.

Inputs

Beam section

Pre-fill from a universal beam (AS/NZS 3679.1) Pre-fills b_f, t_f, t_w and D from the standard section tables; check against your section book or the actual beam, and overwrite for welded, tapered or worn sections. Flange width b_f (mm) Flange thickness t_f (mm)Use the measured thickness for an existing beam, less any corrosion loss. Web thickness t_w (mm) Beam depth D (mm)For the Clause 5.12.3.3 web check. Use the depth below partial stiffeners where the trolley passes under them. Beam support (Clause 5.12.3.3)

Single-web beam hung from its top flange (hangers, clamps) — web thickness check applies Connected by end plates that carry the bottom-flange lateral load to the supports — web check not required

Steel grade / yield f_y Yield stress f_y (MPa)Grade 300: 320 (t_f < 11), 300 (11–17), 280 (≥ 17). Grade 350: 360 (< 11), 340 (11–40), 330 (≥ 40). AS 4100 Table 2.1. Older beams may be Grade 250 — use 260/250.

Trolley wheels

Wheel contact centres (mm)Transverse distance between the two wheel contact lines across the flange. C = half of this. C_F, web centreline to wheel load (mm)Derived (half the wheel centres). B_F = b_f/2 for a single-web beam; see Figure 5.12.3.1. Beam end condition — load position factor K_L

Wheels cannot approach within 2B_F of the end of the beam, or the end of the bottom flange is supported (e.g. by an end plate) — K_L = 1.0 Wheels can approach within 2B_F of the end and the flange is not supported at the end — K_L = 1.3

Loads (AS 5221.1 factors)

Rated capacity MRC (kg) Hoist + trolley mass (kg) Hoisting class Hoist speed v_h (m/min)φ₂ = φ_2,min + β₂·v_h (v_h in m/s), AS 5221.1 Cl 6.1.2. φ₂ hoisting dynamic factor φ₁ dead-load dynamic factorApplied to the hoist and trolley mass (AS 5221.1 Cl 6.1.1). Wheels sharing the load Or enter max dynamic wheel load N (kN)Overrides the load build-up above when entered.

Beam bending stress at the wheel position

Longitudinal bending stress f_b (MPa)Stress in the bottom flange from global bending at the trolley position. Enter from your beam analysis, or use the helper. Helper: simple span L (mm) Helper: Z_x (10³ mm³)f_b ≈ (ΣN·L/4) / Z_x with the trolley at mid-span, self-weight ignored. Simply supported only. Monorail classification (AS 5246.1 Table 5) C5.12.3.1: A02 is deemed the upper bound for maintenance monorails; the A02-or-higher equation suits production monorails (Gorenc 2003). When in doubt use A02 or higher.

Results

—Enter the section, wheel centres and loads to run the check.

Indicative only. Not professional engineering advice and not a design verification — see the disclaimer above. Have an appropriately qualified engineer verify any design before fabrication, installation or use.

Ask an engineer to check it →

Method — what the calculator does

The check is AS 1418.18:2024 Crane runways and monorails, Clause 5.12.3.1, which gives the minimum bottom flange thickness T_f of a monorail beam under the wheel loads of a hoist trolley. It treats the flange outstand as a plate loaded by the wheel at distance C from the beam centreline, and reduces the available yield stress by the longitudinal bending stress f_b the flange already carries.

1. Dynamic wheel load

Unless you enter the hoist manufacturer's maximum dynamic wheel load directly, the calculator builds it with the AS 5221.1:2021 dynamic factors — φ₂ on the hoisted load and φ₁ on the hoist and trolley mass — and divides by the number of wheels that share the load:

φ2 = φ2,min + β2 · vh          (vh in m/s)          AS 5221.1 Cl 6.1.2
N  = (MRC·φ2 + m_hoist·φ1) · g / n_wheels   [kN]

AS 1418.18 C5.12.3.1 warns that a four-wheel trolley may carry the load predominantly on two wheels, so two sharing wheels is the default.

2. Required flange thickness

C_F is half the wheel contact centres for a single-web beam; B_F is half the flange width. K_L is 1.0 where the wheels cannot approach within 2B_F of the end of the beam or the end of the bottom flange is supported (e.g. by an end plate), and 1.3 where they can and it is not. Where the beam hangs from its top flange within 2B_F of the end, the top flange should be at least 1.3 T_f unless strengthened. Clause 5.12.3.2 separately requires enough flange width for clearance between the wheels and the root radius or weld, allowing for float and wear.

Utilisation is reported as (T_req/t)², the ratio of applied to available stress, since each equation is a square root of load over stress.

3. Bearing under the wheels (Clause 5.12.3.4)

The bottom flange must also be checked for bearing stress under the wheel loads to AS 5228.1:2021 Clause 4.1.1, using both P_max and P_mean; the limiting pressure P_L is governed by the ultimate strength of both wheel and flange, and may call for a higher flange grade or hardening than flexure does. The results panel links to the wheel & rail calculator with this wheel load pre-filled.

4. What it does not do

It does not design the beam. Bending, shear, torsion (Appendix C), lateral-torsional buckling, deflection limits (Clause 5.13.2), supports and prying (Clause 5.12.4, bolt force +30 %), curved beams (Clause 5.12.5), flange stresses at cantilever attachments (AS 3990 / AS 4100) and fatigue (Section 6) are all separate checks.
It does not size the trolley wheels — use the wheel & rail sizing calculator (AS 5228.1).
It assumes a single-web parallel-flange I-section. For double-web, box and fillet-welded box beams C_F and B_F are measured from the line of web action (Figure 5.12.3.1) — enter them by hand. Tapered-flange beams need a specific assessment.

Frequently asked questions

Which standard does this bottom flange calculator follow?

AS 1418.18:2024 Cranes, hoists and winches, Part 18: Crane runways and monorails, Clause 5.12.3.1, which gives the required bottom flange thickness of a monorail beam under the hoist trolley wheel loads (two equations, by monorail classification), and Clause 5.12.3.3 for the web of a single-web beam hung from its top flange. The dynamic wheel load is built from the AS 5221.1:2021 hoisting dynamic factor φ2 and dead-load factor φ1, and yield stresses follow AS/NZS 3679.1 / AS 4100 Table 2.1.

Why yield strength and not tensile strength?

AS 1418.18 writes the flange equation in terms of fy, the yield stress of the beam material, reduced by the longitudinal bending stress already in the flange. Tensile strength plays no part in the local flange bending check; some overseas calculators use it, which overstates capacity for Australian structural grades.

What are 'wheel centres' and why do they matter?

The transverse distance between the two wheel contact lines across the bottom flange. Half of it is C in AS 1418.18 — the distance from the beam centreline to the wheel load — and the larger C is, the longer the cantilever of flange the wheel loads. Measure it on the trolley at the flange width it is set to, or take it from the hoist manufacturer's data.

How many wheels carry the load?

Clause C5.12.3.1 of AS 1418.18 notes that the wheel loads of a hoist trolley may be unequally distributed, so a four-wheel trolley may carry the design load predominantly on two wheels, and that the maximum dynamic wheel load should be as advised by the hoist manufacturer. The calculator lets you choose the number of wheels that share the load; two per trolley is the conservative default for four-wheel trolleys.

Does this replace an engineer's design?

No. It is an indicative check only and is not a substitute for professional engineering advice. The monorail beam as a whole must still be designed for bending, shear, torsion, lateral-torsional buckling, deflection and fatigue to AS 1418.18 and AS 4100 (or AS 3990), and the design must be verified by an appropriately qualified (and, where required, registered) professional engineer.

References: AS 1418.18:2024 Clauses 5.12.3.1–5.12.3.4 and C5.12.3.1 (pages 35–37); AS 5221.1:2021 Clauses 6.1.1–6.1.2; AS/NZS 3679.1:2016 Table 14 / AS 4100:2020 Table 2.1; AS 5246.1:2021. Standards are copyright Standards Australia — this page paraphrases the method and reproduces only the values needed to run it.

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