Bridges · Girders & decks
SM1600 bridge girder: moving load, envelope, girder check calculator
Simply supported bridge span under the AS 5100.2 SM1600 family. The M1600 vehicle (four tri-axle groups of 3 × 120 kN with the 6.25 m minimum variable gap, plus 6 kN/m) is run across the span in both directions to build the moment envelope; S1600 (80 kN axles + 24 kN/m, no dynamic allowance) and the A160 axle are compared. Lane loads are combined with the accompanying lane factors and distributed to the critical girder, then added to dead and superimposed dead loads for the ULS girder check.
Standard: AS 5100.2-2017 Cl 7.2 (M1600, S1600, A160), Cl 7.7 dynamic load allowance, Cl 7.5 accompanying lane factors · AS 5100.5 / .6 girder capacity (input)
Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Span (simply supported) | 25 | m |
| Design lanes | 2 | |
| Girders | 6 | |
| Distribution multiplier for the critical girder | 1.25 | |
| Dynamic load allowance M1600 | 0.3 | |
| Dynamic load allowance A160 | 0.4 | |
| Traffic ULS load factor | 1.8 | |
| Girder + deck dead load per girder | 22 | kN/m |
| Superimposed dead load per girder (wearing surface, barriers) | 6 | kN/m |
| Girder design capacity φMu | 9500 | kNm |
| Girder design shear capacity φVu | 1900 | kN |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| M1600 truck moment (max, no DLA) | 3,905 | kNm |
| M1600 lane moment (1 + α) + UDL | 5,545 | kNm |
| S1600 lane moment | 4,478 | kNm |
| A160 axle moment (1 + α) | 1,400 | kNm |
| Governing lane moment (M1600) | 5,545 | kNm |
| Midspan lane moment M1600 / S1600 (moving-load table) | 5,539 / 4,475 | kNm |
| Lane factors Σ (1, 0.8) → girder share | 1.80 → 0.375 | lanes |
| Girder M*: 1.2G + 2.0Gs + 1.8·share·Ml | 6,743 | kNm |
| Girder V* at support | 1,178 | kN |
| Girder SLS moment | 4,267 | kNm |
- ✓ M* ≤ φMu — 71 %
- ✓ V* ≤ φVu — 62 %
Method, formulas and assumptions
- M1600 (AS 5100.2 Fig 7.2.2): axle groups of 3 × 120 kN at 1.25 m; group gaps 3.75 m, 6.25 m (variable, minimum used) and 5.0 m; plus 6 kN/m over the lane. S1600: same layout with 80 kN axles plus 24 kN/m, α = 0. A160: one 160 kN axle, α = 0.4.
- Envelope: the vehicle is stepped 50 mm at a time across the span in both directions; the shear is the maximum support reaction.
- Accompanying lane factors 1.0, 0.8, 0.4…; girder share = Σ lane factors / girders × distribution multiplier (use a grillage or the lever rule for the edge girder).
- ULS: 1.2 × self-weight, 2.0 × wearing surface (Cl 6), 1.8 × traffic. Enter φMu and φVu from the girder design (AS 5100.5 concrete, AS 5100.6 steel).
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.