Model uniform lane loads and custom axle trucks across your span easily. See factored demand, distribution effects, and quick exports for documentation clear reports.
| Span (m) | Lane w (kN/m) | Lanes | Truck Loads (kN) | Truck Spacings (m) | Governing (Factored) |
|---|---|---|---|---|---|
| 20 | 9.3 | 1 | 60, 120, 60 | 4, 4 | Often truck moment governs |
| 40 | 9.3 | 2 | 80, 160, 80 | 4.3, 4.3 | Often lane moment increases strongly |
| 60 | 10.0 | 3 | 90, 180, 90, 90 | 3.6, 3.6, 3.6 | Check both moment and shear |
The axle train is shifted across the span in small steps. At each position, the calculator evaluates:
Live-load models can produce different demand envelopes on the same span. A uniform lane load spreads force over length and can dominate bending as spans increase. A truck concentrates forces and often controls shorter spans or support actions. Comparing both helps prevent unconservative sizing.
The calculator sweeps each case across a simply supported span and records envelope maxima for midspan bending moment and left support shear. The lane case includes full-span uniform load and an optional tandem pair. The truck case uses a custom axle train defined by loads and spacings.
For a full-span uniform load, maximum moment scales approximately with L², while shear scales with L. Longer spans can therefore become lane-controlled for moment, especially when multiple design lanes are applied. The distribution factor converts that global demand to girder-level demand.
Truck effects depend on axle configuration. Heavier axles near midspan increase peak moment; heavier axles near a support increase peak shear. Shorter spacing can intensify midspan moment because more weight fits within the critical region simultaneously.
Distribution factors represent load sharing among girders and depend on spacing, stiffness, and load path. Impact factors account for dynamic amplification from vehicle interaction and surface conditions. The calculator applies impact using (1+IM) so both moment and shear are amplified consistently.
Load factors reflect the selected design format and target reliability. Separate factors for lane and truck cases allow rapid scenario testing when criteria differ by limit state. Governing notes are based on factored values, matching typical design comparisons.
One case may govern moment while the other governs shear. Multi-lane uniform loading often governs bending on longer spans, while a heavy axle group can govern support shear on shorter spans. Use the two governing statements to focus detailing, bearings, and connections.
Begin with preliminary span and distribution assumptions, then test a conservative truck arrangement. Adjust lane count, impact, and load factors to match project criteria and export each run for traceability. Final design should confirm with the governing specification and a full structural analysis model. This workflow supports consistent checks during concept and preliminary design stages.
It assumes a simply supported span and evaluates envelope maxima for midspan moment and left support shear. Continuous spans, fixity, and secondary effects are not included.
For a simply supported span, the maximum end shear usually occurs at a support. The tool reports the left reaction as a consistent reference; the right support is comparable by symmetry for many cases.
It scales global lane or truck effects to a single girder or design line. Choose a factor consistent with your structural system, spacing, stiffness, and applicable guidance.
Use the dynamic allowance specified by your design criteria. If uncertain, run sensitivity checks with a low and high value to see how strongly the governing case changes.
This version models one truck train per run. To study multiple-presence effects, you can approximate by adjusting distribution factors or by running separate scenarios and comparing envelopes.
Uniform load moment grows roughly with the square of span length, while a fixed truck weight does not increase in the same way. As spans grow, distributed loading can become more critical.
They are designed for quick documentation of inputs and results. For formal submittals, include your project assumptions, governing criteria, and any model verification steps required.
Build safer designs by comparing loads before construction decisions.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.