Calculator Inputs
Enter geometry and rigging details, then calculate lifting point reactions and rigging tensions.
Example Data Table
Sample scenario to demonstrate typical inputs and outputs.
| Case | L (m) | W (t) | x1 (m) | x2 (m) | Points | DAF | SF | Angle (°) | Design load per point (kN) |
|---|---|---|---|---|---|---|---|---|---|
| A | 30 | 60 | 3 | 27 | 2 | 1.15 | 1.50 | 60 | ≈ 507.49 |
| B | 24 | 45 | 2.5 | 21.5 | 4 | 1.10 | 1.60 | 55 | ≈ 194.17 |
Formula Used
This calculator treats the girder as a straight member with uniformly distributed self-weight across its full length.
- w = W / L where W is total weight (kN) and L is length (m).
- With lifting points at x1 and x2 from the left end, reactions follow static equilibrium:
- R2 (x2 − x1) = W (L/2 − x1), and R1 = W − R2
- For four-point lifting, each end line is assumed to share its reaction equally between two points.
- Design load per lifting point: R_design = R_each × DAF × SF
- Sling tension estimate per leg: T = R_design / sin(θ) if angle is from horizontal, or T = R_design / cos(θ) if angle is from vertical.
- Bending moment is scanned numerically along the beam using: M(x) = R1·H(x−x1)(x−x1) + R2·H(x−x2)(x−x2) − w x²/2
Use engineered lift plans, insert ratings, and project requirements for final approvals.
How to Use This Calculator
- Enter the girder length and total weight using your preferred unit.
- Set the number of lifting points and input the two lift line locations.
- Choose a dynamic factor and safety factor suitable for the operation.
- Enter the rigging angle and select how that angle is measured.
- Press Calculate to see reactions, design loads, sling tensions, and moment checks.
- Use the download buttons to save a CSV or PDF for documentation.
Professional Article
1) Why lifting point selection matters
Precast girders behave like long, heavy beams that can crack if picked poorly. The calculator uses girder length and total weight to estimate reactions at two lift lines. Those reactions become the minimum vertical demand each lifting point must resist before extra multipliers are applied.
2) Turning weight into usable engineering load
Field weights are often supplied in tonnes, while rigging and lifting hardware is frequently rated in force units. This tool converts tonnes using 1 t ≈ 9.80665 kN so the same input set can be compared consistently against rated capacities and design checks during planning.
3) Reaction forces from simple statics
With lift points at x1 and x2, the model assumes uniformly distributed self-weight across the full span. Using equilibrium, the right reaction depends on the distance between lift points and how far the left lift point sits from midspan. The second reaction follows from total balance.
4) Dynamic and safety multipliers in planning
Real lifts include small accelerations, travel, and positioning effects. The calculator applies a dynamic factor (DAF) and a safety factor (SF) to produce a conservative design load per lifting point. These multipliers help align estimates with lift plan expectations and permit-based controls.
5) Sling angle drives tension demand
The same vertical load can produce very different sling tensions depending on angle. If the angle is measured from horizontal, vertical capacity is T·sin(θ). If measured from vertical, it is T·cos(θ). Smaller angles from horizontal increase tension rapidly, so avoid shallow rigging.
6) Bending moment awareness during lift
Even when reactions look acceptable, bending demand can peak between lift points or near ends. The calculator scans the span numerically to report the maximum positive and negative bending moments for the uniform load model. Use these values to compare against girder handling limits and detailing.
7) Two-point versus four-point assumptions
Two-point lifting is treated with classic two-support statics. For four-point lifting, the tool assumes each end line shares its reaction equally between two points, which is a practical approximation for symmetric rigging. If geometry or equalization is uncertain, validate with a detailed rigging analysis.
8) Documenting results for lift plans
Good lift planning pairs calculated demand with equipment ratings, inspection status, and site procedures. After computing, export CSV for quick recordkeeping and PDF for approvals. Confirm pickup locations, edge protection, insert ratings, and communication steps before execution. Strong documentation reduces rework and keeps picks controlled.
Use competent-person review and project specifications for final acceptance.
FAQs
1) What does the calculator assume about the girder load?
It assumes the self-weight is uniformly distributed along the full length and that the girder is lifted by two lift lines located at x1 and x2. This is a planning-level model.
2) Can I use tonnes instead of kN for weight?
Yes. Select tonnes and enter the total weight. The tool converts using 1 t ≈ 9.80665 kN so reactions, design loads, and tension estimates are consistent with rigging ratings.
3) Why do I see a negative reaction?
A negative reaction means the chosen lift points cannot balance the uniform load as modeled. Move the lift points farther apart or closer to the appropriate regions until both reactions are positive and practical.
4) How should I choose DAF and SF?
Use project requirements, lift plan standards, and equipment guidance. DAF covers handling dynamics, while SF adds conservatism. Typical values vary by method, site controls, and risk level.
5) What angle definition should I select?
Select “from horizontal” if you measure the sling angle above the horizontal line. Select “from vertical” if you measure the sling angle away from vertical. The tool adjusts the tension calculation accordingly.
6) How accurate is the four-point option?
It assumes each end line shares its reaction equally across two points, which is reasonable for symmetric rigging with equalizers. If the rigging is uneven, verify loads using a detailed rigging and geometry check.
7) Do the moment results replace structural handling checks?
No. They provide a quick comparison for planning under the uniform load model. Always confirm insert capacities, reinforcement detailing, camber effects, and manufacturer handling limits before any lift.