Calculator Inputs
Example Data Table
| Case | Element (L×W×T) | Points | Angle | Factors (Dyn/Wind/Ecc) | Factored Load | Tension / Leg | Outcome |
|---|---|---|---|---|---|---|---|
| A | 6000×2500×200 mm | 4 | 30° | 1.10 / 1.00 / 1.05 | ~3.64 t | ~1.31 t | PASS |
| B | 8000×3000×180 mm | 2 | 45° | 1.20 / 1.10 / 1.10 | ~7.24 t | ~3.21 t | CHECK |
| C | 4000×1200×150 mm | 1 | 0° | 1.05 / 1.00 / 1.00 | ~0.91 t | ~0.91 t | PASS |
Examples are illustrative. Real lifts must use approved insert layouts, rigging plans, and verified weights.
Formula Used
1) Volume and self mass
Volume = L × W × T
Self Mass (kg) = Volume × Density
2) Gross and factored load
Gross = (Self + Extra + Rigging)
Factored = Gross × Dynamic × Wind × Eccentricity
3) Sling tension per leg
Angle Factor = 1 / cos(θ)
Tension/Leg = (Factored / Legs) × Angle Factor × Distribution
4) Insert demand per point
Insert Demand = (Factored / Points) × Distribution
Utilization = Demand / Rated Capacity
Notes: θ is measured from vertical. Distribution accounts for unequal share in multi-leg bridles. This tool uses tonnes-force approximations; confirm with your project’s standard method and approved charts.
How to Use This Calculator
- Enter element dimensions, density, and any extra attached load.
- Add rigging weight to reflect the full lifted assembly.
- Select lifting points and the rigging configuration used onsite.
- Set sling angle from vertical, then apply suitable load factors.
- Provide sling WLL, insert capacity, and crane chart capacity.
- Press calculate and review PASS or FAIL and utilization.
- Download CSV or PDF for records and lift planning files.
Field Guide: Precast Lifting Capacity Checks
Use this guide to interpret the checker outputs and document safer picks on site.
1) What this checker verifies
This calculator compares factored lift demand against three controls: sling working load per leg, insert capacity per lifting point, and crane chart capacity at the working radius. It reports utilization so you can see which limit governs the lift.
2) Typical precast densities and weights
Normal-weight concrete is commonly around 2,400 kg/m³. A 6.0 m × 2.5 m × 0.20 m panel is about 3.0 m³ and roughly 7,200 kg before embeds. Adding 120 kg of rigging and 0–300 kg of attachments is common for planning.
3) Why sling angle drives tension
Tension rises as legs spread. The checker uses 1/cos(θ), with θ from vertical. At 30° the factor is ~1.155; at 45° ~1.414; at 60° it doubles. Keeping legs near-vertical reduces demand quickly and protects hardware.
4) Practical load factors and when to increase them
Dynamic factors cover acceleration, sudden hoists, and pick-and-carry. Many teams start at 1.05–1.20 and raise it for tighter control or frequent starts. Wind factors for large panels often sit at 1.00–1.15. Eccentricity factors of 1.00–1.10 help cover unequal load share.
5) Insert capacity checks that save time
Insert demand is computed per point from the factored load and a conservative distribution allowance. If utilization exceeds 100%, improve the lift method, use a spreader where approved, add points per the design, or select higher rated inserts that match the certified layout.
6) Matching crane chart capacity to real radius
Capacity must come from the correct chart line for boom length, outrigger setting, counterweight, and quadrant. Enter the rated capacity at the planned working radius. The “crane required” value here already includes rigging weight and your chosen factors.
7) Reading utilization for safer decisions
Many lift plans aim to stay below 85% utilization to allow for small weight changes, radius drift, and minor rigging differences. This file highlights values above 85% and flags over 100% as a failure. “Required sling WLL” is an informational design check.
8) Recordkeeping and site communication
Save the CSV or PDF with the element mark, lift ID, and date. Record rigging weight, angle, and factors so another crew can repeat the pick consistently. Combine results with the approved lift plan, insert certificate, and a pre-lift briefing.
FAQs
1) Does this replace a certified lift plan?
No. It supports planning by showing demand versus capacities. Always use an approved lift plan, manufacturer insert data, qualified rigging selection, and competent supervision for final authorization.
2) What angle should I enter?
Enter the sling angle measured from vertical. If your rigging is near vertical with a spreader beam, use 0°. If you only know the angle from horizontal, convert: vertical angle = 90° − horizontal angle.
3) Why do I add rigging weight?
Crane and inserts must carry the element plus hooks, slings, shackles, and spreaders. Ignoring rigging weight underestimates load and can push a lift over capacity, especially near chart limits.
4) What if the insert check fails but the crane passes?
The governing limit becomes the inserts. Reduce angle, add points per design, revise the lift method, or select inserts with higher rated capacity that match the manufacturer’s permitted configuration and edge distances.
5) How should I choose load factors?
Use your project standard and risk level. Increase factors for pick-and-carry, gusty wind, difficult rotations, or poor control. Decrease only when you have verified conditions, stable handling, and documented procedures.
6) Why is my per-leg tension higher than gross/legs?
Two effects increase it: the angle factor (1/cosθ) and the distribution factor for unequal leg sharing. As slings spread, tension rises rapidly even when the lifted mass stays the same.
7) Can I export results for records?
Yes. Run a calculation, then use Download CSV or Download PDF. The export includes your inputs, computed loads, and pass/fail checks for basic recordkeeping and toolbox discussions.