Enter project inputs
Use consistent units. The calculator converts internally and returns uniform spacing.
Example data table
| Scenario | Total length | End offset | Max spacing | Total load | Capacity | Safety factor | Result (count) | Result (spacing) |
|---|---|---|---|---|---|---|---|---|
| Beam shoring run | 12.000 m | 0.300 m | 1.500 m | 180.000 kN | 25.000 kN | 1.300 | 10 | 1.267 m |
| Short trench brace | 6.000 m | 0.250 m | 1.200 m | 60.000 kN | 20.000 kN | 1.200 | 6 | 1.100 m |
Example outputs assume uniform spacing and typical planning values. Always confirm with engineered shoring plans and site conditions.
Formula used
Effective length
Remove end clearances before placing jacks.
Leff = L − 2 × offset
Count by spacing limit
Ensure uniform spacing stays at or below the limit.
nspacing = ceil(Leff / Smax) + 1
Count by load capacity
Use design load and rated capacity per jack.
nload = ceil((Load × SF) / Capacity)
Final count and spacing
Pick the most conservative count, then compute spacing.
n = max(nspacing, nload, nmin)
S = Leff / (n − 1)
This tool assumes evenly spaced jacks on a straight run. For point loads, irregular supports, or engineered shoring, consult a qualified professional.
How to use this calculator
- Choose your unit system and enter the total support length.
- Enter the end offset to keep jacks away from edges.
- Set a maximum spacing based on your method statement.
- If you know loads, enter total load, capacity, and safety factor.
- Press Calculate to show results above the form.
- Use the CSV/PDF buttons to save results for records.
Load planning and safety margins
This calculator converts your estimated supported load into a design load using the selected safety factor. Use it to reflect uncertainty in material condition, crew handling, dynamic effects, and uneven bearing. For lifting operations, consider impact allowances and temporary eccentricity. When loads are unknown, enter zero and size by spacing, then confirm capacities with an engineered plan and manufacturer ratings.
Spacing control for deflection and stability
Maximum spacing is often governed by allowable deflection, shoring system stiffness, and local method statements. The tool first computes a spacing based jack count to keep every interval at or below the limit. If you tighten the spacing, the required count rises, and the actual spacing is recalculated for a uniform layout. If your layout must follow a grid, use the positions list to verify field marks.
Edge offsets and end bearing zones
End offsets keep jacks away from brittle edges, voids, and weak bearing zones. The effective length equals total length minus two offsets, so large offsets can reduce the usable run quickly. Set offsets from drawings or field measurements, and verify that the first and last jacks have sound bearing surfaces. Where edges are irregular, increase offsets and reduce spacing to maintain stability.
Interpreting jack positions on site
Positions are reported from the start reference, including the initial offset. Mark the start line, measure each position, and place jack centers consistently. If obstacles exist, keep the same count and distribute small adjustments while ensuring no spacing exceeds the maximum limit or violates end clearances. After placement, remeasure intervals and confirm the line remains straight.
Documentation and quality checks
For records, download the CSV for an audit trail and the PDF for toolbox talks. Confirm that design per jack load stays below rated capacity, and recheck after any scope change. Good practice includes photographing bearing pads, noting ground condition, and recording jack identification numbers for traceability. If settlement occurs, stop work, reset levels, and recalculate spacing before proceeding.
FAQs
How does the calculator choose the final jack count?
It calculates a count needed for spacing and a count needed for load. It then selects the highest value, also respecting your minimum jack setting.
What if I only want spacing based results?
Set total load to 0. The tool will size jacks using spacing and offsets, and still report positions and actual spacing.
Why can actual spacing be smaller than my maximum spacing?
The final count may be increased by load or minimum rules. When the count rises, the effective length is split into more intervals, reducing actual spacing.
Should I use rated or working capacity for each jack?
Use the most conservative value allowed on site, considering manufacturer guidance and any derating for extension, eccentric loading, or base conditions.
Do the listed positions include the end offset?
Yes. Position 1 starts at the entered end offset from the start reference, then each next position adds the computed uniform spacing.
Can I shift a jack to avoid an obstacle?
Yes, within limits. Keep the same count and adjust locally, but ensure no interval exceeds the maximum spacing and end clearances are maintained.