Calculator Input Form
Example Data Table
| Input | Column A | Column B | Purpose |
|---|---|---|---|
| Section size | 300 × 300 mm | 300 × 350 mm | Find area and bending resistance. |
| Service load | 420 kN | 455 kN | Build proof load demand. |
| Eccentricity | 25 mm | 20 mm | Estimate secondary bending. |
| Settlement | 5 mm | 7 mm | Check movement tolerance. |
Formula Used
Proof load: Pp = Ps × Fp
Area: A = width × depth
Axial stress: fa = Pp / A
Eccentric moment: M = Pp × e
Section modulus: S = width × depth² / 6
Bending stress: fb = M / S
Combined stress: fc = fa + fb
Radius of gyration: r = √(Imin / A)
Slenderness: λ = K × L / r
Adjusted allowable stress: Fa = base allowable × condition factor × slenderness factor
Safety factor: SF = Fa / fc
Utilization: U = fc / Fa × 100
How to Use This Calculator
Enter the project name and common proof settings first. Add the proof load factor, allowable stress, spacing, and movement limits.
Then enter the size, height, service load, eccentricity, settlement, and condition factor for each column. Use measured values where possible.
Press the calculate button. The result block appears below the header and above the form. Review capacity, stress, utilization, safety factor, settlement, and status.
Use the chart to compare both columns quickly. Export the result as CSV for spreadsheets or PDF for reports and site records.
Construction Guide for Two Column Proof Checks
Why Paired Column Proof Checks Matter
A two column proof check helps compare two nearby supports under planned or measured construction loads. It is useful during temporary works, renovation checks, shoring reviews, repair planning, and early site assessment. The goal is not only to see one column in isolation. The goal is also to understand how the pair behaves together. When one column carries more load, settles faster, or has a weaker section, the shared system can become uneven.
What the Calculator Reviews
This calculator estimates proof load demand from the entered service load and proof factor. It then calculates area, axial stress, eccentric bending, combined stress, adjusted capacity, utilization, and safety factor. It also checks settlement and differential settlement. These checks help identify clear warning signs before a field decision is made. The load balance value shows how evenly the two columns are sharing the proof demand.
Why Eccentricity Is Important
Real column loads are rarely perfectly centered. Beams, brackets, corbels, slab offsets, and temporary jacks can move the load path away from the column center. That offset creates moment. Moment adds bending stress to axial stress. A column with acceptable axial stress may still need review when eccentricity is high. For that reason, this tool includes a separate bending stress estimate.
Using Results on Site
Start by checking the overall status. Then review the governing column. A high utilization percentage means the column is closer to its adjusted limit. A low safety factor means less reserve is available. If settlement or differential settlement exceeds the selected limit, the system should be reviewed before more load is added. Use conservative inputs when data is uncertain. Keep field notes, measurements, and photos with the exported report.
Important Design Note
This page gives a practical proof estimate, not a final code design. Actual construction decisions may require reinforcement details, concrete strength tests, masonry condition, foundation capacity, lateral restraint, load duration, and local code checks. Always ask a qualified professional to confirm critical work.
FAQs
1. What is a two column proof calculator?
It estimates proof load demand, stress, capacity, settlement, and safety for two nearby construction columns. It helps compare both supports before planning or reviewing site loads.
2. Can this calculator replace an engineer?
No. It is a planning and reporting aid. A qualified engineer should review final structural decisions, local code requirements, material tests, and actual site conditions.
3. What is proof load factor?
Proof load factor increases the service load for checking. It represents a higher test or review load. The correct value depends on project requirements and engineering guidance.
4. Why does eccentricity matter?
Eccentricity means the load is not centered. It creates bending moment. This bending adds extra stress, so the column may be less safe than an axial-only check suggests.
5. What is utilization percentage?
Utilization compares calculated combined stress with adjusted allowable stress. A lower value shows more reserve. A value above 100 percent needs review.
6. What is differential settlement?
Differential settlement is the movement difference between the two columns. Excessive difference can cause cracking, load transfer, frame distortion, and serviceability problems.
7. Why is slenderness included?
Slender columns can lose strength due to instability. The calculator applies a simple reduction factor when slenderness rises, giving a more cautious proof estimate.
8. What data should I collect first?
Collect column dimensions, height, load estimate, eccentricity, settlement readings, material condition, spacing, and allowable stress. Better field data creates more useful results.