Calculator Inputs
Example Data Table
This sample table shows example input combinations and representative output values for quick comparison.
| Case | Lateral Load (kN) | Height (m) | Span (m) | Columns | Spans | Story Stiffness (kN/m) | Drift (mm) | Governing Moment (kN·m) |
|---|---|---|---|---|---|---|---|---|
| Steel Office Portal | 300 | 3.50 | 6.00 | 2 | 1 | 6762.97 | 44.36 | 579.00 |
| Retail Mid-Span Frame | 450 | 4.00 | 7.00 | 3 | 2 | 11662.17 | 38.59 | 539.83 |
| Wide Industrial Frame | 700 | 4.20 | 8.00 | 4 | 3 | 18415.66 | 38.01 | 639.33 |
Formula Used
This tool uses a simplified preliminary elastic model for a regular one-story moment frame. It is intended for screening, concept design, and fast option comparison.
Kcolumns = n × α × (12EIc / h³) Kbeams = s × (12EIb / L³) Kstory = 1 / (1 / Kcolumns + 1 / Kbeams) Drift = V / Kstory Drift Ratio = Drift / h Overturning Moment = V × h Approx. Column End Moment = (V / n) × h × c Approx. Beam End Moment = (V × h / 2s) + (wL² / 12) Approx. Beam Midspan Moment = wL² / 24 Edge Column Axial Couple = (V × h) / (s × L) Required Section Modulus ≈ Mmax × 10⁶ / (0.60Fy)Where n is the number of columns, s is the number of spans, h is story height, L is beam span, V is lateral load, w is gravity load, E is elastic modulus, and α is the base restraint factor. This page uses α = 1.0 for fixed bases and α = 0.25 for pinned bases. The column moment factor c is 0.50 for fixed bases and 0.333 for pinned bases.
How to Use This Calculator
- Choose the frame material and select whether the column bases are fixed or pinned.
- Enter the number of columns, number of spans, story height, and average beam span.
- Input the factored lateral load, gravity load on the beam, elastic modulus, and the member inertias.
- Set stiffness modifiers if you want to reflect cracked sections, reduced stiffness, or trial assumptions.
- Enter the drift limit denominator, then click Calculate Moment Frame.
- Review stiffness, drift, overturning, beam moment, column moment, and the required section modulus.
- Use the CSV and PDF buttons to export the calculation summary and example table.
FAQs
1. What does this calculator estimate?
It estimates one-story frame stiffness, drift, overturning, beam end moment, column shear, edge axial couple, and a preliminary section modulus. It is meant for fast early-stage comparison of framing options before building a full analytical model.
2. Is it suitable for final design?
No. Use it for screening and concept design only. Final design should use code-compliant load combinations, member checks, P-Delta effects, connection design, and detailed frame analysis with project-specific geometry.
3. Why do fixed and pinned bases change the answer?
Base restraint changes rotational resistance at the column foot. Fixed bases increase overall frame stiffness and usually reduce drift. Pinned bases allow more sway, so calculated drift and moment distribution change.
4. Can I use reinforced concrete values?
Yes. Enter concrete-appropriate elastic modulus and cracked-section inertia values. That gives a reasonable preliminary estimate, but reinforced concrete design still needs reinforcement detailing, cracked stiffness checks, and code-based load combinations.
5. What if drift exceeds the limit?
Increase column inertia, beam inertia, or the number of columns. Reducing story height, reducing span, or improving base restraint also lowers drift. Then rerun the estimate and compare.
6. Why is beam end moment often large?
Rigid beam-column joints transfer sway moments into the beams. Gravity load also adds fixed-end demand, so beam end moment can become the governing value even when column shear appears moderate.
7. What does required section modulus mean?
It is a quick steel sizing indicator based on the governing preliminary moment and an allowable stress of 0.6Fy. Treat it as a screening value, not a final section selection.
8. Does this include torsion, irregularity, or P-Delta effects?
No. The model assumes a regular, symmetric frame and does not capture torsional response, higher-mode effects, foundation flexibility, or second-order amplification. Check those separately during detailed analysis.