Live Demo — Pole Bending Moment & Stress Check Calculator
Enter your pole geometry, design wind speed and mounted equipment wind area to check the base bending stress and deflection instantly.
Pole Bending Moment & Stress Check Calculator
Free professional pole bending moment and stress check calculator for solar street lighting poles. Input the pole height, top/bottom diameters, wall thickness, design wind speed, mounted equipment wind area and steel grade to compute the base section modulus, total bending moment and base stress, and verify the strength and top deflection of the pole under strong winds.
Key Features
Pole Geometry
Set the total height, top and bottom diameters and wall thickness to compute the hollow base section modulus of the tapered pole.
Wind Load & Material
Input the design wind speed (33 ft reference), the mounted equipment wind area and its load height, plus the Q235/Q355 steel grade.
Wind Pressure
Uses q = 0.00256 × V² (psf) with a quick reference table from 56 mph (8.2 psf) to 94 mph (23.0 psf) for common site conditions.
Bending Moment
Superimposes the pole self wind load M_pole = F_pole × H/2 and each mounted item's moment Σ(F_i × H_i) into the total base moment.
Base Stress Check
Verifies σ = M_total / W against the allowable stress [σ] (Q235: 20.3-23.2 ksi) to confirm the pole will not fail by bending.
Deflection Estimate
Estimates the tip horizontal deflection δ = M_total × H² / (3EI) and compares it with the H/100 allowable to keep the lamp aimed and stiff.
Technical Specifications
| Platform | HTML5 Web App | Android (via WebView) |
| Core Calculation | q = 0.00256 × V²; σ = M_total / W ≤ [σ] |
| Pole Height | ≥ 3 ft (default 26.3 ft) |
| Diameters | Top ≥ 1 in, bottom ≥ 2 in; wall thickness ≥ 0.08 in |
| Wind Speed | 11 - 100+ mph (design at 33 ft reference) |
| Steel Grade | Q235 (yield 34.1 ksi) / Q355 (yield 51.5 ksi) |
| Allowable Stress | Q235: 20.3 - 23.2 ksi (incl. safety factor) |
| Section Modulus | W = π × D³ × [1 - (1 - 2t/D)⁴] / 32 (in³) |
| Industry Standards | EN 40-5, EN 1991-1-4, AS/NZS 1170.2, ASCE/SEI 7-16 |
| Output | Pass/fail strength check with stress value + tip deflection |
Frequently Asked Questions
How is the base section modulus computed?
For a hollow tapered pole the base section modulus is W = π × D_bottom³ × [1 - (1 - 2t/D_bottom)⁴] / 32, numerically equal to π × (D⁴ - d⁴) / 32D where d = D - 2t is the inner diameter. It measures how well the section resists bending.
What does the strength check result mean?
The base bending stress σ = M_total × 12 / W (psi) must stay below the allowable stress [σ]. For example, a 7,540 ft·lbf moment on a 5.03 in³ section gives 18.0 ksi, which is below the 23.2 ksi allowable for Q235, so the pole passes with about 23% margin.
Why prioritize a thicker wall in strong-wind areas?
Bending stress scales inversely with the section modulus W, and W grows faster when the wall thickness is increased than when only the diameter is enlarged. In typhoon areas, raising the wall thickness first (for example 7.1 in diameter × 0.24 in wall for 101 mph) is the most effective fix.
What is the tip deflection check?
For a cantilever pole under wind load the top horizontal deflection is estimated as δ = M_total × H² / (3EI) with steel modulus E = 29,000 ksi. It must stay within H/100 so the lamp keeps its aim and the pole remains visually stiff under gusty wind.
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