M4X4.08 Steel Miscellaneous beam — Section Properties
Dimensions
| Property | Value | Unit |
|---|---|---|
| Depth (d) | 4 | 101.6 mm |
| Flange Width (bf) | 2.25 | 5.71 cm |
| Flange Thickness (tf) | 0.17 | 4.3 mm |
| Web Thickness (tw) | 0.115 | 2.9 mm |
| Area (A) | 1.27 in² | 8.2 cmÃÂò |
| Weight | 4.08 lb/ft | 6.1 kg/m |
Elastic Section Properties
| Property | Strong Axis (X-X) | Weak Axis (Y-Y) | Unit |
|---|---|---|---|
| Moment of Inertia (I) | 3.53 | 0.325 | in⁴ |
| Elastic Section Modulus (S) | 1.77 | 0.289 | in³ |
| Plastic Section Modulus (Z) | 2 | 0.453 | in³ |
| Radius of Gyration (r) | 1.67 | 0.506 | in |
Torsional Properties
| Property | Value | Unit |
|---|---|---|
| Torsional Constant (J) | 0.015 | in⁴ |
| Warping Constant (Cw) | 1.19 | in⁶ |
| Distance Between Flange Centroids (ho) | 3.83 | in |
| Effective Radius (rts) | 0.593 | in |
Section Profile Summary
This is a standard hot-rolled light I-beam profile covered by AISC 360. The tabulated section properties are computed from the nominal dimensions per the governing material standard. With Ix = 3.53 in⁴, the strong-axis flexural stiffness is suitable for preliminary sizing of beams and beam-columns.
At 4" deep — one of the smallest standard sections available. Used for light-duty lintels, bracing, handrail posts, and miscellaneous structural iron.
Key Design Checks (AISC 360)
| Check | Formula | This Section |
|---|---|---|
| Plastic moment | Mp = Zx × Fy | 100 kip-in |
| Deflection | Δ = 5wLâÃÂô/(384EIx) | Use Ix = 3.53 in⁴ |
| Torsion | St. Venant = GJ/L | J = 0.015 in⁴ |
| Column buckling | KL/r âÃÂàFcr | r_x = 1.67 in |
Design Notes
- Compactness: Verify flange and web slenderness against AISC 360 Table B4.1 classification limits for the governing load case (pure compression, pure flexure, or combined).
- Combined loading: For members under simultaneous axial force and bending, use the interaction equations in AISC 360 Section H. The governing equation depends on the ratio of required to available axial strength.
- Connection limit states: Check bolt bearing, tear-out, block shear, and weld strength at all connections. The governing connection limit state often controls the member size selection.
Verification (AISC 360): All designs using this section must be verified by a licensed Professional Engineer. Before finalizing member selection, check beam-column interaction (P-M), lateral-torsional buckling, serviceability deflections, and all connection limit states. See Engineering Disclaimer.
Worked Example: Parking garage beam — m4x4_08
Scenario: Parking structure floor beam — asphalt topping included in dead load. Simply supported light I-beam, 10 ft span, 9 ft tributary width. Service loads: 80 psf dead + 50 psf live (1170 plf total).
Given:
- Span L = 10 ft (120 in)
- Total service load w = 1170 plf
- Live load portion w_L = 450 plf
- Section m4x4_08: Ix = 3.53 in⁴, Sx = 1.77 in³, Zx = 2 in³
- Steel: ASTM A992, Fy = 50 ksi, E = 29,000 ksi
- Design moment strength: φMn = 0.9 × Zx × Fy = 8 kip-ft
Step 1 — Live load deflection check:
Δ_LL = 5 w_L LâÃÂô / (384 E Ix)
Δ_LL = 5 × (450/12) × (120)âÃÂô / (384 × 29,000,000 × 3.53)
Δ_LL = 0.99 in
Step 2 — Allowable deflection (IBC Table 1604.3, L/240):
Δ_allow = L / 240 = 120 / 240 = 0.50 in
Step 3 — Dead + live deflection:
Δ_total = 2.57 in
Step 4 — Design check:
âÃÂàLive load deflection exceeds L/240 — consider a deeper section, reduce tributary width, or shorten the span.
The required flexural strength at ultimate is approximately w_u LÃÂò/8. With factored loads 1.2D + 1.6L, verify φMn = 8 kip-ft is adequate per AISC 360 Chapter F. Also check shear capacity (φVn = 0.6 Fy Aw × 0.9) and bearing at supports.
Related Resources
- Steel Beam Capacity Calculator
- Column Capacity Calculator
- Beam Deflection Calculator
- Section Properties Calculator
- Steel Grades Reference
- Section Comparison Tool
Design Resources
- Section Properties Lookup — Compare with similar sections
- Steel Beam Sizes Reference — Standard beam dimensions
Educational reference only. Verify all section properties against the current AISC 360 Manual and mill certificates before design. Results are PRELIMINARY — NOT FOR CONSTRUCTION.