Two Section Families That Look Alike
H-beams and I-beams share the same general shape: two flanges joined by a web. The difference lies in the flanges and in the resulting behaviour. A hot rolled H-beam has parallel flange faces of equal thickness, so its inner surface is flat and the section behaves symmetrically about both axes. A hot rolled I-beam, the older profile, has a tapered inner flange face, traditionally with a 1:6 slope, and the flange thickness decreases towards the edge. The two products are covered by different standards: H-beams by GB/T 11263, which also covers the split T sections produced from them, and I-beams by GB/T 706, which covers hot rolled section steel including channels and angles.
Geometric Comparison
| Feature | H-beam (GB/T 11263) | I-beam (GB/T 706) |
|---|---|---|
| Flange faces | parallel, equal thickness | tapered 1:6 on the inner face |
| Width to height ratio | higher, wide and medium flange series | lower, narrow flanges |
| Series coding | HW, HM, HN and HT steel pile | I10 to I63 by height |
| Bolted connection | high strength bolts direct through the flange | requires tapered washers or welded cleats |
| Torsional stiffness | higher for the same mass | lower |
| Rolling method | universal mill with horizontal and vertical rolls plus edger | two-high or universal mill with grooved passes |
An important point for designers: the codes HW, HM, HN and HT replaced the older hz, hk and hu terminology used in the 1998 edition of GB/T 11263, so drawings that quote the old codes must be translated before ordering. Modern specifications also reference IPE, HEA and HEB profiles from EN 10365 or W shapes from the ASTM A6 range for imported designs.
Why the Geometry Matters for Capacity
Bending resistance depends mainly on the section modulus, which grows with the flange area and with the distance between the flanges. The parallel flange of an H-beam places more material far from the neutral axis for the same profile height, so a wide flange H section typically has a higher section modulus and lower mass per metre than an I-beam of similar height. The width of the flange also raises torsional resistance and improves stability against lateral torsional buckling, which is why H-beams are used for free spanning beams and for columns. The narrow, tapered flanges of an I-beam mean that the second moment of area about the weak axis is much smaller, so an I-beam is efficient when it bends only in the plane of its web and it is inefficient as a compression member or when loads act outside that plane. This is a design limitation rather than a defect: the profile simply reflects the rolling technology and the connection practice of the period when it was standardised.
Application Guidance
H-beams are the default choice for columns, long span beams, portal frame rafters, bridge girders, crane runways, platform structure and bolted steel frames, because they connect easily with ordinary high strength bolts and behave predictably in both axes. I-beams remain practical for comparatively short spans carrying loads in the plane of the web, for machine frames, trolley rails, temporary works, walkway supports, brackets and stiffeners, and for composite sections where they are welded into a larger assembly. The economic comparison should always be made on total installed cost: an I-beam may be cheaper per tonne, but if it requires welded cleats or tapered washers and heavier sections to reach the same capacity, the H-beam usually wins.
Fabrication and Supply Notes
Rolled H sections are produced up to roughly 1000 mm in height; beyond that size welded built-up sections are used, fabricated to GB/T 33814. Holes for connections should be drilled rather than punched in the flange of a heavily loaded section, and the hole pattern must respect the edge distance rules of the connection design. Cutting is by saw or by thermal process with the cut face dressed, and the section should be supported during cutting to prevent the web from distorting. Where sections will be exposed to weather, the surface is either painted to a defined system or hot-dip galvanized to GB/T 13912 or ISO 1461. Sections are supplied with a mill certificate and a heat number marked on the web, so that the delivered material can be traced to the certified chemical and mechanical results.
Frequently Asked Questions
Q: Is an H-beam simply a wider I-beam?
A: Functionally that is a useful description, but the difference is geometric rather than only dimensional. The H-beam has parallel, equal thickness flanges, while the I-beam has a tapered inner flange face, and the two are covered by different standards.
Q: Which section is stronger for the same weight?
A: For bending about the strong axis and for torsion, a wide flange H-beam normally provides a higher section modulus per unit mass, so it is more efficient in most beams and columns.
Q: Can high strength bolts be used directly on an I-beam flange?
A: Not without preparation. The tapered inner face requires tapered washers or a welded cleat, whereas an H-beam flange accepts high strength bolts directly.
Q: What do HW, HM and HN mean?
A: They are the current series codes in GB/T 11263 for wide, medium and narrow flange H sections, and they replaced the older hz, hk and hu designations.
Q: Can large H-beams be rolled in one piece?
A: Rolled sections are produced up to about 1000 mm in height. Above that, sections are welded from plate to GB/T 33814 and are designed against the welded section rules rather than the rolled section tables.
Q: Which section suits a compression member?
A: An H-beam. Its wider flange and greater weak axis stiffness make it much more stable in axial compression than an I-beam of comparable height.
