H-Beam Spec Table

In-Depth Guide

H-beam vs I-beam — the real difference between parallel and tapered flanges

An I-beam (KS D 3502) has about a 1/6 taper on the inner flange faces, so those faces are sloped. A flat washer or bolt head therefore does not sit flat against them — you need a beveled washer — and splice plates are awkward to attach, so I-beams now survive only in limited uses like monorail and hoist runway beams. An H-beam has parallel inner and outer flange faces, so bolts seat directly and splice plates attach easily, and its wide flange resists weak-axis buckling well, making it the de facto standard for columns and beams. If the drawing calls for an H-beam but I-beams arrive on site, the flange taper throws off bolting and splicing, so verify the section shape at delivery.

Wide (HW), medium (HM) and narrow (HN) flange — column vs beam at the same height

Even at the same nominal height, the flange width decides the use. A wide-flange section (HW, width ≈ height, e.g. H-200×200) is nearly square, so strong- and weak-axis buckling are balanced — ideal for compression columns. Narrow and medium sections (HN/HM, height > width, e.g. H-250×125) are narrow relative to height, giving high bending efficiency, so they are used for beams. So even within the "300 class," H-300×300 (wide) and H-340×250 differ greatly in unit weight and weak-axis stiffness. If the order does not state the series (HW/HM/HN), a section matching only the height can be delivered, so pin down the series along with the size.

The rolling fillet radius and stiffeners/splice plates — why a square member will not sit in the corner

An H-beam has a rolled radius (fillet R) in the inner corner where the web meets the flange. So if you fit a square stiffener or gusset plate straight into that corner, its corner catches on the R and stands off instead of sitting tight. You must cut the stiffener corner with a scallop (a clipped arc) larger than the R so it bears properly on the flange and web. Nominal and actual dimensions can also differ (even within a "400×400 class," the real H, B, web and flange thickness vary by series), so measure before fabricating the connection, and preheat before welding once the flange thickness exceeds about 25 mm.

Material grades — SS400 / SM490 / SN490, when to use which

The grade names are not a simple strength ladder; they differ in guaranteed weldability, toughness and seismic performance. SS (general structural, e.g. SS400) does not guarantee weldability or Charpy impact value (toughness), so it is unsuitable for important welded structures. For welded frames and machine frames use weldable SM (e.g. SM490), and for building frames under seismic load use SN490B/C, which guarantee a yield-ratio cap and impact value. So read the grade names in the table not as strength but along the axes of welded-or-not, seismic demand and plate thickness, and check the toughness grade (B/C) for thick plate or low-temperature service.

Mill scale, paint preparation, and weathering steel (COR-TEN) as an alternative

Rolled sections carry mill scale — a black oxide film — on the surface. Paint over it without removing it and, in time, the coating peels off together with the scale. So the basic practice is to shot-blast (e.g. grade SP) the scale off, or pickle, before painting. For a structure left bare outdoors, you can consider weathering steel (SMA / COR-TEN), which builds its own stable rust layer instead of paint. And when cutting and connecting sections, get not only the cut-face squareness (within ±1°) but also the bevel preparation of thick flanges and the preheat right, to secure weld quality.