How to distinguish between I-beams and H-beams?

I-beams are primarily categorized into standard I-beams, light I-beams, and wide-flange I-beams. Based on the ratio of flange width to web height, wide-flange I-beams are further divided into wide, medium, and narrow types. The first two types are manufactured in sizes ranging from No. 10 to No. 60, corresponding to heights of 10 to 60 cm.

At the same height, light I-beams have narrower flanges, thinner webs, and lighter weight. Wide-flange I-beams, also known as H-sections, feature parallel flanges with no inward slope on their inner edges. They belong to economical section steel and are rolled on four-high universal mills, hence also called "universal I-beams." Standard and light I-beams have already been standardized nationally.

As the name suggests, an I-beam has a cross-section shaped like the Chinese character “工” (a vertical bar with two horizontal bars at top and bottom). The inner surfaces of the upper and lower flanges are sloped—typically at a 1:6 gradient—making the outer edges thin while the inner edges are thick. This results in significant differences in cross-sectional properties between the two principal planes, limiting the full utilization of the steel's strength characteristics in practical applications.

Although thicker versions of I-beams have appeared in the market, their structural design inherently limits their torsional resistance.

H-Beams

H-beams are high-efficiency, economical sections with more optimized cross-sectional area distribution and superior strength-to-weight ratios. They derive their name from their cross-section resembling the English letter "H."

Since all parts of an H-beam are arranged at right angles, it offers excellent bending resistance in all directions, simple construction, cost efficiency, and lightweight structure, making it widely used.

H-beams are now extensively applied in modern steel structure buildings and differ significantly from I-beams. First, their flanges are wider; second, the inner surfaces of the flanges are not sloped, and the top and bottom surfaces remain parallel.

The cross-sectional performance of H-beams is clearly superior to that of traditional I-beams, channel sections, and angle irons.

The inner edges of the two outer flanges of H-beams are straight and flat, which simplifies welding and splicing compared to I-beams, improves mechanical properties per unit weight, and saves substantial material and construction time.

I-beams perform well under direct compression and tension but suffer from poor torsional resistance due to their narrow flanges. In contrast, H-beams excel in torsion resistance, each having its own advantages and disadvantages.

Differences and Applications Between H-Beams and I-Beams

1. Both standard and light I-beams have relatively tall and narrow cross-sections, resulting in large differences in moment of inertia along the two principal axes. Therefore, they are generally suitable only for members subjected to bending within the plane of the web or for forming lattice-type load-bearing components. They are unsuitable for axially loaded columns or members experiencing bending perpendicular to the web plane, severely restricting their application scope.

2. H-beams are high-efficiency, economical sections (other examples include cold-formed thin-walled sections and profiled steel sheets). Due to their rational cross-sectional shape, they allow steel to achieve higher performance and greater load-carrying capacity. Unlike standard I-beams, H-beams have widened flanges, with both inner and outer surfaces typically parallel, facilitating connections using high-strength bolts and other structural elements. Their dimensions form a rational series with complete model ranges, making them convenient for design and selection (except for crane beams, where I-beams are still preferred).

3. H-beams have uniform flange thickness and can be either rolled sections or composite sections made by welding three plates together. I-beams are exclusively rolled sections, and due to manufacturing limitations, their inner flange edges have a slight 1:10 slope. Rolling H-beams differs from conventional I-beam rolling, which uses only a set of horizontal rolls. Because H-beams have wider flanges and minimal or no slope, additional vertical rolls are required during rolling. As a result, the rolling process and equipment are more complex than those for ordinary rolling mills. The maximum rollable height of H-beams currently achievable domestically is 800 mm; beyond this size, welded composite sections must be used.

4. I-beams have small flange widths and large heights, enabling them to resist forces in only one direction.

5. H-shaped steel has deep flanges and greater thickness, enabling it to withstand forces in two directions.

6. With the development of steel structure buildings, I-beams alone are insufficient; even thickened I-beams used as load-bearing columns are prone to instability.

7. I-beams can only be used for beams, whereas H-shaped steel is suitable for structural load-bearing columns.

8. H-shaped steel is an economical section with superior mechanical properties compared to I-beams, named for its cross-sectional shape resembling the English letter "H." Hot-rolled H-sections have wider flanges than I-beams, offering greater lateral stiffness and bending resistance. For the same specifications, H-shaped steel is lighter in weight than I-beams.

9. The flanges of I-beams have a variable cross-section—thicker near the web and thinner at the outer edges—while those of H-shaped steel have a uniform cross-section.

10. HW, HM, and HN are general terms for H-shaped steel; H-type steel refers to welded sections, while HW, HM, and HN are hot-rolled.

11. HW indicates that the height and flange width of the H-shaped steel are approximately equal; it is primarily used as a steel core column (also known as a composite steel column) in reinforced concrete frame structures, and mainly serves as columns in steel structures.

12. HM has a height-to-flange width ratio of approximately 1.33 to 1.75; it is mainly used as steel frame columns in steel structures and as frame beams in dynamic load-bearing frames, such as equipment platforms.

13. HN has a height-to-flange width ratio of 2 or greater and is primarily used for beams; its application is similar to that of I-beams.