1. I-Beam versus H-Beam Shapes
The I-beam has tapered inner flange faces and a narrow flange relative to its height, which makes it efficient for bending about the major axis but weak in torsion and weak-axis bending. The H-beam has parallel flange faces and a flange width close to the section height, giving higher stiffness about both axes. For this reason H-beams have largely replaced I-beams in modern framing, while I-beams remain common in crane rails, shafts and older structures.
2. Grade Coverage: SS400, S235JR and S355JR
SS400 is the JIS G3101 general structural grade with 400 to 510 MPa tensile strength, S235JR is the EN 10025-2 grade with 235 MPa yield, and S355JR provides 355 MPa yield with guaranteed impact energy. The three grades cover the full range of ordinary building and industrial structures. Sections in SS400 and S235JR are used for general framing, while S355JR is chosen where higher strength reduces the member size.
3. Standard Size Ranges
I-beams are commonly rolled in sizes from 100x50 up to 630x180 in the Chinese GB/T 706 series and the equivalent JIS and EN families. H-beams range from 100x100 up to 900x300 in the GB/T 11263, JIS G3192 and EN 10365 series. Each size has a fixed set of section properties, and the availability of a particular size depends on the mill rolling program and the stocking policy of the supplier.
4. How to Select the Section Size
The required section modulus follows from the maximum bending moment and the allowable stress of the grade. The engineer then chooses the smallest section whose modulus is sufficient, checks the deflection under service loads, and verifies shear, web bearing and local stability. For columns, the check becomes buckling about the weak axis, which favors wide-flange H sections. Standard design tables list the section modulus, radius of gyration and moment of inertia for every size.
5. Ordering and Delivery
When ordering, the specification should state the section designation, grade, length, quantity and any processing such as drilling or cutting. Beams are delivered in bundles with marks showing the size and grade, together with mill certificates for the material. Stocked sizes are dispatched quickly, while non-standard sections are scheduled against the mill rolling program.
Frequently Asked Questions
Q: What is the difference between an I-beam and an H-beam?
The I-beam has tapered flanges and a narrow flange width, while the H-beam has parallel flanges and a flange width close to its height, giving better stiffness about both axes.
Q: What sizes are I-beams available in?
I-beams are commonly rolled from 100x50 up to 630x180 in the GB/T 706 series and equivalent international families.
Q: Which grade should I choose for a general building frame?
SS400 or S235JR is adequate for most general frames, while S355JR is used when higher strength is needed to reduce member sizes or increase spans.
Q: Are H-beams stronger than I-beams of the same height?
For bending about the major axis the difference is small, but the H-beam is much stiffer about the weak axis and in torsion, which matters for columns and laterally unsupported beams.
Q: Can beams be cut to length?
Yes, beams are cut to the required length at the mill or in the stocking yard, and drilling and other processing can be arranged.
Q: How is the correct beam size determined?
The size is determined by calculating the required section modulus from the bending moment and allowable stress, then checking deflection, shear and stability.