What is the difference between NPB and WPB sections?

NPB (Narrow Parallel Flange Beams) have a smaller flange width to depth ratio, optimized for use as beams. WPB (Wide Parallel Flange Beams) have a larger flange width to depth ratio, making them stockier and more suitable for columns or members under combined axial load and bending.

What material grade should be used for these sections?

The material must conform to IS 2062 'Hot Rolled Products in Structural Steels'. The specific grade (e.g., E250, E350) should be specified by the designer (Clause 5).

How are these sections designated?

They are designated by the series abbreviation followed by the nominal depth in mm. For example, 'NPB 300' is a Narrow Parallel Flange Beam with a 300 mm depth (Clause 3).

Are these sections better than traditional ISMB sections from IS 808?

They offer better structural efficiency (higher strength-to-weight ratio), especially the wide flange sections for columns, and allow for much simpler and more reliable connection detailing.

IS 12778

: 2004

Hot Rolled Parallel Flange Steel Sections for Beams, Columns and Bearing Piles – Dimensions and Section Properties

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This standard specifies the dimensions, mass, and sectional properties for hot-rolled parallel flange steel beams (NPB, WPB) and bearing pile (PBP) sections. It serves as the primary reference for engineers and fabricators to select and use these modern, efficient structural members in construction.

Hot Rolled Parallel Flange Steel Sections for Beams, Columns and Bearing Piles – Dimensions and Section Properties

Quick Reference Values

Mass per metre tolerance± 2.5%

Straightness tolerance (sweep)0.15% of length

Depth tolerance for h <= 450 mm± 3.0 mm

Flange width tolerance for b > 220 mm± 4.0 mm

Web thickness of WPB 600-212.0 mm

Moment of Inertia (Izz) of NPB 40023377.9 cm^4

Practical Notes

Parallel flange sections (like WPB/NPB) are generally more efficient for bending and compression than tapered flange sections (like ISMB/ISHB) from IS 808.

The parallel flanges greatly simplify bolted and welded moment connections compared to tapered flanges, which often require custom-angled washers or welds.

Always verify the available steel grade (e.g., E250, E350, E410) as per the latest revision of IS 2062 before finalizing the design.