IPE 300 and HEB 300 share the same section depth. Their mass per meter differs by a factor of 2.8: 42.2 kg against 117 kg. Much of that difference comes from the HEB’s wider and substantially thicker flanges, together with its thicker web. This article covers what separates the I and H families numerically, and how that choice plays out in bridge girders, industrial portal frames, platform deck framing, and crane runways.
What Separates the Families in the Standards
EN 10365 draws the formal line. It fixes nominal geometry and mass for hot-rolled sections, putting IPE in the narrow-flange family and HEA, HEB, and HEM in the wide-flange one. Tolerances sit in a separate standard, EN 10034. The American nomenclature splits the same way, between S-shapes and W-shapes under ASTM A6.
At the same 300 mm depth, the IPE 300 flange measures 150 mm wide and the HEB 300 flange measures 300 mm. Strong-axis moment of inertia rises from 8,356 to 25,160 cm⁴, and the weak-axis value from 603.8 to 8,562 cm⁴.
The Iy/Iz ratio is the numerical signature of each family: 13.8 for IPE 300 against 2.94 for HEB 300.
The extra mass in the H-profile buys little bending strength. Plastic section modulus about the strong axis triples while mass grows by a factor of 2.8, so in pure strong-axis bending the two profiles are equally efficient per kilogram of steel. The payoff sits elsewhere: weak-axis moment of inertia is 14 times higher, and the torsion constant goes from 20.1 to 189.1 cm⁴.
Why the Geometry Changes the Design Check
Euler’s formula sits behind the family choice. Critical load Ncr = π²EI/(KL)² takes the moment of inertia about whichever axis the member is not braced against, so for equal unbraced length the smaller radius of gyration governs. For IPE 300, that value is 33.5 mm, against 75 mm for HEB 300.
The effective length factor K depends on whether the frame allows its joints to sway. Holding end restraint constant, moving from a non-sway case (K = 0.7) to a sway case (K = 2.0) changes the buckling load by a factor of eight. Misclassifying the frame cancels out any careful section selection.
A narrow flange adds a third mechanism. Open thin-walled sections with narrow flanges are the shapes most susceptible to lateral-torsional buckling, and on flexural members the I beam vs H beam choice often turns on that check. A beam that clears its cross-section bending resistance can still fail on stability when the compression flange runs unrestrained.
Bridges: Where Rolled Sections Run Out
Rolled beams stay economical in bridge spans up to roughly 36 meters. Past that, fabricated plate girders take over, covering 30 to 120 meters in normal design practice.
The limit is physical. The deepest rolled section in the British range, UB 1016×305×584, stands 1,056 mm deep, and rolling cannot deliver more web depth than that.
Span is not the only criterion. A plate girder can be required at 12 meters if the design load reaches 340 kN/m. A fabricated section gets its proportions set from scratch, with flange width around twenty times flange thickness so the flange does not drop into Class 4 under Eurocode 3. The set of checks does not change: EN 1993-2 refers lateral-torsional buckling curves back to EN 1993-1-1 and layers fatigue and durability requirements on top. AASHTO LRFD covers the same ground in American practice.
Industrial Frames: The Member’s Role Decides Nothing
Portal frames give the clearest counterexample to the rule that a column means an H-section. In the UK, half of all constructional steel goes into portal frame construction.
Columns and rafters in these frames are usually specified from the UB range, the I-section family, rather than from the UC column range. The eaves connection is rigid, lateral load is carried by the bending stiffness of the members themselves, and there is no separate bracing system. The column works mainly in in-plane bending, and an I-section, with more section modulus per unit mass, beats a wide-flange section at that job.
The H-for-columns rule holds in braced multi-story frames, where the column carries mostly axial compression. In a moment-resisting frame, bending dominates instead. Section family follows the governing action, not the label attached to the member.
Platforms: Corrosion Allowance Enters the Selection
Offshore, wide-flange sections sit alongside tubulars, and API RP 2A names them explicitly among the structural member types it covers. Tubulars go into jacket legs and braces. Rolled I and H sections go into deck beams and grating support framing.
The difference from an onshore structure shows up when thicknesses are assigned. NORSOK M-001 calls for a 3 to 5 mm corrosion allowance on structural steel in the splash zone, with the figure depending on the coating system and the design life. Flange thickness drives both section modulus and moment of inertia, so that allowance pushes the selection up a size. The check under DNV-OS-C101 or API RP 2A has to pass on end-of-life thicknesses.
Crane Runways: Three Actions at Once
A crane runway beam carries vertical wheel loads, horizontal loads from braking and skewing, and a torsional moment from load eccentricity relative to the shear center. EN 1993-6 assigns each of these to a different part of the section. The main beam under the rail takes the vertical wheel loads. Lateral load from top-running cranes goes to the top flange or a surge girder, and torsion is resisted by a couple acting horizontally on the top and bottom flanges.
The standard states plainly that the methods in EN 1993-1-1 Section 6.3 do not cover torsional moments. An ordinary stability check, adequate for a floor beam, is incomplete here.
The industry answer looks nearly the same everywhere: a wide-flange section with a channel welded to the top flange. That mono-symmetric section is designed on the basis that the top flange takes all the lateral load while the bottom flange helps resist torsion. Without lateral restraint, the beam is checked for bending about both axes.
Then there is fatigue. Deflection limits under EN 1993-6 run from L/600 to L/1000 against L/250 for building floors, and CMAA duty classes reach two million full load cycles, so the final section size is more often set by fatigue and stiffness than by static strength.
Where Section Selection Breaks Down
The most common substitution error looks harmless. A section is swapped for another with equal or greater section modulus, and the bending resistance check still passes. But IPE 300 and HEB 300 differ by a factor of three in Wpl,y and by a factor of 14 in weak-axis moment of inertia, so a substitution that clears strength can fail deflection or out-of-plane stability. Neither of those checks runs by itself when the section comes off a table.
Another source of rework is purely geometric. A bolted connection through the flange has to respect minimum distances under EN 1993-1-8: end distance and edge distance no less than 1.2d₀, pitch perpendicular to the load no less than 2.4d₀. For M20 bolts, a two-row group occupies roughly 106 mm of usable flange width, and on the 150 mm flange of an IPE 300, once web and root radii are deducted, almost nothing is left. A section that passes bending frequently gives way to a wider one during connection design.
Section selection on a real project is not a comparison of two catalog rows. A single member goes through checks for bending resistance, lateral-torsional buckling, weak-axis stability, deflection, fatigue, and connection geometry, and each repeats across every design load combination. A bridge span or a deck module runs to thousands of members. At that scale, automated verification across the whole model becomes increasingly valuable for applying Eurocode 3, AISC 360, and other standards consistently and tracing governing results.
