WT 12X65.5 vs ST 12X53
WT 12X65.5 is an WT section from the American AISC Shapes Database; ST 12X53 is the closest equivalent in the American AISC Shapes Database. They are close to interchangeable in bending: 719.39 cm³ against 709.56 cm³ of plastic modulus, a difference of 1.4%. ST 12X53 is the lighter of the two at 78.9 kg/m against 97.5 kg/m, a saving of 23.6% on steel weight. Both are about 311 mm deep, so either fits the same construction zone.
| Property | WT 12X65.5 WT | ST 12X53 ST | Difference |
|---|---|---|---|
| Mass | 97.5 kg/m | 78.9 kg/m | +23.6% |
| Depth | 309.9 mm | 312.4 mm | -0.8% |
| Width | 327.7 mm | 199.9 mm | +63.9% |
| Web thickness | 15.4 mm | 15.7 mm | -1.9% |
| Flange thickness | 24.4 mm | 27.7 mm | -11.9% |
| Area | 124.5 cm² | 100.6 cm² | +23.8% |
| Second moment, major (Iy) | 9,906 cm⁴ | 8,991 cm⁴ | +10.2% |
| Plastic modulus, major (Wpl,y) | 719.39 cm³ | 709.56 cm³ | +1.4% |
| Elastic modulus, major (Wel,y) | 406.4 cm³ | 394.93 cm³ | +2.9% |
| Second moment, minor (Iz) | 7,076 cm⁴ | 1,598 cm⁴ | +342.8% |
| Plastic modulus, minor (Wpl,z) | 666.95 cm³ | 273.66 cm³ | +143.7% |
| Radius of gyration, minor (iz) | 7.54 cm | 3.99 cm | +89.0% |
| Torsion constant (It) | 197.3 cm⁴ | 210.2 cm⁴ | -6.1% |
WT 12X65.5 to AISC Shapes Database v16.0; ST 12X53 to AISC Shapes Database v16.0. Difference is expressed relative to ST 12X53.
How to choose between them
On stiffness, WT 12X65.5 has the larger second moment of area: 9,906 cm⁴ against 8,991 cm⁴, a difference of 10.2%. This matters more often than the strength comparison, because on normal floor spans deflection rather than bending capacity sets the beam size - so if the two are close on modulus but apart on inertia, the stiffer one is usually the better answer even when it is not the stronger one.
Measured as bending capacity per kilogram of steel, ST 12X53 is the more efficient section: 9.0 against 7.4 cm³ per kg/m, 18.0% better. Over a floor of repeated beams that difference is real tonnage, though it is often outweighed by whichever section the fabricator can actually source.
The two diverge much more about the minor axis: WT 12X65.5 has 666.95 cm³ of minor-axis plastic modulus against 273.66 cm³, 143.7% more. If the member sees any minor-axis bending, or if it is unrestrained over a long length and lateral-torsional buckling governs, that gap decides the comparison even though the major-axis numbers looked equivalent.
In short, WT 12X65.5 is the stronger section and ST 12X53 is the lighter one; where those are the same section, it is the clear choice, and where they are not, decide on whether your design is governed by capacity or by tonnage.