W10 Beam Series: What the Designation Means
W10x60, W10x68 and W10x77 belong to the wide flange W shape family defined in ASTM A6, the general requirements standard for rolled structural steel shapes. In this family the web and the flanges are essentially parallel, which makes the sections efficient in bending and simple to connect with bolted plates or welded details. The designation gives the nominal depth in inches followed by the nominal mass in pounds per foot, so W10x60 is a section of about 10 inches nominal depth weighing 60 pounds per foot, equal to approximately 89.3 kg per metre.
The three sections share a similar nominal depth of roughly 260 mm to 270 mm, and they differ mainly in flange thickness and web thickness. That is why their structural properties diverge sharply even though the outside profile looks almost the same on a drawing.
Section Properties and How They Govern Design
| Section | Nominal mass (kg/m) | Moment of inertia Ix (in4) | Section modulus Sx (in3) |
|---|---|---|---|
| W10x60 | about 89.3 | about 341 | about 66.7 |
| W10x68 | about 101.2 | about 394 | about 75.7 |
| W10x77 | about 114.6 | about 455 | about 85.9 |
The two properties answer two different questions. The moment of inertia Ix measures bending stiffness and therefore deflection: a beam must have enough Ix for the sag under service load to stay inside the permissible limit. The section modulus Sx measures bending strength: the maximum bending moment in the span divided by Sx gives the bending stress, which must remain below the design stress of the steel.
Compared with W10x60, the W10x77 gives roughly 33 % more bending stiffness and about 29 % more bending strength for roughly 28 % more mass per metre. Where deflection rather than stress controls the design, which is common on long spans with moderate loads, the deeper and heavier section is often the only way to satisfy the serviceability check without adding a second beam.
Structural Grades and Their Mechanical Properties
| Grade | Standard | Minimum yield strength (MPa) | Tensile strength (MPa) |
|---|---|---|---|
| A36 | ASTM A36 | 250 | 400 to 550 |
| A572 Grade 50 | ASTM A572 | 345 | 450 min |
| A992 | ASTM A992 | 345 to 450 | 450 min |
A992 is the shape specific grade written for building frames. It fixes both a minimum and a maximum yield strength, a maximum yield to tensile ratio and a maximum carbon equivalent, so that the overstrength and ductility assumed by seismic design rules and the weldability assumed by connection design both stay within a known band. Where a project follows United States practice for buildings, A992 is normally the default grade, while A572 Grade 50 remains common for industrial, crane and bridge work and A36 is used for lightly loaded secondary steel.
Selecting Between W10x60, W10x68 and W10x77
| Section | Typical role |
|---|---|
| W10x60 | medium spans and moderate loads: floor beams in low and medium rise buildings, platform framing, bracing members |
| W10x68 | industrial structures with higher load concentration: equipment support frames, crane runways of light duty, transfer beams |
| W10x77 | heavy load and long span duties: main bridge girders, primary building beams, heavily loaded transfer and column members |
Selection should start from the load combination that governs, then check bending stress, shear, deflection, and where relevant the web shear buckling and lateral torsional buckling resistance. The section that satisfies all four checks with the lowest mass per metre is the economical choice, which is why the three sections exist so close together in depth.
Supply, Tolerances and Fabrication
W sections are ordered by designation, grade and length, with lengths normally in the 6 m to 12 m range and cut to length service for fabrication. Dimensions, mass, camber and straightness tolerances follow ASTM A6. The sections can be sawn, drilled, coped and welded without special procedures for A36 and A572 Grade 50; A992 requires welding procedures qualified to AWS D1.1 as usual for structural work. Where the structure is exposed, hot dip galvanising or a protective coating system is applied after fabrication, and bolted connections are normally made with high strength structural bolts to the current ASTM F3125 specification.
Frequently Asked Questions
Q: What does the designation W10x60 mean?
A: It is a wide flange beam of about 10 inches nominal depth weighing 60 pounds per foot, which is approximately 89.3 kg per metre, as defined in the ASTM A6 shape range.
Q: Which of the three sections is the strongest in bending?
A: W10x77, with a section modulus of about 85.9 in3 and a moment of inertia of about 455 in4, followed by W10x68 at about 75.7 in3 and W10x60 at about 66.7 in3.
Q: What is the difference between moment of inertia and section modulus?
A: Moment of inertia controls deflection and bending stiffness, while section modulus controls bending stress for a given moment. Both are needed for a complete beam check.
Q: Which grades are available for these W sections?
A: The common structural grades are ASTM A36, ASTM A572 Grade 50 and ASTM A992, and the section can also be produced in weathering steel for exposed service.
Q: Can W10 beams be used as columns?
A: Yes, provided the compressive resistance and buckling length are checked; W10 sections are regularly used as columns and as bracing members in building frames.
Q: What standards cover the tolerances?
A: ASTM A6 covers dimensions, mass, straightness and camber tolerances for rolled W shapes, and ASTM A992 or A572 covers the mechanical properties of the steel.