W18x97 wide flange beam: what the designation tells you
W18x97 is an American standard wide flange beam rolled to the dimensional practice of ASTM A6, supplied in this case in ASTM A992 steel. The imperial name gives the nominal depth in inches followed by the nominal mass per unit length, so the section is about 18 in deep and weighs 97 lb/ft, or roughly 144.3 kg per metre. The heaviest W18 shapes share the same nominal depth band but differ greatly in flange and web thickness, which is why the weight figure, not the 18, is the discriminator when comparing candidates.
Because W18x97 is rolled with parallel flanges in a universal mill, the web to flange junction is a continuous rolled fillet with no weld seam, and the flange faces accept bolted end plates and shear tabs without tapered washers. The relatively heavy flange compared with a light W18 gives the section useful out of plane stiffness, which is helpful both in compression and in the restrained bending that governs most crane and bridge work.
ASTM A992 material characteristics
ASTM A992 is the specification written for structural shapes in building frames. It sets a minimum yield strength of 345 MPa, an upper yield limit of 450 MPa, a minimum tensile strength of 450 MPa, a tensile to yield ratio of at least 1.05 and a maximum carbon equivalent of 0.45%. The steel is microalloyed with vanadium and niobium so that the strength is reached with low carbon rather than with hardness, which is what keeps the material weldable in the fabricator's shop and on site.
| Property | ASTM A992 requirement |
|---|---|
| Minimum yield strength | 345 MPa (50 ksi) |
| Maximum yield strength | 450 MPa (65 ksi) |
| Minimum tensile strength | 450 MPa (65 ksi) |
| Tensile to yield ratio | Not less than 1.05 |
| Minimum elongation | 18% in 200 mm gage length; typical results 18% to 21% |
| Carbon, maximum | 0.23% |
| Carbon equivalent, maximum | 0.45% |
| Microalloying elements | Vanadium and niobium |
The combination of a guaranteed minimum yield, a capped maximum yield and a controlled tensile to yield ratio produces a steel that yields predictably before it fractures. That behaviour is the reason A992 is specified for moment frames and for members that must absorb energy in an earthquake, where a sudden brittle failure would be far more damaging than controlled yielding and local buckling. The same ductility also helps members that see fatigue loading, such as crane runway beams and bridge stringers.
Nominal dimensions and section properties of W18x97
The table lists the nominal tabulated properties of the W18x97 shape. ASTM A6 permits rolling tolerances on depth, flange width and element thickness, so a delivered piece can differ slightly from nominal; the values used in design must come from the governing edition of the standard.
| Parameter | Imperial | Metric |
|---|---|---|
| Nominal depth d | 18.59 in | 472.2 mm |
| Flange width bf | 11.145 in | 283.1 mm |
| Flange thickness tf | 0.870 in | 22.1 mm |
| Web thickness tw | 0.535 in | 13.6 mm |
| Section area A | 28.5 in2 | 183.9 cm2 |
| Moment of inertia Ix | 1,750 in4 | 72,840 cm4 |
| Elastic section modulus Sx | 191 in3 | 3,130 cm3 |
| Radius of gyration rx | 7.83 in | 19.9 cm |
The section modulus of about 3,130 cm3 combines with the 345 MPa yield stress to give a yield moment of roughly 1,080 kN.m, a useful order of magnitude check before any buckling or shear reduction is applied. Lateral torsional buckling along the unbraced length, web shear at the supports and serviceability deflection usually decide the final usable capacity, and all three should be checked for the actual bracing arrangement rather than assumed from the section modulus alone.
Design, fabrication and processing notes
Cutting and drilling: the shape is readily sawn to length, and holes for end plates, shear tabs and stiffeners are normally drilled in the shop. Thermally cut edges are dressed where coatings, fatigue details or weld access holes require a smooth surface.
Welding: covered electrodes of the E70XX class and matching gas shielded solid wires suit this grade. With carbon equivalent at or below 0.45%, preheat requirements stay modest, but procedure qualification and joint preparation remain the fabricator's responsibility and are recorded before production starts.
Cold working: cutting, drilling and bending operations are straightforward, and the fabrication sequence can follow the same shop practice used for lighter W shapes because the profile geometry is similar.
Details: web stiffeners at concentrated loads, doubler plates at heavily loaded column connections and continuity plates at moment connections are added where the analysis calls for them.
Handling: heavy W18 members should be lifted with a spreader or soft slings that bear on the web rather than on a flange edge, so that the coating is not damaged and the flange is not locally bent.
Applications of W18x97 beams
Primary beams and shear wall frame columns in high rise and long span buildings, where a heavier rolled section can avoid a fabricated plate girder.
Moment frame members designed for ductile behaviour, using the controlled yield and tensile to yield ratio of A992.
Crane runway beams and heavy mill building framing subject to repeated loading.
Bridge main beams, floor beams and pier cap members exposed to vehicle and wind action.
Equipment foundations, racks and support frames in industrial facilities where vibration and impact occur.
Compared with a design based on ordinary 250 MPa carbon steel, the 345 MPa minimum yield of A992 allows a strength governed member to be roughly a quarter lighter for the same force, and often more once deflection and buckling checks are applied, because the heavier W18 shapes carry a large moment of inertia as well as a high yield stress.
FAQ about W18x97 wide flange beams
Q: Does 97 in the name mean the depth or the weight?
It is the nominal mass per unit length, about 97 lb per foot or 144.3 kg per metre. The nominal depth is about 18.6 in, or 472 mm, which is slightly more than the 18 in in the name because the name rounds to the nearest inch.
Q: Why specify A992 rather than A572 Grade 50 for this beam?
Both grades reach 345 MPa minimum yield. A992 adds an upper yield limit, a tensile to yield ratio of at least 1.05 and a carbon equivalent cap, which make the material a better choice for moment frames and other members designed to yield safely, and for structures in seismic regions.
Q: What moment can a W18x97 carry in bending?
The yield moment at 345 MPa is approximately 1,080 kN.m based on a section modulus of about 3,130 cm3. The design moment is lower once the resistance factor and lateral torsional buckling over the unbraced length are accounted for, so the governing value must be calculated for each case.
Q: Is a fabricated plate girder cheaper than a W18x97?
A rolled section usually wins on cost, inspection effort and delivery time while its section modulus suits the demand. A welded girder becomes economical when the required depth, stiffness or geometry cannot be met by a rolled shape, or when material thickness across a flange has to be varied along the span.
Q: How should the beams be protected and maintained?
Shop primer with a site topcoat is standard for internal framing, while hot dip galvanizing or a heavy duty coating system suits bridges, marine sites and external crane structures. Vent and drain holes are detailed so that galvanizing reaches internal surfaces of the connections.