7/30/2019 30743_HSS_specs

1/2

By Tabitha S. Stine, P.E.

Specifying HSS

While Hollow StructuralSections (HSS) are in-creasingly popular, manydesigners still have ques-tions about these sections,

especially about the various grades ofmaterial available.

Designating HSSHSS is the correct designation forstructural tubing, rather than TS (tubeshape). In 1990, the industry adopted theterm HSS to keep in step with producersaround the world. In 1997, the Steel TubeInstitute and AISC officially implement-ed this change with the publication of theSpecification for the Design of Steel HollowStructural Sections and the correspondingAISC/STI/AISIHSS Connections Manual.

HSS are available in round, square, orrectangular shapes. Round shapes arespecified using decimal numbers andthree decimal points. For example, HSS5.563 0.258 indicates a round HSS withan outside diameter of 5.563 and a wallthickness of 0.258. Rectangular andsquare shapes are similarly specified butin terms of rational numbers. For exam-ple, HSS 5 4 3/8 indicates a rectangu-lar HSS with a depth of 5, a width of 4,and a wall thickness of 3/8.

Design Wall ThicknessIts important to note that the nominal

wall thickness is not the design thickness

for designing with HSS. As originallynoted in the 1997 HSS Specification (andnow incorporated into AISCs 2005 Speci-fication), the design wall thickness shouldbe taken as 0.93 times the nominal wallthickness. This 7% reduction in strengthis due to the allowance given by ASTMA500, which allows for a minus 10% tol-erance on wall thickness. Since HSS pro-ducers can procure flat-rolled steel at ornear this tolerance, the resulting manu-factured sections fall close to this lowerbound tolerance on wall thickness. AISC

incorporated this practice by reducing

July 2005 Modern Steel Construction

Knowing the basics about HSS specifications will help you

avoid mistakes and misunderstandings on your next HSS project.

HSS Tips and TricksKeep the following tips in mind when specifying HSS to minimize unnecessary

costs.

Specifying common sizes that are readily available over a custom size that

may seem more efficient in terms of tonnage can achieve significant cost

savings.

When considering round HSS, it may be more practical to specify A53 Grade

B pipe. Depending on the location, this pipe section may be more readily

available.

Architecturally Exposed Structural Steel (AESS) is a common application for

HSS. Projects should reference the AESS provisions the AISC Code of Stan-

dard Practicewhen true AESS is required. Refer to the supplement Archi-

tecturally Exposed Structural Steel in the May 2003 issue of Modern Steel

Construction(www.modernsteel.com) for a visual comparison of standard

HSS fabrication results versus AESS steel.

Eliminate extraneous notes that require unnecessary and costly practices.

The note All welds shall be ground flush is a good example of this. The ap-

pearance of grinding the weld gives a smooth surface. However, there are

many times when HSS connections are not at a location easily seen by the

public. Also, grinding weldsespecially fillet weldssometimes will not sig-

nificantly improve appearances but will significantly increase the cost of the

connection. Often it is best to simply follow the HSS provisions, which require

reasonably smooth and uniform welds, when possible.

the design wall thickness to 0.93 of thenominal thickness for all design tablesin the HSS Connections Manual and theLRFD Manual of Steel Construction, thirdedition.

Producing HSSHSS is currently produced to four

ASTM specifications (as noted in the 2005AISC Specification), which also have ac-companying qualifiers: grades, line itemspecifications, and requests. The mostcommon AISC specifications are ASTMA500, ASTM A501, ASTM A618, andASTM A847.

ASTM A500 and ASTM A847ASTM A500 and ASTM A847 are

produced by the Electric ResistanceWelding (ERW) process and the Form-Square Weld-Square process (a type of

ERW process). Electric Resistance Weld-ing is a cold-formed process by whicha flat steel strip is formed continuouslyaround its longitudinal axis to produce around tube by moving the strip througha progressive set of rolls. The strip edgesare then heated by either high frequencyinduction or contact welding and then

forged together by weld rolls to createa continuous longitudinal weld withoutthe addition of filler metal.

The Form-Square Weld-Square Pro-cess is used in some HSS productionshops. In the weld mill, driven formingdies progressively shape the flat stripof steel by forming the top two cornersof the square or rectangular tube at theinitial forming station. Subsequent sta-tions form the bottom two corners of theshape. No cold working of the sides ofthe shape is performed, and the shapes

7/30/2019 30743_HSS_specs

2/2

seam is welded by high-frequency con-tacts when the tube is near its final shapeand size.

The Submerged Arc Welding (SAW)Process is also used to produce HSS, butis not supported by an ASTM designa-tion. This process can be used to producesizes larger than 64 in periphery. Thehot-formed process, as designated byASTM A501 and A618, is generally notproduced in square and rectangular sizesin the United States, but round sectionsare typically available in mill quantities.

ASTM A500 is the standard designa-tion for common structural applicationsof HSS. A500 is available in round, square,and rectangular sections and is common-ly specified in grades B or C. Grade B ismore commonly specified in square andrectangular shapes. Dual certification ofboth grades B and C can be requested toensure more readily available supplies

from the service centers. ASTM A500 alsodescribes a grade D, which is commonlyreferred to as stress relieved or heattreated steel, and can be done at variousHSS producer facilities. Grade D is notreadily available off the shelf.

Flash removal is another request

that can be made as a line item to the re-quired grade. Flash is the upset portionon the inside of the HSS that remains onthe back face of the weld. This processcan be costly and is generally specifiedfor mechanical uses such as telescopingapplications rather than structural build-ing applications.

Hollow structural sections are readilyavailable in a large number of sizes, interms of outside diameter, width, depth,and wall thickness. ASTM A500 limitsthe size of the section to a perimeter of64 and a wall thickness of 5/8. TheAISC Manual of Steel Construction, thirdedition, lists all common available sizesthat can be ordered based on this limita-tion. It should be noted that special wallthickness requirements up to the A500thickness limitation can be ordered, butminimum mill quantities may be re-quired for order. Custom orders can be

more costly and are only available fromcertain producers. For a complete list ofproducers of custom sizes, consult theSteel Tube Institute of North America atwww.steeltubeinstitue.org.

HSS are also available in atmosphericcorrosion resistant steel, more com-

monly referred to as weathering steel.Produced from hot-formed ASTM A588steel coil, this shape is available in round,square, or rectangular sizes. The mechan-ical properties of the material are higherthan that of ASTM A500. This product isnot as readily available in all sizes andat all locations in comparison to A500.Check for availability before specifyingthis product.

ASTM A501 and ASTM A618ASTM A618 (lower-alloy/higher-

strength HSS) and A501 are hot-formedproduct specifications that cover square,rectangular, and round HSS. Althoughsquare and rectangular products are notavailable domestically, round sectionsare available in mill quantities. Alwayscheck the availability of these two gradesbefore specifying them.

Tabitha S. Stine is an advisor for AISCsSteel Solutions Center. She can be reachedat stine@aisc.org. More information andanswers to frequently asked questions about

HSS can be found at www.aisc.org or bycontacting the Steel Solutions Center atsolutions@aisc.org or 866.ASK.AISC.

July 2005 Modern Steel Construction