The ASTM A501 standard (ASTM, 2007b) for hot-formed tubing is included in the AISC Specification even though these products have not been produced in North America for several decades. However, ASTM A501 has recently been revised to add Grade B, which is a hot-finished product with the mechanical properties shown in Table 1-1. The manufacturing process is similar to cold-formed HSS, but the final shaping and sizing are completed after the steel has been heated to a full normalizing temperature. These products are made by European manufacturers in round, square, rectangular and elliptical shapes (Packer, 2008). Such sections are essentially produced to the European standard EN10210 Parts 1 and 2 (CEN, 2006a, 2006b), and the elliptical hollow sections have a major-to-minor axis dimension ratio on the order of 2:1. Sections up to 16-in. square and 0.625-in. thick are produced with ERW seams and are available in several sizes. There is also a product line of jumbo HSS in sizes up to 32-in. square and thicknesses up to 2.36 in. For thicknesses up to 1 in., the sections are manufactured with ERW seams. For greater thicknesses, submerged arc welding (SAW) is used for the seams. SAW box sections can be produced from plate material (such as ASTM A572 Grade 50 as used in Example 3.3), but they generally are of a size that exceeds the 64-in. periphery limitation in ASTM A500. As such, these cross sections do not necessarily meet the requirements in ASTM A500. The specifier should contact the producer(s) of such cross sections to determine the cross sections that are made, as well as their cross-sectional properties and applicable production requirements. This information is also available in the EN10210 standard (CEN, 2006a, 2006b). 1.2
HSS CONNECTION DESIGN STANDARDS AND SCOPE
The 2005 AISC Specification supersedes all previous AISC Specifications, including the 1999 Load and Resistance Design Specification for Structural Steel Buildings (AISC, 1999), the 1989 Specification for Structural Steel Buildings – Allowable Stress Design and Plastic Design (AISC, 1989) including Supplement No. 1, and the 2000 Load and Resistance Factor Design Specification for Steel Hollow Structural Sections (AISC, 2000). Direct HSS-to-HSS welded connecUJPOT BSF OPX DPWFSFE JO $IBQUFS , PG UIF "*4$ Specification. 'SBNJOH DPOOFDUJPOT VTF UIF DSJUFSJB JO $IBQUFS , for concentrated loads and applicable portions of Chapter J for welding, bolting and connecting elements. Some aspects of HSS connection design, such as prying action, do not appear directly in the AISC Specification, but use guidelines from the AISC Manual or published research.
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ADVANTAGES OF HSS
HSS are very efficient sections for torsion and compression loading. For compressive loading, this is due to the favorable weak-axis radius of gyration, which often controls the available compressive strength. It is not possible to make direct cost comparisons with other shapes because prices vary with time, application and geographic location. However, Table 1-2 compares two of the key factors that influence cost: weight and surface area that may require some type of preparation. The comparisons are between ASTM A992 wide-flange shapes, ASTM A500 Grade B round HSS, and ASTM A500 Grade B square HSS. Sections are selected for a particular length and load using AISC Manual Tables 4-1, 4-4 and 4-5. The load and resistance factor design (LRFD) load is 1.5 times the allowable strength design (ASD) load, and because this is the calibration load ratio in the AISC Specification, the same sections are determined in LRFD and ASD. The selected sections have comparable depths and available strengths. Data is provided for two cases: a compression member with moderate length (KL 16 ft) and load, and a longer compression member (KL 32 ft) with a higher load. The wide-flange section is used as the basis for comparison and is assigned 100% for weight and surface area. It is apparent from Table 1-2 that these example HSS are 10 to 20% lighter than the corresponding wide-flange members, and have one-third to one-half less surface area. The latter is particularly influential for decreasing painting costs. Moreover, one should also bear in mind that this section comparison is performed using ASTM A500 Grade B material, which is readily available. If ASTM A500 Grade C material (with higher yield strength) were used, the advantage is even greater.
AISC DESIGN GUIDE 24 / HOLLOW STRUCTURAL SECTION CONNECTIONS / 3