One of the many hidden gems within the CISC’s Handbook of Steel Construction is the Unit Factored Compressive Resistances, Cr/A tables in Part 4. These tables provide a quick and easy method of calculating the compressive resistances of compression members, such as columns or struts.
Essentially, the tables list the unit factored compressive resistance, Cr/A (in MPa), calculated in accordance with Clause 13.3.1 of the CSA S16-14. In the 11th edition of the Handbook, Table 4-3 contains Cr/A values for members with varying yield strength (range of Fy from 250 to 700 MPa) and varying slenderness (range of KL/r from 1 to 200) for n=1.34. These resistances apply to hot-rolled, fabricated structural sections and hollow structural sections manufactured in accordance with CSA G40.21, Class C (cold-formed non-stress-relieved), ASTM A500, or ASTM A1085.
Alternatively, Table 4-4 contains Cr/A values for doubly symmetric welded three-plate members with flange edges oxy-flame-cut and hollow structural sections manufactured in accordance with CSA G40.21, Class H (hot-formed or cold-formed stress-relieved), where n=2.24. Although Table 4-4 contains Cr/A values for members with varying slenderness (range of KL/r from 1 to 200), resistances have only been provided for Fy = 350 MPa. Table 4-4 may also be used for HSS manufactured in accordance with ASTM A1085 with Supplement S1; however, an adjustment would be required to account for the small difference in yield strength (Fy =345 MPa versus 350 MPa).
The following example illustrates the simplicity in obtaining the factored compressive resistance, Cr, for an HSS column using Table 4-3. For class 1, 2 or 3 sections, simply multiply the unit factored compressive resistance, Cr/A, for the appropriate Fy and KL/r ratio, by the cross-sectional area, A, of the section. (For class 4 sections, see Clause 13.3.5.)
HSS 203x203x6.4 class C column of CSA G40.21 Grade 350W (Fy =350 MPa)
KL = 4 800 mm
r = 79.9 mm
A = 4 900 mm2 (see tables of properties and dimensions in Part 6)
KL/r = 4 800 mm / 79.9 mm = 60
Since n = 1.34, use Table 4-3, with KL/r = 60 and Fy =350 MPa, Cr/A = 227 MPa
Therefore, Cr = 227 MPa x 4 900 mm2 = 1 112 kN
