Steel Columns

Important Note – These are descriptions to changes implemented in version 10 and may not reflect current program behaviour.

The program now includes square, rectangular and round Hollow Structural Section (HSS). steel columns from the CISC Handbook of Steel Construction Manual, 11^th Edition, 2^nd Printing May 20, 2016, using the CSA S16-14 design standard.

Program Mode
The implementation is limited to Column Mode and is not included in Concept mode
Assumptions
Steel columns may be loaded in either axial compression or tension, or combined with bending about one or axis.

Steel columns are pin-ended; thus, their bending stiffness does not contribute to the lateral resistance of the structure. i.e., we assume the frame is braced against sway. This allows us to make some simplifying assumptions such as effective length factor K ≤ 1.0, no second-order drift effects, and absence of torsion.
Steel Strengths and Modulus of Elasticity
The following yield strength F_y, and modulus of elasticity values are used
- G40.21 Class C and G40.21 Class H (Fy = 350 MPa)
- ASTM A500 Grade C (F_y = 345 MPa for square and rectangular shapes; F_y = 317 MPa for round shapes)
- ASTM A1085 (F_y = 345 MPa)
- E = 200,000 MPa
Database
A steel column database file is included based on steel sections from the CISC handbook, pages 6-97 to 6-107 for all steel strengths except ASTM A500 which uses pages 6-108 to 6-117.

Imperial values for the steel column dimensions are found on pages 6-31 to 6-33

The moment capacity M_r (including M_rx and M_ry for rectangular HSS) are found on pages 4-32 to 4-100.
1. Size Limits
  The following size limits are adopted
  
  Square maximum dxb = 305x305, minimum dxb = 76x76 mm
  
  Rectangular maximum dxb = 305x203, minimum dxb = 76x51 mm
  
  Round maximum diameter = 273, minimum diameter = 76 mm
2. Dimensions
  In Sizer, square and rectangular sections are represented as d x b x t using the nominal database values. Round HSS are displayed as D x t where D is the nominal diameter. t is the wall thickness.
3. Grades
  The database is organized into the following four grades: G40.21 Class C, G40.21 Class H, ASTM 500 Grade C, ASTM A1085.
4. Omitted ASTM 500 Grade C Sections
  For ASTM 500 Grade C, a section appearing on pages 6-108 to 6-117 in the steel handbook may be absent on pages 4-80 to 4-92. Since CISC has decided to omit some sections from their resistance tables we decided to do the same. This is only true for the following square and rectangular sections, respectively,
305x305x6.4 254x254x4.8 203x203x4.8 178x178x4.8 127x127x3.2

305x203x6.4 305x152x6.4 254x152x4.8 203x152x4.8 203x102x4.8 152x102x3.2 152x76x3.2 127x76x3.2
User interface
1. Material
  Steel is added as a column material
2. Strength
  The Species field is retasked as Strength and populated with grades from the database. Unknown is not an option.
3. Shape
  The Grade field is retasked as Shape and includes Square, Rectangular, and Round. Unknown is not an option
4. Depth
  The Width field is renamed Depth and used to store HSS depths. For round sections, it is called Diameter. It includes an unknown field.
5. Width
  The Depth field is renamed Width and used to store HSS widths. It includes an unknown field.
6. Thickness
  The Spacing field is renamed Thickness and used to store wall thicknesses. It includes an unknown field.
7. Disabled Inputs
  The following inputs are disabled: Modification factors data group, Built-up members, Ke for lateral support, Fixed and Free end conditions.
Design
1. Design Criteria
  Design values are compressive resistance C_r, tensile resistance T_{r ,} shear resistance V_r, moment resistance M_r.These are compared to the factored forces C_f, T_f, V_f, and M_f.
2. Design Procedures
  The following S-16 design code clauses are implemented
  - 10.4.2 - Maximum slenderness ratio
  - 11.1 - Axial and Flexural Classification
  - 11.3 – Widths and thickness [used for design]
  - 13.2 - Axial Tension
  - 13.3 - Axial Compression
  - 13.4 - Shear
  - 13.5 – Bending - Laterally supported members
  - 13.6 - Bending – Laterally unsupported members
  - 13.8 - Axial compression and bending
  - 13.9 - Axial tension and bending
3. Special Assumptions
  The following assumptions about specific provisions are implemented:
  - 13.2 Axial Tension: it is assumed that the steel column is welded to its bearing plate, thus there is no need to calculate a net area based on the presence of bolt holes.
  - 13.3 - Axial Compression: There are no round HSS sections from the database that will buckle locally so 13.3.1 can be used
  - 13.3.5 - Compression members subjected to elastic local buckling: We reviewed the C_r values produced by 13.3.5 and found that for HSS sections the C_r values from 13.3.5(a) are always within 1% of the values in the CISC Steel Manual. The values calculated by 13.3.5(b), however, produce values that can differ from -30% to 7% from those in the CISC Steel Manual. Thus, we will ignore clause 13.3.5(b) and just use 13.3.5(a).
  - 13.6 - Bending – Laterally unsupported members - As an upper limit, 13.6(b)(i) says to use 0.90* _My for class 3 and to use clause 13.5(c)(iii) for sections with a flexural class 4 flange. However, when loaded on the b face, there are no rectangular HSS sections with a class 4 flange hence, 0.90*My will be used as the upper limit.
Output
1. Analysis vs. Design
  The design criteria listed above are shown in the Analysis vs. Design table, along with the design ratios for a passing design, i.e. C_f/C_r ≤ 1, T_f/T_r ≤ 1, V_f/V_r ≤ 1 and M_f/M_r ≤ 1.
  
  For the Combined criterion, the program shows the equations for all 3 relevant code clauses, 13.8.3(a), (b), (c)) but only when a combined C_fand M_f load combination governs
2. Additional Data
  In the Calculations section, the program shows the following:
  
  The axial classification if an axial compressive load (C_f) is present.
  
  The flexural classification if bending (M_f) is present.
  
  A table showing the values U₁, ω₁, C_r, and M_rfor the governing load combination and for each each equation in 13.8.3(a), (b) and (c).