Introduction
Since 1974, when the Canadian Standards Association first introduced the limit states design standard for structural steel, S16.1-1974 “Steel Structures for Buildings—Limit States Design”, the Standard has undergone a number of technical improvements, but its major requirements have remained virtually unchanged. However, with the introduction of the 1989 edition, a number of more significant changes were introduced, in part reflecting the maturing of the Standard but also the acquisition of more detailed information on behaviour during the intervening years. The 1994 edition continued this process with the refining of some requirements and the addition of a new lateral-load-resisting system, the steel-plate shear wall. The 2001 edition of the Standard has been reorganized in a more logical order. In addition, the Standard has undergone a number of technical improvements reflecting the incorporation of research results. In this Introduction, the new order of the Clauses and Appendices in the 2001 Standard are listed and linked to the 1994 Standard. The changes to the clauses are then highlighted in the Introduction, followed by detailed comments on a clause-by-clause basis in the body of the Commentary.
Comments on re-naming and re-ordering of Clauses and Appendices in CAN/CSA-S16-01
Clauses
1. Scope and Application
2. Definitions and Symbols
3. Reference Publications
4. Structural Documents (previously “Drawings”)
5. Material: Standards and Identification
6. Design Requirements
7. Loads and Safety Criterion
8. Analysis of Structure
9. Stability of Structures and Members (previously Clause 20)
10. Design Lengths and Slenderness Ratios (previously Clauses 9 and 10)
11. Width-to-Thickness Ratios: Elements in Compression
12. Gross and Net Areas
13. Member and Connection Resistance (Clause13.3.2 previously Appendix D)
14. Beams and Girders (previously Clause 15)
15. Trusses (new Clause)
16. Open-Web Steel Joists
17. Composite Beams, Trusses, and Joists (previously “Composite Beams”)
18. Composite Columns (previously “Concrete-Filled Hollow Structural Sections”)
19. General Requirements for Built-up Members
20. Plate Walls (previously “Steel Plate Shear Walls” and Appendix “M”)
21. Connections
22. Design and Detailing of Bolted Connections (previously “Bolting Details”)
23. Installation and Inspection of Bolted Joints (previously “Structural Joints Using ASTM A325M, A490M, A325, or A490 Bolts)
24. Welding
25. Column Bases and Anchor Rods (previously Clauses 25 and 26)
26. Fatigue (previously Clause 14 and Appendix “K”)
27. Seismic Design Requirements
28. Shop and Field Fabrication and Coating (previously Clauses 28 and 29)
29. Erection (previously Clause 30)
30. Inspection (previously Clause 31)
Appendices
A — Standard Practice for Structural Steel
B — Margins of Safety (previously Appendix “E”)
C — Crane-Supporting Structures (new Appendix)
D — Recommended Maximum Values for Deflection for Specified Design Live and Wind Loads (previously Appendix “I”)
E — Guide for Floor Vibrations (previously Appendix “G”)
F — Effective Lengths of Columns (previously Appendix “B”)
G — Criteria for Estimating Effective Column Lengths in Continuous Frames (previously Appendix “C”)
H — Deflections of Composite Beams Due to Shrinkage of Concrete (previously Appendix “L”)
I — Arbitration Procedure for Pretensioning Connections (previously Clause 23.7.4)
J — Ductile Moment-Resisting Connections (new Appendix)
Appendices “D”, “K” and “M” of the 1994 Standard have been incorporated into the 2001 Standard. Appendices “F” and “J” of the 1994 Standard have been deleted.
Highlights of Changes to Some Clauses of CAN/CSA S16-01.
Clause 1
In Clause 1.4, second sentence, that the word “supplemented” replaces “used” to emphasize that this Standard is the one to be used for the design of steel buildings in Canada, that it takes precedence, and any other criteria used are in fact supplementary.
Clause 2
New definitions introduced. Some new symbols are defined. Other definitions and symbols, where appropriate, brought forward to Clause 2
Clause 3
Brought up-to-date. CGSB Standards no longer referenced. New Standards added.
Clause 4
Title broadened to included structural documents. Information on structural design documents broadened. Note new Clauses 4.1.3 and 4.1.2.3 and 4.2.4.
Clause 5
New bolting assemblies introduced.
Clause 6
Clause 6.2.5 deleted as redundant.
Clause 7
Currently consistent with NBCC 1995 but are to be revised when the new rules for load combinations, currently under review, are adopted in the National Building Code of Canada 2005 edition.
Clause 8
1. Clause 8.3.2 – Deleted due to lack of use and replaced by Clause 8.4.
2. Clause 8.5 – Limit for Fy increase to 0.85 of Fu.
3. Clause 8.6.1 – Removed notes to simplify.
4. Clause 8.6.2 – Notional Loads are now required for all load combinations. The notional load compensates for the fact that an effective length factor of 1.0 is used for sidesway.
Clause 9
1. Clause 9.1 – Some of the material that used to appear here (in Clause 20.1) has been moved to Clause 4.
2. Clause 9.2 – The initial misalignment, Δo , is defined more succinctly.
3. Clause 9.2.5 – The old simplified analysis (2% rule) has been reintroduced with some limitations.
4. Clause 9.2.6 – Detailed analysis has been expanded.
5. In Clause 9.2.8 – The use of the statistically reduced value of the initial misalignment is reduced.
Clause 10
1. Design lengths and slenderness ratios are now logically combined.
2. Previous Clause 9.3.4 has been moved to new Clause 15. Trusses.
Clause 11
The table has been split into two parts: (a) elements in axial compression and (b) elements in flexural compression easier use.
Clause 12
No substantive changes.
Effective net areas, An2 and An3 have been revised for elements connected by welds.
Clause 13
All resistance factors used are listed in Clause 13.1.2.
In Clause 13.3.1, which shapes are used for which column curve has been clarified.
Appendix D has been brought into the Standard as Clause 13.3.2
In Clause 13.3.3, for Class 4 members, simpler options are now available.
Clauses 13.4.1.3 and 13.4.1.4, dealing with girders, have been moved to that clause (14).
Clause 13.4.4 eliminated as being redundant, now part of new 13.4.3.
Clause 13.5 – no longer sends the user to CSA S136
Clause 13.6 – in (c) emphasizes that lateral-torsional buckling is not a problem for closed square and circular sections.
Clause 13.7 – new clause now consistent with seismic requirements
Clause 13.8 – The changes herein are covered in the paper by Essa and Kennedy and include:
(a) distinction between members in braced and unbraced frames (which are defined).
(b) re-establishment of Class 2 sections with Class 1 sections
(c) A modification in the interaction expression for the weak axis bending moment term reflects the effect of plastic hinge length in weak axis bending.
Clause 13.11, Φb is increased to 0.80. See reference material. An attendant change is in the reduction factor for the shear strength of bolts in long lap splices, which was masked by the unrealistically low resistance factor used previously.
Clause 13.12.2 – Added new values for c1 applicable for joints using new F959 and F1852 bolt assemblies.
Clause 13.14 of S16.1- 94 is now Clause 20 entitled simply Plate Walls: because it is known that they are made of steel and are really flexural members.
Clause 14
1. Has been reordered from top to bottom: 14.1 Proportioning is followed by 14.2 Flanges, 14.3 Webs, 14.4, Bearing Stiffeners and 14.5 Intermediate Transverse Stiffeners. Other items are then considered.
2. Clause 14.3.2 - Web Crippling and Yielding – See reference material. Is much simplified based on the latest available research on beams ranging in depth from 200-1800 mm and appropriate resistance factors are provided.
Clause 15
1. In new Clause 15, the simplified method of analysis, long established to be valid, of assuming the members to be pin-connected is first presented with few restrictions.
2. The detailed method considers joint fixity.
3. The factored resistances in Clause 15.3.4 of the first compression web member and its connections are reduced to encourage more ductile modes of failure.
4. The slenderness ratio of tension chords is limited to 240 for erection.
Clause 16
1. The distinction between standard and non-standard OWSJ no longer exists as OWSJ are designed specifically for each situation by the joist manufacturer. There is now only one loading clause instead of two.
2. 16.6.8.3 as for trusses.
3. Camber is now considered to vary linearly with the span.
4. Clause 16.12.2.5 added to limit differential elevations between adjacent joists.
Clause 17
1. Ec is now provided in Clause 17.2 for Clauses 17 and 18.
2. The shear resistance for studs in ribbed slabs with ribs parallel to the beam has been revised based on research at U. of Saskatchewan.
3. Clause 17.9.9 guards against inadequate composite action in the end panel of composite trusses and OWSJs.
Clause 18
1. The expressions for the compressive resistance and bending resistance of concrete filled HSS have been modified as has that for Crcm in 18.2.4.
2. Clause 18.3 describes partially encased composite columns acting in compression.
3. Clause 18.4, for the first time in this Standard, deals with rolled steel shapes encased in concrete.
Clause 19
No substantive changes.
Clause 20
1. Existed previously as Appendix M. It considers plate walls with thin web plates that develop tension field action to carry the transverse shears.
2. For preliminary proportioning, the plate wall is approximated by a vertical truss with tension diagonals. From this model the web plate thickness is determined.
3. The angle of inclination of the tension field, Clause 20.3, depends on the stiffness of the surrounding beams and columns and the aspect ratio of the panel.
4. Clause 20.4.2 limits the flexibility of the columns to ensure that a full tension field develops.
Clauses 21, 22 and 23
1. Contain the material previously existing in Clauses of the same numbers.
2. There has been some re-ordering of the material.
3. The old 50% rule (previously Clause 21.5.2) has been withdrawn. It does not exist in sister standards, and was frequently misapplied.
4. Clause 21.8.1 has been reworded to define better the force to be developed in fillers.
5. Clause 22.1 introduces F1852 bolt assemblies.
6. Clause 23.1 defines firm contact and snug-tightness.
7. Clause 23.7 recognizes that fastener components for pretensioned bolt assemblies must be properly stored on the site.
8. Clauses 23.9.3 and 23.9.4 cover use of F959 washers and F1852 twist-off bolts.
9. Clause 23.10 is enlarged to cover inspection procedures for all the bolting situations now covered in the Standard.
10. The arbitration procedure to be used when there is a disagreement with respect to the results of bolt tension have been relegated to Appendix I.
Clause 24
1. Clause 24.1 has been re-written to emphasis the fact that the factored resistance to static loading is found in Clause 13.13 and to fatigue loading in Clause 26.
2. Clause 24.3 permits work to be sublet to a Division 3 erector.
Clause 25
1. The term anchor rod is used instead of anchor bolt as they are in fact threaded rods and may be of various grades of steel.
2. The clause has been re-ordered to give (a) 25.1 Loads, (b) 25.2 Resistances, (c) 25.3 Fabrication and Erection Requirements to provide a more logical approach and eliminate duplication.
Clause 26
1. A considerable amount of descriptive material has been eliminated.
2. The entire clause is more oriented towards buildings, such as crane supporting structures where fatigue is a consideration rather than towards bridges. Because of this, in Clause 26.3.3, the limit on stress range is now set as the constant amplitude threshold stress range, rather than ½ of it, in conjunction with change 3 below.
3. Miner’s rule has been introduced for cumulative fatigue damage.
4. Clause 26.3.5 express the limit on the number of cycles below which no special consideration is required as a function of the fatigue detail as given by the fatigue life constant.
5. The material given in Appendix K has been brought into the Standard.
6. Detailed categories for HS bolts in tension have been added.
Clause 27
The numerous changes on seismic design requirements are discussed in the body of the Commentary.
Clause 28
1. Shop and field fabrication and coating have been combined into one clause
2. Steel building systems manufactured to CAN/CSA-A660-M are included in S16-01
Clause 29
No substantive changes
Clause 30
No substantive changes
David H. MacKinnon, P.Eng.
Director of Codes and Standards
Canadian Institute of Steel Construction
201 Consumers Road, Suite 300
Toronto, Ontario M2J 4G8