A-4.1.1. Revisions to Part 4. Part 4 of the 2006 edition of the BC Building Code was significantly revised from the 1998 BC Building Code. Because of the extensive revisions and reorganization, for ease of reading, angle brackets indicating changes from the previous edition have not been included in the printed version of the 2006 BC Building Code. In the electronic versions, changes are indicated by a green underline.
A-4.1.1.1. Scope. The protection of buildings against unstable slopes in an earthquake is beyond the scope of this Code. The User’s Guide — NBC 2005, Structural Commentaries (Part 4 of Division B) states that the hazard of landslides caused by earthquakes is not addressed by the building code; this hazard should be addressed primarily through planning and site selection. Refer to Commentary J — Design for Seismic Effects in the User’s Guide for further explanation on seismic design objectives and expected performance.
It is recognized that a slope stability assessment involves a comprehensive analysis of hazards and risks, the scope and contents of which are developed collaboratively by the professional, the client, the property owner, and the authority having jurisdiction. The provincial government with all parties involved began in 2006 to develop an approach to address this issue.
Slope stability associated with liquefaction should be investigated in further detail with references to 4.1.8.16.(7).
A-4.1.1.3.(1) Structural Integrity. The requirements of Part 4, including the CSA design standards, generally provide a satisfactory level of structural integrity. Additional considerations may, however, be required for building systems made of components of different materials, whose interconnection is not covered by existing CSA design standards, buildings outside the scope of existing CSA design standards, and buildings exposed to severe accidental loads such as vehicle impact or explosion. Further guidance can be found in the Commentary entitled Structural Integrity in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
A-4.1.1.5.(2) Structural Equivalents. Sentence 4.1.1.5.(2) provides for the use of design methods not specified in Part 4, including full-scale testing and model analogues. This provision is usually used to permit the acceptance of new and innovative structures or to permit the acceptance of model tests such as those used to determine structural behaviour, or snow or wind loads. Sentence 4.1.1.5.(2) specifically requires that the level of safety and performance be at least equivalent to that provided by design to Part 4 and requires that loads and designs conform to Section 4.1.
Sentence 4.1.1.5.(2) and the provision for alternative solutions stated in Clause 1.2.1.1.(1)(b) of Division A are not intended to allow structural design using design standards other than those listed in Part 4. The acceptance of structures that have been designed to other design standards would require the designer to prove to the appropriate authority that the structure provides the level of safety and performance required by Clause 1.2.1.1.(1)(b) of Division A. The equivalence of safety and performance can only be established by analyzing the structure for the loads and load factors set out in Section 4.1. and by demonstrating that the structure at least meets the requirements of the design standards listed in Sections 4.3. and 4.4.
A-4.1.2.1.(3) Major Occupancies. In a building containing more than one major occupancy and classified in more than one Importance Category, the classification of each independent structural system shall be the same as for any part of the building that is dependent on that structural system and for the highest usage group according to Table 4.1.2.1.
A-Table 4.1.2.1. Importance Categories for Buildings.
Low Importance Category Buildings
Low human-occupancy farm buildings are defined in the National Farm Building Code of Canada 1995 as having an occupant load of 1 person or less per 40 m2 of floor area. Minor storage buildings include only those storage buildings that represent a low direct or indirect hazard to human life in the event of structural failure, either because people are unlikely to be affected by structural failure, or because structural failure causing damage to materials or equipment does not present a direct threat to human life.
Buildings Containing Hazardous Materials
The following buildings contain sufficient quantities of toxic, explosive or other hazardous substances to be classified in the High Importance Category of use and occupancy:
The following types of buildings may be classified in the Normal Importance Category: buildings that are equipped with secondary containment of toxic, explosive or other hazardous substances, including but not limited to, double-wall tanks, dikes of sufficient size to contain a spill, or other means to contain a spill or a blast within the property boundary of the facility and prevent the release of harmful quantities of contaminants to the air, soil, groundwater, surface water or atmosphere, as the case may be.
A-Table 4.1.3.2. Load Combinations. One of the combinations that must be considered is the principal load acting alone.
A-4.1.3.2.(2) Load Combinations. The load combinations in Table 4.1.3.2. apply to most situations for loadbearing building structures. Guidance on special situations such as load combinations for fire resistance and building envelopes is given in the Commentary entitled Limit States Design in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
A-4.1.3.2.(3) Effects of Lateral Earth Pressure, H, Pre-stress, P, and Imposed Deformation, T, in Design Calculations.
Effects of Lateral Earth Pressure, H, in Design Calculations
For common building structures below ground level, such as walls, columns and frames, 1.5 H is added to load combinations 2 to 4. For cantilever retaining wall structures, see the Commentary entitled Limit States Design in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
Effects of Pre-stress, P, and Imposed Deformation, T, in Design Calculations
For structures and building envelopes designed in accordance with the requirements specified in the standards listed in Section 4.3., with the exception of Clauses 8 and 18 of CSA A23.3, P and T need not be included in the load combinations of Table 4.1.3.2. For structures not within the scope of the standards listed in Section 4.3., including building envelopes, P and T must be taken into account in the design calculations. For recommended load combinations including T, see the Commentary entitled Limit States Design in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
A-4.1.3.3.(1) Failure due to Fatigue. Failure due to fatigue of building structures referred to in Section 4.3. and designed for serviceability in accordance with Article 4.1.3.6. is, in general, unlikely except for girders supporting heavily used cranes, on which Article 4.1.5.12. provides guidance.
A-4.1.3.4.(1) Loads and Load Combinations for Serviceability. The loads and load combinations for serviceability depend on the serviceability limit states and on the properties of the structural materials. Information on loads and load combinations for the serviceability limit states, other than those controlled by deflection, can be found in the Commentary entitled Deflection and Vibration Criteria for Serviceability and Fatigue Limit States in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
A-4.1.3.5.(1) Deflections. Serviceability criteria for deflections that cause damage to non-structural building components can be found in the standards listed in Section 4.3. Information on deflections can be found in the Commentary entitled Deflection and Vibration Criteria for Serviceability and Fatigue Limit States in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B). Information on loads and load combinations for calculating deflection can be found in the Commentary entitled Limit States Design in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
A-4.1.3.5.(3) Lateral Deflection of Buildings. The limitation of 1/500 drift per storey may be exceeded if it can be established that the drift as calculated will not result in damage to non-structural elements. Information on lateral deflection can be found in the Commentary entitled Wind Load and Effects in the User's Guide – NBC 2005, Structural Commentaries (Part 4 of Division B).
A-4.1.4.1.(6) Counteracting Dead Load Due to Soil. Examples of structures that traditionally employ the dead load of soil to resist loadings are pylon signs, tower structures, retaining walls, and deadmen, which resist wind uplift and overturning in light structures.
A-Table 4.1.5.3. Considerations for Live Loads.
Attics - Limited Accessibility
Attic live loading is not required when the ceiling below the attic consists of removable panels that permit access to the ceiling space without loading the ceiling supporting members. Attic live loading is not required in any area of the attic where the least dimension of the attic space is less than 500 mm.
Floor Areas That Could Be Used As Viewing Areas
Some interior balconies, mezzanines, corridors, lobbies and aisles that are not intended to be used by an assembly of people as viewing areas are sometimes used as such; consequently, they are subject to loadings much higher than those for the occupancies they serve. Floor areas that may be subject to such higher loads must, therefore, be designed for a loading of 4.8 kPa.
A-Table 4.1.5.10. Loads Due to Concentrations. Special study is required to determine concentrated loads for the design of floors and areas used by vehicles exceeding 9 000 kg gross weight, and of driveways and sidewalks over areaways and basements. Where appropriate the designer should refer to CAN/CSA-S6, “Canadian Highway Bridge Design Code.”
A-4.1.5.12. Crane-Supporting Structures. Guidance on crane-supporting structures can be found in CAN/CSA-S16, “Limit States Design of Steel Structures.”
A-4.1.5.15. and 4.1.5.16.(1) Design of Guards. In the design of guards, due consideration should be given to the durability of the members and their connections.
A-4.1.6.4.(3) Flow Control Drains. The National Plumbing Code of Canada 2005 (NPC) contains requirements regarding the use of flow control roof drains. The designer must ensure that the building complies with both the NPC and the NBC.
A-4.1.8.16.(6) Alternative Foundation Ties. Alternative methods of tying foundations together, such as a properly reinforced floor slab capable of resisting the required tension and compression forces, may be used. Passive soil pressure against buried pile caps may not be used to resist these forces.
A-4.2.2.1.(1) Subsurface Investigation. Where acceptable information on subsurface conditions already exists, the investigation may not require further physical subsurface exploration or testing.
A-4.2.2.3.(1) Responsibilities of the Designer as Defined in Part 4. In certain situations, such as when the design is highly technical, it may be necessary for the “other suitably qualified person” to be someone responsible to the designer. In such cases the authority having jurisdiction may wish to order that the review be done by the designer.
A-4.2.4.1.(1) Innovative Designs. It is important that innovative approaches to foundation design be carried out by a person especially qualified in the specific method applied and that the design provide a level of safety and performance at least equivalent to that provided for or implicit in the design carried out by the methods referred to in Part 4. Provision must be made for monitoring the subsequent performance of such structures so that the long-term sufficiency of the design can be evaluated.
A-4.2.4.4.(1) Depth of Foundations. When adfreezing has occurred and subsequent freezing results in soil expansion beneath this area, the resulting uplift effect is sometimes referred to as frost jacking.
A heated building that is insulated to prevent heat loss through the foundation walls should be considered as an unheated structure unless the effect of the insulation is taken into account in determining the maximum depth of frost penetration.
A-4.2.7.1.(1) Deep Foundation Units. A deep foundation unit can be pre-manufactured or cast-in-place; it can be driven, jacked, jetted, screwed, bored or excavated; it can be of wood, concrete or steel or a combination thereof.
A-4.2.7.2.(2) Load Testing of Piles. ASTM D 1143, “Piles Under Static Axial Compressive Load,”defines routine load test procedures that have been extensively used.
A-4.3.1. Wood. The design criteria for wood, CAN/CSA 086 "Engineering Design in Wood", makes asumptions that the wood products being used are in a condition as intended by their grading. This includes the limits of moisture content as specified by the grade. However, conditions such as transportation, site storage, and construction conditions can impact the original design ammumptions.
Design considerations should include and be specific to shrinkage that may occur due to changes in moisture content of the wood. This is of particular concern where the building height can be up to 6 storeys, such as being build under Article 3.2.2.45. The potential building movement due to shrinkage should be indicated to other design professionals for their considerations such as cladding systems, mechanical systems, hold-down devices for structural walls and connections to non-shrinking elements including firewalls and elevator shafts.
[Rev. 4, B.C. Reg. 1/2009.]
A-4.3.3.1.(1) Precast Concrete. CSA A23.3, “Design of Concrete Structures,”requires precast concrete members to conform to CAN/CSA-A23.4, “Precast Concrete – Materials and Construction.”
A-4.3.4.1.(1) Welded Construction. Qualification for fabricators and erectors of welded construction is found in Clause 24.3 of CAN/CSA-S16, “Limit States Design of Steel Structures.”
A-4.3.4.2.(1) Cold-Formed Stainless Steel Members. There is currently no Canadian standard for the design of cold-formed stainless steel structural members. As an interim measure, design may be carried out using the limit states design provisions of ANSI/ASCE 8, “Design of Cold Formed Stainless Steel Structural Members,” except that load factors, load combinations and load combination factors shall be in accordance with Subsection 4.1.3.